Evidence of re-entrant spin-glass behavior in the GdAgGa compound

Structural, magnetic, calorimetric, and magnetocaloric properties of the GdAgGa polycrystalline intermetallic compound are reported. This compound crystallizes with an orthorhombic CeCu2-type structure. Magnetization data reveal a phase transition from a paramagnetic to a ferromagnetic state around Curie temperature (T-C) = 30 K and a low-field-dependent anomaly (T*) below 14 K. Features on the time dependence of magnetic relaxation, thermomagnetic irreversibility below T*, absence of a lambda-type peak on zero-field heat capacity, and the frequency dependence of imaginary and real components of ac susceptibility indicate a complex magnetic structure, in which a re-entrant spin-glass (RSG) phase coexists with long-range ferromagnetism. The RSG phase arises due to the nonmagnetic atom disorder, which induces a non-uniform ferromagnetic phase. As temperature decreases, such non-uniformity contributes to the development of spin-glass correlation. The applied external magnetic field destabilizes the RSG phase, and the magnetization increases reaching similar to 6.1 mu(B) per Gd ion at T = 2 K for a magnetic field of 50 kOe. Isothermal magnetic entropy change (Delta S-M) exhibits a broad curve with its maximum around T-C and a long tail over a wide temperature range above T-C. The inverse magnetocaloric effect (MCE) for T < 10 K is consistent with antiferromagnetic interactions from the RSG phase. An appreciated magnetic entropy change was observed with a maxima value of similar to 7 J/kg K and a relative cooling power of 264 J/kg for a magnetic field change of 50 kOe. The nature of the magnetic state is a critical factor influencing the GdAgGa compound magnetocaloric effect.