Effect of surface-topology on magnetic properties in (La0.6Eu0.4)0.67Ca0.33MnO3 of anisotropic shape of nanoplates

Abstract

(La0.6Eu0.4)0.67Ca0.33MnO3 has been prepared in the shape of nanoplates of single crystallites (an orthorhombic structure) through polymer templates. HRTEM images reveal 18, 25, and 30nm thicknesses of plates after heating a precursor powder at 873, 1073, and 1273K in air for 2h. These values present average crystallite size determined from broadening of the X-ray diffraction peaks. A spin-glass-like surface (GS) overlayer (3–5nm thickness) in such plates facilitates a ferromagnetic→ferrimagnetic reordering with markedly suppressed Curie point TC, i.e., as small as 90K in a 873K heated sample, from the parent value 268K. The TC point increases to 103K (or 120K) when heating at higher temperature 1073 (or 1273K), during which the core grows at the expense of the overlayer. The GS tailors as high coercivity Hc as 617Oe in the zero field cooled (ZFC) sample that is decreased to 500Oe in the field cooled (FC) sample in the surface spin-freezing along the field direction. The Hc-value (ZFC) that steps down successively to 252Oe on the overlayer is thinned down by heating at 1273K. Samples heated at 873, 1073, or 1273K have regularly increased saturation magnetization 35.3, 63.9, or 69.6emu/g in ZFC, while 43.7, 70.2, or 75.5emu/g in FC measured at 10K. The ferrimagnetic reordering are described based on the scenario of an antiferromagnetic exchange coupling between the Eu3+ and Mn3+ (or Mn4+) sublattices.