Element-specific and bulk magnetism, electronic, and crystal structures of La0.70Ca0.30Mn1-x Crx O3.

The magnetic interactions in Lao.7oCao.30Mn1-xCrx03 (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 L2,3 edges support stable single valent Cr3+ 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 TN = 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 Tc= 224 K. For x = 0.50, a reduced ferrimagnetic component dominated by Mn spins is present below Tc = 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. [ABSTRACT FROM AUTHOR]