Stability of high frequency magnetic properties of metallic glasses

We report studies of magnetic aging in several Fe- and Co-based metallic glasses. In situ measurements of 50 kHz permeability, core loss, and exciting power at 150 and 200°C were made for up to 1000 h. For the Fe-based alloys, the core loss was stable, but permeability and exciting power degraded with a\log tkinetic. The zero magnetostriction Co-based glasses likewise degraded as\log tin permeability and exciting power with modest increase in core loss. The\log tkinetic is attributed to relaxation processes with a distribution of activation energies beginning at ∼ 1.4 eV for the Fe alloys and at ∼ 1.25 eV for the Co alloys. The apparent rate of decay is less in alloys with higher induced uniaxial anisotropy. Surface studies indicate that below 250°C, oxidation plays at most a minor role in aging.