Reversal behavior of exchange-biased submicron dots

Li, Zhi-Pan; Petracic, O.; Eisenmenger, Johannes; Schuller, Iván K.

doi:10.1063/1.1863449

Cited by 30 publications

(34 citation statements)

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“…7,[22][23][24] Recently size effects involved in the EB phenomenon have been extensively studied. [25][26][27][28] This includes the dependence of the EB on the AF and FM film thicknesses as well as size effects induced by lateral structuring of the FM and AF components of EB heterostructures. Various characteristic length scales influencing the EB have been identified.…”

Section: Introductionmentioning

confidence: 99%

Scaling behavior of the exchange-bias training effect

2007

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The dependence of the exchange-bias training effect on temperature and ferromagnetic film thickness is studied in detail and scaling behavior of the data is presented. Thickness-dependent exchange bias and its training are measured using the magneto-optical Kerr effect. A focused laser beam is scanned across a Co wedge probing local hysteresis loops of the Co film which is pinned by an antiferromagnetic CoO layer of uniform thickness. A phenomenological theory is best fitted to the exchange-bias training data resembling the evolution of the exchange-bias field on subsequently cycled hysteresis loops. Best fits are done for various temperatures and Co thicknesses. Data collapse on respective master curves is achieved for the thickness and temperature-dependent fitting parameters as well as the exchange bias and coercive fields of the initial hysteresis loops. The scaling behavior is strong evidence for the validity and the universality of the underlying theoretical approach based on triggered relaxation of the pinning layer towards quasiequilibrium.

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Section: Introductionmentioning

confidence: 99%

Scaling behavior of the exchange-bias training effect

2007

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“…Investigations of the role of magnetic vortices in exchange bias systems have begun only recently [27][28][29][30][31]. In previous experiments, we have shown that the interplay between the unidirectional exchange bias and vortex structures can give rise to angular-dependent magnetization reversal, when the exchange bias is established with a saturated ferromagnet [27,31].…”

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Imprinting Vortices into Antiferromagnets

et al. 2006

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The effect of imprinting symmetric and displaced vortex structures into an antiferromagnetic material is investigated in micron-sized disks consisting of exchange coupled ferromagnetic-antiferromagnetic bilayers. The imprint of displaced vortices manifests itself by the occurrence of a new type of asymmetric hysteresis loops characterized by curved, reversible, central sections with nonzero remanent magnetization. Such an imprint is achieved by cooling the disks through the blocking temperature of the system in small fields. Micromagnetic simulations reveal that asymmetric vortexlike loops naturally result from the competition between the different energies involved in the system. DOI: 10.1103/PhysRevLett.97.067201 PACS numbers: 75.60.Jk, 75.50.Ee, 75.70.Cn In ferromagnets and antiferromagnets, there are often domains with differently ordered spin states observed instead of a single homogeneously long-range ordered region. It turns out that domain structures in antiferromagnetic (AFM) materials have been far less studied than domains in ferromagnets [1]. This is partially due to the fact that the staggered AFM spin structure with its lack of a net magnetization makes the detection of domains and domain walls more challenging [2,3]. Moreover, the physical properties of AFM domains differ significantly from ferromagnetic (FM) domains. Domains in a ferromagnet are generally determined by balancing magnetostatic with exchange and anisotropy energies. Thus, in nanostructured systems, ferromagnets can develop welldefined unusual spin states, such as magnetic vortices [4 -9]. The absence of a net magnetization in antiferromagnets means that magnetostatic energy is vanishing, and, therefore, domains in antiferromagnets are generally metastable, since typically the gain in configurational entropy is not sufficient to overcome domain wall energies. Without any direct explicit driver for domain formation, the AFM domains may originate from random nucleation of long-range order due to randomly distributed defects [10]. For these reasons, the formation and evolution of AFM domains remain a research area with many open questions.Nevertheless, domains in antiferromagnets have received increased attention recently due to their role in exchange bias, i.e., the shift of the hysteresis loop observed in FM-AFM coupled systems [11,12], which is a key ingredient in spintronic devices [13]. Many exchange biased systems exhibit unusual properties, one of which is a pronounced asymmetry in the hysteresis loop, caused by different irreversible reversal mechanisms on either side of the hysteresis loop [14 -18]. Since the ferromagnet and the antiferromagnet are exchange coupled, measurements of the FM behavior provide an indirect probe of the properties of the antiferromagnet, for example, the spin-flop field [19], the surface order parameter [20], the crystalline anisotropy [21], or the domain wall width [22,23]. Furthermore, it has recently been demonstrated that nonuniformly magnetized ferromagnets can modify the antiferromagnetic s...

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“…Many models attribute this effect to the formation of domains either in the FM or in the AFM layer [14 -17]. Hence, apart from its crucial technological importance, the study of exchange bias in nanostructures is interesting from a fundamental point of view since the reduction of the lateral dimensions is likely to cause significant alterations to the domain structure of each layer [18][19][20][21][22][23][24][25].…”

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Magnetization Reversal in Submicron Disks: Exchange Biased Vortices

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Hoffmann

et al. 2005

Phys. Rev. Lett.

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Submicron, circular, ferromagnetic-antiferromagnetic dots exhibit different magnetization reversal mechanisms depending on the direction of the magnetic applied field. Shifted, constricted hysteresis loops, typical for vortex formation, are observed for fields along the exchange bias direction. However, for fields applied close to perpendicular to the exchange bias direction, magnetization reversal occurs via coherent rotation. Magnetic force microscopy imaging together with micromagnetic simulations are used to further clarify the different magnetic switching behaviors.

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Reversal behavior of exchange-biased submicron dots

Cited by 30 publications

References 18 publications

Scaling behavior of the exchange-bias training effect

Scaling behavior of the exchange-bias training effect

Imprinting Vortices into Antiferromagnets

Magnetization Reversal in Submicron Disks: Exchange Biased Vortices

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