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

Y N Fang; H Hahn; S Kobe; R Witte; S P Singh; T Feng; M Ghafari

doi:10.1038/s41598-018-36891-2

Modifying the transition temperature, 120 K ≤ T_c ≤ 1150 K, of amorphous Fe_90-xCo_xSc₁₀ with simultaneous alteration of fluctuation of exchange integral up to zero

Sci Rep. 2019 Jan 23;9(1):412. doi: 10.1038/s41598-018-36891-2.

Authors

Y N Fang¹, H Hahn^{1

2}, S Kobe³, R Witte², S P Singh², T Feng¹, M Ghafari⁴

Affiliations

¹ Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, Nanjing, 210094, China.
² Institute for Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz- Platz 1, 76344, Eggenstein- Leopoldshafen, Germany.
³ Technische Universität Dresden, Institut für Theoretische Physik, D-01062, Dresden, Germany.
⁴ Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, Nanjing, 210094, China. ghafarijorabi@gmail.com.

Abstract

Amorphous (a-) Fe_90-xCo_xSc₁₀ 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- Fe₅Co₈₅Sc₁₀, 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-Fe₉₀Sc₁₀ 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- Fe₅Co₈₅Sc₁₀ does not exhibit any trace of the fluctuation of the exchange integral.