Shell-ferromagnetic precipitation in martensitic off-stoichiometric Ni-Mn-In Heusler alloys produced by temper-annealing under magnetic field

Abstract

The variety of the multifunctional properties of martensitic Ni-Mn based Heusler alloys are related to the presence of a magnetostructural transition. We report here on a new functionality based on a newly observed property. The observed property is that all off-stoichiometric Ni-Mn-based Heuslers, here in the form Ni50Mn50−xInx with 0<x<25, decompose into predominantly cubic ferromagnetic Ni50Mn25In25 and tetragonal antiferromagnetic NiMn components when temper-annealed. The new functionality is based on magnetic field assisted temper-annealing of a compound with stoichiometry x=5, whereby precipitates of Ni50Mn25In25 with a ferromagnetic shell are formed with spins in the field direction, strongly pinned by the surrounding antiferromagnetic anisotropy, even at temperatures as high as 500 K. The remanent pinning at high temperatures survives any thermal cycling between lowest temperatures and the annealing temperature and any magnetic field cycling between −9 and +9 T. The resulting product can serve as a thermally stable, magnetic-field-proof memory.