Directional ordering in amorphous Co–Si–B alloys

Abstract

Directional ordering in the amorphous Co75Si15B10 alloys by means of the magnetic after-effect (MAE) of the initial reluctivity and its influence on the Perminvar effect have been investigated. Two peak MAE spectra were obtained from isochronal measurements for as-cast as well as annealed samples. The spectrum of the as-cast sample has peak maxima at 383 and 545 K. Comparing this MAE spectrum with the spectrum of amorphous Co75B25 alloy, we identified the first peak as a result of Co–B atom pair reorientation (B-type relaxation) and the second one at higher temperatures as a result of Co–Si atom pair reorientation (Si-type relaxation). After annealing, the peaks shift to 442 and 576 K, respectively. For the numerical analysis of Co75Si15B10 MAE spectra we modified the micromagnetic model assuming the existence of more relaxation processes, where each process is connected to the relaxation of one metalloid element. The pre-exponential factor for B-type relaxation was found to be τ0,AC(B) = 7 × 10−17 s with the most probable activation energy QAC*(B) = 1.31 eV. These values correlate very well with the magnetic relaxation (MR) activation parameters of Co75B25 alloy, τ0,AC = 2 × 10−17 s and QAC* = 1.35 eV. Si-type relaxation has activation parameters τ0,AC(Si) = 6 × 10−18 s and QAC*(Si) = 1.96 eV. After annealing the sample at 683 K for 30 min they change to values τ0,AN(B) = 2 × 10−15 s, QAN*(B) = 1.38 eV and τ0,AN(Si) = 3 × 10−17 s, QAN*(Si) = 2.01 eV. The complicated shapes of the long-time isotherms reflect the superposition of two relaxation processes. We have numerically split each isotherm into two sub-isotherms representing the particular contributions of the two relaxation processes. The MAE spectrum of the critical field measured on the as-cast sample also has two peaks, like the reluctivity spectrum. The impact of Co–B and Co–Si atom pairs on the behaviour of the domain wall stabilization potential is discussed for the explanation of the observed MR results.

Magnetic and Structural Properties of Amorphous Co-Cr-Si-B Alloys

“…1). Qualitatively similar concentration dependence of the domain wall critical fields was observed on the same alloys [10]. The annealing at 573 K for 1 hour causes annealing-out of the internal stresses, leading to the decrease of H C for alloys with 6 and 8 at.…”

Perminvar Effect in Amorphous Hitperm Alloy

“…Chemical composition, amorphous structure and ferromagnetic state bring about intensive time-temperature directional ordering in the alloy [2] stabilizing the actual domain structure and deepening the domain wall (DW) potentials manifested by several macroscopic phenomena [3]. One of them is the Perminvar effect (PE) characterized by constant permeability (susceptibility) for measuring field amplitudes H 0 < H CR [4].…”

“…The critical field H CR is the lowest pinning field. At this field the susceptibility stops to be constant and begins to rise [2]. The total relaxation consists of several elementary relaxation processes (119) which contribute to the DW potential.…”

Magnetic relaxations in amorphous soft magnetic alloys

“…Therefore, an overall picture of amorphous ferromagnetic material must incorporate consideration of the thermodynamic and magnetic driving forces for atomic motion except for its magnetic properties and chemical and topological short-range order [3]. An experimental method of in situ monitoring structural magnetic relaxation (MR), caused by the atom-pair directional ordering (DO) in amorphous and crystalline alloys, is the magnetic after-effect (MAE) spectroscopy [4,5]. It provides data on changes of soft magnetic properties caused by the structural reordering as well as activation parameters characteristic for this thermo-activated process.…”

“…The term magnetic relaxation is used to emphasize the free energy minimization of a ferromagnetic body during DO of atom pairs. The atom-pair concept of the MR in multicomponent amorphous alloys [5,6] is accepted in this article.…”