Collinear spin-density-wave ordering in Fe/Cr multilayers and wedges

Journal Article · Tue Jun 01 04:00:00 EDT 1999 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.59.13849· OSTI ID:341401

Fishman, R S ^[1]; Shi, Z ^[2]

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1. Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6032 (United States)
2. Read-Rite Corporation, R D Division, 345 Los Coches Street, Milpitas, California 95035 (United States)

Several recent experiments have detected a spin-density wave (SDW) within the Cr spacer of Fe/Cr multilayers and wedges. We use two simple models to predict the behavior of a collinear SDW within an Fe/Cr/Fe trilayer. Both models combine assumed boundary conditions at the Fe-Cr interfaces with the free energy of the Cr spacer. Depending on the temperature and the number {ital N} of Cr monolayers, the SDW may be either commensurate ({ital C}) or incommensurate ({ital I}) with the bcc Cr lattice. Model I assumes that the Fe-Cr interface is perfect and that the Fe-Cr interaction is antiferromagnetic. Consequently, the {ital I} SDW antinodes lie near the Fe-Cr interfaces. With increasing temperature, the Cr spacer undergoes a series of transitions between {ital I} SDW phases with different numbers {ital n} of nodes. If the {ital I} SDW has n=m nodes at T=0, then {ital n} increases by one at each phase transition from {ital m} to m{minus}1 to m{minus}2 up to the {ital C} phase with n=0 above T{sub IC}(N). For a fixed temperature, the magnetic coupling across the Cr spacer undergoes a phase slip whenever {ital n} changes by one. In the limit N{r_arrow}{infinity}, T{sub IC}(N) is independent of the Fe-Cr coupling strength. We find that T{sub IC}({infinity}) is always larger than the bulk N{acute e}el transition temperature and increases with the strain on the Cr spacer. These results explain the very high IC transition temperature of about 600 K extrapolated from measurements on Fe/Cr/Fe wedges. Model II assumes that the {ital I} SDW nodes lie precisely at the Fe-Cr interfaces. This condition may be enforced by the interfacial roughness of sputtered Fe/Cr multilayers. As a result, the {ital C} phase is never stable and the transition temperature T{sub N}(N) takes on a seesaw pattern as n{ge}2 increases with thickness. In agreement with measurements on both sputtered and epitaxially grown multilayers, model II predicts the {ital I} phase to be unstable above the bulk N{acute e}el temperature. Model II also predicts that the {ital I} SDW may undergo a single phase transition from n=m to m{minus}1 before disappearing above T{sub N}(N). This behavior has recently been confirmed by neutron-scattering measurements on CrMn/Cr multilayers. While model I very successfully predicts the behavior of Fe/Cr/Fe wedges, a refined version of model II describes some properties of sputtered Fe/Cr multilayers. {copyright} {ital 1999} {ital The American Physical Society}

• OSTI ID: 341401
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 21 Vol. 59; ISSN 0163-1829; ISSN PRBMDO
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
66 PHYSICS
CHROMIUM
ELECTRON EXCHANGE
EXCHANGE INTERACTIONS
FREE ENERGY
IRON
LAYERS
NEEL TEMPERATURE
SPIN WAVES