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Long-range magnetic order in Fe 3 O 4 /NiO superlattices

1995; American Physical Society; Volume: 51; Issue: 13 Linguagem: Inglês

10.1103/physrevb.51.8276

1095-3795

J. A. Borchers, R. W. Erwin, S. D. Berry, D. M. Lind, John F. Ankner, Eric Lochner, K. A. Shaw, David K. Hilton,

Magnetic properties of thin films

Using neutron diffraction, x-ray scattering, and bulk-magnetization methods, we have characterized the magnetic structure for ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$/NiO superlattices grown by molecular-beam epitaxy. The antiferromagnetic NiO order extends through several superlattice bilayers, even though the intervening ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ layers are ferrimagnetic. The structural and magnetic coherence of the ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ is limited by interfacial stacking faults between adjacent layers resulting from symmetry differences between the NiO rocksalt and ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ spinel unit cell. The diffraction data manifest this interfacial disorder via a broadening of selected reflections. Using a structure-factor model based upon a Hendricks-Teller description of the random-stacking sequence, we have separated the magnetic order parameters of the ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ and NiO interlayers. The NiO appears to order at temperatures larger than ${\mathit{T}}_{\mathit{N}}$ for bulk (520 K) due to coupling to the ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ layers (${\mathit{T}}_{\mathit{C}}$=858 K). The dependence of this enhancement on the relative NiO composition is qualitatively consistent with the predictions of mean-field theory.