Magnetic and Magneto-Optical Properties of Some Rare-Earth and Yttrium Orthochromites

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Abstract
From the magnetic susceptibility measurement on YCrO3 above TN=141°K, two exchange constants J1 and J2 are estimated to be J1=−8.7 cm−1 and J2=−1.0 cm−1. In DyCrO3 weak ferromagnetism is observed along the a axis, with TN=146°K. When temperature goes below 5°K, the direction begins to rotate towards the b axis. In SmCrO3 a spin reorientation is found. The direction of weak ferromagnetism changes from the c axis to the a axis when the temperature is lowered below the reorientation temperature Tr=35≈40°K. The magnitude of the weak ferromagnetic moment of Cr3+ decreases rapidly below Tr. Using the values of J1 and J2, we estimate the magnon energies at high‐symmetry points on the Brillouin zone surfaces in YCrO3. By comparing these magnon energies with the optically observed sidebands of the R lines, one may assign the sidebands to the combined excitations of one exciton and one magnon, and of one exciton and two magnons. The observed temperature dependence of these sidebands supports this assignment. The zero‐magnon absorption lines due to Cr3+ ions were also observed in DyCrO3. However, the polarization and the magnetic field dependence of the lines are found to be quite different from those in YCrO3.