Mictomagnetism in Pd–Cr and V–Mn Alloys

Abstract

Face‐centered cubic Pd–Cr alloys with 25%–35% Cr, quenched from 1200°C, have an average paramagnetic moment μ̄_Cr of 0.5–1.2 μ_B. Below T_f=36°–76°K the moments are largely frozen, without long‐range magnetic order, but ferromagnetic clusters of up to about 24 μ_B account for the thermomagnetic or isothermal remanence. These giant moments can be aligned in successive small thermally activated steps by cooling in a magnetic field. Once aligned, the giant moments can be turned collectively by much smaller fields. The bcc V–Mn alloys with 50%–76% Mn have similar magnetic properties, but with supergiant moments of more than 1000 μ_B, as quenched from 1200°C. For the Pd alloys with more than 25% Cr the minimum fields and temperatures necessary to align the moments are decreased considerably by annealing at 400°C, when the ferromagnetic clusters acquire dipole moments of up to 3600 μ_B, as measured in the superparamagnetic state, above T_f. The total moment of all supergiant clusters in the annealed 33% Cr alloy is equal to the thermomagnetic remanence of this alloy at 4.2°K. In the quenched as well as in the annealed condition the alloys with 29% and 33% Cr show the largest thermomagnetic remanence, presumably because the tendency for atomic ordering is largest at these compositions.