Modifying the transition temperature, 120 K ≤ Tc ≤ 1150 K, of amorphous Fe90−xCoxSc10 with simultaneous alteration of fluctuation of exchange integral up to zero

• Published in: Scientific reports Vol. 9; no. 1; p. 412
• Main Authors: Fang, Y. N., Hahn, H., Kobe, S., Witte, R., Singh, S. P., Feng, T., Ghafari, M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 23.01.2019; Nature Publishing Group UK
• Subjects: Alloys; Magnetism; Phase transitions; Temperature effects
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-36891-2

Abstract Amorphous (a-) Fe 90−x Co x Sc 10 alloys have been produced by rapid quenching from the melt. The Curie temperature, T C, was determined using both mean field theory and Landau’s theory of second-order phase transitions in zero and non-zero external fields. The dependence of T C on the atomic spacing can be explained by the empirical Bethe-Slater curve. The value of T C of a- Fe 5 Co 85 Sc 10 , determined by the above theoretical approaches is 1150 K, which is the highest T C ever measured for amorphous alloys. The flattening of the measured normalized magnetization, M(T)/M(0), as a function of the reduced temperature, T/T C , is explained within the framework of the Handrich- Kobe model. According to this model the fluctuation of the exchange integral is the main reason for the flattening of M(T)/M(0). In the case of a-Fe 90 Sc 10 without Co, however, the fluctuation of the exchange integral is dominant only at zero external field, B ex  = 0. At B ex  = 9 T, however, the fluctuation of the exchange integral has no conspicuous effect on the reduction of the magnetization. It is shown that at B ex  = 9 T the frozen magnetic clusters control the behaviour of the reduced magnetization as function of T/T C . In contrast to other ferromagnetic alloys, where the flattening of M(T)/M(0) is characteristic for an amorphous structure, the a- Fe 5 Co 85 Sc 10 does not exhibit any trace of the fluctuation of the exchange integral.