Coexisting ferro- and antiferromagnetism in Ni2MnAl Heusler alloys

The structural and magnetic properties of stoichiometric Ni2MnAl are studied to clarify the conditions for ferromagnetic and antiferromagnetic ordering claimed to occur in this compound. X-ray and magnetization measurements show that although a single phase B2 structure can be stabilized at room temperature, a single L21 phase is not readily stabilized, but rather a mixed L21+B2 state occurs. The mixed state incorporates ferromagnetic and antiferromagnetic parts for which close-lying Curie and a Néel temperatures can be identified from magnetization measurements.