Search

NiO nanoparticles have garnered significant interest due to their diverse applications and unique properties, which differ markedly from their bulk counterparts. NiO nanoparticles are p-type semiconductors with a wide bandgap, high discharge capacity, and high carrier density, making them ideal for use in batteries, sensors, and catalysts. Their ability to generate reactive oxygen species also imparts disinfectant and antibiotic properties. Additionally, the higher Néel temperature of NiO compared with other antiferromagnetic materials makes it suitable for high-temperature applications in spintronic devices and industrial settings. This review focuses on the critical role of structure and composition in determining the magnetic properties of NiO nanoparticles. It examines how finite-size surface effects, morphology, crystallinity, and nickel distribution influence these properties. Fundamental physical properties and characterization techniques are discussed first. Various synthesis methods and their impact on NiO nanoparticle properties are then explored. Their magnetic phenomenology is examined in detail, highlighting the effects of finite size, particle composition and surface, and crystal quality. The review concludes with a summary of key insights and future research directions for optimizing NiO nanoparticles in technological applications. [ABSTRACT FROM AUTHOR]

The structural, electronic, magnetic, magnetocaloric, and thermoelectric properties of the SrXO3 (X = Mn and Fe) perovskite compounds were investigated using first-principles calculations. It was observed that the SrXO3 compounds are G-anti-ferromagnetic perovskites with partial magnetic moment with a value of 2.7 μ B and 2.4 μ B for Mn-3d and Fe-3d orbitals for SrMnO3 and SrFeO3, respectively. Moreover, by using Monte Carlo simulation (MCs) combined with the Metropolis algorithm, the calculated coupling interactions between the magnetic atoms Mn–Mn and Fe–Fe are J 1 Mn = 5. 1 7 meV and J 2 Mn = − 0. 6 meV for SrMnO3, J 1 Fe = 3. 4 4 meV and J 1 Fe = − 0. 4 meV for SrFeO3, respectively. Furthermore, a significant magnetocaloric effect (MCE) was observed around the Néel temperature of T N Mn = 2 6 0 K (for SrMnO3) and T N Fe = 1 3 4 K (for SrFeO3), and the maximal simulated magnetic entropy and relative cooling power values of all the studied compounds are found to be 100 J/kg (for SrMnO3) and 110 J/kg (for SrFeO3), respectively, with an applied magnetic field of H = 4. 0 T. These results are in complete agreement with the experimental results and more specifics than other theoretical calculations. Hence, SrXO3 compounds are considered promising candidates for magnetic refrigeration at low temperature. [ABSTRACT FROM AUTHOR]

We studied solid solutions of the system (1−x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 using X-ray and Neuron diffraction, and Mössbauer spectroscopy. To obtain ceramics, we used the method of two-stage solid-phase synthesis and sintering according to the conventional ceramic technology. Pure solid solutions of the (1−x)PbFe1/2Nb1/2O3-xPbFe2/3W1/3O3 system were obtained. A deviation of the unit cell parameters from the Vegard rule was revealed, which indicates stratification of the structure into microregions differing in composition. The introduction of PbFe2/3W1/3O3 into the system led to partial ordering (clustering) of cations in the B position. An increase in magnetic moment with growing amount of PbFe2/3W1/3O3 was shown. [ABSTRACT FROM AUTHOR]

We studied solid solutions of the system (1−x)PbFe1/2Nb1/2O3 - xPbFe2/3W1/3O3 using X-ray and Neuron diffraction, and Mössbauer spectroscopy. To obtain ceramics, we used the method of two-stage solid-phase synthesis and sintering according to the conventional ceramic technology. Pure solid solutions of the (1−x)PbFe1/2Nb1/2O3-xPbFe2/3W1/3O3 system were obtained. A deviation of the unit cell parameters from the Vegard rule was revealed, which indicates stratification of the structure into microregions differing in composition. The introduction of PbFe2/3W1/3O3 into the system led to partial ordering (clustering) of cations in the B position. An increase in magnetic moment with growing amount of PbFe2/3W1/3O3 was shown. [ABSTRACT FROM AUTHOR]

In this work, nanocrystalline Sm 1-x R x FeO 3 (x = 0.0 and 0.5; R Pr, Nd, and Gd) samples have been synthesized via auto-combustion method and characterized to understand their microstructural, optical, electrical and multiferroic properties. X-ray diffraction data in combination with the FTIR spectra revealed the monophase and distorted orthorhombic configuration of all the samples with Pbnm space group. Rietveld refinement displayed a reduction in the bond length as well as the bond angle in the Sm 0.5 Gd 0.5 FeO 3 sample. Raman spectra exhibit compressive strain in Sm 0.5 Gd 0.5 FeO 3 nanoparticles; this finding is further supported by the XRD analysis. UV–visible spectroscopy manifests a reduction in the optical energy bandgap on moving Gd to Pr in Sm 0.5 R 0.5 FeO 3 system. Transmission electron microscopy (TEM) images in combination with energy dispersive x-ray (EDX) spectra reveal the non-uniform surface morphology with the agglomerated nature of nanoparticles and affirm the elemental compositions of all the samples. The room temperature P-E and M − H loops infer the multiferroic nature of all samples. Electron paramagnetic resonance (EPR) analysis divulges the weakening of the super-exchange interactions in Sm 0.5 R 0.5 FeO 3 system. DC electrical resistivity measurements reflect semiconductor-like behaviour in all prepared samples. The dielectric behaviour of the samples is in accordance with the "universal dielectric response" model. The temperature-dependent dielectric measurements of all prepared samples have been performed at 1 kHz to determine the Néel temperature (T N). The photocatalytic investigation depicts the superior photocatalytic response of Sm 0.5 Pr 0.5 FeO 3 nanoparticles under solar-light irradiation through the synergism of semiconductor-photocatalyzed oxidation and heterogeneous Fenton-like reaction. [ABSTRACT FROM AUTHOR]

Emission 57Fe Mössbauer spectroscopy (eMS), following the implantation of radioactive 57Mn+ ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO3 (BFO) thin films. 57Mn β decays (t1/2 = 90 s) to the 14.4 keV Mössbauer state of 57Fe, thus allowing online eMS measurements at a selection of sample temperatures during Mn implantation. The eMS measurements were performed on two thin film BFO samples, 88 nm and 300 nm thick, and doped to 15% with Ba ions. The samples were prepared by pulsed laser deposition on SrTiO3 substrates. X-ray diffraction analyses of the samples showed that the films grew in a tetragonal distorted structure. The Mössbauer spectra of the two films, measured at absorber temperatures in the range 301 K–700 K, comprised a central pair of paramagnetic doublets and a magnetic sextet feature in the wings. The magnetic component was resolved into (i) a component attributed to hyperfine interactions at Fe3+ ions located in octahedral sites (Bhf); and (ii) to Fe3+ ions in implantation induced lattice defects, which were characterized by a distribution of the magnetic field BDistr. The hyperfine magnetic field at the Fe probes in the octahedral site has a room temperature value of Bhf = 44.5(9) T. At higher sample temperatures, the Bhf becomes much weaker, with the Fe3+ hyperfine magnetic contribution disappearing above 700 K. Simultaneous analysis of the Ba–BFO eMS spectra shows that the variation of the hyperfine field with temperature follows the Brillouin curve for S = 5/2. [ABSTRACT FROM AUTHOR]

We investigate the magneto-optic Kerr effect in perpendicularly magnetized Pt/Co/Ir/Cr2O3/Pt thin films, associated with the antiferromagneticâ€"paramagnetic transition of the Cr2O3 layer. The magneto-optic Kerr rotation angle (θ K) shows oscillatory behavior as a function of the photon energy of incident light owing to interference in the Cr2O3 layer. The temperature dependence of θ K at 2.67 eV (λ = 465 nm), at which the largest θ K is obtained, shows a sharp dip at 287.0 K. The dip temperature is similar to the reported NĂ©el temperature for Cr2O3 thin films. Although the θ K spectra measured at several temperatures are generally explained by the classical interference model, θ K is enhanced at 2.36â€"2.79 eV (λ = 525â€"445 nm) close to the dip temperature. This peculiar enhancement in θ K is discussed on the basis of the anomaly in the optical parameters of the Cr2O3 layer associated with the antiferromagneticâ€"paramagnetic transition. [ABSTRACT FROM AUTHOR]

We report antiferromagnetic order in gadolinium nickel zinc ferrite (GNZF) nanoparticles with insulating characteristics. Two samples defined by stoichiometries, Gd 1.39 Ni 0.1 Zn 0.02 Fe 0.89 O 4 and Gd 1.53 Ni 0.12 Fe 0.79 O 4 , with varying Gd to Fe ratios are prepared. Major phases identified in the GNZF nanoparticles are GdO and GdFeO 3 , exhibiting antiferromagnetic coupling. Optical absorption onset occurs at 1.9 eV and 1.7 eV for the respective samples. An additional absorption edge, situated 0.1 eV above the fundamental onset, is attributed to the split-off valence band induced by spin-orbit interaction. Néel temperatures (T N) are determined to be 17 K and 18 K for the two stoichiometries, respectively. Optical absorption analysis suggests the presence of spin excitons, indicating quantum confinement effects on electrons and holes in GNZF nanoparticles. We propose that the spin excitons mediate the antiferromagnetic exchange coupling within the nanoparticles. [ABSTRACT FROM AUTHOR]

The previously reported X 2 O 3 (X=V, Cr, Mn, Ta) monolayers crystallize in a honeycomb–kagome (HK) structure and are found primarily to be ferromagnetic Chern insulators with remarkable quantum anomalous Hall (QAH) properties. However, in this study, it was found that the HK Fe 2 O 3 monolayer exhibits antiferromagnetic semiconducting properties suitable for advanced spintronics applications. Through first-principle calculations based on density functional theory (DFT) calculations, we show that the Fe 2 O 3 monolayer has good energetic, mechanical, and dynamic stability. We further evaluate the magnetic anisotropy energies (MAE) of the Fe 2 O 3 monolayer and find that it prefers the out-of-plane easy axis magnetization direction with a sizeable MAE value of 248.75 μ eV per Fe atom. Moreover, by performing Monte Carlo (MC) simulations based on the 2D classical anisotropic Heisenberg model, we predict a Néel temperature of 631.7(5) K for the Fe 2 O 3 monolayer. We demonstrate that the Fe 2 O 3 monolayer belongs to the 2D Ising-like universality class based on the estimated critical exponent ratios of magnetic susceptibility, magnetization, and the exponent of the correlation length. Our findings demonstrate that the Fe 2 O 3 monolayer can be a suitable candidate for future antiferromagnetic spintronic device applications, especially in ultra-high data processing and storage, due to the coexistence of AFM and semiconducting properties. [Display omitted] • Fe 2 O 3 monolayer has been investigated using DFT+U and Monte Carlo (MC) calculations. • The Fe 2 O 3 monolayer exhibits robust antiferromagnetic semiconducting properties. • We predict a Néel temperature of 631.7(5) K for the Fe 2 O 3 monolayer. • We demonstrate that the Fe 2 O 3 monolayer belongs to the 2D Ising-like universality class. [ABSTRACT FROM AUTHOR]

The crystal structure, and cryogenic magnetic and magnetocaloric properties in RE2T2Al (RE = Dy, Ho, Er, and Tm; T = Co and Ni) compounds have been investigated. All the compounds belong to an orthorhombic W2B2Co-type structure (Immm space group). A second order paramagnetic to ferromagnetic phase transition exists for RE2Co2Al compounds at TC = 62, 27, 32, and 11.5 K, whereas the compounds of RE2Ni2Al undergo a paramagnetic to antiferromagnetic phase transition with the Néel temperatures (TN) of 19, 12, 12.5, and 6 K for RE = Dy, Ho, Er, and Tm, respectively. Moreover, an additional low temperature magnetic transition occurs for all present RE2T2Al compounds. An obvious hysteresis was observed at a low temperature in the Dy2Co2Al, Ho2Co2Al, and Er2Co2Al compounds. The values of the maximum magnetic entropy change (−ΔSMmax) are 10.4, 11.5, 5.9, 7.7, 6.0, and 16.2 J/kg K for Dy2Co2Al, Ho2Co2Al, Er2Co2Al, Tm2Co2Al, Ho2Ni2Al, and Er2Ni2Al compounds with a field change (ΔH) of 0-5 T, respectively. Moreover, two peaks (or shoulder) in the −ΔSM (T) curves of Ho2Co2Al can be observed, which lead to a wide cooling temperature interval. [ABSTRACT FROM AUTHOR]

The effects of cationic vacancies on the structural, dielectric, and magnetic properties are investigated in polycrystalline GdMnO3 samples. Samples with reduced cationic vacancies are synthesized by annealing under the forming gas atmosphere. The x-ray photoelectron spectroscopy studies show evidence for excess oxygen in terms of the Mn4+ content and reveal the increase in the Mn3+/Mn4+ ratio with increase in annealing time under forming gas conditions. Dielectric studies reveal two thermally activated relaxations in the low and high temperature regimes. Notably, the near stoichiometric Mn3+ rich samples show a negative temperature coefficient of ac conductivity in a certain temperature region along with better insulating properties. The magnetic measurements exhibit a gradual increase in the onset of weak ferromagnetic transition temperature with increase in the Mn3+ content in the sample and coincides with the Neel temperature (42 K) near stoichiometric composition. The studies demonstrate the effect of subtle change in oxygen non-stoichiometry on the dielectric and magnetic properties and bring out the importance of controlling stoichiometry in GdMnO3. [ABSTRACT FROM AUTHOR]

The effects of cationic vacancies on the structural, dielectric, and magnetic properties are investigated in polycrystalline GdMnO3 samples. Samples with reduced cationic vacancies are synthesized by annealing under the forming gas atmosphere. The x-ray photoelectron spectroscopy studies show evidence for excess oxygen in terms of the Mn4+ content and reveal the increase in the Mn3+/Mn4+ ratio with increase in annealing time under forming gas conditions. Dielectric studies reveal two thermally activated relaxations in the low and high temperature regimes. Notably, the near stoichiometric Mn3+ rich samples show a negative temperature coefficient of ac conductivity in a certain temperature region along with better insulating properties. The magnetic measurements exhibit a gradual increase in the onset of weak ferromagnetic transition temperature with increase in the Mn3+ content in the sample and coincides with the Neel temperature (42 K) near stoichiometric composition. The studies demonstrate the effect of subtle change in oxygen non-stoichiometry on the dielectric and magnetic properties and bring out the importance of controlling stoichiometry in GdMnO3. [ABSTRACT FROM AUTHOR]

We investigated the anomalous behaviour in the dielectric properties, occurring nearly at room temperature and at elevated temperatures (near the Neel temperature TN) of the polycrystalline samples of YFeO3 (YFO) ceramics. On the prepared YFO ceramics, the magnetic measurements showed the Neel temperature of YFO to be 650 K, below which the compound exhibited the weak ferromagnetic behaviour. X-ray photoelectron spectroscopy (XPS) shows the presence of Fe ions (Fe2+ and Fe3+ states) and also revealed the formation of the oxygen vacancies. The frequency dependence of the complex dielectric constant within the frequency domain of 100 Hz–1 MHz shows the presence of grain dominated dielectric relaxation over the thermal window of 300–373 K. The activation energy E act. ε = 0.611 eV extracted from the imaginary permittivity spectrum indicates the involvement of oxygen vacancies in the relaxation process. Above 493 K, the ac conductivity, complex impedance, and modulus studies revealed appreciable conduction and relaxation processes occurring in YFO ceramics with respective activation energies E a c t. σ = 1.362 eV and E a c t. Z = 1.345 eV , which suggests that the oxygen vacancies are also involved for the anomalous behaviour of the dielectric constant at elevated temperatures. The temperature dependent Raman spectroscopic measurements within the thermal window of 298–698 K showed anomalous variations of the line widths and frequencies of several Raman active modes above 473 K up to the vicinity of TN pointing towards the presence of admixtures of the electron-phonon and spin-phonon coupling in the system. A further study on the thermal variation of the B2g(4) mode frequency with [M(T)/MS]2 shows the occurrence of strong spin–phonon (s-p) coupling, while the line shape shows the presence of the Fano asymmetry, suggesting spin dependent electron-phonon (e-p) coupling in the system below TN. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) antiferromagnetic (AFM) materials boasting a high Néel temperature ( T N ), high carrier mobility, and fast spin response under an external field are in great demand for efficient spintronics. Herein, we theoretically present the MoB 3 monolayer as an ideal 2D platform for AFM spintronics. The AFM MoB 3 monolayer features a symmetry-protected, 4-fold degenerate Dirac nodal line (DNL) at the Fermi level. It demonstrates a high magnetic anisotropy energy of 865 μeV/Mo and an ultrahigh T N of 1050 K, one of the highest recorded for 2D AFMs. Importantly, we reveal the ultrafast demagnetization of AFM MoB 3 under laser irradiation, which induces a rapid transition from a DNL semimetallic state to a metallic state on the time scale of hundreds of femtoseconds. This work presents an effective method for designing advanced spintronics using 2D high-temperature DNL semimetals and opens up a new idea for ultrafast modulation of magnetization in topological semimetals.

In this study, we theoretically investigate the structural, electronic and magnetic properties of the Cu2OX2 (X = Cl, Br, I) compounds. Previous studies reported potential spin-driven ferroelectricity in Cu2OCl2, originating from a non-collinear magnetic phase existing below T N ∼70 K. However, the nature of this low-temperature magnetic phase is still under debate. Here, we focus on the calculation of J exchange couplings and enhance knowledge in the field by (i) characterizing the low-temperature magnetic order for Cu2OCl2 and (ii) evaluating the impact of the chemical pressure on the magnetic interactions, which leads us to consider the two new phases Cu2OBr2 and Cu2OI2. Our ab initio simulations notably demonstrate the coexistence of strong antiferromagnetic and ferromagnetic interactions, leading to spin frustration. The T N Néel temperatures were estimated on the basis of a quasi-1D AFM model using the ab initio J couplings. It nicely reproduces the T N value for Cu2OCl2 and allows us to predict an increase of T N under chemical pressure, with T N = 120 K for the dynamically stable phase Cu2OBr2. This investigation suggests that chemical pressure is an effective key factor to open the door of room-temperature multiferroicity. [ABSTRACT FROM AUTHOR]

Emission 57Fe Mössbauer spectroscopy (eMS), following the implantation of radioactive 57Mn+ ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO3 (BFO) thin films. 57Mn β decays (t1/2 = 90 s) to the 14.4 keV Mössbauer state of 57Fe, thus allowing online eMS measurements at a selection of sample temperatures during Mn implantation. The eMS measurements were performed on two thin film BFO samples, 88 nm and 300 nm thick, and doped to 15% with Ba ions. The samples were prepared by pulsed laser deposition on SrTiO3 substrates. X-ray diffraction analyses of the samples showed that the films grew in a tetragonal distorted structure. The Mössbauer spectra of the two films, measured at absorber temperatures in the range 301 K–700 K, comprised a central pair of paramagnetic doublets and a magnetic sextet feature in the wings. The magnetic component was resolved into (i) a component attributed to hyperfine interactions at Fe3+ ions located in octahedral sites (Bhf); and (ii) to Fe3+ ions in implantation induced lattice defects, which were characterized by a distribution of the magnetic field BDistr. The hyperfine magnetic field at the Fe probes in the octahedral site has a room temperature value of Bhf = 44.5(9) T. At higher sample temperatures, the Bhf becomes much weaker, with the Fe3+ hyperfine magnetic contribution disappearing above 700 K. Simultaneous analysis of the Ba–BFO eMS spectra shows that the variation of the hyperfine field with temperature follows the Brillouin curve for S = 5/2.

The ground state of Co2+ in the octahedral CoO6 crystal field has often been assumed to be in high spin state with S = 3/2. As a result, the effective magnetic moments of Co2+ are overestimated in Co(OH)(2−x)Fx. Herein, it is argued that the ground state of Co2+ in Co(OH)(2−x)Fx has effective spin S= 1/2 but not S = 3/2, due to spin–orbit coupling in distorted octahedral crystal field. Analysis of the published magnetic susceptibility (χ) data on three samples of Co(OH)(2−x)Fx is reported here with the new result that the Néel temperature TN decreases with an increase in χ as TN = 36.5, 30.5, and 26.5 K are determined for x = 1.09, 1.14, and 1.26, respectively. The employment of modified Curie–Weiss (CW) law along with S = 1/2 ground state eliminates the reported disagreement between the magnetic moment μ(Co2+) obtained from CW law above TN and neutron powder diffraction (NPD) below TN. The fits of the χ versus T data to the predictions of the linear chain model yield the exchange constant J/kB = −30.5, −28.1, and −24.7 K for x = 1.09, 1.14, and 1.26, respectively, supporting the chain‐like antiferromagnetic ordering observed using NPD. [ABSTRACT FROM AUTHOR]

The ground state of Co2+ in the octahedral CoO6 crystal field has often been assumed to be in high spin state with S = 3/2. As a result, the effective magnetic moments of Co2+ are overestimated in Co(OH)(2−x)Fx. Herein, it is argued that the ground state of Co2+ in Co(OH)(2−x)Fx has effective spin S= 1/2 but not S = 3/2, due to spin–orbit coupling in distorted octahedral crystal field. Analysis of the published magnetic susceptibility (χ) data on three samples of Co(OH)(2−x)Fx is reported here with the new result that the Néel temperature TN decreases with an increase in χ as TN = 36.5, 30.5, and 26.5 K are determined for x = 1.09, 1.14, and 1.26, respectively. The employment of modified Curie–Weiss (CW) law along with S = 1/2 ground state eliminates the reported disagreement between the magnetic moment μ(Co2+) obtained from CW law above TN and neutron powder diffraction (NPD) below TN. The fits of the χ versus T data to the predictions of the linear chain model yield the exchange constant J/kB = −30.5, −28.1, and −24.7 K for x = 1.09, 1.14, and 1.26, respectively, supporting the chain‐like antiferromagnetic ordering observed using NPD. [ABSTRACT FROM AUTHOR]

We report layered TiCl2 monolayer to be a robust antiferromagnetic (AFM) semiconductor by investigating its geometry, stability, electronic and magnetic properties using first-principles calculation and Monte Carlo (MC) simulation. The TiCl2 monolayer exfoliated from layered TiCl2 bulk is verified to be an AFM semiconductor with a relatively wide band gap by spin-polarized density of states and energy band structure calculations. Phonon dispersion and elastic modulus calculations show that the TiCl2 monolayer is dynamically and mechanically stable, respectively. The Néel temperature is evaluated to be 368 K by MC simulation based on Ising model. Additionally, the band gap, the magnetic moment of a single Ti atom and the Néel temperature can be significantly tuned by applied biaxial strain, but the AFM semiconducting behavior is robust against the applied strains, indicating that the TiCl2 monolayer is a potential candidate for high-speed AFM spintronic applications. [ABSTRACT FROM AUTHOR]

Three different models, viz. Qi model, Jiang model and Lu model, have been used in the present paper for studying the size and shape dependence of magnetic properties of the nanomaterials. The magnetic properties considered here are Curie temperature (T C) , magnetisation (M S) and Neel temperature (T N) . It is observed that Curie temperature, magnetisation and Neel temperature decrease with decrease in the size of the nanomaterial. This decrease is due to the increase in the surface atoms with reduction in size. The variations in Curie temperature, magnetisation and Neel temperature are studied for cylindrical nanowires, thin films, spherical, regular tetrahedral nanoparticles, and regular triangular cross-section nanowires. The models used in the study give similar trend of variation and after the comparison of the computed results with experimental data, it is found that Qi model works well compared to Lu and Jiang models. A close agreement between the available experimental results and the calculated results from Qi model justifies the validity of the present work. [ABSTRACT FROM AUTHOR]

The study aims at investigating dielectric properties and DTA signal of composite ceramics (BiFeO3)1-x/(BaTiO3)x (x = 0, 0.25, 0.50, 0.75) from 300 to 720 K. The obtained results indicated that the Neel temperature determined at the peaks of dielectric constant near the antiferromagnetic phase transition in (BiFeO3)1-x/(BaTiO3) shifted toward lower temperatures with increasing barium titanate content. This anomaly was also confirmed by the movement of DTA signal peaks. [ABSTRACT FROM AUTHOR]

The phase content and sequence, the crystal structure, and the magnetic properties of perovskite solid solutions of the (1-y)BiFeO3-yBiZn0.5Ti0.5O3 series (0.05 ≤ y ≤ 0.90) synthesized under high pressure have been studied. Two perovskite phases, namely the rhombohedral R3c and the tetragonal P4mm, which correspond to the structural types of the end members, BiFeO3 and BiZn0.5Ti0.5O3, respectively, were revealed in the as-synthesized samples. The rhombohedral and the tetragonal phases were found to coexist in the compositional range of 0.30 ≤ y ≤ 0.90. Magnetic properties of the BiFe1-y[Zn0.5Ti0.5]yO3 ceramics with y < 0.30 were measured as a function of temperature. The obtained compositional variations of the normalized unit-cell volume and the Néel temperature of the BiFe1-y[Zn0.5Ti0.5]yO3 perovskites in the range of their rhombohedral phase were compared with the respective dependences for the BiFe1-yB3+ yO3 perovskites (where B3+ = Ga, Co, Mn, Cr, and Sc). The role of the high-pressure synthesis in the formation of the antiferromagnetic states different from the modulated cycloidal one characteristic of the parent BiFeO3 is discussed. [ABSTRACT FROM AUTHOR]

Exchange-biased nanostructures of the "spin valve" type, which include an additional layer of the rare-earth metal dysprosium, are made by magnetron sputtering. Temperature variations in the magnetotransport properties of the spin valves are used as an indicator of change in the magnetic state of the dysprosium nanolayer. Information on the formation of unidirectional magnetic anisotropy at the CoFe/Dy interface upon the transition through Néel temperature of dysprosium is obtained. It is shown that the antiferromagnetic phase in the polycrystalline dysprosium layer has noncollinear magnetic ordering. The temperature dependence of the angle between the directions of the magnetic moments at the dysprosium-layer boundaries is determined. The change in this angle observed in the entire temperature region of the existence of helicoidal ordering in dysprosium reflects the change in the period of the magnetic helicoid in dysprosium with temperature. Thus, a new method for studying chiral magnetics is proposed, in which the indicator of the helicoidal magnetic state is a spin valve possessing giant magnetoresistance, containing a layer of the helimagnet under investigation. [ABSTRACT FROM AUTHOR]

With the rapid development of spintronics, two-dimensional antiferromagnetic materials have attracted much attention because of their unique physical properties. Here, the monolayer Mn _2 Cl _8 is discovered to be an intrinsically antiferromagnetic semiconductor in current work. The results show that monolayer Mn _2 Cl _8 and Mn _2 Cl _4 X _4 (X = F, Br) are stable semiconductors with indirect bandgaps of 0.34eV, 0.95eV, and 0.55eV, respectively, and Mn _2 Cl _8 has a Néel temperature (T _N ) of 245 K. In the systematic study of strain effects, T _N changes significantly under strains from −4% to 4% when the antiferromagnetic ground state is not affected. And the compression strain can increase T _N to 469 K due to the enhancement of antiferromagnetic coupling of the nearest adjacent magnetic atoms. Moreover, the bandgap and T _N of monolayer Mn _2 Cl _8 can be tuned by hydrogenation. This work finds that elemental substitution, strains, and hydrogen passivation is efficient routes to tune the electronic properties of monolayer antiferromagnetic semiconductor Mn _2 Cl _8 .

The (1-x)BiFeO3-xBiZn0.5Ti0.5O3 solid solutions (0.05 ≤ x ≤ 0.25) were prepared using high-pressure synthesis. Up to 25 at.% substitutions of Fe by the combination of [Mg0.5Ti0.5] were found to increase the unit cell volume of the primitive perovskite cell, while the crystal structure remains the rhombohedral perovskite, as that in the parent BiFeO3. With increasing temperature, the as-prepared ceramics of the x = 0.25 composition reversibly transform into a cubic modification between about 970 and 1070 K. However, this phase transition is overlapped with a gradual decomposition of the perovskite phase, which starts above 770 K. The perovskite phase with the substitution rate corresponding to x = 0.25 is antiferromagnetic below TN∼460 K. Peculiarities of the temperature-dependent magnetic behavior of this composition at about 220 and 315 K, which might indicate transitions between the states with different magnetic orderings, have been observed. [ABSTRACT FROM AUTHOR]

We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO2 dielectric and different thickness of high-k HfO2 dielectric. The results show that transform characteristic (Ids–Vgs) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO2 and HfO2 dielectric (SiO2-GFETs and HfO2-GFETs). The gate voltage reduces drastically in HfO2-GFETs compared with that in SiO2-GFETs, and it becomes much smaller with the decline of HfO2 thickness. The left charge neutrality point in Id-Vg curves of all HfO2-GFETs is negative, compared to the positive ones in SiO2-GFETs, which means that there exists n-doping in graphene with HfO2 as bottom dielectric. We speculate that this n-doping comes from the HfO2 layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO2-GFETs contrast to that in SiO2-GFETs. In a series of HfO2-GFETs with different HfO2 dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO2 film from atomic layer deposition process, the concentration of which varies from the thickness of HfO2 layer. [ABSTRACT FROM AUTHOR]

Néel temperature (TN), the antiferromagnetic to paramagnetic phase transition temperature, is also one of the important magnetic properties of antiferromagnets. Antiferromagnets could be used to write and read information below TN in electronic memory devices. Perovskite manganites are an important antiferromagnetic material with superior magnetic properties. However, it is challengeable to seek novel perovskite manganites with TN higher than room temperature by trial-and-error method. In this work, the maximum correlation minimum redundancy (mRMR) integrated machine learning approaches were used to screen the optimal subset of features, which included chemical compositions and atomic parameters of perovskite manganites. The machine learning model called support vector regression (SVR) was constructed to predict the TN of perovskite manganites. The correlation coefficient (R) between experimental TN and predicted TN reached as high as 0.87 for the training set in leave-one-out cross-validation (LOOCV) and 0.86 for the independent testing set, respectively. The high-throughput screening of new perovskites with higher TN temperature was then carried out by using our online computation platform for materials data mining (OCPMDM). The TN of designed perovskite manganites (Sr0.7Pm0.3MnO3) was predicted to be 307.5K, increasing by 6% compared to the maximum TN of Sr0.9Ce0.1MnO3 (290K) reported. Our machine learning model can be accessible for public on web server: http://materials-data-mining.com/lkl/lkl_model. [ABSTRACT FROM AUTHOR]

In this contribution, we reported our findings on NdFeO3–PbTiO3 composite system synthesized by conventional solid-state reaction route. The cell parameters, density and bond lengths (Fe-OI, Fe-OII) are determined by Rietveld refinement of X-ray diffraction data. Phase purity of the system was further confirmed through Fourier transform infrared (FTIR) and Raman spectroscopy techniques. The FTIR spectra reflected two important absorption bands around 656–505 cm−1 and 486–412 cm−1, corresponding to stretching (ν1) and bending (ν2) vibrational modes. The stretching vibrational mode (ν1) represents the absorbed IR energy in metal oxide (M–O) bonds. If the Raman spectra are related to two different symmetries, this includes the presence of two different phases in the sample. Thus, the phase purity is absent. The blue shift of Raman active mode at 720 cm−1 in pristine sample suggests that the increase in PbTiO3 concentration enhances the structural distortion in the system. The particle sizes as estimated using SEM micrographs were found to be in the range 147–250 nm. The ferroelectric behavior of NdFeO3 has been improved drastically with increase in PbTiO3 concentration. The P-E loops fitted by ferroelectric capacitor model established a good agreement between experimental and simulated data. The thermal properties of the powder samples were analyzed in a wide temperature range (300–900 K). The room temperature dielectric permittivity (ε′) and loss tangent (tanδ) for all the samples were analyzed in a broad frequency range (75 kHz–5 MHz). The behavior of dielectric permittivity in low-frequency region followed Maxwell–Wagner interfacial model, while in the high-frequency region, the composite system exhibited capacitive nature. The Néel temperature of the composite system decreased as compared to that of NdFeO3. The energy bandgap as determined with the help of Tauc's plots exhibits a slight decrease for composite samples in respect of pristine NdFeO3. [ABSTRACT FROM AUTHOR]

We report on the increase in spin re-orientation transition temperature (TSR) and Neel temperature (TN) in Nd0.95Gd0.05FeO3 compound, by substituting Gd3+ ions at the A-site of NdFeO3. Structural and magnetic properties of Nd1−xGdxFeO3 (x = 0, 0.03 and 0.05 mol%) have been analysed by employing solid-state reaction method. Crystallite size reduction and lattice contraction have been observed with increase in Gd substitution in NdFeO3. M–H curves depict strong ferromagnetic behaviour of Nd1−xGdxFeO3 with a non-saturating and large coercive hysteresis loops. The crystallite size of Nd1−xGdxFeO3 influences the magnetic property, resulting in the ferromagnetic behaviour with higher M and Hc values at room temperature and low temperatures. [ABSTRACT FROM AUTHOR]

This work investigates the role of p-d orbital hybridization in the structural transition from tetragonal I4 1 /amd to cubic Fd 3 ̅ m and enhancement in Néel temperature (T N) from 43 K to 175 K in (Mn 1−x Co x) 3 O 4 (where x = 0.0, 0.1, 0.2, 0.3, 0.5, and 0.6). X-ray absorption spectra of Co- L 2,3 and Mn- L 2,3 edges show that the high-spin Co2+ cations initially substitute the Mn2+ at the tetrahedral-sites. When the tetrahedral-sites are fully occupied, then the high-spin Co3+ cations begin to occupy the octahedral-site. The substitution of Co cations at both the tetrahedral and octahedral-sites increases the bond angle between adjacent tetrahedral and octahedral site cations via O- 2p orbitals, suppressing the orbital instability of Mn3+ cations. These effects dramatically enhance the superexchange interaction and hence the T N. • We observed structural transition and enhanced TN in Co-doped Mn 3 O 4. • We have investigated the p-d hybridization between O and TM ion using XAS. • Hybridization between p-d orbitals increases with Co substitution in Mn 3 O 4. • There is linear correlation between T N and p-d hybridization in Co-doped Mn 3 O 4. [ABSTRACT FROM AUTHOR]

• A theoretical model has been augmented to predict Curie temperature and Neel temperature of Ni and Fe 3 O 4 nanoparticles. • Model has incorporated size, shape and relaxation factor of nanoparticles ranging from cubic, spherical, wire and film. • Curie temperature and Neel temperature both have decreased with the decrement in particle size. • The effect has been found prominent as shape is changed from film to cubic. • Predicated results are closer to experimental/simulation data particularly up to 20 nm particle size. A simple and unified model, based on size, shape, and surface effect is reported to estimate the magnetic properties of Ni and Fe 3 O 4 nanomaterials. The relaxation factor, which is the ratio of dangling bonds to an atom's total bonds, is reported in the theory to estimate the properties of magnetic nanomaterials. The Curie temperature is projected to decrease with the decrement in particle size. The particle shape influences the Curie temperature of Ni and Fe 3 O 4 nanoparticles and this effect becomes prominent with the reduction in particle size. The model is extended on the same ground to analyze the Neel temperature of Ni and Fe 3 O 4 nanomaterials. Neel temperature also decreases as particle size decreases. The variation of Curie temperature and Neel temperature is projected for spherical, cubic, wire, and film shaped nanoparticles. It is also observed that the effect of size is more appreciable when the shape changes from cubic to the film of nanoparticles. Although, model predictions are valid throughout the size range of nanoparticles, but more noticeable up to the size of 20 nm. Moreover, the reported model is valid for all conducting and semiconducting crystalline nanostructured materials. Our theoretical calculations are in agreement with the standing experimental data and the simulation results for nanoparticles in varying shapes and sizes. [ABSTRACT FROM AUTHOR]

The residual stresses in a dense yttria‐stabilized zirconia (YSZ) layer bonded to a porous NiO‐YSZ substrate were measured by X‐ray diffraction in air between 25°C and 900°C. It was found that the residual stresses on the outer surface of the YSZ layer were compressive, that their magnitude increased with decreasing temperature, and that the temperature dependence was nonlinear particularly at temperatures below 600°C. An elastic model that incorporates micromechanics and laminate theory was formulated to successfully predicts the nonlinearity of the temperature dependence of the residual stresses by accounting for the effect of the order‐disorder transition experienced by YSZ around 600°C and the magnetic transition of NiO at the Néel temperature around 265°C, on the properties of these materials. The implications of the results for the reliability of solid oxide fuel cells are discussed. [ABSTRACT FROM AUTHOR]

A simple model based on the bond energy analysis is developed. The model is used to compute the size and shape dependence of magnetic properties, viz. Curie temperature TC(D), magnetization MS(D), and Neel temperature TN(D), where D denotes the size of nanoparticles. It is found that TC(D) and MS(D) decrease with a decrease in size. TN(D) is found to increase or decrease with dropping D, depending on the interaction strength at the film/substrate interface. The model predictions have been compared with the available experimental data. There is a reasonably good agreement between model predictions and experimental results. The model may be extended to other nanomaterials in different size and shape, due to its simplicity. The results obtained for corresponding bulk material are also included for comparison purposes. [ABSTRACT FROM AUTHOR]

Cobalt monoxide (CoO) nanocrystals were synthesized by thermal decomposition of cobalt oleate precursor in a high boiling point organic solvent 1-octadecene. The X-ray diffraction pattern and transmission electron microscopy studies suggest that pure face-centered-cubic (fcc) phase of CoO can be synthesized in the temperature range of 569-575 K. Thermolysis product at higher synthesis temperature 585K is a mixture of fcc and hexagonal-closed-packed (hcp) phases. These nanocrystals are single crystals of CoO and exhibit mixture of two types of morphologies; one is nearly spherical with 5-25 nm diameter, and other one is 5-10 nm thick flake. The pure fcc-CoO nanocrystals show enhanced, and mixture of fcc- and hcp-CoO nanocrystals show reduced antiferromagnetic ordering temperature. Such results provide new opportunities for optimizing and enhancing the properties and performance of cobalt oxide nanomaterials. [ABSTRACT FROM AUTHOR]

The magnetic properties and magnetocaloric effect (MCE) in RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds have been investigated. All these compounds possess an antiferromagnetic (AFM)-paramagnetic (PM) transition around their respective Neel temperatures. The RCu2Si2 compounds undergo spin-glassy behavior above Neel temperature. Furthermore, a field-induced metamagnetic transition from AFM to ferromagnetic (FM) states is observed in these compounds. The calculated magnetic entropy changes show that all RCu2Si2 and RCu2Ge2 (R = Ho, Er) compounds, especially, ErCu2Si2 exhibits large MCEs with no thermal hysteresis and magnetic hysteresis loss. The value of -ΔSMmax reaches 22.8 J/Kg K for magnetic field changes from 0 to 5T. In particular, for field changes of 1 and 2 T, the giant reversible magnetic entropy changes -ΔSMmax are 8.3 and 15.8 J/kg K at 2.5K, which is lower than the boiling point of helium. The low-field giant magnetic entropy change, together with ignorable thermal hysteresis and field hysteresis loss of ErCu2Si2 compound is expected to have effective applications in low temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

(Ni48Co6)Mn26Al20 polycrystalline ribbons with B2 structure at room temperature are investigated. Considering the presence of competing magnetic interactions, Arrott-plot analysis gives TN ∼ 170 K. A broad ferromagnetic-paramagnetic transition (TC) is observed at ∼200 K. H-T phase-diagram is used to validate the presence of competing exchange interactions that persist till very close to TC. Based on Néel theory, a cluster model is used to explain the presence of ferromagnetic and antiferromagnetic clusters in the sample. Formation of ferromagnetic clusters can be understood in terms of positive exchange interactions among the Mn atoms that are neighboring Co atoms located at Ni sites. [ABSTRACT FROM AUTHOR]

The magnetic properties of antiferromagnetic Mn3ZnN anti-perovskite nanoparticles have been studied using Monte Carlo simulations within the Ising model. The considered Hamiltonian includes the exchange interactions between Mn–Mn and the external magnetic field. The thermal magnetizations and magnetic susceptibilities of Mn3ZnN anti-perovskite nanoparticles are computed for different sizes. The Néel temperature is deduced. The exchange interaction between Mn and Mn atoms is obtained. Beyond the coupling value 2 K, the magnetization of system becomes independent of effect temperature. In addition, the variation of magnetizations with external magnetic field and crystal filed are also established for different temperatures. Mn3ZnN anti-perovskite nanoparticles exhibits the superparamagnetic behaviour for different temperatures value. [ABSTRACT FROM AUTHOR]

Spin valves with holmium layers and three-layer structures metal/Ho/metal were prepared by magnetron sputtering. A holmium layer in the spin valves is polycrystalline with weak axial <002> texture. The structural coherence length along the hexagonal c-axis is approximately 2/5 of the total thickness of the holmium layer. Field dependences of the spin valves magnetoresistance were measured at different temperatures. Correlation was revealed between magnetic state in holmium layer and the shape of magnetoresistive curve. Deviation of magnetic moments of the reference layer and the adjacent part of holmium from the applied magnetic field was investigated. The field induced mobility of the magnetic helicoid in holmium layers was revealed. Image 1 • Neel temperature of Ho layer depends on the thickness and microstructure perfection. • Antiferromagnetic Ho layer carries out exchange bias in the adjacent ferromagnetic. • Spin valve magnetoresistance correlates with the magnetic state in Ho layer. • Period of the magnetic helicoid in Ho layer varies with temperature. • The magnetic helicoid in Ho layer is rotated around c-axis by magnetic field. [ABSTRACT FROM AUTHOR]

Ternary Mn2FeSi alloy was synthesized from pure elemental powders by mechanical alloying, using a high-energy planetary ball mill. The formation of an inverse-Heusler phase after 168 h of milling and subsequent annealing at 1173 K for 1.5 h was confirmed by X-ray diffraction. The diffractogram analysis yielded XA structure and the lattice parameter 0.5677 nm in a good agreement with the theoretically obtained value of 0.560 nm. The final powder was formed by particles of irregular shape and median diameter D50 of 3.8 μm and their agglomerates. The chemical analysis resulted in the mean composition of 49.0 at.% Mn, 25.6 at.% Fe and 25.4 at.% Si. At room temperature, the prepared samples featured a heterogeneous magnetic structure consisting of dominant paramagnetic phase confirmed by Mössbauer spectrometry and a weak ferro-/ferrimagnetic contribution detected by magnetization curves. From the field-cooled and zero-field-cooled curves the Néel temperature of 67 K was determined.

The phase content and sequence, the crystal structure, and the magnetic properties of perovskite solid solutions of the (1−y)BiFeO3–yBiZn0.5Ti0.5O3 series (0.05 ≤ y ≤ 0.90) synthesized under high pressure have been studied. Two perovskite phases, namely the rhombohedral R3c and the tetragonal P4mm, which correspond to the structural types of the end members, BiFeO3 and BiZn0.5Ti0.5O3, respectively, were revealed in the as-synthesized samples. The rhombohedral and the tetragonal phases were found to coexist in the compositional range of 0.30 ≤ y ≤ 0.90. Magnetic properties of the BiFe1−y[Zn0.5Ti0.5]yO3 ceramics with y < 0.30 were measured as a function of temperature. The obtained compositional variations of the normalized unit-cell volume and the Néel temperature of the BiFe1−y[Zn0.5Ti0.5]yO3 perovskites in the range of their rhombohedral phase were compared with the respective dependences for the BiFe1−yB3+yO3 perovskites (where B3+ = Ga, Co, Mn, Cr, and Sc). The role of the high-pressure synthesis in the formation of the antiferromagnetic states different from the modulated cycloidal one characteristic of the parent BiFeO3 is discussed.

The effect of co-doping on structure and magnetic properties of the BiFeO3-based multiferroics with a partial isovalent substitution of bismuth for La3+, Gd3+, Dy3+, and Er3+ ions have been experimentally investigated by X-ray diffraction and magnetic methods. The ceramic R1xR20.2-xBi0.8FeO3 type (x = 0, 0.05, 0.10, 0.15, 0.20; R1, R2 = La, Gd, Dy, Er) samples have been prepared by a solid-state reaction method under cold pressing at high pressure P = 4 GPa. Temperature dependences of magnetization for the co-doped BiFeO3 demonstrate magnetic "weak ferromagnetic-antiferromagnetic" phase transitions in a high temperature range T = 550-650 K. The presence of a weak ferromagnetism in all compositions is confirmed by open loops of magnetic field dependences. It has been found out that the magnetic characteristics strongly depend on the degree of substitution, temperature, and magnitude of magnetic field. [ABSTRACT FROM AUTHOR]

NdFeO3 single crystals have been grown by optical floating-zone technique using Nd2O3 and Fe2O3 as the source by solid-state reaction method. The crystalline structure of NdFeO3 belongs to orthorhombic symmetry and the presence of a distorted perovskite structure was confirmed by powder X-ray diffraction (XRD) analysis. From the XRD results, it is visualized that the lattice expansion has been observed in the unit cell parameters which may appear due to interstitial defects in the NdFeO3 matrix. The deficiency of oxygen atoms and the presence of excess Fe ions in NdFeO3 have been confirmed with EDX spectra. The spin-reorientation region (T = 120 K) exhibits lower coercive field and the hysteresis loops depict enhanced magnetization (Ms and Mr) values of NdFeO3 single crystal. Presence of compensation temperature point at Tcomp = 7.5 K denotes the anti-parallel alignment of rare-earth ions with Fe magnetic moments. At high temperatures, Fe3+ magnetic moments show strong antiferromagnetic interactions ensuing in Neel temperature (TN) at 690 K. [ABSTRACT FROM AUTHOR]

Spin valves with nanostructure CoFe/Dy/CoFe and three-layer structures metal/Dy/metal were prepared by magnetron sputtering. The measurements of field dependences of magnetoresistance and magnetization were held at different temperatures. The changes of magnetotransport properties of spin valve containing CoFe/Dy/CoFe structure were used for getting information on the magnetic ordering in the dysprosium layer. The characteristic changes of magnetotransport properties caused by the formation of helical ordering in dysprosium layer were detected. Special attention was paid to the estimation of Neel temperature and to the investigation of microstructure of dysprosium nanolayer. • Neel temperature for the dysprosium layer with thickness 40 nm surrounded by Ta, NiFe and CoFe layers is 152, 157 and 154 K. • The magnetotransport properties of spin valve containing Dy layer were used for getting information on the magnetic ordering in dysprosium. • In spin valve containing nanostructure CoFe/Dy/CoFe the Dy layer at T < 133 K reveals properties of antiferromagnet. • Noncollinear magnetic structure forms in polycrystalline dysprosium nanolayer. [ABSTRACT FROM AUTHOR]

The influence of an external magnetic field on the phase-transition temperature for antiferromagnetic thin films is investigated. The computer modeling method for the antiferromagnetic Ising model with a thin film geometry is used. Films with thicknesses from 4 to 16 layers have been investigated. It is shown that the temperature of the antiferromagnetic phase transition decreases according to the square law as the external magnetic intensity increases. The rate of decrease of the phase-transition temperature depends on the film thickness and on the relationship between the exchange integrals on the surface and the bulk of the system. For each system, there is a limit value of the magnetic intensity such that no antiferromagnetic phase transition occurs if it is exceeded. The dependence of the limit value of the magnetic intensity on the relationship between the exchange integrals obeys the square law as well. [ABSTRACT FROM AUTHOR]

Magnetoelectric multiferroic materials are those which can be influenced by both electric and magnetic fields and have wide applications. Single-phase materials that show magnetoelectric effects are very few compared to composites. Recently, several studies have been conducted on magnetic and dielectric properties of single-phase double perovskite Sr 2 FeNbO 6 , while magnetoelectric effects have not been reported yet. The present study aims to explore the magnetoelectric effects of Sr 2 FeNbO 6 prepared through solid-state reaction route. Rietveld refinement confirms the orthorhombic symmetry of the material with Pbnm space group. The existence of Fe2+, Fe3+, and Nb5+ ions were investigated by XPS analysis. The room temperature magnetic and electric hysteresis loops display the simultaneous existence of magnetism and ferroelectricity in Sr 2 FeNbO 6. A high Curie temperature of 727 K is obtained from temperature-dependent variation of magnetization, making it suitable for spintronics applications. Further, this room temperature multiferroicity of Sr 2 FeNbO 6 was confirmed using magnetoelectric coupling measurement and obtained a coupling coefficient of 4.4 mV cm−1 Oe−1. The conclusion of Sr 2 FeNbO 6 showing ferrimagnetic nature is obtained through density functional theory (DFT) calculations. [Display omitted] • Single-Phase multiferroic Sr 2 FeNbO 6 has an orthorhombic structure with Pbnm space group. • A high value of ferrimagnetic Curie temperature (T C = 727 K) is obtained. • Unusual behavior of coercivity with temperature. • Magnetoelectric coupling measurement shows a coupling coefficient of 4.4 mV cm−1 Oe−1. • Density Functional Theory calculations confirm the ferrimagnetism. [ABSTRACT FROM AUTHOR]

The characterization of materials is an area of extreme importance for engineering, it uses a range of instrumental techniques to provide an information bank for material analysis and selection. In the treatment of iron ore the mineralogical characterization is done, almost exclusively, by optical microscopy. However, materials with very fine granulometry, below 4 µm, make their preparation and visualization restricted in this equipment. The present work aims to identify the minerals Hematite, Magnetite and Goethite in samples of tailings from the iron ore processing, employing a Bartington MS3 that evaluates the magnetic susceptibility as a function of the temperature. These measurements make it possible to identify Curie temperatures characteristic of Magnetite (580 °C) and Hematite (675 °C), as well as Goethite's Neel temperature (120 °C). The results showed that the application of the technique is of great value for the identification of the magnetic bearing minerals and the quantification of the magnetic potential of the sample.

Polycrystalline samples of Nd 0.5 R 0.5 FeO 3 (R = La, Pr and Sm) synthesized by sol-gel combustion method have been investigated for their structural, optical, thermal and magnetic properties. X-ray diffraction in combination with Fourier transform infrared (FTIR) spectra confirm the single-phase orthorhombic structure with Pbnm space group of all the samples. Rietveld refinement employed to determine the bond lengths (Fe–O, R–O) and bond angles (Fe–O–Fe) show a decrease in the bond angle with Sm doping. Transmission electron microscopy (TEM) micrographs reveal the nano-size particles and selected area electron diffraction (SAED) patterns indicate good crystallinity with a uniform distribution of particles throughout the samples. Raman spectra clearly indicate the compressive strain in the Sm doped sample that has been correlated with the structural parameters obtained from Rietveld refinement. The shift in wavenumber is the main cause of change in bond length (Fe–O) and tilt of octahedra due to rare earth ions. The optical bandgap is determined using Tauc's relation from the diffuse reflectance spectra. The variation of specific heat has been investigated with temperature in a broad temperature range. The endothermic peak in specific heat has been correlated with magnetic order. The value of Néel temperature increases in the case of La-doped sample and reduces for the Pr doping. However, the decrease of specific heat in Sm doped sample around 300 °C may be attributed due to the spin reorientation. Magnetic studies at room temperature reveal antiferromagnetic behavior with weak ferromagnetic component due to the canted ordering of Fe3+ spins. Magnetic properties are strongly dependent on the type of rare earth ion as the maximum magnetization (M m) is enhanced from 0.259 to 0.434 emu/g with the doping of rare earth ions (La, Pr and Sm). The increase in magnetization has been correlated with increased distortion which is evident from the decrease in the bond angle. Exchange bias (EB) effect is observed for all samples as single-phase orthorhombic structure is composed of antiferromagnetic (AFM) and ferromagnetic (FM) phases. • Nd 0.5 R 0.5 FeO 3 (R = La, Pr, and Sm) have been successfully synthesized using sol-gel auto-combustion route. • Fe–O–Fe bond angle is found to decrease from on doping with different rare earth ions. • Room temperature magnetic hysteresis loops show the antiferromagnetic behavior with weak ferromagnetism. • Neel temperature is found to increase in case of La doped sample and decreases in case of Pr doped sample. [ABSTRACT FROM AUTHOR]