Low-Temperature Phase Transitions In The Induced-Moment System Prb4

We report the results of measurements of the electrical resistivity, the magnetization, and the specific heat of PrB4 below room temperature. The crystal electric field (CEF) splits the 4f(2) multiplet of the Pr ions into nine singlets. In its ground state, PrB4 is an induced-moment ferromagnet with a saturation magnetization as high as 2.1 mu(B)/(Pr ion). Contrary to previous experiments, we observe a first-order ferromagnetic to antiferromagnetic transition at T-C approximate to 15.9 +/- 0.1 K with a latent heat Delta Q=8.6 J/mol. The antiferromagnetic long-range order is quenched above T-N=19.5 K. Susceptibility and specific heat data, as well as the enormous magnetic anisotropy, can quantitatively be reproduced by a mean-field calculation which takes into account the CEF, obtained from a point-charge model using effective charges obtained from a self-consistent electronic band-structure calculation and a Zeeman term, as well as an anisotropic dipolar magnetic exchange and an effective quadrupole-quadrupole interaction term.