Ferromagnetic cluster glass behavior in U2IrSi3

Measurements of the ac susceptibility, dc magnetization, magnetic relaxation, specific heat, and electrical resistivity of U2IrSi3 are reported. The investigated compound crystallizes in an AlB2-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 U2IrSi3.