Finite size effects in patterned magnetic permalloy films

Abstract

Electron beam lithography has been used to prepare 250-Å-thick square-shaped permalloy dots whose width and separation are in the range between 1 and 4 m. The static and dynamic magnetic properties of these structures have been investigated by complementary techniques such as magneto-optic Kerr effect ͑MOKE͒, magnetic force microscopy ͑MFM͒, and Brillouin light scattering ͑BLS͒. Longitudinal MOKE enabled us to compare the hysteresis loops of the specimens with different dot size and interdot separation, showing a marked influence of the demagnetizing field inside the dots. MFM images recorded at zero applied field showed that, depending on the interdot spacing, there is a prevalence of either four-or seven-domain patterns together with a minority of nonsolenoidal patterns that possess a net magnetic moment. BLS from thermally activated spin waves were then used to determine the intrinsic magnetic parameters of the permalloy films and to show evidence of the discretization of the spin-wave peak due to the wave vector resonance condition within each dot.

Ferromagnetic nanorings

“…While in bulk systems the number of available states tends to be large, as the size is reduced the separation in energy between the different magnetic states becomes progressively larger, leading to the stabilization of a few relatively simple magnetic conf gurations that tend to ref ect the geometrical symmetry of the element. For example, mesoscopic square elements tend to fall into the quadrant, or Landau-Lifshitz, state [24][25][26][27], while discs tend to fall into the vortex state [19,[28][29][30], even though other high symmetry states are accessible in these geometries, such as the diamond and triangle state in disc elements [30][31][32][33][34] or other less symmetric states in squares [35,36]. As mentioned previously, micrometre size magnetic rings fall into two distinct magnetic states during the magnetization process.…”

MFM imaging of micron-sized permalloy ellipses

“…Many different techniques have been used to study the magnetic behaviour of the elements, for example, Lorentz transmission electron microscopy [1][2][3], magneto-optical Kerr effect [4][5][6], and magnetic force microscope (MFM) measurements [7][8][9]. Understanding the magnetization processes of these elements is of great fundamental value.…”

“…The elements are also of technological interest, the most usual application cited being computer data storage. Consequently, many magnetic materials such as cobalt [2], iron [4] and permalloy [1,5,[7][8][9] have been studied.…”

Ferromagnetic Nanorings

“…While in bulk systems the number of available states tends to be large, as the size is reduced the separation in energy between the different magnetic states becomes progressively larger, leading to the stabilization of a few relatively simple magnetic conf gurations that tend to ref ect the geometrical symmetry of the element. For example, mesoscopic square elements tend to fall into the quadrant, or Landau-Lifshitz, state [24][25][26][27], while discs tend to fall into the vortex state [19,[28][29][30], even though other high symmetry states are accessible in these geometries, such as the diamond and triangle state in disc elements [30][31][32][33][34] or other less symmetric states in squares [35,36]. As mentioned previously, micrometre size magnetic rings fall into two distinct magnetic states during the magnetization process.…”