GMI in the reentrant spin-glass Fe₉₀Zr₁₀ alloy: Investigation of the spin dynamics in the MHz frequency regime

Giant magnetoimpedance (GMI) in the reentrant spin-glass (SG) phase of ferromagnetic Fe₉₀Zr₁₀ is reported. The temperature (T) dependence of the GMI allows the investigation of the spin dynamics in the SG phase in the MHz frequency regime and thus very short relaxation times τ (∼10^-8 s). The GMI shows a broad maximum around 150 K and diminishes with decreasing T below the glass temperature T_g of 15 K. The magnetic permeability data obtained from the GMI data show the general features observed in the ac magnetic susceptibility measured at lower frequencies (10 ≤ f ≤ 10⁴ Hz), yielding values of T_f (=T_g(f)) that allow testing the validity of the power-law scaling used for describing the dynamics of SG-phases up to 15 MHz. A log-log plot of τ (=1/f) versus the reduced critical temperature shows two distinct regimes in the time-domain: (1) a critical slowing-down is observed for values τ > 3 × 10^-3 s; and (2) for 7 × 10^-8≤ τ ≤ 3 × 10^-3 s. In the latter case a fitting to the power-law yields the value 7.4 for the product of the critical exponents zν, and 1.6 × 10^-7 s for the microscopic relaxation time τ₀. The product of the exponents is appropriate for an Ising spin glass.