Magnetostriction studied with precise high temperature powder diffraction

Thermal expansions of alpha-Fe2O3 (Hematite) and Yttrium-Iron-Garnet (YIG) were studied with high temperature X-ray powder diffraction using a newly developed high temperature chamber (PMP1600). YIG was investigated in the temperature range from 25 degrees C to 1430 degrees C, while hematite was studied from 25 degrees C to 1380 degrees C. Lattice parameters were derived from Rietveld analysis of high temperature patterns. The unit cell of YIG is found to expand isotropically, and to show a slight anomaly around 270 degrees C where it has a magnetic phase transition from the ferrimagnetic to the paramagnetic state. Hematite expands anisotropically, with an anomaly around 645 degrees C, close to its Neel temperature (antiferromagnetic to paramagnetic transition); the anomaly is more pronounced in the a direction, than in the c direction. Thermal expansion of YIG and hematite parallel to the a direction shows 'lambda-type' behaviour at the Curie and Neel temperatures, respectively.