Frequency- and time-domain investigation of the dynamic properties of interlayer-exchange-coupledNi81Fe19∕Ru∕Ni81

Abstract

Pulsed inductive microwave magnetometer ͑PIMM͒, conventional ferromagnetic resonance ͑FMR͒, and vector network analyzer FMR ͑VNA-FMR͒ have been used for complementary studies of the various excited modes in exchange-coupled NiFe͑30 nm͒ /Ru͑d Ru ͒ / NiFe͑30 nm͒ films with variable Ru thicknesses d Ru . For antiferromagnetically coupled layers, two modes, which vary in their relative intensity as a function of the bias field, are detected. These two modes, which are observable simultaneously over a limited range of the bias field with PIMM, are identified as optic and acoustic modes. The mode frequencies and the interlayer exchange coupling are found to oscillate as a function of the Ru layer thickness with a period of 8.5 Å. The frequency oscillations of the optic mode are coupling dependent, while those of the acoustic mode are indirectly related to coupling via the canting angle of the layer magnetizations below the saturation. Comparison between PIMM and VNA-FMR in terms of frequency of modes shows good agreement, but the optic mode is observed over a wider field range with VNA-FMR. Furthermore, we clearly observed different behaviors of the FMR linewidths as a function of the spacer thickness for the optic and acoustic modes. In addition, perpendicular standing spin waves have been studied as a function of coupling. The FMR linewidth of the different modes increases with the microwave frequency and typical damping constants of ␣ = 0.0073 have been measured. The effect of the pulse field amplitudes on the properties of the various excited modes has been simulated and studied experimentally.

Microwave spectroscopy with vector network analyzer for interlayer exchange-coupled symmetrical and asymmetrical NiFe/Ru/NiFe

“…As expected, this method allowed us to investigate the optic mode and to compare the measurements with the simulations over larger field ranges ( figures 1 and 4). Figure 2(a) shows an easy axis VSM room temperature magnetization loop of the asymmetrical NiFe(13.6 nm)/Ru (0.47 nm)/NiFe(27.2 nm) system with the corresponding simulation using the model described in [5]. The NiFe layers are antiferromagnetically coupled and their magnetizations are antiparallel at low magnetic field.…”

“…In prior work [5], we used a pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR) and vector network analyzer FMR (VNA-FMR) for complementary studies of the dynamic properties of the symmetrical exchange-coupled NiFe(30 nm)/Ru(d Ru )/NiFe (30 nm) films with variable Ru thicknesses d Ru . We focused our study on the effect of coupling on the characteristics of the different excited modes and we addressed the consequences of the nonlinear excitation resulting from the use of high amplitude and extremely short pulsed fields in such systems.…”

“…It is thus of great interest to see how this thickness difference between the two ferromagnetic coupled layers can affect the properties of the various modes. Therefore, the aim of this paper is to investigate the dynamic properties of asymmetrical NiFe(13.6 nm)/Ru(d Ru )/NiFe(27.2 nm) exchange-coupled films with variable Ru thicknesses (d Ru ) and to address their differences with those of the symmetrical trilayers NiFe(30 nm)/Ru(d Ru )/NiFe(30 nm) studied in detail in [5]. We focused our study on the difference in the mode amplitudes and frequencies as well as the effect of biquadratic coupling on the mode frequency.…”

“…We thus took advantage of the VNA-FMR which, in contrast to FMR, allows us to follow the different excited modes over a large frequency range and on low applied bias fields not sufficient to saturate the specimens, to study these asymmetrical layers and to show the main differences with the symmetrical layers. Therefore, some prior results on the symmetrical systems [5] will be presented here for clarity of comparison. Moreover, we introduced and tested a new measurement procedure different from the conventional one usually used in VNA-FMR spectroscopy, allowing us to follow the optic mode frequency variations over a larger field range and thus increase the accuracy on coupling constants' estimation when fitting with theoretical models.…”

Interlayer coupling in spin valves studied by broadband ferromagnetic resonance

“…This coupling was extensively studied in the past by several experimental techniques as magnetization measurements and magneto-resistance 13,14 , ferromagnetic resonance [15][16][17][18] , Brillouin light scattering (BLS) [19][20][21] , and others 22,23 .…”