Heisenberg-like ferromagnetism in 3d-4 f intermetallic La0.75Pr0.25Co2P2 with localized Co moments

The critical behavior near the continuous paramagnetic to ferromagnetic transition in a single crystal of La0.75Pr0.25Co2P2 has been determined based on high-resolution bulk magnetization data near T-C similar to 167 K, where long-range order is established in the Co sublattice. Scaling equation of state analysis and the Kouvel-Fisher method under a moderate appliedmagnetic field yielded critical exponents (beta = 0.3685 +/- 0.0017, gamma = 1.3361 +/- 0.0083), consistent with the d = 3, n= 3 Heisenberg model of short-range interactions. Calculation of the Rhodes-Wohlfarth ratio confirmed that a localized rather than itinerant description of the 3d Co moments is appropriate in the ferromagnetic region of the sample. The critical susceptibility exponent gamma was found to decrease systematically from the Heisenberg model value toward the mean-field model value as the maximum applied magnetic field considered in the analysis was increased above 2 T. The phenomenon is discussed in terms of mixed exchange mechanisms due to the coexistence of 3d and 4f magnetic sublattices and ordered clusters in the paramagnetic region.