FN ISI Export Format VR 1.0 PT Journal AU Vavassori, P Grimsditch, M Fullerton, EE TI Biquadratic exchange coupling in an unequal Fe/Cr/Fe(100) trilayer SO JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS AB we have investigated the magnetic properties of a (100)- oriented unequal trilayer, Fe(45 Angstrom)/Cr(30 Angstrom)/Fe(15 Angstrom), by means of Brillouin light scattering and magnetization measurements. The experimental results show that this sample highlights the effect of biquadratic coupling which aligns the magnetization of the Fe layers at 90 degrees to each other. We extracted the bilinear and biquadratic coupling strengths by fitting the experimental results with a theory that treats the static and dynamic responses on an equal footing. Our results confirm that the model describes both the static and dynamic properties even when the magnetization of the layers is aligned at 90 degrees. The coupling strengths, and their temperature dependence, are discussed and compared with other results reported in the literature, (C) 2001 Elsevier Science B.V. All rights reserved. TC 0 BP 284 EP 292 PG 9 JI J. Magn. Magn. Mater. PY 2001 PD FEB VL 223 IS 3 GA 399NA J9 J MAGN MAGN MATER UT ISI:000166818200013 ER PT Journal AU Marrows, CH Langridge, S Hickey, BJ TI Determination of equilibrium coupling angles in magnetic multilayers by polarized neutron reflectometry SO PHYSICAL REVIEW B AB We have performed polarized neutron reflectometry (PNR) on Co/Cu multilayers grown by sputter deposition at the first antiferromagnetic (AF) maximum of the coupling oscillation. The growth of the Cu spacer layers was paused halfway through each layer for a variable amount of time to allow residual gases to be adsorbed onto the surface. A sample with clean Cu spacers shows good AF coupling, with low remanence and high saturation field. The PNR spectra show a strong 1/2-order Bragg peak and little splitting between the reflectivities for incident up arrow and down arrow spin neutrons at zero field, characteristic of AF ordering. Meanwhile, a more heavily gas- damaged sample with a remanent fraction of similar to root2/2 has strongly spin-split PNR spectra at the critical edge and nuclear Bragg peak, showing a significant ferromagnetic component. A strong 1/2-order Bragg peak is still present. We are able to fit accurately the magnetization and PNR data by assuming that such a sample shows considerable biquadratic coupling, with moments coupled close to 90 degrees at zero field. TC 0 BP 11340 EP 11343 PG 4 JI Phys. Rev. B PY 2000 PD NOV 1 VL 62 IS 17 GA 371WH J9 PHYS REV B UT ISI:000165201900018 ER PT Journal AU Nikolaev, KR Dobin, AY Krivorotov, IN Cooley, WK Bhattacharya, A Kobrinskii, AL Glazman, LI Wentzovitch, RM Dahlberg, ED Goldman, AM TI Oscillatory exchange coupling and positive magnetoresistance in epitaxial oxide heterostructures SO PHYSICAL REVIEW LETTERS AB Oscillation in the exchange coupling between ferromagnetic La2/3Ba1/3MnO3 layers with paramagnetic LaNiO3 spacer layer thickness has been observed in epitaxial heterostructures of the two oxides. This behavior is explained within the RKKY model employing an ab initio calculated band structure of LaNiO3, taking into account strong electron scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a positive current-in-plane magnetoresistance. TC 1 BP 3728 EP 3731 PG 4 JI Phys. Rev. Lett. PY 2000 PD OCT 23 VL 85 IS 17 GA 366GN J9 PHYS REV LETT UT ISI:000089996600046 ER PT Journal AU Vavassori, P Grimsditch, M Fullerton, E Giovannini, L Zivieri, R Nizzoli, F TI Brillouin light scattering study of an exchange coupled asymmetric trilayer of Fe/Cr SO SURFACE SCIENCE AB The magnetic response of a (211) oriented asymmetric Fe trilayer [Fe(100 Angstrom)/Cr(9 Angstrom)/Fe(20 Angstrom)/Cr(20 Angstrom)/Fe(20 Angstrom)], in which the thickness of the Cr spacer layers was chosen to produce ferromagnetic coupling (F) between the two thinner Fe layers and antiferromagnetic coupling (AF) between the thicker Fe layer and the adjacent thin one, has been investigated using magnetization and Brillouin light scattering (BLS) measurements. The coupling coefficients, extracted by fitting the BLS and magnetization measurements with a theory treating the static and dynamic response on an equal footing? produced consistent values of the magnetic parameters. Our results confirm that the theoretical model used in interpreting both static and dynamic properties is valid even in systems in which F and AF coupling of the layers are simultaneously present. The theoretical model has also been extended to include the field dependence of the intensity of the Brillouin peaks. The calculated intensities are compared with the BLS spectra at different applied fields. (C) 2000 Elsevier Science B.V. All rights reserved. TC 1 BP 880 EP 884 PG 5 JI Surf. Sci. PY 2000 PD MAY 20 VL 454 GA 326ZB J9 SURFACE SCI UT ISI:000087766200167 ER PT Journal AU Aitchison, PR Chapman, JN Holloway, H Kubinski, DJ Parsons, M TI Magnetization processes and magnetoresistance in Co/Cu multilayers as a function of the Cu layer thickness. SO JOURNAL OF APPLIED PHYSICS AB We have studied Co(15 Angstrom)/Cu(t) multilayers with nominal Cu spacer layer thicknesses of 7, 8, 9, and 10 Angstrom. For multilayers with identical dimensions, transport measurements showed that the introduction of oxygen during growth increased the magnetoresistance while transmission electron microscopy revealed the effect of the oxygen bleed on the microstructure was reduced grain size, suppression of the Co-hcp phase, and reduced texturing. Lorentz microscopy was used to determine the angle between magnetization vectors in adjacent magnetic layers and the values so deduced were found to correlate well with the variation of magnetoresistance within the multilayer sets. (C) 2000 American Institute of Physics. [S0021-8979(00)45108-X]. TC 0 BP 5753 EP 5755 PG 3 JI J. Appl. Phys. PY 2000 PD MAY 1 VL 87 IS 9 PN 2 GA 308RT J9 J APPL PHYS UT ISI:000086727200350 ER PT Journal AU Marrows, CH Hickey, BJ Herrmann, M McVitie, S Chapman, JN Ormston, M Petford-Long, AK Hase, TPA Tanner, BK TI Damage caused to interlayer coupling of magnetic multilayers by residual gases SO PHYSICAL REVIEW B AB The oscillatory interlayer indirect exchange coupling in Co/Cu multilayers is known to be highly sensitive to structural defects, In this paper the dependence of the antiferromagnetic exchange coupling on the background pressure in the vacuum chamber is investigated, Co/Cu multilayers were grown by de magnetron sputtering in a system equipped with a leak valve to allow the introduction of low levels of air or O-2 Below a relatively narrow band of pressure the samples exhibit excellent antiferromagnetic coupling and consequently a high giant magnetoresistance, similar to 40% for {Co(8 Angstrom)/Cu(8 Angstrom)} x 25 samples. Above this transitional band of pressure no antiferromagnetic coupling, and hence no giant magnetoresistance, is observed. X-ray diffraction measurements reveal no change of any significance in any of the layer thicknesses or roughnesses. Whilst the high-field magnetic behavior is found to be isotropic in the sample plane, the reversal of the remanent moment around zero field is found to show a varying degree of uniaxial anisotropy. Lower remanent moments are found to be associated with a more isotropic reversal mechanism. A thorough characterization of the physical and magnetic microstructure by means of various modes of transmission electron microscopy is presented. Cross-sectional images reveal subtle changes in the crystallinity and layer quality of the samples as the background pressure is increased. Plan-view Lorentz microscopy reveals that the isotropic reversal mechanism of the low remanence samples involves a complete domain structure. The reversal mechanism of multilayers with a significant remanent moment varies markedly with field direction and can be dominated by rotation or comparatively simple domain processes. Samples with a significant giant magnetoresistance similar to 20% and remanent fractions similar to 0.7 are found to still show highly anisotropic reversal mechanisms around zero field, Indeed when demagnetized along the easy axis the samples are in a single domain state at remanence. This is compelling evidence for substantial noncollinear ordering of the moments through biquadratic coupling. TC 2 BP 4131 EP 4140 PG 10 JI Phys. Rev. B PY 2000 PD FEB 1 VL 61 IS 6 GA 285AH J9 PHYS REV B UT ISI:000085364700056 ER PT Journal AU Bruno, P TI Theory of interlayer exchange interactions in magnetic multilayers SO JOURNAL OF PHYSICS-CONDENSED MATTER AB This paper presents a review of the phenomenon of interlayer exchange coupling in magnetic multilayers. The emphasis is put on a pedagogical presentation of the mechanism of the phenomenon, which has been successfully explained in terms of a spin-dependent quantum confinement effect. The theoretical predictions are discussed in connection with corresponding experimental investigations. TC 0 BP 9403 EP 9419 PG 17 JI J. Phys.-Condes. Matter PY 1999 PD DEC 6 VL 11 IS 48 GA 265NW J9 J PHYS-CONDENS MATTER UT ISI:000084251100011 ER PT Journal AU Drovosekov, AB Zhotikova, OV Kreines, NM Kholin, DI Meshcheryakov, VF Milyaev, MA Romashev, LN Ustinov, VV TI Inhomogeneous ferromagnetic resonance modes in [Fe/Cr](n) superlattices with a high biquadratic exchange constant SO JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS AB In a set of [Fe/Cr](n) superlattices, magnetization curves and spectra of ferromagnetic resonance under an in-plane magnetic field have been studied at room temperature. Along with the acoustic branch, several additional branches have been observed in resonance spectra. Resonance spectra have been calculated analytically for a structure with an infinite number of layers and numerically for finite numbers of layers in real samples using a model of biquadratic exchange taking account of the fourth-order magnetic anisotropy. A possibility of describing both static and resonance properties of the system in terms of this model has been demonstrated. (C) 1999 American Institute of Physics. [S1063-7761(99)02311-2]. TC 0 BP 986 EP 994 PG 9 JI J. Exp. Theor. Phys. PY 1999 PD NOV VL 89 IS 5 GA 261FC J9 J EXP THEOR PHYS UT ISI:000083997800023 ER PT Journal AU Stiles, MD TI Interlayer exchange coupling SO JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS AB The extensive research done on interlayer exchange coupling in transition metal multilayers has resulted in a deep understanding of this coupling and a remarkable agreement between theoretical results and measurements. The coupling between two magnetic layers separated by a non-magnetic spacer layer is mediated by the electrons of the spacer layer. The coupling, which oscillates in sign as a function of the thickness of the spacer layer, is closely related to the well- known RKKY interaction between magnetic impurities. Due to the existence of many high-quality measurements, it has been much more fully developed theoretically than the interaction between impurities. Theory predicts that the periods of the oscillatory coupling should depend on critical spanning vectors of the Fermi surface belonging to the spacer-layer material There is remarkable agreement far the measured periods and those predicted from the Fermi surfaces. There is also substantial agreement between theory and experiment on the strength of the coupling. This review presents the comparison between theory and experiment in some detail. (C) 1999 Published by Elsevier Science B.V. All rights reserved. TC 6 BP 322 EP 337 PG 16 JI J. Magn. Magn. Mater. PY 1999 PD OCT VL 200 IS 1-3 GA 241DP J9 J MAGN MAGN MATER UT ISI:000082867700020 ER PT Journal AU Arias, R Mills, DL TI Theory of roughness-induced anisotropy in ferromagnetic films: The dipolar mechanism SO PHYSICAL REVIEW B AB When ferromagnetic films are grown on stepped surfaces, or rough surfaces upon which there is a preferred direction, additional magnetic anisotropy associated with the presence of the roughness is found in experiments. This paper presents the theory of the contribution of one mechanism to this anisotropy, that is associated with the roughness-induced increase in magnetic dipolar energy. When the film surface profiles are modulated, the magnetization of the film fluctuates in direction, thus generating stray dipolar fields. The energy stored in such fields depends on the angle between the mean magnetization, and the preferred axis of the modulated surface profile. We present explicit calculations for various models of films on stepped surfaces. [S0163-1829(99)00218-0]. TC 2 BP 11871 EP 11881 PG 11 JI Phys. Rev. B PY 1999 PD MAY 1 VL 59 IS 18 GA 197HN J9 PHYS REV B UT ISI:000080359500039 ER PT Journal AU Rezende, SM Chesman, C Lucena, MA de Moura, MC Azevedo, A de Aguiar, FM Parkin, SSP TI Biquadratic coupling in sputtered Fe/Cr/Fe still in need of a new mechanism SO JOURNAL OF APPLIED PHYSICS AB The bilinear (J(1)) and biquadratic (J(2)) exchange coupling constants were measured in sputtered trilayers of (100) Fe(40 Angstrom)/Cr(s)/Fe(40 Angstrom) for several Cr spacer layer thicknesses in the range s = 8-35 Angstrom and as a function of temperature T, using magneto-optical Kerr effect magnetometry, Brillouin light scattering, and ferromagnetic resonance. In the samples in the range s = 8-13 Angstrom, corresponding to the first antiferromagnetic peak of J(1), J(2) follows J(1) with a room temperature ratio J(2)/J(1) congruent to 0.1, while in the range 25-35 Angstrom, corresponding to the second antiferromagnetic peak, J2 also follows J(1) but with a much larger ratio J(2)/J(1) congruent to 1. This result, as well as the temperature dependence of J(2) in all samples but the one with s = 15 Angstrom, cannot be explained by any of the intrinsic or extrinsic mechanisms that have been proposed for the origin of the biquadratic exchange coupling in Fe/Cr/Fe. (C) 1999 American Institute of Physics. [S0021-8979(99)68008- 2]. TC 2 BP 5892 EP 5894 PG 3 JI J. Appl. Phys. PY 1999 PD APR 15 VL 85 IS 8 PN 2B GA 188NF J9 J APPL PHYS UT ISI:000079853500199 ER