skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern

Abstract

Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studiedmore » with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω{sup 2}/Λ/t in quantitative agreement with Schlömann's prediction for a surface anisotropy entirely ruled by dipolar interaction. The limits of UMA tuning by a ripple pattern are discussed in terms of the surface local angle with respect to the mean surface and of the onset of ripple detachment.« less

Authors:
 [1];  [2];  [3]
  1. Facultad de Ciencias Químicas, Universidad de Castilla-La Mancha, Avda. Camilo J. Cela 10, 13071 Ciudad Real (Spain)
  2. Instituto de Nanociencia, Nanotecnología y Materiales Moleculares, Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, 45071 Toledo (Spain)
  3. Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, c/ Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain)
Publication Date:
OSTI Identifier:
22275552
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 18; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; COBALT; COBALT SILICIDES; COERCIVE FORCE; EMISSION SPECTROSCOPY; FERROMAGNETISM; INTERFACES; ION BEAMS; ION DENSITY; IRRADIATION; MORPHOLOGY; NANOSTRUCTURES; PHOTOEMISSION; SILICON; SUBSTRATES; SURFACES; THIN FILMS; X-RAY SPECTROSCOPY

Citation Formats

Arranz, Miguel A., Colino, Jose M., E-mail: josemiguel.colino@uclm.es, and Palomares, Francisco J. On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern. United States: N. p., 2014. Web. doi:10.1063/1.4876232.
Arranz, Miguel A., Colino, Jose M., E-mail: josemiguel.colino@uclm.es, & Palomares, Francisco J. On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern. United States. doi:10.1063/1.4876232.
Arranz, Miguel A., Colino, Jose M., E-mail: josemiguel.colino@uclm.es, and Palomares, Francisco J. Wed . "On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern". United States. doi:10.1063/1.4876232.
@article{osti_22275552,
title = {On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern},
author = {Arranz, Miguel A. and Colino, Jose M., E-mail: josemiguel.colino@uclm.es and Palomares, Francisco J.},
abstractNote = {Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω{sup 2}/Λ/t in quantitative agreement with Schlömann's prediction for a surface anisotropy entirely ruled by dipolar interaction. The limits of UMA tuning by a ripple pattern are discussed in terms of the surface local angle with respect to the mean surface and of the onset of ripple detachment.},
doi = {10.1063/1.4876232},
journal = {Journal of Applied Physics},
number = 18,
volume = 115,
place = {United States},
year = {Wed May 14 00:00:00 EDT 2014},
month = {Wed May 14 00:00:00 EDT 2014}
}
  • Ion sculpting of ultrathin Fe/Ag(001) films induces the self-assembled formation of nanometric surface ripples oriented along the ion beam direction and the corresponding onset of an in-plane uniaxial contribution to magnetic anisotropy. The authors show that fine tuning of the ion dose impinging on the film allows to tailor the in-plane magnetic anisotropy of such films from purely biaxial in the as-grown state to purely uniaxial. The magnitude of magnetic anisotropy in the pure uniaxial state can be tailored by varying the Fe film thickness prior to irradiation.
  • Magnetic particles moving freely in a fluid can organize dense phases (3D clusters or linear chains). We analyze the spectrum of magnetic oscillations of a chain of spherical magnetic particles taking into account the magnetic anisotropy of an individual particle for an arbitrary relation between the anisotropy energy and the energy of the dipole interaction of particles. For any relation between these energies, the spectrum contains three branches of collective oscillations: a high-frequency branch and a weakly split doublet of low-frequency branches. The frequency of the high-frequency branch is determined by a stronger interaction, while the frequencies of the low-frequencymore » branches are determined by the weakest interaction. Accordingly, the dispersion is maximal for oscillations formed by the dipole-dipole interaction of particles, which have high frequencies in the case of a strong dipole interaction or low frequencies in the case of a strong anisotropy.« less
  • We present a method to preselect the direction of an induced in-plane uniaxial magnetic anisotropy (UMA) in thin single-crystalline Fe films on MgO(001). Ion beam irradiation is used to modulate the MgO(001) surface with periodic ripples on the nanoscale. The ripple direction determines the orientation of the UMA, whereas the intrinsic cubic anisotropy of the Fe film is not affected. Thus, it is possible to superimpose an in-plane UMA with a precision of a few degrees - a level of control not reported so far that can be relevant for example in spintronics.