High-frequency permeability of thin NiFe/IrMn layers

Abstract

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.

Ultra-high ferromagnetic resonance frequency in exchange-biased system

“…There are several methods to increase the uniaxial anisotropy field such as patterning thin films [3], field annealing [4], oblique deposition [5,6], employing multilayerstructure films [7], and using exchange bias effect [9][10][11][12][13][14]. When using exchange bias to obtain high FMR frequency, most groups tried to decrease the ferromagnetic (FM) thickness while keeping the antiferromagnetic (AF) thick enough so as to get the largest exchange bias field (H E ) [9][10][11][12][13][14]. This method however has a drawback that the filling ratio (t FM /t AF ) is small causing a reduction of effective permeability since the thick AF layer does not contribute to the total permeability of the film [11].…”

Generalization of Snoek’s law to ferromagnetic films and composites

“…Such non-uniformities may arise from differences in anisotropy between the layers, 29 from antiferromagnetic coupling, 30 or from exchange coupling, provided that these fields are much smaller than the saturation magnetization. Non-uniformities may also arise from unwanted phenomena 31 , or interfacial anisotropies.…”

Annealing temperature dependence of microwave permeability in CoFe/MnIr bilayers

“…The f FMR corresponds to the change of the sign of the real permeability and it can be extracted from Eq. (1). If the resonance frequency is much larger than the width at half maximum of the loss peak, the resonance frequency also corresponds to the peak of the imaginary permeability.…”

“…Recently, the microwave permeability spectra of F/AF bilayers have been studied in order to know the dynamic response [1][2][3][4][5][6] or to apply for the microwave devices [7]. Most of these works focused on the variations of the ferromagnetic resonance frequency (f FMR ) with exchange bias field in terms of F [1] or AF [2][3][4][5] layer thickness. In addition to the f FMR behaviour, the loss performance, which is identified by the Gilbert damping constant (α G ), is also a very import parameter for applications of micromagnetic devices at microwave frequencies.…”