Magnetic properties of (La,Gd)Al2 alloys

Theac anddc susceptibilities of (La_1–x Gd _x )Al₂ alloys were measured for moderate Gd concentrations (0.01x0.08) between 0.05 and 4.2 K. Sharp spin glass like maxima in ^AC are observed at temperaturesT _f which scale asT _f /x 26 K for all samples. However, scaling of ^AC is not observed indicating that the RKKY interaction at short distances which becomes more important with increasing Gd concentration, is ferromagnetic in this system. The amplitudeV ₀ of the RKKY interaction is obtained from both the approach to the saturation magnetization and ^AC forT0, yielding a mean value ₀=(1.5±0.3) 10^–26 eV cm³ which is in agreement with that observed in other systems with Gd impurities. Furthermore, the inferred value of the exchange integral is in accord with other measurements (T _c depression, reverse resistance anomaly) on (La, Gd)Al₂. A superposeddc magnetic field rounds the maximum of ^AC and shifts it to lower temperatures. ^AC is completely flat below 4.2 K in a field which saturates the isothermal remanent magnetization, showing once again the correlation between the peak in ^AC and the onset of irreversible properties.This work is part of the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln