Integer spin-chain antiferromagnetism of the 4d oxide CaRuO3 with post-perovskite structure

A quasi-one dimensional magnetism was discovered in the post-perovskite CaRuO3 (Ru4+: 4d4, Cmcm), which is iso-compositional with the perovskite CaRuO3 (Pbnm). An antiferromagnetic spin-chain function with -J/kB = 350 K well reproduces the experimental curve of the magnetic susceptibility vs. temperature, suggesting long-range antiferromagnetic correlations. The anisotropic magnetism is probably owing to the dyz - 2p- dzx and dzx - 2p- dyz superexchange bonds along a-axis. The Sommerfeld coefficient of the specific heat is fairly small, 0.16(2) mJ mol-1 K-2, indicating that the magnetism reflects localized nature of the 4d electrons. As far as we know, this is the first observation of an integer (S = 1) spin-chain antiferromagnetism in the 4d electron system.Comment: Accepted for publication in Phys. Rev.

Heat capacity and thermal expansion data for TiO2 rutile, TiO2-II and corundum

High-temperature isobaric heat capacity (Cp) data for rutile and TiO2-II were measured using DSC. Also, low-temperature Cp data for rutile, TiO2-II and corundum were measured using PPMS. Harmonic isochoric heat capacity (Cv) data were calculated with a lattice vibrational model calculation using the Kieffere model. Thermal expansivity (α) data were calculated from the Grüneisen relation equation

High pressure Raman spectroscopy, vibrational mode calculation, and heat capacity calculation of calcium ferrite type MgAl2O4 and CaAl2O4

High pressure micro Raman spectroscopic measurements of calcium ferrite type MgAl2O4 and CaAl2O4 were made using a diamond anvil cell high pressure apparatus. The pressure dependence of frequencies of 18 Raman peaks for calcium ferrite type MgAl2O4 and 26 Raman peaks for calcium ferrite type CaAl2O4 were determined up to 20 GPa at ambient temperature. The mode Grüneisen parameter for each observed Raman mode was obtained from the pressure dependence of frequencies. Vibrational mode calculations by first principles using density functional theory were also performed for assignment of Raman peaks and for estimating frequencies of Raman inactive modes. From the obtained mode Grüneisen parameters and the results of the vibrational mode calculations, thermal Grüneisen parameters were determined to be 1.50 5 for calcium ferrite type MgAl2O4 and 1.31 3 for calcium ferrite type CaAl2O4. These thermal Grüneisen parameters were applied to heat capacity and vibrational entropy calculations using Kieffer mode