Abstracts:Employing the all electron augmented plane wave  + local orbital (APW + lo) method based on the density function theory (DFT), we have performed ab initio calculations of electronic structure and magnetic properties of dilute Fe impurity in ${\text{PdH}}_x$ alloys $(0⩽x⩽1.0)$. Here we present our results for the H induced changes in the density of state (DOS), local magnetic moment and the macroscopic magnetic properties. The calculations performed for ${\text{PdH}}_x$ without the Fe impurity reveal H concentration dependent lattice expansion and Pd-H bonding which results in large change in electronic band structure and the DOS at the Fermi energy. The nonmagnetic DOS calculated for Fe doped ${\text{PdH}}_x$ is analyzed within Stoner model and the condition for local moment formation is found to hold for all concentrations of H. With an increase of the H content in the Pd matrix, the local moment of Fe declines from 3.43${\mu }_B$ at x = 0 to 2.72${\mu }_B$ at x = 1.0. More significantly, the giant magnetic moment, associated with the Fe impurity in Pd, progressively decreases with H concentration as the positive spin polarization of Pd-4d band electrons diminish and crossover to negative sign for x $\>$ 0.75. We show that H induced changes in s-d and d-d hybridization plays a crucial role on the magnetic properties of Fe doped ${\text{PdH}}_x$ alloys. In particular, we suggest that the rapid decline of the giant moment in ${\text{PdH}}_x$ alloys results from the weakening of ferromagnetic d-d exchange interaction between Fe-3d and Pd-d band electrons caused by changes in density of states arising from H induced filling up of the Pd-4d band.

Abstracts:We have performed a systematic study of the critical properties of Pr0.8K0.2MnO3 manganite synthesized using two various methods in the vicinity of the ferromagnetic–paramagnetic phase transition. Our compound was successfully prepared by using the solid state reaction at high temperatures and Pechini sol-gel method. The X-ray diffraction pattern shows that all our samples adopt an orthorhombic structure with Pnma space group. Moreover, the critical exponents β, γ and δ are estimated through various techniques such as the modified Arrott plot, the Kouvel–Fisher method and the critical isotherm analysis founded on the data of the magnetic measurements on record near the Curie temperature. Compared to standard models, the estimated critical exponents are close to the theoretical values of 3D-Heisenberg model for the sample elaborated by solid state reaction and tricritical mean-field model for the sample elaborated by the sol-gel method. These results indicate the presence of a ferromagnetic short-range order in our samples. The calculated values using the Widom scaling equation are proximate to those obtained values from critical isotherm M (TC, µ0H). The accuracy of the critical exponents values was confirmed with the scaling hypothesis, the magnetization curves fall onto two sides independents below and above TC. Interestingly, the change of the universality class is due to the relevant the diminution of grain size. These results imply that the critical behavior of our samples depended sorely on the synthesis technique.

Abstracts:SrFe12O19/Ni0.6Zn0.4Fe2O4 composites were synthesized by one-pot solution combustion method. The effects of NiZn ferrite content on phase, structure, microstructure and magnetic properties of composites were investigated by X-ray diffractometry, infrared spectroscopy, electron microscopy and vibrating sample magnetometry techniques. Strontium hexaferrite and NiZn ferrite phases were well crystallized following calcination at 900 °C without any impurities being formed. The composites were composed of platelet-like SrFe12O19 particles being mixed with quasi-spherical NiZn ferrite particles. The composites containing 10 wt% Ni0.6Zn0.4Fe2O4 exhibited a single magnetization curve with maximum saturation magnetization of 56 emu/g, as a confirmation of exchange coupling, while other composites had “bee waist” type hysteresis loop. The coercivity of composites decreased from 5143 to 1778 Oe with addition of NiZn ferrite phase. The microwave absorption measurements in X-band (8–12 GHz) showed a maximum absorption of −23.5 dB at 9.9 GHz for SrFe12O19-10 wt% Ni0.6Zn0.4Fe2O4 composite in comparison with the other composites.