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• Synthesis of single-phase ferrite nanoparticles. • Doping of Jahn-Teller active Cu2+ ions. • Lowering of crystal symmetry. • Observation of superparamagnetic behavior. • Good dielectric below 100 Hz. Samples with empirical formula Ni 1-x Cu x Fe 2 O 4 (x = 0.00, 0.25, 0.50, and 1.00) were prepared using chemical route. All the samples showed single spinel phase without any impurity. Average crystallite sizes were observed in the range of 12 nm to 39 nm as calculated by using Williamson-Hall (W-H) graphs. Raman spectra of all samples confirmed the lowering of crystal symmetry of octahedral sublattices with increasing Cu content. Signature of Jahn-Teller distortion due to substitution of Cu2+ (3d9) ions was detected using Raman spectroscopy. Absorption spectra of all the samples were recorded using UV–Vis spectroscopy, which confirmed the opaque character near red and infrared (IR) region. Onset of superparamagnetic behaviour has been observed by incorporating Cu2+ in the nickel ferrite with the mean blocking temperatures for all samples well below 300 K. Dielectric studies revealed that the grain boundaries played a major role in controlling the properties with increase in Cu2+ percentage. [ABSTRACT FROM AUTHOR]

Ni 2.14 Mnd 0.55 Sb 1.3 Heusler alloy has been prepared by the conventional arc melting method with vacuum-sealed annealing. The sample has been crystallized to Fm 3 ¯ m space group in L2 1 phase, and it is the parent crystal structure of the Ni-based Full Heusler alloy. It has been found that the sample has the Curie temperature (para to ferromagnetic transition temperature) at 290K. It was determined from magnetization ∼ temperature plot (M ∼ T) as well as by employing the Arrott plot method. Also, critical exponent analysis by employing the Arrott plot and Kouvel-Fisher methods confirm that the sample (Ni 2.14 Mn 0.55 Sb 1.31) obeys mean field theory with long range spin ordering. Analysis of temperature dependent resistivity data interestingly reveals the phonon-phonon and magnon-manon scattering dominance above and below the Curie temperature, respectively. The electrical and magnetic properties investigation endorse that there is a correlation between magnetic and electrical properties of the above sample. The magnetocaloric effect (MCE) analysis is carried out by using the Maxwell's equations in isothermal magnetization data. It is interesting to note that the sample exhibits maximum MCE near the room temperature (∼290K), i.e., the magnetic Curie temperature. Hence the present alloy may be a potential material to be used for magnetic refrigeration application. • Para to ferromagnetic transition temperature (Curie temperature, T C) is at 290 K, which is near room temperature. • There is semi-metallic behaviour at 60 K–130 K and at 300 K–400 K, there is metallic behaviour. • There is metal to semimetal transition with reasonable RCP value near about 290 K, which is a magnetic Curie temperature. [ABSTRACT FROM AUTHOR]

• The magnetic and magnetocaloric property is investigated for Pt doped Ni 2− x Pt x MnGa (x = 0.2, 0.3 and 1.0) alloys at ambient pressure. • The pressure also induces the AFM/FM interaction at low temperature for x = 0.2 alloy, where previously not observed in Ni-Mn based alloys under pressure. • The metamagnetic transition and crossover of magnetization are suppressed for x = 1.0 alloy. • The application of chemical and hydrostatic pressure increases the T M and decreases Δ S M. The magnetocaloric effect (MCE) on Ni 2− x Pt x MnGa (x = 0.2, 0.3 and 1.0) shape memory Heusler alloys around martensite phase transition temperature (T M) is investigated by varying chemical pressure (Pt concentration). The magnetic entropy change (Δ S M) decreases with increasing chemical pressure for various external applied magnetic fields up to 3 T, and the width of thermal hysteresis increases with the increases of Pt concentration. The effect of hydrostatic pressure on both T M and ΔS M for Ni 1.8 Pt 0.2 MnGa is also investigated. We observed that the application of hydrostatic pressure increases T M (3.5 K/GPa) and stabilizes the martensite phase. The maximum magnetic entropy change (Δ S max) of 9.31 J Kg−1 K-1is observed for a field change of 9 T at ambient pressure for Ni 1.8 Pt 0.2 MnGa. Further, the application of external pressure leads to the decrease of ΔS max to 5.52 J Kg−1 K−1 at 0.91 GPa. [ABSTRACT FROM AUTHOR]

• Increase in M r , M S and H c with increase in BHF percentage BLFO-BHF composite. • ΔH ~ M plot explains the magnetic interaction between BLFO and BHF magnetic phase. • Vegard's law has been used to calculate the theoretical magnetization. • Law of approach to saturation has been employed to analyze the magnetic hysteresis. Two different sets of multiferroic nanocomposites i.e., (1-x)Bi 0.85 La 0.15 FeO 3 -(x)BaFe 12 O 19 with x = 0.00, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50 and 1.00 have been synthesized by the solid-state reaction method and high energy planetary ball mill techniques. The peaks in the XRD patterns can be indexed to R3c crystal symmetry of Bi 0.85 La 0.15 FeO 3 and P63/mmc crystal symmetry of BaFe 12 O 19. It suggests the absence of any major chemical reaction between the two phases. Moreover, it is assumed thatBi 0.85 La 0.15 FeO 3 and BaFe 12 O 19 crystal symmetries are present in the composite independently. Magnetic properties have been improved significantly due to the incorporation of BaFe 12 O 19 in the composites. Vegard's law suggests that the experimentally observed magnetizations are higher than that of theoretically calculated value. The difference between the theoretical and experimental magnetization as well as the anomaly in the magnetic hysteresis have been explained by considering the magnetic interaction correlation length between Bi 0.85 La 0.15 FeO 3 and BaFe 12 O 19 magnetic phases. The hysteresis loop width (ΔH) versus M plots has been introduced to understand the magnetic interaction (exchange bias) between Bi 0.85 La 0.15 FeO 3 and BaFe 12 O 19. Magnetocrystalline anisotropy increases with the increase in the percentage of BaFe 12 O 19 in the composite. [ABSTRACT FROM AUTHOR]

The Rietveld refinement of XRD patterns reveals the crystallization of all the materials (BaFe 12-x Zn x O 19 for x = 0.0, 0.2, 0.4, and 0.6) to hexagonal symmetry with space group P6 3 /mmc. The lattice strain created in the crystal due to the ionic size mismatch of Zn and Fe. The Law of Approach (LA) to saturation method is employed to obtain the saturation magnetization (M s) and magnetocrystalline anisotropy constant (K 1) from M − H hysteresis loop. The maximum saturation Magnetization (M s) and minimum coercivity are found to be for BaFe 11·8 Zn 0·2 O 19 (i.e., x = 0.2). The magnetocrystalline anisotropy constant (K 1) reduces with the increase in temperature. The magnetic properties and magnetic crystalline anisotropy in Zn modified barium hexaferrite have been explained by considering the strain in the lattice site and superexchange interaction. [ABSTRACT FROM AUTHOR]

Crystallographic parameters and their correlation with the magnetic and electrical parameters of BaFe 12−x Cu x O 19 for x = 0.00, 0.50, 1.00, 1.50 and 2.00 samples. • Correlation between the crystal structure parameters with the magnetic and dielectric properties of BaFe 12−x Cu x O 19. • Lattice parameters are found to be maximum for 8.3% Cu doping. • The enhanced physical properties (magnetic and dielectric) is found to be for BaFe 11 Cu 1 O 19. • "Law of approach to saturation" could explain the magnetocrystalline anisotropy in BaFe 12−x Cu x O 19. • 8.3% cu doping (BaFe 11 Cu 1 O 19) is the optimized composition. Copper (Cu) doped barium hexaferrite BaFe 12−x Cu x O 19 , (x = 0.0–2.0) were synthesized by the modified citrate sol-gel method. The structural, magnetic and electric properties have been investigated. All samples are crystallized to M-type hexagonal structure with P6 3 /mmc space group. Lattice parameters are found to be maximum for x = 1.0, which has been correlated with the physical properties (magnetic & dielectric) of the material. The particle size distribution (found to be nm order) and surface morphology were analyzed by the FESEM (Field Emission Scanning Electron Microscopy) technique. The magnetic hysteresis (M-H) loops have been analyzed by employing the "Law of approach to saturation" and, important magnetic parameters are obtained. The saturation magnetization and magnetocrystalline anisotropy constants are found to be maximum for x = 1.0 sample, but the coercive field is found to a minimum for the same sample. The modified Debye equation has been employed to understand the impedance response to the frequency. The activation energy was obtained by using the Arrhenius equation. Hence, a correlation between crystal structure parameters and physical (magnetic and dielectric) properties of nano-crystalline Cu-doped barium hexaferrite has been observed. Finally, a correlation between crystal structure parameters and magnetic properties, as well as electrical properties, has been proposed for the Cu doped BHF. [ABSTRACT FROM AUTHOR]

The barium hexaferrite (BaFe 12 O 19) is synthesized by the modified sol-gel method. The nanoparticle BHF with different average particle sizes have been prepared by using the high energy planetary ball mill. The X-ray diffraction (XRD) patterns reveal that all the materials crystallize to hexagonal crystal symmetry with P6 3 /mmc space group. It is observed that the maximum magnetization decreases with the decrease in the average particle size of BHF. However, the maximum dielectric constant is found to be for the BHF with average particle size ~24 nm. [ABSTRACT FROM AUTHOR]

Full Heusler alloy Fe 2 MnSi 0.75 Al 0.25 has been prepared by the arc melting method with proper stoichiometry followed by nitrogen atmosphere annealing. Structural and magnetic characterizations have been carried out. X-ray diffraction data analysis reveals that this alloy crystallizes to L2 1 structure in Fm 3 ‾ m space group. It exhibits ferromagnetic behavior below Curie temperature. Curie temperature is found to be around 290 K. The Kouvel-Fisher plot and the Arrott plot have been employed to understand the nature of para to ferromagnetic transition. Here values obtained for critical exponents (β = 0.5284 , γ = 1.084 , δ = 3.05336 ) are convergent with the mean-field model. Law of Approach (LA) to saturation magnetization has been employed to obtain the saturation magnetization and it is found to be maximum (2.4317 μ B /f.u.) at 50 K. [ABSTRACT FROM AUTHOR]