TEMPERATURE DEPENDENCIES OF THE LATTICE-CONSTANTS AND THERMAL-EXPANSION COEFFICIENTS OF SM3FE5O12 AND ER3FE5O12 SINGLE-CRYSTALS

The temperature dependencies of the lattice parameters of erbium and samarium iron garnets (ErIG and SmIG) are refined from precise x-ray diffraction data obtained on small spherical single crystals in the 20-300 K temperature range; the variations of the thermal linear expansion coefficients are immediately deduced. For ErIG, the lattice constants and the expansion coefficients present anomalies observed at 20, 59, 75, and 105 K, respectively, whereas for SmIG singularities are situated at 40 and 68 K. These anomalies are interpreted as originating from spin-reorientation transition and from the onset of noncollinear magnetic structure of the rare-earth magnetic moments.