Ferromagnetic resonance in a coupled two-layer system

We present a study of the effective magnetization Meff and the effective damping parameter αeff by means of ferromagnetic resonance spectroscopy on the ferromagnetic (FM) materials Ni81Fe19 (NiFe) and Co40Fe40B20 (CoFeB) in FM/Pt, FM/NM, and FM/NM/Pt systems with the non-magnetic (NM) materials Ru, Cr, Al, and MgO. Moreover, for NiFe layer systems, the influence of interface effects is studied by way of thickness dependent measurements of Meff and αeff. Additionally, spin pumping in NiFe/NM/Pt is investigated by means of inverse spin Hall effect (ISHE) measurements. We observe a large dependence of Meff and αeff of the NiFe films on the adjacent NM layer. While Cr and Al do not induce a large change in the magnetic properties, Ru, Pt, and MgO affect Meff and αeff in different degrees. In particular, NiFe/Ru and NiFe/Ru/Pt systems show a large perpendicular surface anisotropy and a significant enhancement of the damping. In contrast, the magnetic properties of CoFeB films do not have a large influence of t...

The role of the non-magnetic material in spin pumping and magnetization dynamics in NiFe and CoFeB multilayer systems

The microstructure and magnetic properties of polycrystalline Fe films with thicknesses of 200–1000 A have been investigated. The films were prepared by rf sputtering onto SiO2 substrates. The investigation was prompted by the lack of data on sputtered Fe films in this thickness regime as well as disagreement in the data for evaporated films. In addition to thickness, substrate temperature and deposition pressure were varied to examine their effect on the microstructure. The film microstructure was characterized by x‐ray diffraction, transmission electron microscopy, and Auger spectroscopy. The polycrystalline films did not display a strong preferred orientation and had average grain sizes of 60–85 A. Surface oxide layers formed upon exposure to air ranged from 10 to 80 A, the thicker oxides formed on films with lower density. Magnetic hysteresis measurements were made with a vibrating sample magnetometer. Below 1000 A, porosity and surface oxidation result in reductions up to 25% in the saturation magnet...

Magnetic properties of sputtered Fe thin films: Processing and thickness dependence

Soft underlayers of FeTaN/IrMn exchange-coupled films for perpendicular media have been investigated. FeTaN(t/sub FeTaN/)/IrMn (10 nm) multilayer films having different FeTaN thicknesses t/sub FeTaN/ from 20 nm to 200 nm were prepared while keeping the total FeTaN thickness at 200 nm. When t/sub FeTnN/ decreased below 100 nm to 20 mn, the exchange bias field increased from 3.6 Oe to 77 Oe, and the pinning field from 25 Oe to 105 Oe. The interfacial exchange energy, J, was 0.10/spl sim/0.13 ergs/cm/sup 2/. As the exchange bias field increased, the angular reversibility increased from 10/spl deg/ to 57/spl deg/ in good agreement with the coherent rotational model. Radially oriented multilayer films of FeTaN (20 nm)/[IrMn(10 nm)/FeTaN(20 nm)]/sub 9/ were successfully prepared on 65 mm disks and showed excellent angular reversibility, a pinning field >70 Oe, and a permeability of 70 up to 2 GHz.

FeTaN/IrMn exchange-coupled multilayer films as soft underlayers for perpendicular media

Broadband in-plane ferromagnetic resonance measurements were performed over a frequency range from 7 to 40 GHz on various Co56Fe24B20 systems with adjacent thin non-magnetic layers of Ru, Ta and Cu. Co56Fe24B20 samples bounded by either Ru or Ta layers exhibit a contribution to the Gilbert damping constant inversely proportional to the thickness of the Co56Fe24B20 layer, consistent with spin-pumping theory. In contrast, samples with 20 nm thick Cu bounding layers did not show a significant dependence of the Gilbert damping constant on the Co56Fe24B20 thickness, which can be understood based on the far larger spin diffusion length of Cu in comparison with Ru or Ta.

https://iopscience.iop.org/article/10.1088/0022-3727/41/21/215001/pdf

Spin pumping in Co56Fe24B20 multilayer systems

We have used ferromagnetic resonance (FMR) at 33 GHz to study the properties of a number of evaporated thin Fe film systems. Values for effective anisotropy field HKeff , g value, and exchange constant A were derived. For Fe on glass, ‖HKeff ‖ was found to increase with increasing thickness. These changes were attributed to stress which decreased with film thickness. The presence of a Cu or a Ti underlayer did not seem to affect HKeff for films grown at room temperature. However, Fe/Ti/glass films made at higher substrate temperatures, Ts, did show an increase in ‖HKeff ‖. The appearance of a spin‐wave mode in the Fe films enables us to compute the exchange constant A for Fe, A=(2.12±0.14)×10−6 ergs cm−1. The coupling between two thin Fe films through an intervening Cu layer was investigated. A model predicting the number and position of the peaks in the spectrum as a function of coupling is presented. From experiment it was observed that the coupling remains almost constant through the 50–5‐nm Cu thickne...

FMR in evaporated single and multilayer thin Fe films

We have used ferromagnetic resonance (FMR) to investigate magnetic anisotropy in bilayer exchange-coupled thin films. Experiments, using both our 9 and 33 GHz FMR spectrometers, were done on two systems: NiFe/FeMn and NiFe/α-Fe 2 O 3 . In some of the NiFe/α-Fe 2 O 3 specimens an additional response was detected at 33 GHz. We attribute this additional resonance to a region formed by interdiffusion of NiFe and α-Fe 2 O 3 at their common interface. Effective anisotropy field, g-value and the relative volume have been determined for each ferromagnetic region. Auger profile, TEM and CBED (convergent beam electron diffraction) cross-section examinations were performed for an interdiffused specimen, the results are consistent with the presence of a layer containing Fe and Fe 3 O 4 located between the NiFe and α-Fe 2 O 3 regions. A memory effect, due presumably to irreversible spin reorientation at the interface, was observed in some of the NiFe/α-Fe 2 O 3 specimens.

Investigation of anisotropy by ferromagnetic resonance (FMR) in exchange-coupled bilayer films

Forms for the torque, ferromagnetic resonance (FMR) and domain mode FMR (DMFMR) relations are derived for "oblique anisotropy axis" films. The energy derivative scheme, as described by Smit and Beljers for example, is employed. Under magnetic saturation conditions, torque and FMR formulae are obtained for an applied field \vec{H} in the vertical plane containing the tilted uniaxial magnetocrystalline anisotropy axis. Shifts of the torque curve zero-crossings and of the extrema of the FMR line pattern are found. The situation when \vec{H} is in the basal plane is also addressed. For this case specific formulae are given, valid in the H/(2K/M) \gg 1 approximation. The formalism for the derivation of the DMFMR in this system under non-saturation conditions is presented. A stripe domain situation with \vec{H} in the basal plane is modeled.

J. O. Artman

Papers

FMR in evaporated single and multilayer thin Fe films

Investigation of anisotropy by ferromagnetic resonance (FMR) in exchange-coupled bilayer films

Torque, FMR and domain mode FMR relations in thin "Oblique anisotropy axis" films