Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk Ni50Mn45In5 Heusler alloys

Abstract

Shell ferromagnetism is a new functional property of certain Heusler alloys which was recently observed in Ni 50 Mn 45 In 5 . We report the results of a comparative study of the magnetic microstructure of bulk Ni 50 Mn 45 In 5 Heusler alloys using magnetometry, synchrotron x-ray diffraction, and magnetic small-angle neutron scattering (SANS). By combining unpolarized and spin-polarized SANS (so-called POLARIS) we demonstrate that a number of important conclusions regarding the mesoscopic spin structure can be made. In particular, the analysis of the magnetic neutron data suggests that nanoprecipitates with an effective ferromagnetic component form in an antiferromagnetic matrix on field annealing at 700 K. These particles represent sources of perturbation, which seem to give rise to magnetically disordered regions in the vicinity of the particle-matrix interface. Analysis of the spin-flip SANS cross section via the computation of the correlation function yields a value of ∼55 nm for the particle size and ∼20 nm for the size of the spin-canted region.

Structure, Microstructure, and Magnetic Properties of Melt Spun Ni50Mn50−xInx Ribbons

“…The lattice parameters of the 14M structure vary as a function of indium content and heat treatment. For the AQ-In10, the lattice parameters are lower than those of the Ni 50 Mn 40 In 10 bulk alloy [5], while the lattice parameters of the L1 0 are different from those reported for the Ni 50 Mn 45 In 5 alloys [5,27]. The discrepancies between the present results and those reported earlier might be ascribed to the experimental conditions, such as the preparation method, alloy composition, and heat treatments (time and temperature), that can influence the structure, phase transformation, structural defects, lattice parameters, crystallite sizes, etc.…”

Neutron Scattering as a Powerful Tool to Investigate Magnetic Shape Memory Alloys: A Review

“…They observed fewer and larger clusters when higher temperature and longer time ageing processes were used. They also determined that the martensitic phase decomposition is a process characterized by a two-step linear kinetic regime: the first one with a larger slope was observed for aging times below 16 h, and the second one with a smaller slope for aging times larger than 16 h. The presence of ferromagnetic nanoprecipitates in an antiferromagnetic matrix was reported by Benacchio et al [78] in a bulk Ni 50 Mn 45 In 5 MetaMSMA field-annealed at 700 K. The results were obtained by combining unpolarized and spin-polarized SANS. This phenomenon was also studied by Sarkar et al [79], who demonstrated the presence of spin-clusters of structural origin in a Ni 45 Co 5 Mn 38 Sn 12 MetaMSMA, which are related to the martensitic transformation.…”

Understanding magnetic phase coexistence in Ru2Mn1−xFexSn Heusler alloys: A neutron scattering, thermodynamic, and phenomenological analysis

“…The moment in such systems is strongly confined to Fe and Mn, with the FM or AFM arising from a subtle balance between Sn-mediated AFM superexchange and the itinerant electron FM RKKY (Ruderman-Kittel-Kasuya-Yoshida) interaction [20]. These calculations also highlighted a tendency to chemical phase separation [20], no doubt frustrated by quenching, as in other Heusler-based systems [22][23][24]. A tendency to form (111)-oriented stripes and short-range-ordered clusters of Fe-and Mn-rich FM and AFM phases was uncovered [20].…”