The effect of atomic volume on exchange interaction integrals in R-Fe amorphous alloys and crystalline compounds

Magnetization and magnetic susceptibility under applied hydrostatic pressures of up to 10 kbar were studied for R-Fe amorphous alloys and crystalline compounds, where R is a heavy rare-earth metal. The results are discussed in terms of the molecular field theory. The difference in exchange integral versus applied pressure relationships between R-Fe amorphous alloys and crystalline compounds are explained by the difference in the short-range order. Hydrostatic pressure induces a noncollinear magnetic structure in $Y_2Fe_{17}$ and $Er_2Fe_{17}$ crystals and transforms two paramagnetism-asperomagnetism-reversible spin-glass phase transitions into a single paramagnetism-spin-glass phase transition in the amorphous $Y_{19}Fe_{81}$ alloy. This is explained by a reversal of the ratio between the positive and negative exchange interactions within the iron subsystem.