Asymmetric metal-insulator transition in disordered ferromagnetic films

TL;DR

This paper investigates the metal-insulator transition in thin ferromagnetic Gd films, combining experimental data with theoretical analysis to understand the scaling behavior and critical exponents near the transition.

Contribution

It provides the first combined experimental and theoretical study of the asymmetric metal-insulator transition in disordered ferromagnetic films, highlighting the role of spin wave scattering and scaling laws.

Findings

Conductivity follows a fractional power law near the transition.

Scaling curves collapse for metallic and insulating regimes.

Critical exponents are estimated: z ≈ 2.5, ν' ≈ 1.4, ν ≈ 0.8.

Abstract

We present experimental data and a theoretical interpretation on the conductance near the metal-insulator transition in thin ferromagnetic Gd films of thickness b approximately 2-10 nm. A large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L_phi < b in the range of sheet resistances considered, so that the effective dimension is d = 3. The observed approximate fractional temperature power law of the conductivity is ascribed to the scaling regime near the transition. The conductivity data as a function of temperature and disorder strength collapse on to two scaling curves for the metallic and insulating regimes. The best fit is obtained for a dynamical exponent z approximately 2.5 and a correlation length critical exponent \nu' approximately 1.4 on the metallic side and a localization length exponent \nu approximately 0.8 on the insulating side.