Probing the spin-dynamics in reentrant spin-glass phase with giant magnetoimpedance

In a relatively narrow concentration range amorphous FeZr alloys undergo a phase transition from a ferromagnet state to a spin-glass phase at low temperatures. To investigate the high frequency dynamics of this reentrant transition we have used measurements of the giant magnetoimpedance (GMI). In general the GMI is a measurement of the transverse magnetic permeability, $\mu_{T}$, as a function of temperature, $T$, and frequency, $f$, through their relation to the skin-depth $\delta$ $(=[\rho/\pi f \mu_{T}]^{1/2})$. In our recent work [Appl. Phys. Lett. 109, 102404 (2016)], the GMI was used to explore the relation between the scaling-law of the relaxation time,$\tau$, $(\tau =1/f)$ and the reduced freezing temperature $(t=1-T_f/T_G)$ in the MHz $f$-regime for a Fe$_{90}$Zr$_{10}$ sample with a $T_{G}$ of 14.0 K. We will review this work and present GMI and $\chi_{ac}$ data for a Fe$_{91}$Zr$_{9}$ sample with $T_{G}$ equal to 38.4 K. For the Fe$_{91}$Zr$_{9}$ sample it was found that the product of the critical exponents $z\nu$ $(=7.8)$ is comparable to the Fe$_{90}$Zr$_{10}$ sample $(=7.4)$ despite the different values of $T_{G}$. We conclude the alloys belong to the short-range Ising class of universality up to the MHz $f$-regime.