The critical behavior near the continuous paramagnetic to ferromagnetic transition in a single crystal of ${\mathrm{La}}_{0.75}{\mathrm{Pr}}_{0.25}{\mathrm{Co}}_2{\mathrm{P}}_2$ has been determined based on high-resolution bulk magnetization data near $T_C$ ∼ 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 applied magnetic field yielded critical exponents ($\beta =0.3685\pm 0.0017$, $\gamma =1.3361\pm 0.0083$), 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 γ 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.

• Received 5 August 2014
• Revised 5 October 2014

DOI:https://doi.org/10.1103/PhysRevB.90.174404