Magnetic and magnetocaloric properties of crystalline DyFe1−xMnxO3

DyFe[Formula: see text]Mn[Formula: see text]O3 (x[Formula: see text]=[Formula: see text]0, 0.025, 0.075, 0.15) polycrystalline samples were prepared using a traditional solid-state reaction route. The structural, magnetic and magnetocaloric properties of these samples were investigated. X-ray diffraction patterns showed that the samples exist as single-phase crystallines without peaks. The results of the Scanning Electron Microscopy (SEM) revealed that the average size of the polycrystalline particles decreased from 4.34 to 3.00 [Formula: see text]m as the Mn doping amount increased from 0.00 to 0.15. The magnetization versus temperature (M[Formula: see text]−[Formula: see text]T[Formula: see text]) plots showed that the order temperature of dysprosium (Dy) ions gradually decreased and the Morin-like transition temperature moved to the high-temperature region as x increased. The T[Formula: see text] gradually decreased from 13 to 10 K and the isotropic interaction of Fe[Formula: see text]-Fe[Formula: see text] was weakened as x increased from 0.00 to 0.15. The polycrystalline samples appeared as pre-formed clusters. The magnetization (M[Formula: see text]−[Formula: see text]H[Formula: see text]) plots revealed that all the samples underwent a first-order magnetic phase transition. The maximum magnetic entropy change, occurring near the Curie temperature, obtained at a magnetic-field span of 7 T, was 18.2 J/kg K. The maximum cooling capacity of the polycrystalline DyFe[Formula: see text]Mn[Formula: see text]O3 (x[Formula: see text]=[Formula: see text]0, 0.025, 0.075, 0.15) samples was 441 J/kg.

Упругие свойства монокристаллов La-=SUB=-0.7-y-=/SUB=-Pr-=SUB=-y-=/SUB=-Ca-=SUB=-0.3-=/SUB=-MnO-=SUB=-3-=/SUB=- (0≤ y≤0.3)

Results of the investigation of the temperature dependences of the velocity of longitudinal sound and internal friction in the ferromagnetic La 0.7-y Pr y Ca 0.3 MnO3 single crystals (0≤ y≤0.3) with first-order magnetic phase transition are presented. In the paramagnetic state, the temperature dependences of the velocity of sound and the internal friction demonstrate extended temperature hysteresis, which indicates the ingomogeneity of the paramagnetic state. It seems likely that the main reason of this ingomogeneity is structural phase separation.

Peculiarities of the magnetocaloric effect in FeRh-based alloys in the vicinity of the first order magnetic phase transition

Medical applications of magnetocaloric effect (MCE) require possibility for precision shift of a temperature of the magnetic phase transition at the same MCE value and minimize irreversibility. Thus, detail dynamic MCE investigation of such alloys with non-toxic biocompatible dopants need to be done. In present work, the giant magnetocaloric effect, which is observed in the whole family of Fe-Rh alloys, has been investigated in Pd-doped samples in slowly cycled magnetic fields of up to 1.8 T in magnitude for a range of temperatures, 250 K < T < 350 K. The shift of the ferromagnetic/antiferromagnetic transition temperature down towards room temperature and the decrease in the MCE have been observed in these alloys in comparison with a quasi-equiatomic FeRh alloy. The measurements have also shown an asymmetric behaviour of the first order magnetic phase transition with respect to whether the transition is traversed by heating from lower temperatures or cooling from above. These peculiarities have been explained in the framework of the ab-initio density functional theory-based disordered local moment theory of the MCE. The results have been compared with the those for the non-doped FeRh alloy. Thus features of the first order magnetic phase transition that these alloys have in common have been revealed which enable some predictions to be made appropriate for practical applications.