Magnetic Phase Transition of MnBi under High Magnetic Fields and High Temperature

Abstract

Magnetization measurements and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in magnetic fields up to 14 T and in 300-773 K, in order to investigate the magnetic phase transition. The magnetic phase transition temperature (T t ) at a zero magnetic field is 628 K and linearly increases with increasing fields up to 14 T at the rate of 2 KT À1 . A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above T t . The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in 626-623 K, which relates to the metamagnetic transition. The obtained results were discussed on the basis of a mean field theory.

Magnetic and structural phase transitions of MnBi under high magnetic fields

“…The mean field calculation shows that the Curie temperature T C of LTP-MnBi is ∼720 K [8,16]. In addition, T t linearly increases at a rate of 2-2.3 KT −1 in fields up to 14 T, as shown in figure 8.…”

“…In addition, T t linearly increases at a rate of 2-2.3 KT −1 in fields up to 14 T, as shown in figure 8. Assuming that this rate is constant at higher temperatures and in higher magnetic fields, T t will reach the peritectic temperature (T MnBi m ∼ 720 K) of HTP upon applying a magnetic field of ∼45 T. Our mean field calculation suggested that the field-induced magnetic moment of LTP-MnBi is approximately 2 µ B Mn −1 in a magnetic field of 45 T at 720 K [8]. This means that we may control the first-order magnetic and structural transitions of MnBi up to the peritectic temperature T MnBi m and solidify MnBi using a high magnetic field without inducing the PM phase.…”

“…However, it seems that the volume in both states is not greatly different. On the other hand, the magnetic properties of LTP-MnBi have been explained well by a mean field model with localized magnetic moments [8,16], and the spin-orbit coupling affects the magnetic properties. Therefore, the ratio c/a in the crystal probably plays an important role in the spin reorientation.…”

“…Recently, on the basis of magnetic measurements for MnBi, Liu et al [7] reported that T t increases linearly with increasing magnetic field up to 10 T at a rate of ∼2 KT −1 . Differential thermal analysis (DTA) performed by Koyama et al [8] also showed an increase in T t with increasing magnetic field at a rate of 2 KT −1 . In addition, they observed a metamagnetic phase transition between the PM state and a field-induced ferromagnetic (FFM) state in the vicinity of T t [9].…”

Thermodynamic Assessment of the Bi-Mn System

“…14) Recently, phase diagram changes by means of a strong magnetic field have been reported. [15][16][17][18][19][20] On the basis of magnetic measurements, Liu et al reported that the peritectic temperature increased with an increase in the magnetic field. 15) Koyama et al also confirmed an increase in the peritectic temperature with an increase in the magnetic field at a rate of 2 K/T by using a differential thermal analysis technique.…”