MAGNETIC-PROPERTIES OF CU-MN-AL ALLOYS WITH SHAPE-MEMORY EFFECT

The magnetization of Cu-Mn-Al alloys with a shape memory effect in the composition line Cu-3 Al-Cu3Mn2 was measured From 5 K to room tempera ture and at fixed temperatures up to (5 x 10(7))/(4 x pi) A/m magnetic fields. It was found that from room temperature to about 90 K (depend ing upon composition) the samples behaved as superparamagnets [1]. Thi s behavior is described in terms of the magnetic cluster size, the clu ster concentration and the interaction between clusters for different compositions and temperatures by fitting the results with the Brilloui n function proposed by Beck [2]. Evidence was also Found that below th is temperature, micromagnetism (a mixture of ferromagnetism and antife rromagnetism) is present in these alloys. Careful measurement of the m agnetization during the martensitic transformation, for a sample with 11.9 at.% Mn was done, in order to estimate the magnetic energy change between beta and martensite phases. No noticeable effect on the Ms ma rtensitic transformation temperature, for applied magnetic fields up t o (5 x 10(7))/(4 x pi) A/m, was found. (C) 1997 Acta Metallurgica Inc.