Pressure dependence of magnetic properties in Fe–Mn–B amorphous alloys: evidence for inhomogeneous ferromagnetism

The pressure dependence of the saturation magnetization and Curie temperature was studied in melt-spun Fe60Mn20B 20, Fe56Mn24B20 and Fe 75B25 amorphous alloys up to 0.9 GPa, corresponding to volume changes up to 0.45%. In addition, in situ high-pressure (up to 40 GPa) x-ray diffraction was performed to determine the compressibility of the latter two alloys. Both the Curie temperature TC (at atmospheric pressure TC = 201 ± 3 and 159 ± 3 K) and the low-temperature saturation magnetization M5 K,5 T decrease remarkably with increasing pressure: dTC/dp =- 31 ± 0.5 and -32 ± 5 K GPa -1 and dlnM5 K,5 T/dp =- 0.15 ± 0.02 and -0.13 ± 0.03 GPa-1 for xMn = 20 and 24 at.%, respectively. Compared to dlnM5 K,5 T/dp =- 0.016 ± 0.003 GPa-1 measured for Fe75B25, the pressure dependence of M5 K,5 T is one order of magnitude larger in the ternary alloys. The bulk moduli for the Fe56Mn24B 20 and Fe75B25 glasses were measured to be 152 GPa and 173 GPa, respectively. These data are also compared with the pressure dependence of the hyperfine field and theoretical calculations of the saturation moment for Fe-B alloys reported in the literature. The results were interpreted within an inhomogeneous itinerant-electron model of ferromagnetism