Magnetic Properties and High-Frequency Impedance of Nanocrystalline FeSiBNbCu Ribbons in a 300 to 723 K Temperature Rang
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TRICAL AND MAGNETIC PROPERTIES
Magnetic Properties and High-Frequency Impedance of Nanocrystalline FeSiBNbCu Ribbons in a 300 to 723 K Temperature Range D. A. Bukreeva, *, M. S. Derevyankoa, A. A. Moiseeva, A. S. Kuz’minab, G. V. Kurlyandskayac, d, and A. V. Semirova aIrkutsk
State University, Irkutsk, 664003 Russia Irkutsk National Research Technical University, Irkutsk, 664074 Russia c University of the Basque Country, Leioa, 48940 Spain dUral Federal University Named after the First President of Russia B.N. Yeltsin, Ekaterinburg, 620002 Russia *e-mail: [email protected] b
Received May 16, 2020; revised June 17, 2020; accepted June 23, 2020
Abstract—Magnetic properties and high-frequency impedance of nanocrystalline Fe73.5Si16.5B6Nb3Cu1 ribbons are studied in a high-temperature range of 300 to 723 K. The exchange-coupled state of nanocrystallites was found to be destructed at a temperature of about 530 K, which is substantially lower than the Curie temperature of the amorphous phase that is close to 635 K. It was found that, at an ac frequency of above 5 MHz, the marked magnetoimpedance effect (more than 50% for the magneoimpedance ratio in the case of complete impedance) is observed over the whole temperature range under study. This similar behavior can be essential in designing special-purpose magnetic field sensors intended for high-temperature applications. Keywords: nanocrystalline alloys, magnetoimpedance effect, Curie temperature, random anisotropy model DOI: 10.1134/S0031918X20100026
INTRODUCTION Nanocrystalline ferromagnetic materials prepared from amorphous alloys based on transition metals as a result of controlled heat treatment are systems containing two ferromagnetic phases, residual amorphous and nanocrystalline. The nanocrystalline phase is represented by nanocrystallites about ten nanometers in size [1–3]. Nanocrystallites are separated from each other by the amorphous phase. Materials prepared from the FeSiBNbCu amorphous alloy are one of the most studied nanocrystalline ferromagnets. These materials were described under the name Finemet for the first time in [1]. It was noted in [1] that, in the course of appropriate annealing, excellent soft magnetic properties form; in particular, these are high saturation magnetization (1.2 T and higher), high magnetic permeability (~105), insignificant coercive force, and low effective magnetic anisotropy, which is substantially lower than that of nanocrystallites (in the annealing of the FeSiBNbCu alloy, α-Fe(Si) nanocrystallites 10–20 nm in size form). The low effective magnetic anisotropy was explained in [2]. The random anisotropy model previously suggested for amorphous ferromagnetic alloys [4] was adopted in [2] for nanocrystalline ferromagnets. According to the random anisotropy model, the
magnetic anisotropy can be “averaged” when the exchange-coupled state of nanocrystallites arises. Since the anisotropy axes of nanocrystallites are randomly oriented, the resulting magnetic anisotropy is very small. Active studies of nanocrystalline Finemet-
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