Asymmetric magnetization reversal in exchange-biased NiFe∕CoO submicron-sized structures

Girgis, E.; Portugal, R. D.; Bael, M. J. Van; Temst, Kristiaan; Haesendonck, Chris Van

doi:10.1063/1.1905794

Cited by 12 publications

(6 citation statements)

References 22 publications

(16 reference statements)

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“…It has been shown that for nanostructures, the AFM layer is weakly pinned to the FM layer as compared to the continuous film due to thermal activation effects. 19,21,[49][50][51] This results in lower blocking temperatures for nanostructures when compared to continuous films. For instance, in NiFe/ IrMn systems, the blocking temperature in nanodots is observed to be lower as compared to the continuous film.…”

Section: ͑1͒mentioning

confidence: 99%

“…This "freezing" of AFM spins induces unidirectional anisotropy in the system which can be tailored by controlling several factors such as the field cooling strength, thicknesses of AFM or FM layers, and by structural confinement of AFM domain sizes. Although the microscopic origin of exchange bias effect is still not elucidated completely despite exhaustive experimental 4,6-8 and theoretical studies, [9][10][11][12][13][14][15] there have been few observations on its characteristic features: ͑i͒ the shift in the hysteresis loop along its field axis ͑H EB ͒ and increase in coercivity ͑H C ͒ as the system is cooled in an applied magnetic field below the blocking temperature of the AFM layer, [16][17][18] ͑ii͒ different magnetization reversals for the ascending and descending parts of the hysteresis loop, [19][20][21] and ͑iii͒ the time relation effects of H EB and H C indicate that a stable magnetic state is reached only at very low temperatures. 22 One of the important factors in explaining the origin of exchange bias is the irreversible nature of the AFM interface magnetization arising from volume domains stabilized by defects in the AFM layer.…”

Section: Introductionmentioning

confidence: 99%

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Investigating the exchange bias in multilayer triangular nanorings

Jain

Tripathy

Adeyeye

2009

Journal of Applied Physics

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Effect of polarized current on the exchange bias in a current-in-plane spin valve J. Appl. Phys. 105, 07D106 (2009); 10.1063/1.3057796 Rotating-field magnetoresistance of exchange-biased spin valves J. Appl. Phys. 97, 023910 (2005); 10.1063/1.1836881Current-driven switching of exchange biased spin-valve giant magnetoresistive nanopillars using a conducting nanoprobe Exchange bias effects have been systematically investigated in individual spin valve triangular rings using the synchronous transport measurement technique. Preferential pinning of antiferromagnetic ͑AFM͒ layer and ferromagnetic ͑FM͒ layer domain walls at the corners of the ring results in stronger interface coupling leading to higher blocking temperatures in the ring structure compared to the continuous film of the same film composition. At low temperature, the competition between unidirectional anisotropy and configurational anisotropy results in the formation of large domains at the corners of the ring, which results in lower values of exchange bias in the ring as compared to the continuous film. The effect of cooling field direction was also studied. We observed that the magnitude of bias obtained for negative field cooling direction is larger than that obtained for positive field cooling direction with sweeping field always starting from negative saturation. This observation has been ascribed to the dominance of FM domain magnetization determined by the external magnetic field over the cooling field which defines the AFM-FM interface coupling.

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Section: ͑1͒mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigating the exchange bias in multilayer triangular nanorings

Jain

Tripathy

Adeyeye

2009

Journal of Applied Physics

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“…The asymmetry of the magnetization reversal curves at the patterned film (see the arrows on the figures) varies monotonically with decreasing size of the magnetic dots. A small shoulder appears for the first time in the upper magnetization curve in figure 2(a) and becomes more pronounced as the size of the dots decreases, leading almost to the 'disappearance' of the exchange bias (EB) effect for the sample with the smallest dots [6,7] in figure 2(d). Presumably, this odd behaviour caused by incomplete biasing due to a competition between magnetostatic inter-dot interactions and exchange anisotropy energy at the FM/AFM interface.…”

Section: The Size Dependencementioning

confidence: 99%

Size and shape dependences on magnetization reversal in ferromagnetic/antiferromagnetic bilayer patterned into nano-dot arrays

Girgis¹,

Portugal²,

Temst³

et al. 2006

J. Phys. D: Appl. Phys.

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Magnetization reversal in exchange biased Co/CoO dot arrays has been investigated systematically as a function of shape anisotropy, dot size, temperature, cooling field and training effect. Polycrystalline 24 nm Co films have been sputtered on a pre-patterned Si/SiO2 substrate with the lateral dimensions of the dots varying from 200 to 900 nm at a fixed spacing of 800 nm. The Co dots have been oxidized using pure oxygen to create a Co/CoO bilayer. Below the Néel temperature, the hysteresis loop of this bilayer displays a normal unidirectional shift due to the exchange bias in the continuous film, while the patterned film displays an additional anomaly of the upper part of the hysteresis loop. This anomaly, which is shape dependent, increases with decreasing temperature and cooling field. On the other hand, it decreases for the trained loops with increasing aspect ratio (length/width) of the patterned dot. This anomaly is probably caused by incomplete biasing due to the competition between magnetostatic inter-dot interactions and exchange bias.

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“…Both parameters can be tailored by exchange coupling the ferromagnetic ͑F͒ nanoelement to an extended antiferromagnetic ͑AF͒ substrate. These issues have recently been investigated in experimental studies of arrays of interface biased ferromagnetic dots, Fe/ FeF 2 , [16][17][18][19] Ni/NiO, 21 NiFe/CoO, 22,23 NiFe/IrMn, 24 and Co/CoO. 25 Early reports have shown that the exchange bias of Fe/ FeF 2 patterned bilayers can be tuned by their lateral dimensions.…”

Section: Introductionmentioning

confidence: 99%

Magnetic hysteresis of interface-biased flat iron dots

et al. 2009

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We report a theoretical study of the coercivity and bias of iron dots exchange coupled with an antiferromagnetic substrate. We show that flat dots, with height close to the iron exchange length, and lateral dimensions of a few exchange lengths, exhibit large enhancement of coercivity and exchange bias. For small interface field strength the magnetization reversal is nearly a coherent rotation with symmetrical loops. Interface pinning leads to large reduction in coercivity and asymmetrical loops, if the interface field strength is comparable to the value of the iron exchange field. We discuss the impact of geometrical confinement and interface pinning on the magnetization reversal mechanisms. We show that small area dots with height larger than the exchange length display stronger interface effects.

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Asymmetric magnetization reversal in exchange-biased NiFe∕CoO submicron-sized structures

Cited by 12 publications

References 22 publications

Investigating the exchange bias in multilayer triangular nanorings

Investigating the exchange bias in multilayer triangular nanorings

Size and shape dependences on magnetization reversal in ferromagnetic/antiferromagnetic bilayer patterned into nano-dot arrays

Magnetic hysteresis of interface-biased flat iron dots

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