The magnetization reversal process in the ferromagnetic layer of an exchange-biased Co90Fe10(20 nm)/Ir23Mn77(10 nm) film structure, deposited by dc-magnetron sputtering, is imaged by high-resolution Kerr microscopy. Additionally, high-resolution magnetization loops are measured by deriving the magnetization signal from the average image intensity. The magnetization reversal occurs first by magnetization rotation under the development of ripple-like structures. The modulated structures then partially switch, generating complicated multidomain configurations, which finally annihilate by large angle domain wall movement. The amount of magnetization rotation at different field directions is quantified by measuring the transversal magnetization components during reversal. A strong asymmetry, both in domain behavior and magnetization loop, between the forward and recoil branch of the magnetization reversal is found. The magnitude of asymmetry strongly depends on small angle misalignments between the direction of exchange-bias and the external magnetic field. The observed domain behavior is explained by anisotropy dispersion in the ferro- and antiferromagnetic layer. The observed differences for both branches of the hysteresis loop are described in terms of domain nucleation mechanisms due to changes in the antiferromagnetic layer leading to an effectively wider anisotropy distribution.
The dynamic properties of a 30-nm-thick permalloy film have been investigated through permeability measurements in the 100-MHz to 3-GHz range, in the presence of an external field applied along the easy axis. The permeability depends not only on the applied field, but also on the orientation of the field compared to the remnant magnetization of the sample. The application of an external field antiparallel to the magnetization may decrease the resonance frequency compared to the zero-field permeability. Ferromagnetic resonance equations provide a good description of the dynamic bistability at low fields, but do not account for the observed behavior in the whole bistability range. This is attributed to the occurrence of a nonuniform resonance.
Magnetization reversal and magnetoresistance behavior of perpendicularly magnetized [Co/Pd]4/Au/[Co/Pd]2 nanowires J. Appl. Phys. 112, 073902 (2012) Electric-field control of CoFeB/IrMn exchange bias system J. Appl. Phys. 112, 064120 (2012) Critical effect of spin-dependent transport in a tunnel barrier on enhanced Hanle-type signals observed in threeterminal geometry Appl. Phys. Lett. 101, 132411 (2012) Giant tunneling magnetoresistance in epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions by halfmetallicity of Co2MnSi and coherent tunneling Appl. Phys. Lett. 101, 132418 (2012) Interface mediated ferromagnetism in bulk CuO/Cu2O composites Appl.Thin permalloy films without and with an 8 nm IrMn exchange layer have been grown by sputter deposition. Permalloy thickness ranges from 15 nm to 50 nm. The microwave permeability of these layers has been investigated in the 50 MHz to 3 GHz range using a permeameter based on a microstrip cell. A satisfactory measurement precision is observed on permalloy films as thin as 15 nm. The gyromagnetic resonance frequency increases from 670 MHz for the unbiased sample, to 2.7 GHz for the thinner biased sample. This increase in frequency is slightly larger than expected from the exchange-bias field measured by Kerr effect using a simple model for the gyromagnetic behavior. The properties of a two-period superlattice are also reported.
30 nm permalloy thin films have been grown by sputter deposition with and without an 8 nm IrMn exchange bias layer. The microwave permeability of these layers has been investigated in the 100 MHz–3 GHz range with a permeameter based on a microstrip cell, applying an external field along the easy axis. A comparison between the bias field deduced from magneto-optical Kerr effect measurements and a fit of the dynamic permeability spectra is made. Significant hysteresis effect on the microwave permeability of the biased sample is observed and modeled.
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