Magnetic hardening and antiferromagnetic/ferromagnetic phase coexistence inMn1−xFexRu2SnHeusler solid solutions

Abstract

We investigate the average structure, local structure, and magnetic behavior of Heusler alloys of the composition Mn 1−x Fe x Ru 2 Sn, between antiferromagnetic (AFM) MnRu 2 Sn and ferromagnetic (FM) FeRu 2 Sn (often written Ru 2 MnSn and Ru 2 FeSn). Using a combination of neutron total scattering, electron microscopy, and 57 Fe Mössbauer spectroscopy, we conclude that true solid solutions are formed across the compositional space investigated, with Fe substituting for Mn on the Heusler lattice, with little or no antisite disorder. Despite the lack of chemical phase separation, magnetic phase separation is present in compositions near x = 0.50, where the coexistence of AFM and FM domains is confirmed by 15 K neutron diffraction. At these intermediate compositions a large increase in magnetic coercivity is observed, in excess of 1 kOe, attributed to local exchange interactions.

Modeling magnetic evolution and exchange hardening in disordered magnets: The example of Mn1−xFexRu2Sn Heusler alloys

“…Figure 1(b) shows the phase diagram when only magnetic degrees of freedom are allowed to equilibrate in the presence of quenched in Mn/Fe disorder. This phase diagram emulates the conditions of the experimental studies of Douglas et al [5] Figure 1(b) shows that the magnetic transitions are still present in the chemically-quenched Heusler alloy and that they are similar to those appearing in the fully equilibrated phase diagram of Fig. 1(a) for x < 0.4 and x > 0.75.…”

“…(c) Low-temperature net magnetic moment of the metastable system at 5 K and no field, compared to ab-initio calculations [6] and experiment (saturated moment at 4 K). [5] of the miscibility gap appear to converge to a chemicalmagnetic tricritical point. A more in-depth analysis of this behavior, however, is beyond the scope of this study.…”

“…Our approach uses a chemomagnetic cluster expansion Hamiltonian [8,9] that includes fully-coupled chemical and magnetic degrees of freedom. Prior work [5,6] has shown that significant chemical disorder is present only on the (Mn,Fe) FCC sub-lattice, and that the moments on the Ru and Sn sites do not contribute meaningfully to the magnetic ordering. The relevant chemical and magnetic configurational degrees of freedom can therefore be restricted to the (Mn,Fe) FCC sub-lattice, while the Ru and Sn sub-lattices are present only during the electronic structure calculations used to generate training data to arXiv:1910.07543v1 [cond-mat.mtrl-sci] 16 Oct 2019 parameterize the chemomagnetic cluster expansion.…”

“…Anomalous exchange hardening is observed at intermediate compositions, where the Fe/Mn sublattice of the Heusler alloys is chemically disordered. Prior experimental [4,5] and ab-initio [6] studies on these and similar systems [7] proposed hypotheses of short-range magnetic interactions to explain the observed single-phase Heusler exchange hardening, but were not able to directly demonstrate any local ordering phenomena.…”

Nanoscale Iron Nitride, ε-Fe3N: Preparation from Liquid Ammonia and Magnetic Properties

“…45,46 The present results indicate that the shifting of the hysteresis loops in both the pristine and oxidized samples are likely driven by mixed exchange interactions in the Fe-N caused by disorder at the nanoparticle surfaces.…”