Kunpeng Su

A novel magnetoresistance induced by charge ordering in ferromagnetic/charge-ordered/ferromagnetic trilayers

Microstructure, magnetoresistance (MR) and magnetic properties of Pr 0.7 Sr 0.3 MnO 3 /La 0.5 Ca 0.5 MnO 3 /Pr 0.7 Sr 0.3 MnO 3 trilayers, which are shown to be tunable with different La 0.5 Ca 0.5 MnO 3 spacer thickness, are investigated. The trilayer with 6 nm thick La 0.5 Ca 0.5 MnO 3 spacer show at 195 K in 1 T and at 220 K in 9 T, which is realized through the double-exchange mechanism. In contrast, trilayers with the thicker La 0.5 Ca 0.5 MnO 3 spacer show enhanced MR at a wide low-temperature range. The obtained at 50 K in 1 T in the trilayer with 18 nm thick La 0.5 Ca 0.5 MnO 3 spacer is superior to that of other magnetic nanoscales. We surmise that this MR originates in the ferromagnetic/antiferromagnetic competition accompanied with the formation of a charge-ordered antiferromagnetic state and the collapse of the charge-ordered state at the applied magnetic field, rather than in the double-exchange mechanism. Large and tunable MR can be realized by controlling the strain state (the thickness of the La 0.5 Ca 0.5 MnO 3 spacer), which can be applied in the used devices.

Preparation of MnAlC flakes by surfactant-assisted ball-milling and the effects of annealing

Abstract An alternative approach for preparing anisotropic MnAlC powders is reported. [001] textured MnAlC flakes with various sizes and thicknesses were fabricated by surfactant-assisted ball-milling (SABM) of bulk ingots. After ball-milling for 8 h the flakes have thicknesses below 200 nm and aspect ratios as high as 102∼103. After being annealed at suitable temperatures, both bulk and SABMed powders can transform from ∊-phase to τ-phase completely. C-doping cannot prevent the decomposition of the τ-phase into the β+γ2 phases after annealing at above 500°C. The magnetic properties are strongly dependent on both the fraction of the τ-phase and the thickness. A high coercivity of ∼242.8 kA m−1 has been achieved in SABMed powders. The coercivity value is 128.8% higher than the experimental value for bulk materials.

Exchange bias induced by surface inhomogeneities in epitaxial Pr 0.7 Sr 0.3 MnO 3 / La 0.5 Ca 0.5 MnO 3 bilayer film

The epitaxial growth of bilayer film made of ferromagnetic metal material Pr0.7Sr0.3MnO3 and charge-ordering insulating material La0.5Ca0.5MnO3 on single crystalline SrTiO3 (001) substrate. High resolution X-ray diffraction and atomic force microscopy analyses show the single crystalline nature of the film. Further atomic force microscopy measurement shows the presence of non-stoichiometric large particulates at the film surface, imparting an overall inhomogeneous composition to the film. This implied that the variation of crystalline structure occurred due to inhomogeneous composition. Magnetic measurement results indicate that the inhomogeneous composition could cause inhomogeneity of magnetic phase which in turn reduce ferromagnetism and enhance exchange bias effect.