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

Title: Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: layer-resolved {sup 57}Fe Mssbauer spectroscopy and electronic structure calculations.

Abstract

Magnetization reversal in nanoscale (Sm-Co)/Fe (hard/soft) bilayer exchange-spring magnets with in-plane uniaxial magnetic anisotropy was investigated by magnetometry, conversion-electron Moessbauer spectroscopy (CEMS) and atomistic Fe spin-structure calculations. Magnetization loops along the easy direction exhibit signatures typical of exchange-spring magnets. In-field CEMS at inclined {gamma}-ray incidence onto thin (2 nm) {sup 57}Fe probe layers embedded at various depths in the 20-nm-thick natural (soft) Fe layer provides depth-dependent information (via the line-intensity ratio R{sub 23} as a function of the applied field H) about the in-plane rotation of Fe spins. A minimum in the R{sub 23}-vs-H dependence at (H{sub min}, R{sub min}) determines the field where Fe magnetic moments roughly adopt an average perpendicular orientation during their reversal from positive to negative easy-axis orientation. A monotonic decrease of H{sub min} with distance from the hard/soft interface is observed. Rotation of Fe spins takes place even in the interface region in applied fields far below the field of irreversible switching, H{sub irr}, of the hard phase. Formation of an Fe-Co alloy is detected in the interface region. For comparison, the noncollinear Fe spin structure during reversal and the resulting R{sub 23} ratio were obtained by electronic-structure calculations based on a quantum-mechanical Hamiltonian formore » itinerant electrons. The coupling at the hard/soft interface is described by the uniaxial exchange-anisotropy field, hint, as a parameter. Our calculated R{sub 23} ratios as a function of the (reduced) applied field h exhibit similar features as observed in the experiment, in particular a minimum at (h{sub min}, R{sub min}). R{sub min} is found to increase with hint, thus providing a measure of the interface coupling. Evidence is provided for the existence of fluctuations of the interface coupling. The calculations also show that the Fe spin spiral formed during reversal is highly inhomogeneous. In general, our simulation of the Fe spin structure is applicable for the interpretation of experimental results on layered exchange-spring magnets.« less

Authors:
; ; ; ; ; ;  [1]
  1. Materials Science Division
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); DFG-RFBR Cooperative Grant; German Research Foundation (DFG)
OSTI Identifier:
1033852
Report Number(s):
ANL/MSD.JA-68660
Journal ID: ISSN 1098-0121; TRN: US201203%%131
DOE Contract Number:  
DE-AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 85; Journal Issue: 2; Journal ID: ISSN 1098-0121
Country of Publication:
United States
Language:
ENGLISH
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALLOYS; ANISOTROPY; ELECTRONIC STRUCTURE; ELECTRONS; FLUCTUATIONS; HAMILTONIANS; MAGNETIC MOMENTS; MAGNETIZATION; MAGNETS; MOESSBAUER EFFECT; ORIENTATION; PROBES; ROTATION; SIMULATION; SPIN

Citation Formats

Uzdin, V M, Vega, A, Khrenov, A, Keune, W, Kuncser, V E, Jiang, J S, Bader, S D, St. Petersburg State Univ.), St. Petersburg State Univ. of Information Technologies), Univ. de Valladolid), Univ. Duisburg-Essen), Max-Planck-Inst. fur Mikrostrukturphysik), and National Inst. of Material Physics). Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: layer-resolved {sup 57}Fe Mssbauer spectroscopy and electronic structure calculations.. United States: N. p., 2012. Web. doi:10.1103/PhysRevB.85.024409.
Uzdin, V M, Vega, A, Khrenov, A, Keune, W, Kuncser, V E, Jiang, J S, Bader, S D, St. Petersburg State Univ.), St. Petersburg State Univ. of Information Technologies), Univ. de Valladolid), Univ. Duisburg-Essen), Max-Planck-Inst. fur Mikrostrukturphysik), & National Inst. of Material Physics). Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: layer-resolved {sup 57}Fe Mssbauer spectroscopy and electronic structure calculations.. United States. https://doi.org/10.1103/PhysRevB.85.024409
Uzdin, V M, Vega, A, Khrenov, A, Keune, W, Kuncser, V E, Jiang, J S, Bader, S D, St. Petersburg State Univ.), St. Petersburg State Univ. of Information Technologies), Univ. de Valladolid), Univ. Duisburg-Essen), Max-Planck-Inst. fur Mikrostrukturphysik), and National Inst. of Material Physics). Sun . "Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: layer-resolved {sup 57}Fe Mssbauer spectroscopy and electronic structure calculations.". United States. https://doi.org/10.1103/PhysRevB.85.024409.
@article{osti_1033852,
title = {Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: layer-resolved {sup 57}Fe Mssbauer spectroscopy and electronic structure calculations.},
author = {Uzdin, V M and Vega, A and Khrenov, A and Keune, W and Kuncser, V E and Jiang, J S and Bader, S D and St. Petersburg State Univ.) and St. Petersburg State Univ. of Information Technologies) and Univ. de Valladolid) and Univ. Duisburg-Essen) and Max-Planck-Inst. fur Mikrostrukturphysik) and National Inst. of Material Physics)},
abstractNote = {Magnetization reversal in nanoscale (Sm-Co)/Fe (hard/soft) bilayer exchange-spring magnets with in-plane uniaxial magnetic anisotropy was investigated by magnetometry, conversion-electron Moessbauer spectroscopy (CEMS) and atomistic Fe spin-structure calculations. Magnetization loops along the easy direction exhibit signatures typical of exchange-spring magnets. In-field CEMS at inclined {gamma}-ray incidence onto thin (2 nm) {sup 57}Fe probe layers embedded at various depths in the 20-nm-thick natural (soft) Fe layer provides depth-dependent information (via the line-intensity ratio R{sub 23} as a function of the applied field H) about the in-plane rotation of Fe spins. A minimum in the R{sub 23}-vs-H dependence at (H{sub min}, R{sub min}) determines the field where Fe magnetic moments roughly adopt an average perpendicular orientation during their reversal from positive to negative easy-axis orientation. A monotonic decrease of H{sub min} with distance from the hard/soft interface is observed. Rotation of Fe spins takes place even in the interface region in applied fields far below the field of irreversible switching, H{sub irr}, of the hard phase. Formation of an Fe-Co alloy is detected in the interface region. For comparison, the noncollinear Fe spin structure during reversal and the resulting R{sub 23} ratio were obtained by electronic-structure calculations based on a quantum-mechanical Hamiltonian for itinerant electrons. The coupling at the hard/soft interface is described by the uniaxial exchange-anisotropy field, hint, as a parameter. Our calculated R{sub 23} ratios as a function of the (reduced) applied field h exhibit similar features as observed in the experiment, in particular a minimum at (h{sub min}, R{sub min}). R{sub min} is found to increase with hint, thus providing a measure of the interface coupling. Evidence is provided for the existence of fluctuations of the interface coupling. The calculations also show that the Fe spin spiral formed during reversal is highly inhomogeneous. In general, our simulation of the Fe spin structure is applicable for the interpretation of experimental results on layered exchange-spring magnets.},
doi = {10.1103/PhysRevB.85.024409},
url = {https://www.osti.gov/biblio/1033852}, journal = {Physical Review. B, Condensed Matter and Materials Physics},
issn = {1098-0121},
number = 2,
volume = 85,
place = {United States},
year = {2012},
month = {1}
}