Magnetic Properties and Crystal-Structure Transformation of the Ordered Alloy (MnRh)

Abstract

The magnetization and electrical resistivity of the ordered alloy MnRh were measured during a complete temperature cycle between 4.2° and 700°K. At all temperatures the magnetization is proportional to field. From 700°K down to about 170°K, the susceptibility rises according to a Curie‐Weiss relation, χ=C(T−θ)⁻¹, where θ≃−260°K and C gives an average effective atomic moment of about 3.3 μ_B, and the resistivity decreases slowly, yielding a large spin‐disorder term, about 85 μΩ‐cm, when extrapolated linearly to 0°K. This classical paramagnetic behavior is identified with the ordered cubic (CsCl‐type) phase of this alloy. Below 170°K the susceptibility and resistivity decrease very rapidly and then gradually level off at lower temperatures, reaching values of about 5×10⁻⁶ emu/g and 6 μΩ‐cm, respectively, at 4.2°K. The subsequent return of these properties to their original values at higher temperatures reveals a large temperature hysteresis in this transition. It is discovered from x‐ray diffraction measurements below room temperature that this transition corresponds to a transformation to an ordered tetragonal (CuAu‐type) structure, accompanied by a density increase of over 2%. The small temperature‐independent susceptibility and small residual resistivity of this low‐temperature tetragonal form of MnRh suggest it is a strong antiferromagnet.