Electron holography technique for investigating thin ferromagnetic films

Abstract

A method is presented here for observing micromagnetic structures in ferromagnetic specimens. Experimental apparatuses for forming electron holograms and for reconstructing optical images are described. Special attention is paid to factors limiting measurement precision. The technique is applied to thin ferromagnetic films, for the purpose of observing fine details of magnetization distribution in a contour map of the electron phase.

Magnetic imaging with spin-polarized low-energy electron microscopy

“…As the annealing proceeds, Fe removed from the grooves accumulates on the remaining Fe ribbons, increasing locally the film thickness. The corresponding magnetic images for a spin polarization of the incident electron beam along the [1][2][3][4][5][6][7][8][9][10] and [001] directions are given in Figures 7c and 7d, respectively. Away from the dewetted regions, magnetization lies along the [1-10] direction (large black magnetic domain), as observed for continuous films before annealing (see Fig.…”

“…Mapping the surface magnetization reveals that it follows the edges of the voids, and is not necessarily oriented exactly along the [001] crystal axis. In other words, while the magnetization of the continuous films is aligned along the [1][2][3][4][5][6][7][8][9][10] direction of the W substrate, the direction of magnetization in the elongated Fe islands may or may not be aligned along the [001] direction, depending on how these islands are oriented after the annealing is complete. Reduction of surface anisotropy does not appear to be a key driving force in the observed SRT.…”

“…Fe films become magnetic at a thickness of about 1.5 ML [113] with an easy axis of magnetization parallel to the [1][2][3][4][5][6][7][8][9][10] direction, due to a strong surface anisotropy. This magnetization axis remains stable up to about 50 ML thickness [114], above which a SRT occurs and the [001] direction becomes the new easy axis of magnetization (i.e.…”

“…-optical microscopies, where magneto-optic Kerr microscopy is one of the most widely known techniques [3,4]; -electron microscopies, including scanning electron microscopy with polarization analysis (SEMPA) [5,6], Lorentz microscopy [7,8], and electron holography [9,10]; -scanning probe microscopies such as magnetic force microscopy (MFM) [11,12], spin-polarized scanning tunneling microscopy (SP-STM) [13], or ballistic emission magnetic microscopy (BEMM) [14,15]; -soft X-rays microscopies, including X-ray photoemission electron microscopy (X-PEEM) [16,17] and scanning transmission X-ray microscopy (STXM) [18,19].…”

Laser-Written Domain Observation Using High Resolution Lorentz Microscopy

“…Lorentz TEM [3], Lorentz scanning electron rnicroscopy (SEM) [41, Lorentz STEM [5], spin-polarizing SEM [6], Interference Electron Micrography [7], and Magnetic Force…”