Magnetic origin of enhanced top exchange biasing in Py/IrMn/Py multilayers

Malinowski, Grégory; Hehn, M.; Robert, S.; Lenoble, O.; Schuhl, A.; Panissod, P.

doi:10.1103/physrevb.68.184404

Cited by 36 publications

(28 citation statements)

References 21 publications

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“…[3][4][5][6][7] Nowadays, FM/AFM bilayers are incorporated in magnetic thin film devices such as magnetic spin-valve sensors, magnetic tunnel junction read heads for hard-disk drives, and magnetic random access memories. For continuous FM/AFM bilayers, variations of the exchange bias field with AFM grain size, 5 AFM domain size, 8 and AFM film thickness [9][10][11] have been measured, illustrating the theoretically predicted importance of the AFM domain size.…”

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confidence: 64%

“…The interface coupling energy per unit area can now be written as int =−J int 2 / ͑aJ AFM 2 t AFM ͒, which corroborates the inverse proportionality between the measured exchange bias field and the AFM layer thickness in our experiments and other exchange bias systems. [9][10][11] The absence of the 1 / t variation of the exchange bias field for ͓Pt͑2 nm͒ /Co͑5 nm͔͒ 3 / IrMn͑t͒ multilayers on the nanospheres with t Ն 10 nm indicates that the AFM domains are confined by the size of the particles. In this case, the AFM film is single domain and the AFM domain size scales with the diameter of the spheres instead of the IrMn film thickness.…”

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confidence: 99%

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Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures

et al. 2007

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Size-dependent scaling is studied in exchange biased nanostructures obtained by depositing ͓Pt/ Co͔ 3 / IrMn multilayers with perpendicular magnetization onto an array of monodisperse polystyrene nanospheres with a diameter ranging from 58 nm to 320 nm. We find that the exchange bias field increases with the inverse of the sphere diameter when the IrMn layer is single domain. This scaling behavior, which is favorable for further miniaturization of magnetic devices, can be understood within the context of a random field model by a statistical distribution of Mn spins at the Co/ IrMn interface. DOI: 10.1103/PhysRevB.75.012413 PACS number͑s͒: 75.50.Ee, 61.46.Df, 75.70.Ϫi, 75.75.ϩa Fifty years ago, Meiklejohn and Bean discovered a new form of magnetic anisotropy.1 Their discovery, called exchange bias, was a unidirectional shift of the hysteresis loop along the magnetic field axis for ferromagnetic ͑FM͒ materials in close contact with an antiferromagnet ͑AFM͒. Due to its technological applications, exchange bias coupling has generated intense experimental 2 and theoretical research efforts.3-7 Nowadays, FM/AFM bilayers are incorporated in magnetic thin film devices such as magnetic spin-valve sensors, magnetic tunnel junction read heads for hard-disk drives, and magnetic random access memories. For continuous FM/AFM bilayers, variations of the exchange bias field with AFM grain size, 5 AFM domain size, 8 and AFM film thickness 9-11 have been measured, illustrating the theoretically predicted importance of the AFM domain size.Although there are many reports on exchange biased nanostructures, 12-16 mainly with a ferromagnetic in-plane easy axis, very few of them address in depth the effects of miniaturization on the exchange bias properties, where unique effects will set in at some critical length scales; and even the trends are controversial. While most of the nanosystems exhibit a decrease in exchange bias with size reduction, it has been recently reported for sub-100 nm NiFe-IrMn square dots, that depending on the thickness of the AFM layer, the dots could either have larger or smaller bias field than the respective continuous films.14 In addition, many studies focus on structures with dimensions larger than the AFM domain size or compare properties of single-size nanostructures with those of continuous films. Hence, a detailed understanding of size-dependent scaling of exchange bias in magnetic nanostructures that confine the AFM to a singledomain state is still lacking.Here, we present a conclusive account of the effects of size reduction on exchange bias. In our experiments we use an original self-assembly method to systematically vary the FM/AFM structure size and AFM layer thickness. Measurements on these structures reveal a statistical enhancement of the exchange bias field in magnetic nanostructures. This enhancement, which is explained within the context of a random field model, follows a simple scaling law.To fabricate the nanostructures, we employed dense arrays of monodisperse spherical polystyrene p...

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Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures

et al. 2007

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“…On the contrary, the domain state model [9] considers the entire volume of the AF in order to account for EB, suggesting that the internal magnetic structure of the AF is crucial for the emergence of EB. Several techniques have been applied to study AF domains [10][11][12], and 90 or 180 domain walls were claimed for different systems [13][14][15][16][17][18][19][20]. Although recent experiments [21,22] suggest that the bulk AF sets the EB, whether EB is purely controlled by the interface or AF bulk is still controversial.…”

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Role of the Antiferromagnetic Bulk Spin Structure on Exchange Bias

et al. 2009

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“…[1][2][3] The reasons for this discrepancy and, more generally, the origin of the exchange bias effect have been studied in detail. While many groups found a strong correlation between H ex and the degree of crystalline texture, [1][2][3][4][5] others did not find any and they attributed their exchange bias results to the influence of grain size, 2,[6][7][8] interface roughness, 2,9 or magnetic effects 10,11 instead. The magnetic-field annealing experiments in most of these studies focused primarily on the optimization of the annealing time and temperature.…”

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Influence of the annealing field strength on exchange bias and magnetoresistance of spin valves with IrMn

Kerr

Dijken

Coey

2005

Journal of Applied Physics

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We report on field annealing effects in spin valves with an IrMn pinning layer and spin valves with a synthetic antiferromagnet. The exchange bias field and magnetoresistance of spin valves with an IrMn/ CoFe bilayer at the bottom improve drastically upon annealing in large magnetic fields. The evolution of the exchange bias field with annealing field strength shows a rapid increase up to an applied field of 0.5 T, which is followed by a more gradual improvement up to an annealing field of 5.5 T. The increase of the exchange bias field in large magnetic fields indicates that the interfacial spin structure of the IrMn layer is directly influenced by the annealing field strength.

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Magnetic origin of enhanced top exchange biasing in Py/IrMn/Py multilayers

Cited by 36 publications

References 21 publications

Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures

Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures

Role of the Antiferromagnetic Bulk Spin Structure on Exchange Bias

Influence of the annealing field strength on exchange bias and magnetoresistance of spin valves with IrMn

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