Spontaneous Magneto-Impedance in YCo12B6 and GdCo12B6 Intermetallic Compounds

We report on electrical impedance measurements in variable temperatures and fixed frequencies in the intermetallic compounds YCo₁₂B₆ and GdCo₁₂B₆ and discuss the potential of this technique to probe intrinsic magnetic properties and magnetization dynamics. The studied temperature range that extends from 15 to 300 K encompasses the Curie temperature TC of both systems. Frequencies span the interval from 37 Hz to 1.5 MHz. Effects of magnetic ordering are observed in the impedance results. The Hopkinson effect becomes evident near TC in frequencies above 10 kHz for GdCo₁₂B₆ and above 100 kHz for YCo₁₂B₆. A qualitative analysis of these results suggests that the Hopkinson peaks in both systems result from a critical phenomenon associated with the initial permeability. In frequencies above 100 kHz, a change of slope in the impedance versus temperature curves for GdCo₁₂B₆ occurs at the compensation temperature. We conclude that the impedance measurement is a powerful technique to investigate intrinsic magnetic properties of Y-Co and Gd-Co-based compounds.