Self-organized Substrates Research Articles

Effects of substrate annealing on uniaxial magnetic anisotropy and ferromagnetic resonance frequency of Ni80Fe20 films deposited on self-organized periodically rippled sapphire substrates

Ni80Fe20 (NiFe) films have been deposited on self-organized sapphire substrates with periodical surface ripples formed by 2–10 h thermal annealing at 1400°C. By extracting static and dynamic magnetic parameters from magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) spectra, we quantified and analyzed the substrate annealing effects on the induced in-plane uniaxial magnetic anisotropy and ferromagnetic resonance frequency in these films. The study demonstrates that the uniaxial anisotropy of these NiFe films is strongly related to the annealing-time dependent substrate faceting and coarsening mechanisms. The uniaxial anisotropy field Hu changes from ~170 Oe to ~250Oe, and the maximum value of it is obtained in film on 8-h annealed substrate. The ferromagnetic resonance response and high frequency characteristics of films can be modulated by self-organized substrate is also confirmed. When external magnetic field is parallel to the direction of ripple, the ferromagnetic resonance frequency of films grown on the self-organized substrates is increased by ~0.3−1 GHz compared with that of reference film on plane substrate. This work would be helpful to design the high frequency properties of spintronic devices and micro-wave magnetic devices by utilizing self-organized substrates.

Investigation of Self-Organized Steps and Terraces in SrTiO3 (001) Substrate Inclined in [110] Direction by Scanning Tunneling Microscopy

The features of self-organized steps and terraces on SrTiO3 (001) substrates inclined in a [110] direction with various inclined angles (α) have been investigated by scanning tunneling microscopy (STM). The well-defined triangular step edges forming nanodot structures are observed on the surface. The surface features of SrTiO3 substrates inclined in the [110] direction consist of the combinational features of substrates in the [100] and [010] inclined directions. Details of the distributions of step heights, terrace widths and lengths of step edge dependent on inclined angles are described. The formation of double, triple and triple half steps is observed in self-organized substrates. The surface after self-organization maintains the same ratio of step height to terrace width. The terminations of TiO2 and SrO planes on the surface are observed visually by an analysis of surface structures. The inclined angle of the substrate inclined in the [110] direction is expected to be an important factor for controlling the density of nanodot structures.

Studies of Self-Organized Steps and Terraces in inclined SrTiO3 (001) Substrate by Atomic Force Microscopy

Features of self-organized steps and terraces present in SrTiO3 (001) substrates with various inclined angles (α) have been investigated by atomic force microscopy (AFM). The details of the shape of step edges, the direction of the straight step edges, the distribution of step heights and terrace widths are described. The existence of various step heights such as single, double and triple heights are observed in the self-organized substrates. The surface after the self-organization conserves the same ratio of the step height and terrace width as that before the self-organization. The features of the self-organized steps and terraces, as well as the relative amount of step interaction energy required to influence the formation of the self-organized surface structure are discussed theoretically.