Temperature Dependence of the Ferromagnetic Resonance Linewidth in Thin Ni–Fe Films

Abstract

Linewidths for ferromagnetic resonance with the static magnetic field in the film plane have been measured at frequencies from 1–9 Gc/sec and temperatures from 4.2°–300°K for Ni–Fe alloy films (77% Ni) 150 to 1500 Å thick. The linewidth exhibits a maximum in the vicinity of 80°K and the effect is generally larger in thinner films. The amplitude of the linewidth temperature dependence is independent of frequency and the maximum shifts to slightly higher temperatures with increasing frequency. The amplitude can be enhanced by heating the film at 150°C in air (oxidation) and removed by a similar treatment in a hydrogen atmosphere. This enhancement-removal cycle can be repeated reproducibly. The time required for saturation of the enhancement when the oxidation treatment was slowed down by annealing in a vacuum of 10−3 Torr instead of at atmospheric pressure was observed to be independent of film thickness, indicating that a volume-diffusion process is not involved. The apparent importance of surface oxidation suggests two possible mechanisms, valence exchange and exchange anisotropy, which may contribute to the linewidth temperature dependence. The discovery of a temperature-dependent linewidth in thin films which exhibits a maximum in the vicinity of 80°K and the identification of this dependence with a surface oxidation process are the primary results of this investigation.

Precessional damping of Fe magnetic moments in a FeNi film

“…At the same time we do not observe significant changes in the angle, frequency and in the damping behavior within the temperature range 150−350 K. The increased error bars indicate the afore-mentioned challenges with the temperature feedback loop. This result is in accordance with FMR results on Fe and Ni films in the high frequency regime obtained by Patton and Wilts [26], where the damping was found to be constant within the temperature range considered here, and with more recent FMR results on Py by Sierra et al using a Vector Network Analyzer [27], which also match the low frequency range. In both references, an increase in damping is observed below about 120 K. Future experiments will focus on systems that significantly change their properties with temperature, e.g.…”

Surface oxidation of Permalloy thin films

“…Antiferromagnetic ordering of an intentionally grown surface oxide has been inferred from both low-temperature hysteresis measurements and ferromagnetic resonance studies. 26,27 Such past studies argue for the presence of ␣-Fe 2 O 3 in highly oxidized Permalloy films.…”

Time-Resolved Spin-Torque Switching and Enhanced Damping in Permalloy/Cu/Permalloy Spin-Valve Nanopillars

“…Instead we attribute the significant T dependence of 0 to the presence of a weak AF layer on the sidewalls of the nanopillar. Although no such AF layer was deliberately deposited, the exposure of the nanopillars to air after ion mill definition undoubtedly oxidized the sidewalls [22], thus allowing for an AF oxide to form and act to enhance the low T damping of the nanomagnets in a manner similar to that observed previously for air-exposed Py films [23,24].…”

“…We interpret this as arising from the stochastic nature of the incomplete reorientation of the AF domains with each nanomagnet reversal at low T. In the blocking temperature regime, partial reorientation, rather than reversal, of the exchange coupled AF domains is generally invoked to explain the magnetic rotational hysteresis found with ensembles of surface oxidized F nanoparticles (i.e., nanomagnets) as well as the training effect in extended area AF/F bilayer films, where the exchange bias field is gradually reduced upon multiple F layer reversals and the reversal broadened [25,26]. The average blocking temperature of native oxide AF layers on Py is low and the net exchange field weak for extended films [23,24]. However, the local exchange strength between Py and an individual NiO domain can be quite strong below the latter's Néel temperature [25,26].…”