Magnetostriction of transition-metal-metalloid glasses: Temperature dependence

Abstract

Linear, saturation magnetostrictions ${\lambda }_s$ of a variety of ${\mathrm{}\left(\mathrm{FeCoNi}\right)\mathrm{}}_{80}$ ${\mathrm{B}}_{20}$ glasses have been studied as a function of temperature. Magnetostrictions over the range $4.2 \mathrm{K}\lesssim T\lesssim T_C$ for selected glasses, ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$, ${\mathrm{Co}}_{40}$ ${\mathrm{Ni}}_{40}$ ${\mathrm{B}}_{20}$, and ${\mathrm{Ni}}_{50}$ ${\mathrm{Fe}}_{30}$ ${\mathrm{B}}_{20}$, are shown to follow reasonably well the theory of Callen and Callen for single-ion anisotropy of uniaxial-strain symmetry, i.e., $\frac{{\lambda }_s\mathrm{}\left(T\right)\mathrm{}}{{\lambda }_s\mathrm{}\left(0\right)\mathrm{}}={\hat{I}}_{\frac{5}{2}}\mathrm{}\left(X\right)\mathrm{}\equiv \frac{I_{\frac{5}{2}}\mathrm{}\left(X\right)\mathrm{}}{I_{\frac{1}{2}}\mathrm{}\left(X\right)\mathrm{}}$ with $I_{\frac{3}{2}}\mathrm{}\left(X\right)\mathrm{}\equiv m\left(T\right)\mathrm{}$, the reduced magnetization. The anomalous temperature dependence of the magnetostriction observed in the cobalt-rich ${\mathrm{}\left(\mathrm{FeCo}\right)\mathrm{}}_{80}$ ${\mathrm{B}}_{20}$ glasses is attributed to the combination of a positive two-ion (anisotropic-exchange) term plus a stronger, negative, one-ion (crystal-field) term. A change of sign in ${\lambda }_s$ occurs along the Co-Ni side of the triangular Fe-Co-Ni(${\mathrm{B}}_{20}$) diagram due to a change in sign of the dominant single-ion mechanism. This sign change results from a change in the orbital character of the states at the Fermi energy as it passes from the top of the cobalt or nickel $3d^{\downarrow }$ band to the bottom of the iron $3d^{\downarrow }$ band.