Magnetic properties and specific heat ofRMnO3(R=Pr,Nd)

The ground-state properties of the perovskites ${\mathrm{PrMnO}}_3$ and ${\mathrm{NdMnO}}_3$ were investigated by magnetization, magnetic ac susceptibility, and specific heat measurements. A strongly anisotropic behavior has been detected for temperatures below the antiferromagnetic phase transition $T_{\mathrm{N}}\approx 100\mathrm{K}.$ The susceptibility and the weak spontaneous ferromagnetic moment appear to be different in both compounds due to different anisotropic rare-earth contributions. The specific heat shows strong Schottky-type contributions at low temperatures, which for ${\mathrm{NdMnO}}_3$ strongly depend on the magnetic field. A spin reorientation phase transition (spin-flop type) induced by a magnetic field along the b axis was observed in ${\mathrm{NdMnO}}_3$ at $H\sim 110\mathrm{kOe}$ and $T=5\mathrm{}\mathrm{K}.$ All results can consistently be explained by anisotropic contributions of the rare-earth ions: In ${\mathrm{PrMnO}}_3$ the electronic ground state is determined by a low-lying quasidoublet split by the crystal field $\left(\sim 19\mathrm{K}\right).\mathrm{}$ In ${\mathrm{NdMnO}}_3$ the Kramers doublet is split by the Nd-Mn exchange field $\left(\sim 20\mathrm{K}\right).\mathrm{}$