Search

Evidence for the suppression of collective magnetic behavior of dipolarly interacting Fe nanoparticles is found in Fe-Ag granular multilayers. Interaction of Fe particles separated by an Ag layer is studied as a function of the nominal thickness of the Ag layer. The surprisingly increasing interaction with increasing Ag-layer thickness, verified by memory-effect measurements, is explained by the formation of pinholes in the Ag layer at small Ag thicknesses, allowing direct ferromagnetic coupling between the Fe particles. This coupling may hinder the frustration of superspins favored by dipolar interactions. At larger Ag thicknesses, the Ag layer is continuous without pinholes and frustration leads to the appearance of the superspin-glass state. The effect of increasing interactions correlates well with the growing deviation at low temperatures of the measured field-cooled (FC) magnetization from the interaction-free FC curve calculated by a model based on the relaxation of two-level systems. Similar phenomenon is reported in a recently published paper (Sánchez et al., Small 2022 , 18, 2106762) where a dense nanoparticle system is studied. Here the collective magnetic behavior of the particles due to dipolar interactions is suppressed when the anisotropy energy of the individual particles exceeds a certain threshold. [ABSTRACT FROM AUTHOR]

Highlights • Discussion of the crystal and magnetic structure of ilmenite Mn 2 FeSbO 6. • Ferrimagnetic transition at T N = 270 K. • Identical zero field and field cooled (ZFC-FC) M vs T curves. • Significant changes in M vs T curves with H and T due to unsaturated moments. • Near-zero coercive field in magnetization M vs applied magnetic field H curves. Abstract In the work presented the magnetic properties of the high pressure ilmenite phase Mn 2 FeSbO 6 are investigated in detail. It is shown that Mn 2 FeSbO 6 ilmenite is ferrimagnetic (T N ≈ 270 K) and exhibits a near-zero coercive field H C. Furthermore, the Mn2+-Mn2+, Fe3+-Fe3+ and Mn2+-Fe3+ magnetic exchange interactions exhibit gradual and continuous variations with temperature and magnetic field. The ferrimagnetic moment is unsaturated even at 120 kOe below the theoretical value of 5 μ B per f.u. [ABSTRACT FROM AUTHOR]

Permanent magnet materials based on the MM 2 Fe 14 B (MM = Misch-metal) are widely noted. However, as a room temperature paramagnetic phase, the existence of CeFe 2 phase in MM 2 Fe 14 B alloy is unavoidable. In order to eliminate the CeFe 2 phase, the La substitution on MM in MM 2 Fe 14 B alloys was described. Alloys with nominal composition of (La x MM 1−x ) 33 Fe 66 B (x = 0, 0.025, 0.05, 0.075, 0.1, 0.15) were prepared, and the crystal structure and magnetization of the (La x MM 1−x ) 33 Fe 66 B alloys were investigated. XRD results reveal that the lattice parameter a, c, unit-cell volume V, and c/a ratio of (La x MM 1−x ) 33 Fe 66 B alloys increase linearly with the La increase, indicating that La atoms enter into the main phase. Key to this study is the finding that CeFe 2 phase disappears with the La content above 0.075. It is therefore concluded that La substitution could inhibit formation of CeFe 2 phase. This is consistent with the observation from SEM-EDS. Another interesting finding is that La substitution would cause the change of Nd, Pr, La and Ce ratio in main phase, which means the ratios of four rare earth elements change with the La substitution. With the increase of x, the (Pr + Nd)/(La + Ce) ratio in main phase of (La x MM 1−x ) 33 Fe 66 B alloys decreases first, showing the lowest point at x = 0.075, and then increases. As a result, the saturation magnetization (M s ) of (La x MM 1−x ) 33 Fe 66 B alloys has the same tendency, which decreases from 11.78 kG (x = 0) to 11.35 kG (x = 0.075) first, and then increases to 11.96 kG (x = 0.15). And the Curie temperature (T c ) displays the same trend compared to the M s . These facts show that the MM has a great potential to prepare the low cost sintered permanent magnets. [ABSTRACT FROM AUTHOR]

In this work, we report the structural and magnetic properties of nanocrystalline Cu 1−x Zn x Fe 2 O 4 mixed ferrites synthesized using novel combustion method. The prepared samples are spinel structured and the secondary phase α-Fe 2 O 3 is also present in CuFe 2 O 4 . The size of the crystallites ranges between 9.6 nm and 31 nm and the lattice constant increases from 8.342 Å to 8.435 Å. The FTIR absorption bands of CuFe 2 O 4 are observed at 571 cm −1 and 409 cm −1 for tetrahedral and octahedral sites, respectively. These bands are shifting to 547 cm −1 and 397 cm −1 for Zn substitution. Raman spectra show the change in local environment of tetrahedral and octahedral interstitial sites with Zn. The FE-SEM images show that the prepared samples are nano sized and the substitution of Zn decreases the agglomeration. The magnetic study reveals that the saturation magnetizations initially increases from 21.45 emu/g (x = 0) to 44.16 emu/g (x = 0.2) and then decreases at 300 K. The superparamagnetic behavior is observed for samples of x ≥ 0.4 concentration. The temperature dependent zero field cooled and field cooled magnetic measurements confirm the superparamagnetic nature and the observed blocking temperature decreases from 120.4 K to 32.3 K. The hysteresis curves measured at 20 K show the coercivity and it varies from 663 Oe to 70 Oe for increasing Zn content. [ABSTRACT FROM AUTHOR]

• Polycrystalline specimens of Ba 2 Y 1- x Cu x TaO 6-δ were synthesized by the solid-state reaction route. • The magnetic properties of the Ba 2 Y 1- x Cu x TaO 6-δ solid solutions were investigated and reported for the first time. • The Cu for Y substitution induces paramagnetism and the onset of antiferromagnetic correlations. We carried out a study of the structural and magnetic properties of Ba 2 Y 1- x Cu x TaO 6- δ (0.0 ≤ x ≤ 0.5) compounds. The cubic rock-salt double perovskite structure of Ba 2 YTaO 6 is retained upon the partial substitution of Cu for Y up to x = 0.50 and the lattice parameter a drops at the rate of da/dx ≈ −0.17 ± 0.01 Å/%Cu. While the effective moment μ eff and the Curie-Weiss temperature θ CW are nearly negligible in Ba 2 YTaO 6 , the partial substitution of Cu for Y results shows an increase in μ eff at the rate of ≈ 1.9 ± 0.2 µ B /%Cu, consistently with the paramagnetic behavior expected for Cu2+, and a decrease in θ CW at the rate of −16 ± 2 K/%Cu. The drive of θ CW towards more negative values is suggestive of the onset of antiferromagnetic correlations. [ABSTRACT FROM AUTHOR]

We have studied the effect of replacing Mn 3+ by Cr 3+ on the structure, transport and magnetism in the bilayered manganite LaSr 2 Mn 2 O 7 . Although no structural transition was observed in LaSr 2 Mn 2−y Cr y O 7 (0.1 ≤ y ≤ 0.6), the electrical transport and the magnetic properties were found to be affected significantly by this substitution. Substitution of Cr 3+ reduces the conductivity by restricting the hopping of small polarons. Magnetization increases with increasing Cr 3+ concentration suggesting that Cr 3+ -ions induce ferromagnetic moments . The ferromagnetic and an antiferromagnetic phase observed above ∼60 K merge into an inhomogeneous phase below this temperature. Thermopower yields an essentially concentration independent charge density nearly equal to its value for chromium free composition inspite of its expected decrease with this substitution suggesting that the small charge density of the insulating AFM phase is supplemented by the free carriers in the FM phase. The inhomogeneous phase shows a relaxor type behavior which contrasts with the spin glass behavior seen in La 0.46 Sr 0.54 Mn 0.98 Cr 0.02 O 3 having an identical AFM magnetic state. The difference is attributed to the non-JT character of Cr-ions which reduce the distortion of the Mn O octahedra located within the FM domains. With a higher lattice strain in the surrounding AFM matrix the carriers remain confined within the FM domains leading to the relaxor type behavior. [ABSTRACT FROM AUTHOR]

Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn 2 type, space group P 6 3 /mmc , with lattice parameters a =536.4 pm, c =845.3 pm. Shortest inter-uranium distance 313 pm (along the c- axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10 −8 m 3 mol −1 (at T =2 K), which is slightly higher with magnetic field along the a- axis compared to the c- axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ =36 mJ mol −1 K −2 . [ABSTRACT FROM AUTHOR]

This article reviews magnetic memory effects in spin-glasses (SG), superspin-glasses (SSG) and superparamagnetic (SPM) materials with detailed discussions about protocols and mechanisms. The origin of time (t) and temperature (T) dependent magnetic memory effects in different classes of materials have been discussed starting from the nanoscale towards the bulk magnetism. Magnetic memory effects (T and t dependent) in field cooled (FC) and zero field cooled (ZFC) protocols are focused to understand the physics of ageing and rejuvenation in SG, SSG and SPM materials. The article is enlightened with significant discussion to understand the diverse nature and classified properties of magnetic memory of the said materials. • M emory effects in SG (both in bulk and nano) and SPM materials. • Origin, footprint and diverse characteristics of memory effect. • Significantly covers the field of magnetism especially magnetic metastabilities. • Diverse nature and classified properties of magnetic memory. [ABSTRACT FROM AUTHOR]

The magnetic forces between paramagnetic squares cannot be calculated using a classic dipolar model because the magnetic field distribution is not uniform within square particles. Here, we present the calculation of magnetic forces and torques on paramagnetic squares in a uniform 2-D magnetic field using a Laplace's equation solver. With these calculations, we simulate the variations in equilibrium configurations as a function of number of interacting squares. For example, a single square orients with its diagonal directed to the external field while a system of multiple squares will assemble into chain-like structures with their edges directed to the external field. Unlike chains of spherical magnetic particles, that easily stagger themselves to aggregate, chains consisting of magnetic squares are unable to aggregate due to interchain repulsion. [ABSTRACT FROM AUTHOR]

The precise quantification of catalyst residues in purified carbon nanotubes is often a major issue in view of any fundamental and/or applicative studies. More importantly, since the best CNTs are successfully grown with magnetic catalysts, their quantification becomes strictly necessary to better understand intrinsic properties of CNT. For these reasons, we have deeply analyzed the catalyst content remained in nickel–yttrium arc-discharge single walled carbon nanotubes purified by both a chlorine-gas phase and a standard acid-based treatment. The study focuses on Ni analysis which has been investigated by transmission electron microscopy, X-ray diffraction, thermogravimetry analysis, and magnetic measurements. In the case of the acid-based treatment, all quantifications result in a decrease of the nanocrystallized Ni by a factor of two. In the case of the halogen gas treatment, analysis and quantification of Ni content is less straightforward: a huge difference appears between X-ray diffraction and thermogravimetry results. Thanks to magnetic measurements, this disagreement is explained by the presence of Ni 2+ ions, belonging to NiCl 2 formed during the Cl-based purification process. In particular, NiCl 2 compound appears under different magnetic/crystalline phases: paramagnetic or diamagnetic, or well intercalated in between carbon sheets with an ordered magnetic phase at low temperature. [ABSTRACT FROM AUTHOR]

Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature T B of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co–Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of T B occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces T B further down to 35 K. Additionally, a second blocked magnetic phase with much higher T B emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co–Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix. • Co-rich clusters in nanoporous Pd matrix prepared by electrochemical dealloying. • Co-rich clusters show superparamagnetic behavior. • Annealing leads to diffusion of Co in matrix and shrinkage of magnetic cluster size. • Larger magnetic entities can form at increased annealing temperature of 773 K. • Formation of weakly ferromagnetic Co–Pd alloy phase upon annealing at 973 K. [ABSTRACT FROM AUTHOR]

• The Pb vacancies, O defects and Co ions induce room FM for PbPd 1-x Co x O 2. • F dopant can induce the changed valence states of O, Co and Pd ions. • The enhanced magnetization results mainly from Pd(2−δ)+ and more O1− induced by F. • A magnetization jump at 265 K is observed originate from valence state transformation between O1− and O2−. In this work, Co-doped and Co-F co-doped PbPdO 2 nanoparticles with a body-centered orthorhombic structure were synthesized via sol–gel method. The measured results reveal that, Pb and O vacancies exist in all samples; the valence state of magnetic atom Co is identified as mixed Co2+ and Co3+; all samples exhibit both ferromagnetism and paramagnetism; the incorporation of fluorine results in an evident increase in the magnetic moment of PbPd 0.875 Co 0.125 O 2 @F; a jump of magnetization at about 265 K can be found in both FC and ZFC curves of PbPd 1-x Co x O 2 (x = 0, 0.05, 0.10 and 0.115). Moreover, the origin of the magnetism can be considered as follows: the ferromagnetism for PbPd 1-x Co x O 2 (0 < x ≤ 0.15) results from the combined effect of O1− and magnetic Co ions; fluorine substitution in an oxygen lattice site and the fluorine doping in the interstitial sites can induce both distinct roles on the valence of oxygen, Co and Pd ions, which changes evidently the magnetic properties of PbPd 1-x Co x O 2. Fortunately, the magnetic properties of PbPdO 2 , Co-doped PbPdO 2 , Co-F co-doped PbPdO 2 can be verified by first-principles calculations. It is found that the enhanced magnetization results mainly from Pd(2−δ)+ and more O1− induced by F. Finally, the magnetization jump at about 265 K has been explained by the temperature-dependent valence transformation between O2− and O1−. [ABSTRACT FROM AUTHOR]

We report on the magnetic property of 0.67–WO 3 +0.33–VO x mixture film deposit on the corning glass substrate using the chemical sol–gel and atmospheric pressure chemical vapor deposition (APCVD) methods. The XRD and Raman spectroscopy confirm species of both materials, and the morphological studies with FIB-SEM and TEM reveal segregation of W and V atoms. XPS reveals that V 4+ from VO 2 forms only 11% of the film; V 3+ in the form of V 2 O 3 form 1% of the film, 21% is V 5+ from V 2 O 5 and 67% is given to W 6+ from WO 3 . The analysis of the ESR data shows some sharp changes in the magnetism near the metal-to-insulator (MIT), which could be theoretically interpreted as the ordering or alignment of electron spins from net moment nature to parallel alignment of magnetic moment. The derivatives of magnetic susceptibility established the thermally induced magnetic property: two distinct transitions of 339 K for heating data and 338 K for cooling data for 151.2 mT field were obtained. Similar results were also obtained for 308.7 mT field, 336 K for heating data and 335 K for cooling data. VSM results confirm a paramagnetic phase with a small amount of magnetically ordered phase. [ABSTRACT FROM AUTHOR]

In this work we investigate magnetic effects in terms of the translational and rotational invariances of magnetisation. Whilst Landau-type diamagnetism originates from translational invariance, a new diamagnetism could result from rotational invariance. Translational invariance results in only conventional Landau-type diamagnetism, whereas rotational invariance can induce a paramagnetic susceptibility for localised electrons and also a new kind of diamagnetism that is specific to conducting electrons. In solids, the moving electron shows a paramagnetic susceptibility but the surrounding screening of electrons may produce a new diamagnetic response by Lenz's law, resulting in a total susceptibility that tends to zero. For electricity, similar behaviours are obtained. We also derive the DC-type negative electric susceptibility via two methods in analogy with Landau diamagnetism. [ABSTRACT FROM AUTHOR]

Abstract: Conventional magnetic order in a material requires the partially filled d or f bands. The exchange interactions between the electrons in these partially filled bands give rise to a magnetic order. However, the discovery of unexpected magnetism observed in some nanomaterials, which have the d and f shells either completely empty or full, has challenged our understanding of magnetism in conventional materials. The magnetism in nanomaterials shows the effects of reduced dimensions, reduced coordination of atoms at the surface and some quantum effects which dominate at low dimensions. In this review paper we give a brief review and discuss the unexpected magnetism experimentally observed and/or theoretically predicted in nanomaterials of conventional magnetic and nonmagnetic bulk materials. [Copyright &y& Elsevier]

Abstract: We have studied the effect of Fe for Mn substitution on magnetic properties of NdMn1−x Fe x O3+δ compounds. Our heat capacity, AC susceptibility and magnetization measurements revealed that the transition from paramagnetic to magnetically ordered state of the Mn sublattice decreases linearly from T N=74.9K to T N=49K with doping up to x=0.25. The ordering temperature T 1 of Nd sublattice varies in a non-monotonous way in the temperature range 11–16K. For x=0.3, the ordering of the Mn/Fe sublattice is residual, while the magnetism in Nd sublattice seems to be intact. The broad maximum in heat capacity C(T) at about 10K was ascribed by 2-level Schottky contribution (Δ=21(1)K) for x=0, but this description failed for Fe-doped samples. An upturn of C(T) at temperatures below 0.5K was observed on NdMnO3 and can be accounted to nuclear contribution. A more detailed study of AC susceptibility performed on samples with x=0.1 and 0.2 revealed a shift of both peaks to higher temperature with increasing frequency. The compensation temperature and a large negative field-cooled magnetization was observed for concentrations x=0.2 and x=0.25. [Copyright &y& Elsevier]

Abstract: The AC magnetic susceptibility of water is studied in the frequency range of 1kHz–1MHz at a low magnetic field. The results show a paramagnetic behavior between 500kHz and 1MHz for samples at 37°C and 25°C, which is surprising considering that water is believed to be diamagnetic. AC magnetic susceptibilities for ice and different salt solutions were investigated as well: in such cases the susceptibility is always negative and therefore, such samples remain diamagnetic. [Copyright &y& Elsevier]

Abstract: Iron disilicide has been found to exhibit superparamagnetism in nanoparticles, even though no magnetic ordering occurs in bulk. The unexpected behavior was attributed, based on magnetic studies, to chemical disorder. A lack of sextet-type signals in Mössbauer spectra supports that the observed magnetic order is confined to only a very small fraction of magnetic Fe ions. Moreover, quadrupole-splitting and isomer-shift parameters reveal a significant amount of Fe in a short-range α-FeSi2 structure, while XRD suggests an overall β-FeSi2 structure. Such a compositional heterogeneity is also reflected in a calorimetrically obtained spin-glass-like anomaly at low temperatures. Meanwhile, as the particle size decreases, specific heat and Sommerfeld constant are enhanced due to lattice softening and the emergence of surface charge density of states, respectively, in nanoparticles. [Copyright &y& Elsevier]

Abstract: We demonstrate through experiment and simulation that when mono-domain Fe nanoparticles are formed into chains by the application of a magnetic field, the susceptibility of the resulting structure is greatly enhanced (11.4-fold) parallel to the particle chains and is much larger than transverse to the chains. Simulations show that this significant enhancement is expected when the susceptibility of the individual particles approaches 5 in MKS units, and is due to the spontaneous magnetization of individual particle chains, which occurs because of the strong dipolar interactions. This large enhancement is only possible with nanoparticles, because demagnetization fields limit the susceptibility of a spherical multi-domain particle to 3 (MKS). Experimental confirmation of the large susceptibility enhancement is presented, and both the enhancement and the susceptibility anisotropy are found to agree with simulation. The specific susceptibility of the nanocomposite is 54 (MKS), which exceeds the highest value we have obtained for field-structured composites of multi-domain particles by a factor of four. [Copyright &y& Elsevier]

Abstract: Temperature and field dependencies of the magnetization of melt-spun ribbons of Ni45.7Mn37.2Ga17.1 (T CT A), where T A and T C are the reverse martensitic transformation and Curie temperatures, respectively, have been studied in broad ranges of magnetic fields (±30kOe) and temperatures (10–350K). It was found that the magnetic and thermomagnetic properties have a number of peculiarities and anomalies. Particularly, the magnetization values measured at both low and high magnetic fields increase significantly after annealing. Low-temperature anomalies of magnetization suggest the presence of the superparamagnetic behavior and/or phenomena related to the concurrent exchange interactions in the as-spun state. The obtained results can be explained by the influence of concentration inhomogeneities and atomic disordering in the rapidly quenched ribbons, which can be reduced by annealing. [Copyright &y& Elsevier]

Abstract: Nanoparticles of Ni0.25Co0.25Zn0.5Fe2O4 with different particle sizes were synthesized by chemical coprecipitation technique. The prepared nanoparticles were characterized and studied by X-ray diffraction, room temperature 57Fe Mössbauer spectroscopy and DC magnetization. Increase in annealing temperature leads to inversion of cations from their normal configurations which results in an increase in the hyperfine fields at both tetrahedral A and octahedral B sites. The decrease in saturation magnetization values with an increase in annealing temperature can be attributed to the variation in proportions of superparamagnetic phase and also the redistribution of cations in these ferrite nanoparticles. Variation of coercivity with annealing temperatures can be explained in terms of the size effect. [Copyright &y& Elsevier]

Abstract: Static and dynamic magnetic properties are examined for granular systems Co x (TiO2)1− x with Co volumetric contents of 31.6, 41.4, 49.4 and 57.6vol%. The ferromagnetic resonance (FMR) technique in the 38–45GHz band and the vibrating sample magnetometer technique were applied. The results from comparative analysis of saturation magnetization defined by both methods are discussed and the estimation of the most probable sizes and shapes of magnetic particles forming the nanocomposite is carried out. [Copyright &y& Elsevier]

Abstract: Superparamagnetic γ-Fe2O3 nanocrystallites have been prepared by γ-irradiating ferrocene in the presence of isopropyl alcohol to get Fe nanoparticles in nitrogen atmosphere and at room temperature, followed by oxidization in air to obtain γ-Fe2O3. The final black powder was characterized with X-ray powder diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). From XRD pattern and XPS spectrum, we can confirm to get γ-Fe2O3. The particle size is several nanometers as shown in TEM image. Magnetic hysteresis loop measurements exhibited that the γ-Fe2O3 nanoparticles display superparamagnetism. However, a trace black powder was obtained in kerosene oil using the same method. A possible formation mechanism of the γ-Fe2O3 nanoparticles was suggested. [Copyright &y& Elsevier]

Abstract: Yttrium iron garnet (YIG) powders with particle sizes of 9, 14, 25 and 60nm have been synthesised and their magnetic properties have been studied as a function of particle size and temperature. The particles with sizes of 9 and 14nm exhibited superparamagnetism. The blocking temperature () decreased with decreasing particle size, whereas the anisotropy constant (K) increased. The saturation magnetisation () decreased with decreasing particle size. These variations are attributed to large surface-to-volume ratios in nanoparticles where the surface moments are predominant. [Copyright &y& Elsevier]

Abstract: The magnetic and magnetoresistive properties of nanostructured Fe/Cr multilayers with ultrathin Fe layers (the nominal Fe thickness is down to ) were investigated at low temperatures (down to 4.2K) in magnetic fields up to 90kOe. Nanostructures were MBE grown in ultrahigh vacuum on single crystal MgO substrates. It is shown that Fe layers in nanostructures with are not continuous but consist of separate ferromagnetic clusters. Such cluster-layered nanostructures exhibit the superparamagnetic properties and the Kondo-like behavior of the resistance. [Copyright &y& Elsevier]

Abstract: We report on the rare earth valence and paramagnetic properties of the double filled skutterudites Ce1-yYbyFe4Sb12, BayFe4Sb12 and LayFe4Sb12. The susceptibility of all these compounds are well described by a Curie–Weiss law above 150K. BayFe4Sb12 and LayFe4Sb12 have, respectively, an effective moment of 3.0 and 2.9μB (f.u.)-1 and a paramagnetic temperature (θp) of 29K and -70K. In the Ce1-zYbzFe4Sb12 series, the paramagnetic temperature steadily increases from –80K in CeFe4Sb12 to +55K in Yb0.93Fe4Sb12, underlining a change in the character of the dominant interactions, from antiferromagnetic-to-ferromagnetic when one goes from trivalent cerium to nearly divalent ytterbium (v=2.2). The effective paramagnetic moment has been separated into three contributions, arising, respectively, from cerium, ytterbium and [Fe4Sb12]. The weak contribution of ytterbium to paramagnetism and the great similarity between the thermal variations of susceptibility in Yb0.93Fe4Sb12 and in BayFe4Sb12 seriously challenge previous scenarios for the low-temperature properties of Yb0.93Fe4Sb12. The nearly constant contribution of [Fe4Sb12] across the series (3.1μB(f.u.)-1 in CeFe4Sb12 and 3.2μB(f.u.)-1 in Yb0.93Fe4Sb12) contradicts the prediction of the “ionic model” and demonstrates the itinerant character of [Fe4Sb12] electrons. When substituting Fe by Ni in CeyFe4-xNixSb12, and θp are both affected, reflecting a change in the electronic band structure. [Copyright &y& Elsevier]

In this work, we have studied the magnetocaloric effect (MCE) of Ho(Co1-xNix)2 for 0⩽x⩽0.1. HoCo2 exhibits a first-order ferrimagnetic to paramagnetic transition at TC=78 K. The substitution of Ni for Co lowers TC of the compound. While the character of the transition and the MCE changes from a first-order type to a second-order type by the Ni substitution, the large MCE at around TC is maintained up to x=0.1. The origin of the large MCE of the compounds is discussed. [Copyright &y& Elsevier]

X-ray diffraction, Mo¨ssbauer effect and magnetisation investigations have been performed on sputtered Fe40(Al2O3)60 thin films. Ultrafine Fe particles of nanometer size in an amorphous Al2O3 matrix have been formed by annealing in the temperature range from 100°C to 500°C. Their particle sizes, however, show a rather wide distribution. Mo¨ssbauer spectra are constituted of both paramagnetic and ferromagnetic contributions. The paramagnetic contribution is associated with small grains of Fe, whereas the magnetic component is contributed by large iron grains. This assumption is supported by the ZFC- and FC-measurements, in which the “blocking” temperatures of 60 and 90 K were evidenced for as-deposited and 200°C-annealed films, respectively. [Copyright &y& Elsevier]

• Mn-doped nanosized titanium dioxide powders were synthesized by a sol–gel method. • Mn doping leads to the predominance of the paramagnetic contribution to the magnetization over the diamagnetic contribution and a small increase in the number of the ferromagnetic clusters. • The linear part along with the diamagnetic contribution typical for metal oxides is due to the contribution of two types of paramagnetic centers. • These regions do not interact magnetically, and the powder as a whole exhibits superparamagnetic behavior. Studies of magnetization of undoped and Mn-doped nanosized titanium dioxide powders showed that its dependence on the magnetic field can be approximated by the function that is a linear combination of two Langevin functions with different parameters. The linear part along with the diamagnetic contribution typical for metal oxides is due to the contribution of two types of paramagnetic centers. The first one is present in both undoped and doped powders. As follows from the published models, the centers are complex lattice defects Ti+3 ions + O− vacancies. The second is the vast majority of the manganese ions (and related oxide vacancies) in the doped powders that are uniformly distributed over all nanoparticles. The nonlinear part, even present in the undoped samples, is caused by the contribution of a small number of regions with a high magnetic moment (ferromagnetic clusters). These regions do not interact magnetically, and the powder as a whole exhibits superparamagnetic behavior. According to our estimates, the introduction of Mn into the TiO 2 lattice mainly leads to the predominance of the paramagnetic contribution to the magnetization over the diamagnetic contribution characteristic of the TiO 2 lattice and a small increase in the number of the ferromagnetic clusters. [ABSTRACT FROM AUTHOR]

Abstract: 57Fe Mössbauer measurements of has been carried out in external field . The negative quadrupole splitting QS was enhanced between 70 and 110K. Negligibly small QS in the paramagnetic state was verified by a measurement of the spectrum in the applied field of 10kOe. A correlation between the magnetic state and the electric field gradient implies that the origin of is not only due to the dipole field from magnetic Np atoms, but also from magnetic Fe atoms. [Copyright &y& Elsevier]

Abstract: Liquid crystal doped with a small quantity of ferrofluid produces a ferronematic that can be oriented at low magnetic fields. In order for this orientation to occur the ferrofluid particles must be blocked at room temperature. It will be shown that this is possible only for the case of ferronematics doped with large (order of 10nm) magnetic nanoparticles sizes. But when the ferrofluid added to the liquid crystal has smaller particles sizes it becomes superparamagnetic. Thus, it is observed that the Néel rotation of the smaller magnetic particles are facilitated by the liquid crystal environment, while for the larger ones the coupling to this environment is sufficient to raise the blocking temperature. [Copyright &y& Elsevier]

Abstract: We report on magnetic behavior of the electromagnetic compatibility (EMC) compound FF6.2 and composites prepared by the modified Stöber method using FF6.2 as the magnetic ion-containing (Fe2+/Fe3+) precursor. The composites were characterized by the X-ray diffraction analysis (XRD) and morphology of the magnetic powders was investigated by a scanning electron microscope (SEM) and a high resolution transmision electron microscope (HR TEM). Magnetic properties of the materials were studied by measurements of the magnetization, AC susceptibility and Mössbauer spectra. [Copyright &y& Elsevier]

Abstract: Magnetostriction of amorphous Fe79Mo8Cu1B12, (Fe12Co1)79Mo8Cu1B12 and (Fe9Co1)79Mo8Cu1B12 prepared by planar flow casting was measured using a direct method. The results indicate that magnetostriction in parallel and perpendicular directions of applied magnetic field is linearly dependent on magnetic field. In order to determine the influences of chemical composition and the conditions of sample preparation the magnetostriction of pure BCC-Fe, Cu and Mo were also measured. Samples containing Co with Curie temperatures slightly above room temperatures were shown to exhibit a hybrid magnetostriction behaviour with both ferromagnetic and paramagnetic features. [Copyright &y& Elsevier]

Abstract: Although a common technique to obtain the grain size distribution of an ensemble of magnetic nanoparticles is to fit its high-temperature magnetization to a distribution of Langevin functions, the anisotropy at temperatures close to the blocking temperature produces spurious results. This effect is justified on the basis of a power expansion of the free energy of the system. [Copyright &y& Elsevier]

Abstract: To study the nature of anisotropy effects in samples of polymer (PVA) films containing nanoparticles of magnetite the depth selective conversion Mössbauer spectroscopy (for layer-by-layer phase and magnetic analysis), saturation isothermal remanent magnetization (SIRM) and natural remanent magnetization measurements (NRM) in three mutual—orthogonal directions and atomic force microscopy were used. These investigations revealed formation of “in plane” direction of linear Fe3O4 nanoparticles chains and their number increase with nanoparticles concentration growth in the samples. Significant influence of polymer matrix on macroscopic magnetic properties was revealed from the temperature dependences of saturation magnetization and Mössbauer spectra. [Copyright &y& Elsevier]

Abstract: Magnetic properties of surfactant-coated and uncoated superparamagnetic iron oxide nanoparticles, Fe3O4 (SPION) were investigated by electron spin resonance (ESR) technique. For all samples, a strong and broad single ESR signal has been observed at all temperatures. A strong temperature dependence of ESR linewidth and resonance field is observed. Also, there is a strong effect of surfactant coating on magnetic properties of Fe3O4 nanoparticles. While the resonance field is decreasing by coating, the linewidth of the ESR spectra is increasing. These changes in resonance field and the linewidth are attributed to the decrease in effective magnetic moment due to a non-collinear spin structure originated from the pinning of the surface spins and coated surfactant at the interface of nanoparticles. Also, the changes are due to the contribution of the volume of the diamagnetic coating mass to the sample volume. [Copyright &y& Elsevier]

Abstract: Dynamic magnetic hysteresis in a nanoparticle is treated with the aid of Brown''s kinetic equation. The case in question is the one where the period of the external field falls in between the short intrawell and long interwell magnetic relaxation times. Dependencies of the hysteresis loop on the frequency and amplitude of the field and on temperature are found and analyzed. [Copyright &y& Elsevier]

Abstract: Using a co-precipitation method, perovskite-type manganese oxide La0.7Sr0.3MnO3 nanoparticles (NPs) with particle size 12nm were prepared. Detailed studies of both 55Mn nuclear magnetic resonance and superparamagnetic resonance spectrum, completed by magnetic measurements, have been performed to obtain microscopic information on the local magnetic structure of the NP. Our results on nuclear dynamics provide direct evidence of formation of a magnetically dead layer, of the thickness ≈2nm, at the particle surface. Temperature dependences of the magnetic resonance spectra have been measured to obtain information about complex magnetic properties of La0.7Sr0.3MnO3 fine-particle ensembles. In particular, electron paramagnetic resonance spectrum at 300K shows a relatively narrow sharp line, but as the temperature decreases to 5K, the apparent resonance field decreases and the line width considerably increases. The low-temperature blocking of the NPs magnetic moments has been clearly observed in the electron paramagnetic resonances. The blocking temperature depends on the measuring frequency and for the ensemble of 12nm NPs at 9.244GHz has been evaluated as 110K. [Copyright &y& Elsevier]