Size dependences of crystal structure and magnetic properties of DyMnO3 nanoparticles

• We successfully synthesized DyMnO3 nanoparticles with particle size of 7.5–15.3 nm.
• Lattice strain increases with decreasing particle size.
• Lattice constants exhibit anisotropic change with decreasing particle size.
• Distortion of crystal structure leads to enhancement of magnetic anisotropy constant.
• Blocking temperature and coercive field increases with decreasing particle size.

We synthesized DyMnO3 nanoparticles with particle sizes of about 7.5–15.3 nm in the pores of mesoporous silica and investigated their crystal structure and magnetic properties. As the particle size decreased, the lattice constants of the DyMnO3 nanoparticles deviated from those of the bulk crystal, and the Jahn–Teller distortion in the nanoparticle systems decreased. In addition, the estimated lattice strain increased with decreasing particle size. The DyMnO3 nanoparticles showed superparamagnetic behavior. The blocking temperature and the coercive field increased with decreasing particle size, and this behavior was contrary to the usual magnetic size effects. It is deduced that these unique size dependences of the magnetic properties for the DyMnO3 nanoparticles were derived from the changes in lattice constants and lattice strain. The anisotropic lattice deformation in the crystal structure of the nanoparticles induces an enhancement of the magnetic anisotropy, which results in the increase in blocking temperature and coercive field with decreasing particle size.