Magnetic properties of (La, Gd)Al₂ alloys

Theac anddc susceptibilities of (La1−x Gd x )Al2 alloys were measured for moderate Gd concentrations (0.01≦x≦0.08) between 0.05 and 4.2 K. Sharp spin glass like maxima inχ AC are observed at temperaturesT f which scale asT f /x ≃ 26 K for all samples. However, scaling ofχ 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 andχ AC forT→0, yielding a mean value V¯ 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 ofχ AC and shifts it to lower temperatures.χ 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 inχ AC and the onset of irreversible properties