Magnetic and Structural Properties of Metamagnetic MnCo_0.92Fe_0.08Ge Compound

Abstract

The magnetic and structural properties of ferromagnetic MnCo 0.92 Fe 0.08 Ge were investigated by magnetization and X-ray powder diffraction measurements in magnetic fields up to 5 T. The compound showed first-order transition between the paramagnetic and ferromagnetic state with a thermal hysteresis of approximately 24 K, which was accompanied by the martensitic transformation from the hexagonal Ni 2 In-type structure to the orthorhombic TiNiSi-type structure in the vicinity of 275 K. The cell volume expanded by 4.1% during the martensitic transformation. The magnetic moment of MnCo 0.92 Fe 0.08 Ge was estimated to be 111 Am 2 kg ¹1 (3.7 ® B /f.u.) at 10 K. The compound showed both metamagnetic transition and magnetic field-induced martensitic transformation.

Magnetic and Structural Properties of MnCoGe with Minimal Fe and Sn Substitution

“…The value of a o increased by 11.6% along the c h axis at 170 K with decreasing T, while the other lattice parameters shrank by 0.1% (c o /√3) and 6.3% (b o ) along the a h axes, leading to a cell volume change of 4.4%. This volume change was in good agreement with that (4.1%) reported previously for MnCo 0.92 Fe 0.08 Ge (4.1%) at 276 K. 17) The T dependence of the M (M-T curve) for x = 0.02 (a), 0.05 (b) and 0.1 (c) in ® 0 H = 1 T is shown in Fig. 6.…”

“…Figure 3 shows the DSC curves obtained for MnCo 0.92 -Fe 0.08 Ge 1¹x Sn x with x = 0.02 (a), 0.05 (b) and 0.1 (c). For x = 0.02, exothermic and endothermic peaks with a thermal hysteresis (TH) were apparent during cooling and heating within the T range of 290370 K, which corresponded to MT and reverse transformations (RMT), 17) respectively. Based on the DSC peaks for x = 0.02, the MT starting and finishing T, M s and M f , and the RMT starting and finishing T, A s and A f were determined, and are listed in Table 2.…”

“…In contrast, the peak intensity of the P-phase became smaller with decreasing T. However, the XRD profiles showed that the P-phase remained at 10 K. This may have been caused by partial distortion at low T resulting from the pulverization of the original specimen into a powder sample and/or by the suppression of the large volume expansion due to the frozen grease on the sample holder. 17,20) With increasing T, the intensity of the M-phase decreased above 170 K (³A s ) and was not detected over 210 K (³A f ). The peaks of the P-phase were only seen at 250 K. These characteristic temperatures are consistent with M s , M f , A s and A f as determined by the DSC measurement.…”

“…MnCo 0.94 Fe 0.06 Ge exhibits FOMT and a large change in entropy (¦S ³ ¹27 J kg ¹1 K ¹1 ) at ³315 K. 13) In our previous reports, the phase diagram of MnCo 1¹y Fe y Ge was shown ( Fig. 1), 16) and MnCo 0.92 Fe 0.08 Ge showed FOMT from the PM to FM state, and this was accompanied by MT in the vicinity of 275 K. 17,18) The cell volume expanded by 4.1% during MT, 17) and ¦S was estimated to be ¹14 J kg ¹1 K ¹1 . 18) Magnetic field-induced MT from the PM P-phase with low m to the FM M-phase with high m in MnCo 0.92 Fe 0.08 Ge was measured at 276 K in magnetic fields from H up to ® 0 H = 5 T. 17) However, as seen in Fig.…”

“…1), 16) and MnCo 0.92 Fe 0.08 Ge showed FOMT from the PM to FM state, and this was accompanied by MT in the vicinity of 275 K. 17,18) The cell volume expanded by 4.1% during MT, 17) and ¦S was estimated to be ¹14 J kg ¹1 K ¹1 . 18) Magnetic field-induced MT from the PM P-phase with low m to the FM M-phase with high m in MnCo 0.92 Fe 0.08 Ge was measured at 276 K in magnetic fields from H up to ® 0 H = 5 T. 17) However, as seen in Fig. 1, this phenomenon was observed for a very small range of Fe-content y for MnCo 1¹y Fe y Ge, 16) and the T of FOMT and MT could not be controlled sufficiently for application.…”