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

Abstract

The kinetics of short-range order (SRO) growth in a Cu - 16.4 at.% Mn alloy have been studied by measuring the evolution with time of the low-temperature magnetic properties while aging at temperatures around 100 . This new approach was possible because atomic SRO leads to magnetic clustering at this Mn concentration. Several models, all based on the diffusion of vacancies and their annihilation in fixed sinks, implied that the sink density was higher at 115 than at 100 for identical quenching conditions. It was concluded that the quenched-in vacancies condense in clusters. These act as sinks, halting the growth of SRO when the excess quenched-in vacancies have been absorbed. Quenching faster or aging at a higher temperature nucleates more vacancy clusters, causing earlier vacancy exhaustion. Neutron irradiation was used to continuously supply vacancies, thereby driving the SRO process to equilibrium at about 100 . A much higher magnetic susceptibility was attained than previously reported, some 20 times the as-quenched value at the spin freezing temperature.

Andrei Viktorovich Gaponov-Grekhov (on his seventieth birthday)

“…The scattering crosssection is found to increase continuously with decreasing magnitude of the scattering vector, indicating ferromagnetic spin correlations (figure 2). It is obvious that there is a striking difference in the shape of the curves at small q values above and below 80 K, i.e., near the spin-glass temperature (∼75 K for Cu-16.7 at.% Mn [20]); while the scattering crosssection continuously increases with decreasing temperature at high q values, there is a cusp at about 80 K at the lowest q values. Such a maximum is commonly found at the spin-glass temperature [12].…”

Long-range atomic order in irradiated Cu 80 Mn 20

“…Firstly, the effectiveness of aging in increasing the low-temperature magnetisation (which correlates with ASRO development [4]) was found to be maximum at this composition [7]. Secondly, Cu 4 Mn is one of the superlattices generated by a concentration wave in the (420) series, based on the stacking of (210)-type planes, exhibiting ( [8].…”

“…An article by one of the present authors [4] reviewed studies of short-range order in the Curich alloys and its effects on their magnetic properties. In that work a model for the mechanism of atomic short-range ordering in terms of vacancy migration was proposed.…”

“…• C used in the previous irradiation experiment [4]. This was expected to be advantageous because it was demonstrated [4] that a greater degree of order could be achieved during aging at a lower temperature and that ordering in the absence of radiation was curtailed by annihilation of the necessary vacancies well before equilibrium was attained.…”

“…This was expected to be advantageous because it was demonstrated [4] that a greater degree of order could be achieved during aging at a lower temperature and that ordering in the absence of radiation was curtailed by annihilation of the necessary vacancies well before equilibrium was attained. The samples were chosen to be small (2.9 g total mass) to avoid excessive heating during irradiation.…”