Magnetic and structural phase transitions of MnBi under high magnetic fields

Abstract

High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature T SR (= 90 K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of T SR . By applying a magnetic field of 5 T, the parameter a increases by ∼0.05% when T < T SR and varies smoothly when 8 T 300 K. DTA data show that the magnetic phase transition temperature from the ferromagnetic state to the paramagnetic state increases linearly at a rate of 2 KT −1 with increasing magnetic field up to 14 T.

Bi&ndash;Mn Binary Phase Diagram in High Magnetic Fields

“…5. T p1 is found to increase linearly at a rate of 2 K T ¹1 for B¯18 T. The result obtained is consistent with previous HF-DTA experiments for the BiMn compound 1,17,18) and magnetization measurements for Bi6 mass%Mn. 16) Koyama et al reported that the linear increase in T p1 occurred for B¯20 T, but the T p1 -B curve deviates from linearity for B > 20 T. 1) Figure 6 shows the DTA curves of Bi24 at%Mn near T liq for several magnetic fields up to 18 T. The baseline change according to the liquidus boundary at T liq is observed to shift to higher temperature by applying stronger fields.…”

“…17,18) They also suggested that T p1 reaches the peritectic temperature T p2 (= 719 K) of BiMn 1.08 from ¡Mn + Bi-rich liquid. 17,18) However, recent DTA results reported by Koyama et al showed that T p1 increases from 632 K (at a zero field) to 714 K by applying B = 45 T, but T p1 does not reach T p2 .…”

Change of the equilibrium state of ferromagnetic MnBi by high magnetic fields

“…Differential thermal analysis (DTA) performed by Koyama et al [7,8] also showed an increase in T t with increasing B up to 14 T at a rate of 2 K T −1 . They suggested that T t reaches the peritectic temperature of HTP (T HTP m = 719 K) upon applying a magnetic field of ∼45 T [7,8]. This suggests that HTP van- * Corresponding author.…”

Magnetic anisotropic effects and electronic correlations in MnBi ferromagnet

“…83 and 84 together with the magnetization 83 in MnBi. Yang et al 83 measured temperature dependence of the lattice parameters a, and c in a wide temperature range from 10 to 700 K. Koyoma et al, 84 on the other hand, used a smaller temperature interval (10−300 K). They did use a very fine temperature mesh in the vicinity of T SR .…”

“…To investigate the MAE as a function of the polar angle θ in the vicinity of the spin reorientation phase transition, we fixed the lattice constant a for the spin-reorientation temperature a=4.274Å 84 and vary c from c=6.09Å to . This corresponds to the T =300 K and a=4.272Å (curve 1) and a=4.283Å (curve 2) corresponding to the T =100 K and 300 K, respectively.…”