The random substitutional solid solution between the antiferromagnetic (AFM) full-Heusler alloy Ru2MnSn and the ferromagnetic (FM) full-Heusler alloy Ru2FeSn provides a rare opportunity to study FM-AFM phase competition in a near-lattice-matched, cubic system, with full solubility. At intermediate x in Ru2Mn1-xFexSn this system displays suppressed magnetic ordering temperatures, spatially coexisting FM and AFM order, and strong coercivity enhancement, despite rigorous chemical homogeneity. Here, we construct the most detailed temperature- and x-dependent understanding of the magnetic phase competition and coexistence in this system to date, combining wide-temperature-range neutron diffraction and small-angle neutron scattering with magnetometry and specific heat measurements on thoroughly characterized polycrystals. A complete magnetic phase diagram is generated, showing FM-AFM coexistence between x≈0.30 and x≈0.70. Important insight is gained from the extracted length scales for magnetic phase coexistence (25-100 nm), the relative magnetic volume fractions and ordering temperatures, and remarkable x-dependent trends in magnetic and electronic contributions to specific heat. An unusual feature in the magnetic phase diagram (an intermediate FM phase) is also shown to arise from an extrinsic effect related to a minor Ru-rich secondary phase. The established magnetic phase diagram is then discussed with the aid of phenomenological modeling, clarifying the nature of the mesoscale phase coexistence with respect to the understanding of disordered Heisenberg models.
Bibliographical noteFunding Information:
This work was supported primarily by the U.S. Department of Energy through the University of Minnesota Center for Quantum Materials under Grant No. DE-SC-0016371. E.M. acknowledges financial support from the Natural Sciences and Engineering Research Council of Canada. The work at UC Santa Barbara was supported by the National Science Foundation (NSF) Materials Research Science and Engineering Center (MRSEC) under Grant No. DMR-1720256 (IRG-1). Part of this research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. We thank E. Decolvenaere and D. Ryan for useful conversations.
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