Mn_2V_(0.5)Co_(0.5)Z (Z = Ga, Al) Heusler alloys: High T_c compensated P-type ferrimagnetism in arc melted bulk and N-type ferrimagnetism in melt-spun ribbons

摘要

Ferrimagnetic Heusler alloys with the low moment and high Curie temperature are desired material for spintronic devices utilizing spin transfer torque phenomena. Our earlier report showed compensated ferrimagnetism with high Curie temperature in arc melted bulk Mn(2)V(0.5)Co(0.5)Z (Z = Ga, Al) alloys. The low-temperature M-T behaviour of the bulk alloys was not explored and in this report we discuss the structural and magnetic properties of Mn(2)V(0.5)Co(0.5)Z (Z = Ga, Al) Heusler alloys in the ribbon and bulk forms, particularly concentrating on the distinct low-temperature M-T behaviour. The observed magnetic moment of the parent alloys is around 2 mu(B)/f.u. which was reduced to nearly zero as the Co is substituted at the V site of the Mn(2)VZ (Z = Ga, Al) alloys. The compensated moment value at room temperature for Mn2V0.5Co0.5Ga alloy in the bulk and ribbon forms are 0.13 and 0.09 mu(B)/f.u. respectively. For Mn2V0.5Co0.5Al, a further reduced moment was observed which are 0.08 and 0.04 ( )mu(B)/f.u for the bulk and ribbon samples respectively. The observed Curie temperatures are more than 640 K for both ribbons and bulk samples. A very different temperature dependent magnetic response was observed for the ribbon and bulk samples. The arc melted bulk samples exhibited Neel P-type ferrimagnetic behaviour where there is no full compensation temperature. In contrast to this, the ribbon samples exhibited Neel N-type ferrimagnetic behaviour with a full compensation temperature of 420 K for Mn2V0.5Co0.5Ga and 275 K for MnV0.5Co0.5Al.