Muralidhar, Shreyas ; Gräfe, Joachim ; Chen, Yu-Chun ; Etter, Martin ; Gregori, Giuliano ; Ener, Semih ; Sawatzki, Simon ; Hono, Kazuhiro ; Gutfleisch, Oliver ; Kronmüller, Helmut ; Schütz, Gisela ; Goering, Eberhard J. (2017):
Temperature-dependent first-order reversal curve measurements on unusually hard magnetic low-temperature phase of MnBi.
In: Physical Review B, 95 (2), pp. 024413. American Physical Society, ISSN 2469-9950,
[Article]

Abstract

We have performed first-order reversal curve (FORC) measurements to investigate the irreversible magnetization processes in the low-temperature phase of MnBi. Using temperature-dependent FORC analysis, we are able to provide a clear insight into the effects of microstructural parameters such as grain diameter, shape, and surface composition on the coercivity of nucleation hardened permanent magnet MnBi. FORC diagrams of MnBi show a unique broadening and narrowing of the coercive field distribution with increasing temperature. We were able to microscopically identify the reason for this behavior, based on the shift in the single domain critical diameter from nearly 1 to 2 μm, thereby changing the dependence of coercivity with particle size. This is based on a strong increase in the uniaxial anisotropy constant with increasing temperature. Furthermore, the results also give an additional confirmation that the magnetic hardening in low-temperature phase MnBi occurs due to nucleation mechanisms. In our case, we show that temperature-dependent FORC measurements provide a powerful tool for the microscopic understanding of high-performance permanent magnet systems.

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