Power-Law Dependence of Low-Temperature Magnetic Specific Heat for Hole-Doped Delafossite CuCr1-xMgxO2

Delafossite CuCrO2 is one of the canonical frustrated compounds having an S = 3/2 antiferromagnetic triangular lattice (ATL), wherein a nonmagnetic Cu layer (Cu+; S = 0) and a magnetic CrO2 layer (Cr3+; S = 3/2) are alternatively stacked. Because of various application possibilities, such as in transparent conductor as thermoelectric material and as multiferroic material its magnetic, transport, thermal, structural, and ferroelectric properties have been widely studied. To explore novel phenomena in geometrically frustrated compounds, the effects of various substitutions on the physical properties have also been investigated. Among them, the substitution of nonmagnetic Mg2+ for magnetic Cr 3+ is intriguing, because it produces itinerant holes and dramatically reduces the resistivity, which nontrivially affects the 120° Néel state. In spite of the distinct disorder being introduced into the magnetic state and the antiferromagnetic (AF) correlation being suppressed by the Mg substitution, the Néel temperature (TN) increases and the peak of magnetic specific heat (Cmag) at TN becomes sharper (Fig. 1), indicating the promotion of the AF transition. These effects of the Mg substitution on Cmag around TN are in marked contrast to those of the isovalent substitution such as Al substitution for Cr and Ag for Cu, which clearly suppresses the Néel state owing to the introduced chemical randomness and the enhanced two-dimensional (2D) nature. © 2013 The Physical Society of Japan.