Magnetic properties of Cu–Mn–Al alloys with shape memory effect

Abstract

The magnetization of Cu–Mn–Al alloys with a shape memory effect in the composition line Cu3 Al–Cu3Mn2 was measured from 5 K to room temperature and at fixed temperatures up to (5×107)/(4×π) A/m magnetic fields. It was found that from room temperature to about 90 K (depending upon composition) the samples behaved as superparamagnets[1]. This behavior is described in terms of the magnetic cluster size, the cluster concentration and the interaction between clusters for different compositions and temperatures by fitting the results with the Brillouin function proposed by Beck[2]. Evidence was also found that below this temperature, mictomagnetism (a mixture of ferromagnetism and antiferromagnetism) is present in these alloys. Careful measurement of the magnetization during the martensitic transformation, for a sample with 11.9 at.% Mn was done, in order to estimate the magnetic energy change between β and martensite phases. No noticeable effect on the Ms martensitic transformation temperature, for applied magnetic fields up to (5×107)/(4×π) A/m, was found.