The Influence of Tensile Deformation and Atomic Short-Range Order on the Susceptibility of CuMn Spin Glasses

Abstract

The magnetic ac‐susceptibility of CuMn‐alloys, χ(T), proves to be a very sensitive probe, particularly near the cusp defining the spin glass temperature Tf[1], to detect variations of the structural state χ(T) increases with an increasing degree of atomic short – range order (SRO). It is shown that for well annealed specimens the amount of SRO and simultaneously χ(Tf) pass a minimum as function of the quenching temperature Tq at about Tq = 450°C. The normalized χ(T)‐curves considered as functions of the reduced temperaturesT/Tf are broader for a smaller amount of SRO. A plastic tensile deformation at room temperatrue causes an increase in χ(T). It is detectable already for 5 at% Mn and becomes very pronounced for 13 at% Mn. The effect vanishyes completely when the SRO is dissolved by quenching the sample after an anneal at 450°C. From that it is concluded that the tensile deformation generates a vacancy concentrtation high enough to produce an otherwise unattainable amount of SRO at room temperatrue.

A magnetization study of the development of short-range order in a concentrated - Mn spin glass

“…Note that the peak susceptibility has increased to 20 times that of the fast-quenched sample (3Q2) and T f is obviously higher. This is a much greater effect than achieved by tensile deformation of a 13% alloy [31]. In all other respects, this specimen displays the magnetic behaviour expected at this concentration.…”

Magnetic susceptibility measurements on single crystal

“…Only relatively short time (1 h) annealing at high temperature is needed to locally homogenize alloys which have been well mixed and cold worked during manufacture. The magnetic effects of ASRO (an increase in susceptibility for dilute alloys and a decrease in susceptibility for alloys with more than 60% Mn) has been explained [6] on the basis that Mn-Mn nearest neighbour (nn) coupling is antiferromagnetic while next nearest neighbour (nnn) coupling is ferromagnetic. When anticlustering occurs, ferromagnetic interactions increase at the expense of antiferromagnetic interactions, increasing the susceptibility.…”

“…On the other hand there have been observations of a decrease in the high temperature susceptibility with annealing for dilute alloys [7] and magnetic neutron scattering and other measurements which show a nearest neighbour ferromagnetic correlation [8][9][10]. Interestingly, compressing the alloys decreases the susceptibility, tensile distortion increases susceptibility [1] and severe plastic distortion can almost destroy the spin glass behaviour [6].…”