The magnetic interactions in La${}_{0.70}$Ca${}_{0.30}$Mn${}_{1-x}$Cr${}_x$O${}_3$ ($x=0.15$, 0.50, and 0.70) are investigated by x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), high-resolution x-ray powder diffraction, and bulk magnetization measurements. XAS in the Mn and Cr $L_{2,3}$ edges support stable single valent Cr${}^{3+}$ ions and a varying Mn valence state with $x$, while the O $K$ edge XAS spectrum reveals local maxima in the O $2p$ density of states close to the Fermi level due to mixing with Mn and Cr $3d$ states. A robust antiferromagnetic state is found for $x=0.70$ below $T_N=258$ K. For $x=0.15$, combined XMCD and bulk magnetization measurements indicate a fully polarized ferrimagnetic state for the Mn and Cr spins below $T_c=224$ K. For $x=0.50$, a reduced ferrimagnetic component dominated by Mn spins is present below $T_c=154$ K. No evidence of lattice anomalies due to cooperative charge and orbital orderings is found by x-ray diffraction for all samples. The magnetic properties of this system are rationalized in terms of a competition of ferromagnetic Mn-Mn double exchange and antiferromagnetic Cr-Cr and Cr-Mn superexchange interactions.

• Received 6 May 2011

DOI:https://doi.org/10.1103/PhysRevB.85.104401