• Journal of the Korean Magnetics Society
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• v.12 no.4
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• pp.143-148
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• 2002

We report an experimental evidence of coexistence of the strong and weak exchange couplings in unidirectional NiO/NiFe (antiferromagneticlferromagnetic) bilayer thin films. The exchange bias was measured by VSM and AMR techniques and then, analyzed into the strong and weak exchange couplings by means of a regression method. In NiO(60nm)/NiFe(10nm) film, the ratio of the weak exchange coupling field over the average exchange coupling field was found to be almost unchanged within it range from 0.2 to 0.4 irrespective to the strength of an applied field. However, the ratio increased among the samples with decreasing the average exchange coupling field due to the increment of the weak exchange coupling area.

• Journal of the Korean Magnetics Society
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• v.27 no.3
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• pp.77-81
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• 2017

The rotatable anisotropy effect was observed in the ferromagnetic resonance measurement in exchange coupled ferromagnetic/antiferromagnetic thin films and it was due to rotation of antiferromagnetic layer by the exchange coupling energy. We analyzed the CoFe thickness dependence of rotatable anisotropy field and ferromagnetic resonance linewidth in exchange coupled $CoFe(t_F)/MnIr(2.5nm)$ thin films. The rotatable anisotropy field was inversely propositional to the CoFe thickness and it was well fitted by the rotatable anisotropy energy of $0.96erg/cm^2$. The ferromagnetic resonance linewidth were linearly propositional to the rotatable anisotropy field in $t_F$ < 50 nm, while it was more dominated by the eddy current effect in $t_F$ > 50 nm.

• Journal of the Korean Magnetics Society
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• v.26 no.2
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• pp.50-54
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• 2016

We analyzed the angular dependence of ferromagnetic resonance linewidth in exchange coupled CoFe/MnIr bilayers. The maximum and minimum linewidth was observed in the easy and hard direction of unidirectional anisotropy by exchange coupling, respectively, and it was well agreed with the angular dependence of exchange bias field. The maximum linewidth was due to the twist of CoFe magnetization near CoFe/MnIr interface from direction of pinned MnIr spin to direction of applied magnetic field. While, minimum linewidth more higher than that of CoFe was related to rotatable anisotropy field, and explained by easy axis distribution of MnIr grains.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.24-29
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• 2002

It was observed that exchange bias field was increased with smooth surface and better ${\gamma}$-FeMn formation. Sputtering conditions were varied for the control of the surface roughness and ${\gamma}$-FeMn formation. From the results of Cu deposition as underlayer, it was found that ${\gamma}$-FeMn formation was closely related with the thickness of underlayer. After heat treatment, exchange bias field was increased over three times. This improvement was likely that the crystallites of ${\gamma}$-FeMn were well formed. In Co/Cu/Co/FeMn spin valve structure, magnetoresistance was increased over 1.4 times through the heat treatment. This was due to the disappearance of Co/Cu intermixed dead layer and removal of defect, and this was examined by AES analysis.

• Journal of the Korean Magnetics Society
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• v.15 no.5
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• pp.265-269
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• 2005

Exchange bias effect of a various layered thin films were studied by FMR measurment. In plane angular dependence of a resonance field distribution which measured by FMR was analysed as a combined effect of an unidirectional anisotropy and an uniaxial anisotropy. Exchange biased NiFe/IrMn, IrMn/NiFe/IrMn, and NiFe/IrMn/CoFe thin films showed larger unidirectional anisotropy field and uniaxial anisotropy field with compared to that of an unbiased NiFe single thin film. In case of NiFe/Cu/IrMn, the film with thick Cu layer exhibited a similar trend to the unbiased NiFe thin film. NiFe/IrMn/CoFe thin film showed two resonance field distribution due to different ferromagnetic layers. In additon to the resonance field, the line width was also analysed with related to exchange bias effect.

• Journal of the Korean Magnetics Society
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• v.22 no.6
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• pp.204-209
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• 2012

We measure the ferromagnetic resonance signals in order to analyze the exchange coupling energy due to the uncompensated antiferromagnetic spins in exchange coupled CoFe/MnIr bilayers. The exchange bias fields ($H_{ex}$) and rotatable anisotropy fields ($H_{ra}$) are obtained from the ferromagnetic resonance fields measured with in-plane angle in thermal annealed samples with $t_{AF}$= 0, 3, and 10 nm. The sum of the $H_{ex}$ and $H_{ra}$ do not depend on the MnIr thickness, which means that all the uncompensated AF spins are aligned to one direction in $300^{\circ}C$ annealed samples. Therefore, the uncompensated AF spins are divided into two different parts. One parts are fixed at the interface between CoFe/MnIr bilayers and induces the $H_{ex}$, other parts are rotatable with magnetic field and induces the $H_{ra}$. Finally, the exchange coupling energy can be expressed by the sum of the exchange bias energy and rotatable anisotropy energy.

• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.176-181
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• 2003

The magnetic domain walls at the edges of a large patterned and exchanged-biased NiO(10-60 nm)/NiFe(10 nm) bilayers and their motions with applied field were investigated by magnetic force microscopy. Three kinds of domain walls, namely, head-to-head zig-zag and tail-to-tail zig-zag Bloch walls and straight Neel walls were found at specific edges of the unidirectional biased NiO(30 nm)/NiFe(10 nm) bilayer having the exchange biasing field (H$\sub$ex/) of 21 Oe. No walls were observed for the strong exchange-biased bilayer (60 nm NiO, H$\sub$ex/ = 75 Oe), while the amplitude of the zig-zag domain increased with decreasing exchange biasing. This may be explained by mutual restraint between H$\sub$ex/ and the demagnetization field of edge. We similarly investigated the magnetization reversal process, the subsequent motion of the walls and identified the pinning and nucleation sites during reversal.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.46-47
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• 2002

• Proceedings of the Korean Magnestics Society Conference
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• 1998.10a
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• pp.14-15
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• 1998

• Journal of the Korean Magnetics Society
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• v.14 no.4
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• pp.127-130
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• 2004

Magnetic properties and thermal stability by exchange biased perpendicular magnetic anisotropy in (Pd/Co)$_{N}$FeMn multilayer deposited by do magnetron sputtering system are investigated. We measured the perpendicular magnetization curves of (Pd(0.8nm)/Co(0.8nm)$_{5}$FeMn multilayer as function of FeMn thickness and annealing temperature. As FeMn thickness increases from 0 to 21nm, the perpendicular exchange bias(Hex) obtained 127 Oe at FeMn thickness 15nm. As the annealing temperature increases to 24$0^{\circ}C$, the E$_{ex}$ increased from 115 Oe to 190 Oe and disappeared exchange biased perpendicular magnetic anisotropy effect at 33$0^{\circ}C$.