R. M’nassri

Magnetocaloric effect and its implementation in critical behaviour study of La0.67Ca0.33Mn0.9Fe0.1O3

The magnetocaloric effect (MCE) and the field dependence of the magnetic entropy changes in the perovskite-type La0.67Ca0.33Mn0.9Fe0.1O3 were studied using the phenomenological model. The model parameters were determined from the magnetization data adjustment and used to give better fits to magnetic transition and to calculate the magnetocaloric properties. The entropy curves have been observed to behave a symmetrical broadning of ΔSM peak with the increase in magnetic field. The values of maximum magnetic entropy change, full-width at half-maximum, relative cooling power (RCP) and the refrigerant capacity (RC), at several magnetic field variations, were calculated. The maximum magnetic entropy change of 1.17 J kg−1 K−1 was obtained for 3 T. The theoretical calculations were compared with the available experimental data. The results were found to be in good accordance. The critical exponents associated with ferromagnetic transition have been determined from the MCE methods. By using the field dependence of ΔSmax ≈ a (μ0H)n and the RCP ≈ v (μ0H)w, the critical behaviour of La0.67Ca0.33Mn0.9Fe0.1O3 was investigated. From the analysis of the relationship between the local exponent n and w, other exponents β, γ and δ were calculated. Our results indicated that the ferromagnetic coupling in the La0.67Ca0.33Mn0.9Fe0.1O3 can be well described by the 3D Heisenberg model. This reflects an existence of ferromagnetic short-range order in the sample.

Electrical conductivity analysis and magnetic properties of Pr0.7Ca0.3Mn0.95Co0.05O3 oxide

The structural, electrical, magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn0.95Co0.05O3 have been studied. The X-ray diffraction refinement results indicate that the sample is single phase and crystallizes in the distorted orthorhombic system with Pnma space group. The investigation of the temperature and frequency dependence of conductance indicates that the sample exhibits a semi-insulator character and the conduction mechanism is explained using hopping model. Complex impedance analysis confirms the contribution of grain boundary in the transport properties in the Pr0.7Ca0.3Mn0.95Co0.05O3 system. Magnetocaloric effect and transition order are investigated by using magnetization measurements. The field dependence of magnetic entropy change and relative cooling power are analyzed and showing the power law dependence. The Landau theory for phase transitions framework is applied to describe the magnetocaloric effect in Pr0.7Ca0.3Mn0.95Co0.05O3 manganite. The obtained results are discussed in terms of magnetoelastic and electron interaction contribution to the magnetic entropy.

Studies on the structure, critical behavior and magnetocaloric effect in (LaBi)SrCoO cobaltite

In the present paper, we report the structure, the magnetic, the critical behavior, the magnetocaloric properties and the universal curve of La0.45Bi0.15Sr0.4CoO3 cobaltite. Polycrystalline sample was synthesized in air by the solid state reaction method at a sintering temperature of 1200 °C. Phase purity, structure, size, and crystallinity were investigated using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The Reitveld refinement of XRD pattern shows that the sample adopts a rhombohedral system with

Impact of sintering temperature on the magnetic and magnetocaloric properties in Pr0.5Eu0.1Sr0.4MnO3 manganites

R\overline 3 c

Influence of transition metal doping (Fe, Co, Ni and Cr) on magnetic and magnetocaloric properties of Pr0.7Ca0.3MnO3 manganites

R3¯c space group. Critical exponents obtained by the modified Arrott plot technique, Kouvel–Fisher method, and critical isothermal analysis are close to the theoretical prediction of 3D Heisenberg model values, revealing the characteristic of short-range ferromagnetic interactions. With these values, the M(T,µ0H) relations below and above the curie temperature collapse into two universal branches in the asymptotic critical region following the scaling equation. Moreover, the experimental magnetic entropy changes measured for various fields collapse onto a master curve, confirming the universal behavior of the magnetocaloric effect in this system. Particularly, its magnetic-field dependence obeys a power-law fitting, where the exponent n = 0.98 is quite far from the value calculated at Curie temperature from the critical exponents. This difference is related to the magnetic inhomogeneity in the sample.