Ferromagnetic cluster glass behavior in U₂IrSi₃

Measurements of the ac susceptibility, dc magnetization, magnetic relaxation, specific heat, and electrical resistivity of U₂IrSi ₃ are reported. The investigated compound crystallizes in an AlB ₂-derived hexagonal structure and undergoes a ferromagnetic cluster glass transition at T_f=10.5 K. Typical features of the ferromagnetic cluster glass state include (i) a frequency-dependent cusp in the ac susceptibility, (ii) an irreversibility in the temperature dependence of the dc magnetization, (iii) a very slow decay of the remanence, (iv) a small jump in the initial magnetization curve, and (v) a small specific heat anomaly, which contains a very small amount of magnetic entropy. The specific heat data also demonstrate a large value of the linear specific heat coefficient and the absence of true long-range magnetic order. Furthermore, a Kondo-effect-like behavior is observed in the temperature dependence of the electrical resistivity. It seems that both cluster glass freezing and Kondo-lattice effects make an impact on the low-temperature physical properties of U ₂IrSi₃.