Coexistence of High Magnetization and Anisotropy with Non-monotonic Particle Size Effect in Ferromagnetic PrMnO₃ Nanoparticles

Instances of the coexistence of high ferromagnetic magnetization with large anisotropy are scarce in the rare-earth manganite family. In manganites, high magnetizations are compromised with small coercivity and vice versa. Using nonaqueous sol–gel techniques, the undoped PrMnO₃ nanoparticles with oxygen nonstoichiometry were rendered with exceptional ferromagnetic character. While ∼40 nm sized nanoparticles had magnetization of 84 emu/g and coercivity of 885 Oe with 50 kOe sweeping field, the bulk 2 μm sized particles showed a magnetization of 51 emu/g albeit with a higher coercivity of 2000 Oe. These parameters are so far the highest among manganite systems with similarly sized particles. The competition between the ferromagnetic and antiferromagnetic phases both at the particle core and at the grain boundaries resulted in a non-monotonous trend of magnetic properties between 20, 40, and 2 μm particles. The sudden increase of coercivity toward lower temperatures was a result of the freezing of random spins at the surface of the strongly interacting nanoparticles which also increased the magnetic anisotropy. These results are of prime significance since the coexistence of such a large magnetization with high coercivity was rarely observed in pristine or doped manganites.