L80
K. Koyama et al. / Journal of Alloys and Compounds 509 (2011) L78–L80
ple is heated to 689.5 K in B = 11.5 T. As seen in Fig. 2, the sample
contains PM-Mn1.08Bi and diamagnetic liquid Bi in this condition.
After that, the magnetic field is generated from 11.5 T to 45 T at a
and liquid Bi state by applying a magnetic field. From the point of
view of materials science, the control of the chemical formula and
the synthesis of the magnetic material under high magnetic fields
are expected to be of considerable interest.
−1
rate of 7 T min . After reaching 45 T, the magnetic field is decreased
to 11.5 T at the same rate. As shown in Fig. 3(a), we observed the
exothermic and the endothermic peaks at 36.5 T (=Bt1) for increas-
ing B and at 28.8 T (=Bt2) for decreasing B, respectively. In other
words, this is a magnetocaloric effect: the sample heating (+∼1.2 K)
by applying B and sample cooling (−∼1.5 K) by removing the field,
as shown in Fig. 3(b). Here, B and B were determined by the
4. Conclusion
The high-field DTA experiment was performed in high magnetic
fields up to 45 T in the temperature range of 300–773 K for the
t1
t2
first time. The decomposition temperature T from ferromagnetic
t
onset of the DTA peaks. Considering the phase diagram (Fig. 2),
the exothermic and the endothermic peaks are due to the phase
transitions from PM-Mn1.08Bi and liquid Bi to field-induced fer-
romagnetic (FIFM) MnBi for increasing B and from FIFM-MnBi to
PM-Mn1.08Bi and liquid Bi for decreasing B, respectively. That is,
the field-induced composition and decomposition processes occur
in the Mn–Bi system.
MnBi to paramagnetic Mn1.08Bi and liquid Bi increases from 632 K
(at a zero magnetic field) to 714 K by applying a magnetic field of
45 T. Furthermore, the magnetocaloric effect of MnBi is observed in
11.5–45 T in the vicinity of 689 K. The obtained results show that
we can control the composition and the decomposition tempera-
tures and the equilibrium state of magnetic material MnBi by a high
magnetic field.
The Zeeman energy part (EM = −mB) in the free energy plays
an important role in the effect of the magnetic field on the phase
transition of magnetic materials [10]. For a zero field, m of MnBi is
approximately 2.4 B even at 600 K [7]. The mean field calculation
suggested that the field-induced m of MnBi is approximately 2.0 B
in a magnetic field of 45 T at 720 K [7]. This m of MnBi is much larger
than that of Mn1.08Bi, because m of HTP-Mn1.08Bi is 1.7 B at room
temperature and TC is about 473 K [2]. Therefore, we observe the
increase in Tt by applying a magnetic field to MnBi. On the other
Acknowledgments
This work was carried out at the HFLSM and the NHMFL. The
NHMFL is supported by NSF Cooperative Agreement No. DMR-
0654118, by the State of Florida, and by the DOM. This work was
partly supported by the Iketani Science and Technology Founda-
tion, and a Grant in-Aid for Scientific Research from the MEXT,
Japan.
hand, it is also expected that m of HTP-Mn1.08Bi in the vicinity of
HTP
7
20 K (∼Tm ) is induced by applying a high magnetic field. The
References
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