Characteristic Size Effects On The Crystallographic Structure And Magnetic Properties Of Rmno3 (R = Eu, Gd, Tb, Dy) Nanoparticles

We synthesized lanthanoid manganese oxide RMnO3 (R = Eu, Gd, Tb, and Dy) nanoparticles with particle sizes ranging from approximately 6.5 to 23 nm and investigated both their crystal structure and magnetic properties. The RMnO3 nanoparticles showed a strong correlation between crystal structure and magnetic properties, and particle size effects on these properties vary owing to the different atomic radii of the lanthanoid ions. The magnetic properties of all of the nanoparticles exhibited significant changes as the lattice constants changed at characteristic sizes that depend on the lanthanoid ionic radius; however, the characteristic size for magnetic properties corresponded to the magnitude of the orthorhombic distortion b/a = 1.10, regardless of the lanthanoid ionic radius. With decreasing particle size, EuMnO3, GdMnO3, and TbMnO3 nanoparticles induced tensile strain of MnO6 octahedra, whereas compressive strain occurred in DyMnO3 nanoparticles. The deformation of MnO6 octahedra changed the magnetic interactions, resulting in changes in the magnetic properties. As the particle size decreased, for R = Eu, Gd, and Tb, the magnetic properties, such as transition temperature, coercive field, and blocking temperature, decreased; conversely, these values increased in DyMnO3. The distortion of the unit cell induced changes in the magnetic ordering state due to decreasing particle size.