Structural and magnetic study of the MnAs magnetocaloric compound

Abstract

The temperature induced phase transition in MnAs is analyzed in this work using X ray Rietveld refinement. The results show the presence of the hexagonal phase (P6(3)/mmc) at room temperature and the first-order structural-magnetic transition to the orthorhombic phase (Pnma) around 318 K was followed in detail. The MnAs magnetic characterization allowed to obtain the transition temperature and a maximum value of 47 J/(kg.K) for the measured magnetocaloric effect for a magnetic field variation of 5 T

Hyperfine interactions in MnAs studied by perturbed angular correlations ofγ-rays using the probe Br77→SeGonçalves1, Amaral2, Correia3 et al. 2011Phys. Rev. B10010View full textAdd to dashboardCite

“…As can be seen by the changes in the spectra, the transformations occur near T C,i ≈ 42.3 − 43.5C and T C,d = 30 − 32.6 C. Therefore we estimate the thermal irreversibility to be between 10-13.5 C. This hysteresis is somewhat larger than that reported in other works by X-ray and magnetization measurements (10 C) [13][14][15][16][17] . Figure 7 shows magnetization measurements on the same samples with a vibrating sample magnetometer with B = 0.01 T, showing T C,i = 45 C and T C,d = 30.7 C. The abrupt change over 2 C, at ≈ 44 C, when heating (see fig.…”

“…Thermal hysteresis is measured in this transition: on heating, the hexagonal→orthorhombic phase transformation occurs at temperatures T C,i ≈ 40.5 − 42.5 C, while on cooling this transformation occurs at T C,d ≈ 33.9 − 37.9 C [13][14][15][16][17] (variations in different studies are probably resulting from small differences in the stoichiometry of samples). Phase coexistence in a temperature interval of approximately 2 C is reported by neutron and X-ray diffraction measurements 11,18 .…”

Ferromagnetism and magneto-transport properties of Mn0.92Ca0.08As thin film grown on Al2O3(0001) substrate

“…15 The errors may result from the density and lattice volume change during phase transition from hexagonal to orthorhombic as presentation of first-order transitions. 16,17 However, the values of the entropy change were roughly estimated for the three magnetic fields as references. 15,18 Figure 3(d) shows the entropy changes as a function of temperature for selected applied magnetic fields: 1, 3, and 5 T. The maximum MCE changes were about 150 and 200 J/kgK for the magnetic fields at 3 and 5 T, respectively.…”

Phase Equilibria in Binary and Ternary Systems with Chemical and Magnetic Ordering

“…orthorhombic and hexagonal. [46][47][48][49] As a common feature the compounds with magnetostructural transition often show large thermal and field hysteresis. [49] Unlike for chemical ordering, no restrictions are imposed on magnetic ordering.…”