Anomalous triple point effects in the spin-density-wave Cr_{1 -x}Al_x alloy system

It was recently suggested that for the Cr_{1- x}Al_x alloy system the Sommerfeld specific heat coefficient (γ) as a function of x may peak at the triple point (TP) concentration (x_t) of the x-T magnetic phase diagram. The TP at (x_t, T_t) 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 Cr_1-xAl_x alloys in the concentration range 0 ≤ x ≤ 0.034, that encloses x_t, is reported here for further investigations of the above conjecture and possible anomalous behaviour in other physical properties near x_t. The measurements include the electrical resistivity (ρ), Seebeck coefficient (S), specific heat (C_p), Hall coefficient (R_H), 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 x_t. The present study indicates a value of x_t 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 0 K. A new magnetic phase diagram is therefore proposed for the Cr_1-xAl_x alloy system for x in the region of x_t. This study presents novel experimental evidence of exceptional anomalous magnetic behaviour around the TP concentration of the Cr_1-xAl_x system. It should incite similar studies on other Cr alloy systems with a TP on their magnetic phase diagrams.