J.S.S. Whiting

Spin-wave resonance in single crystal nickel films

Abstract The effect of substrate material and of sodium fluoride coatings on the pinning of spin-wave modes has been investigated in single crystal nickel films.

Correlation of magnetic and microstructural properties of obliquely deposited Co/Cr thin films

Single layers of Si(111)/Co(200 A)/Ag(30 A) and trilayers of Si(111)/Co(200 A)/Cr(15 A)/Co(200 A)/Ag(30 A) were deposited, using e-beam evaporation, at oblique angles of incidence to the sample normal (in particular 0°, 25°, 40°, 70°). The magnetic properties of the samples were studied using the technique of ferromagnetic resonance, while the microstructure was imaged using high resolution electron microscopy. We find that the angle of deposition of Co has a critical effect on the magnetic anisotropy of the samples, and on the interlayer coupling strength between the ferromagnetic layers of the trilayer samples. It is shown that these effects are due to the microstructure of the samples which is controlled by the angle of Co deposition with respect to the sample normal.

Magnetic and theoretical studies of NiFe layers coupled through a chromium interlayer

Abstract MBE prepared epitaxial Permalloy/Cr/Permalloy trilayers have been investigated by FMR and BH hysteresigraph. The film growth was monitored by Reflection High Energy Electron Diffraction (RHEED) and Auger Electron Spectroscopy (AES) which indicate Frank-Van der Merve growth of the Cr. The dependence of resonant field position and coercivity on the thickness of the Cr interfilm indicates the existence of an oscillatory long range exchange coupling of the Permalloy films. A transfer matrix theory previously used to analyse ferromagnetic coupling between magnetic films has been extended to include antiferromagnetic coupling and is used to interpret the FMR results.

Ferromagnetic resonance in coupled permalloy double films separated by a Cu interlayer

Abstract Ferromagnetic resonance (FMR) at 16 GHz was used to study the magnetic coupling between two-layers of permalloy separated by a nonmagnetic Cu layer. Samples with the same thickness (600 A) of both permalloy layers were deposited from e-gun sources onto glass substrates in UHV. The thickness d of the Cu interlayer was varied from 5 to 37 A. The exchange coupling energy ( E = - KM 1 · M 2 ) model was used to describe the interaction between the two magnetic layers. It was found from the ferromagnetic resonance data in the perpendicular configuration that K ( d ) follows an exponential law, K = K 0 e - d / q , where q = 9.3 A .

Magnetic properties of double Permalloy films

Abstract Two-layered Permalloy films with a carhon intermediate layer of different thickness were investigated to correlate the coercivity values and magnetization process with the strength of the exchange coupling. The interpretation of strong, medium and weak coupling is proposed.

Structural and spin wave resonance studies of polycrystalline and epitaxial permalloy-chromium layered structures

Abstract Two sets of magnetic multilayers consisting of two 600 A permalloy (Ni 83 Fe 17 ) films separated by varying thicknesses of Cr, sandwiched between two further layers of Cr have been studied by spin wave resonance (SWR). One series of samples consists of crystalline layers deposited on GaAs (100) with a silver (100) buffer layer to promote epitaxial growth of Cr (100). The permalloy layers display a four-domain (011) structure which is deduced from RHEED and symmetry arguments. The second series of samples has polycrystalline layers deposited onto glass substrates. The magnetic coupling of these samples show the role of interfacial roughness at the interior boundaries of the magnetic layers to be of importance. The epitaxial samples show evidence of oscillatory exchange coupling, whereas the polycrystalline structures shows no clear sign of such behaviour.

Studies of the effect of interfacial interdiffusion on the coupling of NiFe films through a chromium interfilm

Abstract Interfacial interdiffusion in NiFe/Cr/NiFe trilayers prepared by molecular beam epitaxy (MBE) is promoted in a controlled manner by varying the deposition temperature of the interfilm. The resulting progressive removal of one of the sharp interfaces enables studies of the effect of the reduced electronic confinement of the interface. The films were structurally characterised by Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED) and the magnetic properties investigated by ferromagnetic resonance (FMR) and with a vibrating sample magnetometer (VSM). Changes in the coupling were discovered between the films supporting different degrees of interdiffusion and on cooling some of the trilayers, coupling changes were also detected.

Numerical investigations on the interface mode in spin-wave resonance

Abstract The numerical approach of the transfer matrix is used to investigate the effects of the interlayer exchange interaction between magnetic layers separated by a nonmagnetic interlayer, on the spin-wave spectra. The results show that the interface mode is only observed under the conditions of antiferromagnetic coupling and asymmetric pinning conditions on the external surfaces.

Magnetic resonance in coupled double films separated by nonmagnetic interlayer

Spin wave resonance (SWR) at 16 GHz in the perpendicular configuration is studied in double NiFe films separated by Cu interlayer. The influence of Cu thickness d in the range of 0.5–2,.7 nm on the mode splitting is discussed. A theoretical model is proposed, that includes both the ‘bulk’ coupling between the magnetizations M1 and M2 with the energy density E = - KM·M2 and the interface coupling described by E = A12(m1 − m2)2, where m and m2 are the microwave magnetizations. It is shown that the model with two coupling constants K = K0 e -d/q and A12 = A0 e -d/q, where q = 2.5 nm, t = 0.25 nm, K0 = 132 erg/cm2, A0 = 10 erg/cm2 agrees quite well with the experimental data. The existence of two different damping constants q and t indicates that at least two mechanisms are responsible for the interaction between magnetic layers: long range interactions acting across the nonmagnetic interlayer, e.g. stress-induced anisotropy and direct short range exchange.

Brillouin light scattering study of Co/Cr/Co trilayers

Abstract Spin-wave excitations have been observed in Co(212 A)/Cr( d 0 )/Co(200 A)/Si trilayers for 5 d 0 H M s typical of bulk values were obtained from fits to theory. No in-plane orientational frequency dependence was observed.