Deformation induced thermoremanent magnetisation in an FeMnNiCr antiferromagnetic alloy

Abstract In an austenitic Fe 61.5 Mn 23 Ni 7 Cr 8.5 antiferromagnetic (afm) alloy deformation results in a splitting between magnetisation-vs.-temperature curves measured during field cooling (FC) below the Neel temperature and those measured at the same field after zero-field cooling (ZFC). Furthermore, a thermoremanent magnetisation (TRM) appears that corresponds to the splitting between zero-field and field cooled thermomagnetic measurements for a given cooling field and scales with the degree of deformation. This TRM is attributed to the deformation induced defects which act as a source of uncompensated magnetic moments and interact with the bulk afm moments. This interpretation is also supported by the fact that the net magnetic moments vanish above the Neel temperature. The TRM does not saturate in fields of up to 7 T, applied during cooling, and cannot be switched by fields up to 7 T. Within the investigated field range of −7 T to 7 T the magnetisation-vs.-field curves show a stable shift along the magnetisation axis. Thus, the uncompensated moments appear to be strongly exchange coupled to the afm matrix surrounding them. Within the series of experiments the maximum TRM reached after FC in 7 T corresponds to about 4 × 10 −4 μ B /atom (Bohr magneton) of the maximum deformed afm sample. The Neel temperature decreases due to deformation.