Magnetic amorphous alloys obtained by rapid quenching of the melt are excellent soft magnetic materials with a wide range of technological applications. They also represent a significant challenge to the scientific understanding of magnetic materials, since most of the existing theories of solids assume lattice periodicity. For these reasons, the magnetic and other properties of amorphous alloys have been very actively studied over the last decade. In recent years increasing attention has been directed to the fundamental understanding of the structural, thermal and magnetic properties of the amorphous alloys. It is not only scientifically but also technologically important to achieve such an understanding, since the amorphous alloys are, in many respects, so different from conventional crystalline magnetic materials. The author attempts to summarise recent progress in research on magnetic amorphous alloys and critically assesses the present level of understanding of this new class of magnetic materials, focusing mostly on the transition-metal-metalloid glasses. He starts with a review of early developments and a discussion on the nature of glasses and glass formation and proceeds to an extensive discussion of their atomic structure, both from the experimental and theoretical points of view.

https://iopscience.iop.org/article/10.1088/0034-4885/47/12/002/pdf

Magnetic amorphous alloys: physics and technological applications

The temperature dependence of the AC susceptibility Fe-rich Fe-Zr amorphous alloys having mictomagnetic or spin-glasslike behaviour has been measured in a superposed DC field. The Fe-Zr amorphous alloys containing more than 8.6 at.% Zr clearly show sharp peaks at the Curie temperature TC and the spin cluster freezing temperature Tsf. These two temperatures seem to coincide at a critical concentration for the Fe-7.6 at.% Zr alloy, which is considered to be the percolation limit for the long-range ferromagnetic interactions.

http://iopscience.iop.org/article/10.1088/0305-4608/16/7/018/pdf

Mictomagnetism of Fe-rich Fe-Zr amorphous alloys studied by AC susceptibility in a superposed DC field

Small‐angle neutron scattering (SANS) studies of an amorphous Fe91Zr9 alloy have shown that there is no transition to long‐range magnetic order in contrast to previous bulk magnetization results which indicated a transition to a ferromagnetic state at 220 K followed by a reentrant spin‐glass state near 60 K. The scattering line shape is Lorentzian in Q down to below 150 K and yields a spin correlation length which reaches a maximum of only 27 A at the transition T C=210 K and exhibits an essentially constant plateau of 23 A down to helium temperature, with no evidence of a second transition in the 60–80 K range. The line shape departs from Lorentzian below about 120 K and can be represented by a Lorentzian plus Lorentzian‐squared cross section as appropriate for a system in which long‐range order has been replaced by a frozen cluster configuration. The absence of ferromagnetic order in Fe91Zr9 at Fe concentrations far above the percolation threshold suggests the presence of a very broad distribution of ex...

Small‐angle neutron scattering evidence for the absence of long‐range magnetic order in amorphous Fe91Zr9

Low temperature magnetic hardness of melt spun Fe-Zr amorphous alloys

Asymptotic critical exponents and amplitudes as well as the leading `correction-to-scaling' (CTS) amplitudes have been accurately determined through an elaborate analysis of magnetization data taken on amorphous and alloys in the critical region. Consistent with the Harris criterion, asymptotic critical exponents and the universal amplitude ratio do not depend on composition and possess values the same as those predicted by theory for an ordered spin system with n = d = 3. The leading amplitude ratio , which is characteristic of ferromagnets with quenched random disorder and for which no theoretical estimate is presently available, is composition independent and probably universal. The fraction of spins actually participating in the ferromagnetic (FM) - paramagnetic (PM) transition occurring at is small and increases with Co substitution. While the magnetic equation of state (MES) in linear scaling variables and its counterpart in nonlinear scaling variables, valid for a second-order phase transition, form equivalent descriptions of magnetization, M(T,H), data in the asymptotic critical region (ACR), the latter version of MES alone reproduces closely the observed M(T,H) behaviour in a temperature range as wide as . Nonanalytic CTS terms dominate over analytic ones in the ACR but the reverse is true for temperatures outside the ACR. Initial susceptibility follows the generalized Curie - Weiss law from to and thereby permits an accurate determination of atomic moment in the PM state. The results of the present investigation provide strong experimental evidence for weak itinerant ferromagnetism in the glassy alloys in question.

Scaling behaviour of magnetization for temperatures in the vicinity of, and far from, the ferromagnetic - paramagnetic phase transition in amorphous and alloys

K. Hosoyama

Papers

Magnetic inhomogeneity in amorphous Fe-Zr alloys