Anomalous triple point effects in the spin-density-wave Cr1−xAlx alloy system

• Published in: Journal of alloys and compounds 2014-05, Vol.595, p.164-177
• Main Authors: Sheppard, C.J., Prinsloo, A.R.E., Alberts, H.L., Muchono, B., Strydom, A.M.
• Format: Article
• Language: English
• Subjects: Anti-ferromagnetism; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Critical-point effects, specific heats, short-range order; Exact sciences and technology; Hall coefficient; Itinerant; Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.); Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Physics; Sommerfeld coefficient; Spin-density wave; Spin-density waves; Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.); Triple point
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2014.01.129

•Extensive investigation into the physical properties of Cr–Al single crystals.•Unusual and prominent influence of SDW reflected in physical properties.•Alternative magnetic phase diagram suggested for Cr–Al system.•Triple point on phase diagram minimum appears to be deeper and narrower.•Triple point appears to be enigmatic critical point to be further investigated. It was recently suggested that for the Cr1−xAlx alloy system the Sommerfeld specific heat coefficient (γ) as a function of x may peak at the triple point (TP) concentration (xt) of the x–T magnetic phase diagram. The TP at (xt, Tt) represents the intersection point of three magnetic phase transition lines at which incommensurate (I) and commensurate (C) spin-density-wave (SDW) phases are expected to coexist with the paramagnetic (P) phase. A comprehensive experimental study on the physical properties of single crystalline Cr1−xAlx alloys in the concentration range 0⩽x⩽0.034, that encloses xt, is reported here for further investigations of the above conjecture and possible anomalous behaviour in other physical properties near xt. The measurements include the electrical resistivity (ρ), Seebeck coefficient (S), specific heat (Cp), Hall coefficient (RH), magnetic susceptibility (χ) and thermal conductivity (κ). All these properties, except for κ, depict anomalous temperature and concentration dependencies of SDW origin for x close to xt. The present study indicates a value of xt rather close to x=0.022. The x-dependence of γ exhibits an extraordinary large and sharp peak near this concentration. This observation is interpreted as indication that the temperature of the TP is likely situated at 0K. A new magnetic phase diagram is therefore proposed for the Cr1−xAlx alloy system for x in the region of xt. This study presents novel experimental evidence of exceptional anomalous magnetic behaviour around the TP concentration of the Cr1−xAlx system. It should incite similar studies on other Cr alloy systems with a TP on their magnetic phase diagrams.