High-temperature magnetostriction of magnetite

The magnetostriction coefficients λ111 and λ100 of magnetite have been measured by a high-temperature strain gage technique between 20° and 500°C. The measurements were performed on discs cut from two natural single crystals and one synthetic single crystal. The value of λ111 shows a linear decrease from about 80 × 10−6 at 20°C to about 7 × 10−6 at 500°C. Although λ100 values are subject to greater error, they remain negative between 20° (−20 × 10−6) and 500°C (−9 × 10−6). These results permit the estimation of the temperature dependence of coercive force and indicate that magnetostrictive interactions between crystal defects and domain walls can be responsible for thermoremanent magnetization in multidomain grains of magnetite.