Spin-glass behavior of (La,Gd)B6 alloys

The low-frequency ac magnetic susceptibility of (La_1–x Gd _x )B₆ alloys (0.0035x0.0812) was measured between 0.04 and 10 K in very low and moderate applied magnetic fields up to 8 kOe. In addition, the low-field static susceptibility was measured between 4.2 and 200 K. At low temperatures the alloys exhibit the basic features of the spin glass state, that is sharp maxima and time dependent effects in the low-field ac susceptibility. The temperature and field dependence of the susceptibility follows a law of corresponding states forx0.01, which is characteristic for Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Effects from interactions between the Gd ions observed above the freezing temperature are consistent with a recent theory based on a virial expansion of the magnetic free energy for the RKKY model and yield |J|=0.04 eV for the magnitude of thes–f exchange integral. The same value is obtained from the initial susceptibility atT0 when compared with a molecular-field result. Above 1 K the initial susceptibility follows a single-impurity Curie law with the free-ion value of the magnetic moment of the Gd solute.