Magneto-optical study of magnetization reversal asymmetry in exchange bias

Tillmanns, Andrea; Oertker, S.; Beschoten, Bernd; Güntherodt, G.; Leighton, Chris; Schuller, Iván K.; Nogués, J.

doi:10.1063/1.2392283

Cited by 41 publications

(46 citation statements)

References 19 publications

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“…Arenholz et al 8 and Tillmanns et al 9 have observed that in twinned Fe/MnF 2 films, the shape of a kinked hysteresis loop evolves sensitively with the angle between the measurement and bias fields. Other studies have examined the dependence of the magnetization reversal mechanism on the exchange field and anisotropy fields in the samples.…”

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confidence: 99%

Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films

Olamit

Schuller

et al. 2006

Phys. Rev. B

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Exchange anisotropy in ferromagnet/antiferromagnet (FM/AF) films is usually introduced along the cooling field or FM magnetization direction. Here we investigate the dependence of the exchange anisotropy, loop bifurcation, and reversal mechanism on the cooling field direction using vector magnetometry. Three types of samples (FM=Fe, Ni /AF = FeF 2 , MnF 2 ) have been studied where the AF layer is epitaxial (110), twinned (110), and polycrystalline. With an epitaxial AF which has one spin axis, the cooling field orients the exchange field along the spin axis. Applying the cooling field perpendicular to the spin axis results in bifurcated loops, whose shape evolves with the cooling field geometry and strength. With a twinned AF where there are two orthogonal spin axes, the exchange field direction is along the bisector of the spin axes that encompass the cooling field. With a polycrystalline AF, the exchange field direction is the same as the cooling field. Transverse hysteresis loops show that when the exchange field has a component perpendicular to the applied field, the magnetization reversal occurs by rotation in the direction of the perpendicular component. Our results demonstrate that in fluoride films, the exchange field is established primarily by the AF anisotropy direction, and only to a lesser extent the cooling field or the magnetization Phys. Rev. B, in press; cond-mat/0512257 2 direction. The bifurcated loops are due to a distribution of AF anisotropies and large AF domain sizes. Furthermore, the magnetization reversal process is extremely sensitive to the exchange field direction.

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confidence: 99%

Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films

Olamit

Schuller

et al. 2006

Phys. Rev. B

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“…Coercivity in the front side T-MOKE is not the same as that in the back side, and the amplitudes at the left and right coercivities are asymmetric, indicating that the amount of F spins differ from each other during magnetization rotation between the decreasing and increasing field branches of the T-MOKE loops from the front and back sides of the NiFe/FeMn bilayer. This asymmetric magnetization reversal has been experimentally and theoretically attributed to typical phenomena in a number of exchange-biased F/AF systems [3,[7][8][9][10][11][12][13][14][15][16]. The asymmetric T-MOKE loop for a NiFe/FeMn bilayer seems to originate from the competition between the uniaxial and unidirectional anisotropies [3,13,15].…”

Section: Methodsmentioning

confidence: 99%

“…They claimed that the relative strength of the uniaxial and unidirectional anisotropies is responsible for the different magnetization reversals [15]. The origin of the experimentally observed asymmetry has been addressed as a higher magnetic anisotropy [7], an irreversible change of the AF domain state [8], a partial domain wall parallel to the interface in an F or AF layer [9], an anisotropy dispersion in an F or AF layer [11], the competition between anisotropies [3,13,15], the angle between an applied field direction and a cooling field direction [3,14,17]. Although extensive research has been conducted experimentally and theoretically, the fundamental theory explaining all the features of the magnetization reversal in many F/AF systems remains unknown and controversial due to the inherently complex F/AF spin structure and the difficulty in directly probing the spin configuration and crystallographic structure at an F/AF interface [18].…”

Section: Introductionmentioning

confidence: 99%

“…Various measurement techniques such as VSM, anisotropic magnetoresistance, polarized neutron reflectivity, soft x-ray scattering, and MOKE have revealed the asymmetric form of the magnetization reversal of the exchangebiased F layer [3,[7][8][9][10][11][12][13][14][15][16]. The magnetization reversal takes place via magnetization rotation or via nucleation and domain wall propagation along the same or different sides of an applied field during the decreasing (from positive to negative saturation) and increasing (from negative to positive saturation) field branches of the M-H loop.…”

Section: Introductionmentioning

confidence: 99%

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Magnetization Reversal of Exchange-biased Bilayers and Trilayers Probed using Front and Back LT-MOKE

Kim¹,

Kim²,

Choi³

et al. 2009

Journal of Magnetics

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Magneto-optical Kerr effect (MOKE) magnetometry was used to investigate magnetization reversal dynamics in 30-nm NiFe/15-nm FeMn, 15-nm FeMn/30-nm CoFe bilayers, and 30-nm NiFe/(2,10)-nm FeMn/30-nm CoFe trilayers. The in-plane magnetization components of each ferromagnetic layer, both parallel and perpendicular to the applied field, were separately determined by measuring the longitudinal and transverse MOKE hysteresis loops from both the front and back sides of the film for an oblique incident s-polarized beam. The magnetization of the FeMn/CoFe bilayer was reversed abruptly and symmetrically through nucleation and domain wall propagation, while that of the NiFe/FeMn bilayer was reversed asymmetrically with a dominant rotation. In the NiFe/FeMn/CoFe trilayers, the magnetic reversal of the two ferromagnetic layers proceeded via nucleation and domain wall propagation for 2-nm FeMn, but via asymmetric rotation for 10-nm FeMn. The exchange-biased ferromagnetic layers showed the magnetization reversal along the same path in the film plane for the decreasing and increasing field branches from transverse MOKE hysteresis loops, which can be qualitatively explained by the theoretical model of the exchange-biased ferromagnetic/antiferromagnetic systems.

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“…[1][2][3] The magnetization reversal mechanisms in EB systems have been the focus of many studies. [4][5][6][7][8][9][10][11][12][13][14] In certain systems asymmetric reversal processes have been observed, where domain nucleation and growth dominate in one field sweep of the hysteresis loop while magnetization rotation prevails in the opposite field sweep. [6][7][8][9] Other studies have shown the dependence of the reversal mechanism on the exchange and anisotropy fields in the sample.…”

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Irreversibility of magnetization rotation in exchange biased Fe/epitaxial-FeF2 thin films

Olamit

Liu

et al. 2007

Applied Physics Letters

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Magnetization reversal via rotation is typical in ferromagnet/antiferromagnet exchange biased systems. The reversibility of the rotation is a manifestation of the microscopic reversal process. The authors have investigated the magnetization reversal in Fe/epitaxial-FeF2 thin films using vector magnetometry and first-order reversal curves. The reversal is predominantly by rotation as the applied field makes an angle with the antiferromagnet spin axis, mostly irreversible at small angles and reversible at larger angles. A modified Stoner-Wohlfarth model reproduces the overall trend of the irreversibility evolution. The remaining discrepancies between the modeled and measured irreversibilities may be attributed to local incomplete domain walls.

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Magneto-optical study of magnetization reversal asymmetry in exchange bias

Cited by 41 publications

References 19 publications

Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films

Angular dependence of exchange anisotropy on the cooling field in ferromagnet/fluoride thin films

Magnetization Reversal of Exchange-biased Bilayers and Trilayers Probed using Front and Back LT-MOKE

Irreversibility of magnetization rotation in exchange biased Fe/epitaxial-FeF2 thin films

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