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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Magnetization reversal and spin dynamics exchange in biased F/AF bilayers probed with complex permeability spectra

David Spenato, Jamal Ben Youssef, and Henri Le Gall

J. Appl. Phys. 93, 7711 (2003); http://dx.doi.org/10.1063/1.1557959 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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The spin dynamics of the ferromagnetic pinned layer of ferro-antiferromagnetic (FIAE) coupled NiFe/MnNi bilayers is investigated in a broad frequency range (30 MHz–6 GHz). A phenomenological model based on the Landau–Lifshitz equation for the complex permeability of the F/AF bilayer is proposed. The experimental results are compared to theoretical predictions. We show that the resonance frequencies, measured during the magnetization, are likewise hysteretic. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Determination of rotatable anisotropy in exchange-biased bilayers using anisotropic magnetoresistance technique

J. K. Kim, S. W. Kim, K. A. Lee, B. K. Kim, J. H. Kim, S. S. Lee, D. G. Hwang, C. G. Kim, and C. O. Kim

J. Appl. Phys. 93, 7714 (2003); http://dx.doi.org/10.1063/1.1558191 (3 pages)

Online Publication Date: 9 May 2003

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We improved the anisotropic magnetoresistance model to determine the quantity and direction of rotatable anisotropy in FeMn/NiFe structures independent of the thickness of the antiferromagnet layer. In our model, there are two important parameters, the magnitude α=Hrot/Hex and direction β=θrot/θa of rotatable anisotropy, where Hrot and θrot are an effective magnetic field and angle of a rotatable anisotropy, and Hex and θa are the exchange bias field and angle of applied field. As FeMn thickness decreased from 20 nm to 3.5 nm, α value increased from about 0.15 to 0.55. This proves that weak exchange coupling regions increase as the antiferromagnet thickness decreases. The α and β almost did not change as the NiFe thickness increases from 7 nm to 15 nm, even if the Hex was reduced from 170 Oe to 70 Oe. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.47.Np Metals and alloys

Exchange anisotropy and spin-wave damping in CoFe/IrMn bilayers

S. M. Rezende, M. A. Lucena, A. Azevedo, F. M. de Aguiar, J. R. Fermin, and S. S. P. Parkin

J. Appl. Phys. 93, 7717 (2003); http://dx.doi.org/10.1063/1.1543126 (3 pages) | Cited 11 times

Online Publication Date: 9 May 2003

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The magnetic properties and the spin-wave damping in FM/AF bilayers of CoFe/IrMn have been investigated with magneto-optic Kerr effect magnetometry, ferromagnetic resonance (FMR), and Brillouin light scattering (BLS). As observed in other systems, the values of the interlayer exchange field obtained with different techniques are discrepant, but they all exhibit the expected t−1 dependence with the FM film thickness t. On the other hand the spin-wave relaxation rates measured by BLS and FMR are fit with a t−2 dependence plus a constant term. This is interpreted as the sum of two independent contributions, an intrinsic mechanism dominated by Gilbert damping and an extrinsic mechanism dominated by two-magnon scattering due to fluctuations of the interlayer exchange coupling caused by interface roughness. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.30.Ds Spin waves
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.20.Ls Magneto-optical effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.35.Ct Interface structure and roughness
78.66.Bz Metals and metallic alloys

Magnetic field-induced degradation of magnetic properties in molecular beam epitaxy grown FeMn/NiFe exchange-coupled bilayers

Y. S. Choi, A. K. Petford-Long, and R. C. C. Ward

J. Appl. Phys. 93, 7720 (2003); http://dx.doi.org/10.1063/1.1557962 (3 pages)

Online Publication Date: 9 May 2003

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Degradation of magnetic properties has been observed in molecular beam epitaxy grown Si(111)/Cu 2 nm/NiFe 6 nm/FeMn (2–12)nm/Cu 5 nm exchange-biased bilayers during magnetic field sweeping. When the samples are subjected to several magnetic field sweeps, there is blister-shaped deterioration of the film surface quality and the magnetometry data suggest an increasing fraction of the NiFe moments become unpinned from the FeMn layer. Comprehensive characterization using high resolution electron microscopy and electron probe microanalysis revealed that this degradation has been initiated by delamination between the NiFe and FeMn layers and crack formation as a result of magnetostrictive stress buildup during the magnetic field sweeps. Further degradation can then be attributed to the formation of the nonmagnetic FeMn oxide by oxidation of the bare FeMn around the delaminated area. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Et Exchange and superexchange interactions
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.30.Cr Saturation moments and magnetic susceptibilities
68.37.Lp Transmission electron microscopy (TEM)
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains

Exchange bias of NiO/NiFe: Linewidth broadening and anomalous spin-wave damping

Bijoy K. Kuanr, R. E. Camley, and Z. Celinski

J. Appl. Phys. 93, 7723 (2003); http://dx.doi.org/10.1063/1.1557964 (3 pages) | Cited 27 times

Online Publication Date: 9 May 2003

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We studied sputtered NiO(150 nm)/NiFe exchange-biased films using Network Analyzer ferromagnetic resonance spectroscopy (NA-FMR) and Brilliouin light scattering (BLS) techniques. The complex permeability spectra were obtained for NiO/NiFe films and were fitted to the Landau–Lifshitz–Gilbert equation to determine intrinsic and extrinsic contribution to Gilbert damping, in addition to other magnetic parameters. The exchange anisotropy (HEX) was determined from the field variation data of NA-FMR resonance frequency (fres) and BLS mode frequency (fm). HEX was observed to decreases as 1/thickness, from where we derive macroscopic interfacial exchange energy JE=0.021 erg/cm2. Second, we investigated the relaxation mechanism in NiO/NiFe films from NA-FMR linewidth (Δfres) for wave vector k=0 mode and from BLS mode linewidth (Δfm) for k≠0 modes. Interestingly, we observed Δfres to increase with increasing magnetic field but Δfm was observed to decrease with increasing magnetic field. Therefore, it is confirmed that, the relaxation rate measured by FMR and BLS techniques is different. Δfres was observed to increase with decreasing NiFe thickness and follows a t−2 fit function, from which we determine the local interfacial exchange energy J1=3.3 erg/cm2. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.35.+c Brillouin and Rayleigh scattering; other light scattering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Domain formation in exchange biased Co/CoO bilayers

U. Welp, S. G. E. te Velthuis, G. P. Felcher, T. Gredig, and E. D. Dahlberg

J. Appl. Phys. 93, 7726 (2003); http://dx.doi.org/10.1063/1.1540152 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2003

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The magnetic behavior of exchange biased Co/CoO polycrystalline thin films has been investigated using magnetometry and magneto-optical (MO) imaging. For CoO layer thicknesses of about 30 Å, these films exhibit a strong training effect below the blocking temperature of 130 K. A sharp initial reversal of the magnetization of the FM Co layer after field-cooling is followed by S-shaped magnetization loops with reduced coercive fields. The MO images show that during the initial magnetization reversal the remagnetization front moves from the edge of the sample into the homogenously magnetized film, leaving behind an irregular pattern of domains of the order of 10 μm. These domains, once generated during the first reversal, do not expand or move on subsequent magnetization loops and can be erased only by heating above the blocking temperature. This suggests that the domains are related to domains in the antiferromagnetic CoO layer. © 2003 American Institute of Physics.
Show PACS
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.60.Jk Magnetization reversal mechanisms
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.66.Bz Metals and metallic alloys
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