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Title: Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy

Abstract

We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.

Authors:
; ;  [1]
  1. Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin (Germany)
Publication Date:
OSTI Identifier:
22594349
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 109; Journal Issue: 6; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; ANTIFERROMAGNETISM; COBALT; COUPLING; EUROPIUM SULFIDES; GEOMETRY; HYSTERESIS; KERR EFFECT; LAYERS; MAGNETIC FIELDS; MAGNETIC MOMENTS; MAGNETIZATION; PHOTONS; SIGNALS; SPECTRA; SPECTROSCOPY; SUBSTRATES; TEMPERATURE RANGE 0273-0400 K; THICKNESS; ULTRAVIOLET RADIATION

Citation Formats

Goschew, A., E-mail: alexander.goschew@fu-berlin.de, Scott, M., and Fumagalli, P. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy. United States: N. p., 2016. Web. doi:10.1063/1.4960794.
Goschew, A., E-mail: alexander.goschew@fu-berlin.de, Scott, M., & Fumagalli, P. Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy. United States. doi:10.1063/1.4960794.
Goschew, A., E-mail: alexander.goschew@fu-berlin.de, Scott, M., and Fumagalli, P. 2016. "Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy". United States. doi:10.1063/1.4960794.
@article{osti_22594349,
title = {Verification of antiferromagnetic exchange coupling at room temperature using polar magneto-optic Kerr effect in thin EuS/Co multilayers with perpendicular magnetic anisotropy},
author = {Goschew, A., E-mail: alexander.goschew@fu-berlin.de and Scott, M. and Fumagalli, P.},
abstractNote = {We report on magneto-optic Kerr measurements in polar geometry carried out on a series of thin Co/EuS multilayers on suitable Co/Pd-multilayer substrates. Thin Co/EuS multilayers of a few nanometers individual layer thickness usually have their magnetization in plane. Co/Pd multilayers introduce a perpendicular magnetic anisotropy in the Co/EuS layers deposited on top, thus making it possible to measure magneto-optic signals in the polar geometry in remanence in order to study exchange coupling. Magneto-optic Kerr-effect spectra and hysteresis loops were recorded in the visible and ultraviolet photon-energy range at room temperature. The EuS contribution to the magneto-optic signal is extracted at 4.1 eV by combining hysteresis loops measured at different photon energies with polar magneto-optic Kerr-effect spectra recorded in remanence and in an applied magnetic field of 2.2 T. The extracted EuS signal shows clear signs of antiferromagnetic coupling of the Eu magnetic moments to the Co layers. This implies that the ordering temperature of at least a fraction of the EuS layers is above room temperature proving that magneto-optic Kerr-effect spectroscopy can be used here as a quasi-element-specific method.},
doi = {10.1063/1.4960794},
journal = {Applied Physics Letters},
number = 6,
volume = 109,
place = {United States},
year = 2016,
month = 8
}
  • Experimental and theoretical research on magnetic anisotropy of nanoscale multilayers is reviewed. The importance of interfaces and the occurrence of perpendicular magnetic anisotropy is emphasized. Transition-metal multilayers with nonmagnetic and rare-earth metals are discussed, and similarities in properties are pointed out. A detailed model of perpendicular anisotropy due to single-ion interactions is outlined. Magneto-optic properties of RE/TM multilayers are, in general, similar in magnitude to those of the TM. Plasma-enhancement and related effects in magnetic/metallic bilayers are discussed.
  • The predicted perpendicular surface anisotropy is observed for ferromagnetic fcc Fe/Cu(100) via in situ, polar Kerr-effect measurements. Square hysteresis loops are obtained for films 1.5 to 5.7 monolayers thick for 100-K growth. The region of stability of the perpendicularly magnetized state as a function of growth temperature and film thickness is delineated. Combined longitudinal and polar Kerr-effect measurements show that the anisotropy reverts to being in plane for films thicker than approx.6 monolayers.
  • The theoretically predicted prependicular surface anisotropy of ultrathin ferromagnetic Fe films has been confirmed using the magneto-optical Kerr effect. Polar and longitudinal Kerr-effect measurements have been performed in situ on the same fcc Fe/Cu(100) films to study the dependence of the magnetic properties on film thickness and growth temperature conditions. Auxiliary LEED and Auger studies are used to characterize the structure and growth of the films. For films 1.2--5.9 monolayers (ML) thick grown at approx.100 K, for instance, square hysteresis-loop behavior in the polar Kerr effect confirmed the dominance of the perpendicular surface anisotropy. Examples are presented to document howmore » the polar and longitudinal Kerr-effect signals evolve for films thicker than 6 ML due to the easy axis reorienting into the film plane. To differentiate between intrinsic temperature effects and those associated with interfacial compositional changes, the films were thermally cycled and their Kerr signals monitored. Films of thickness around 4 ML retained their characteristic polar Kerr-effect square loops despite thermal cycling between approx.100 and approx.400 K, while those <2 ML thick changed irreversibly. These studies confirm that intermixing can be limited to the monolayer range by low-temperature growth conditions, but the LEED results show that the degree of structural ordering of the films is reduced, as expected.« less
  • Epitaxial films of the ferromagnetic perovskite SrRuO{sub 3} were measured with a bulk magnetometer and with a local magneto-optic Sagnac interferometer in transmission and in reflection. We find a magnetic easy axis perpendicular to the films, and for saturated remanent magnetization along this direction the Faraday rotation and the Kerr rotation at {lambda}=840 nm are about 0.75{times}10{sup 5} deg/cm and 0.85{degree}, respectively. The temperature dependence of the remanent magnetization in the low temperature limit is dominated by spin-wave excitations, yielding a notable decrease with {ital T}{sup 3/2}. Using Sagnac--Kerr scanning and transmission electron microscopy imaging we correlate the coercivity withmore » the grain size.« less