Superferromagnetic domain state of a discontinuous metal insulator multilayer

Bedanta, Subhankar; Petracic, O.; Kentzinger, Emmanuel; Kleemann, W.; Rücker, Ulrich; Paul, Amitesh; Brückel, Thomas; Cardoso, S.

doi:10.1103/physrevb.72.024419

Cited by 34 publications

(45 citation statements)

References 31 publications

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“…Hence, correlated roughness of adjacent layers can be expected in our case-an essential prerequisite for ferromagnetic Néel coupling. 3 Indeed, as shown previously for a nonpercolating CoFe/ Al 2 O 3 multilayer, 12 we find close coincidence of x-ray specular small-angle reflectivity and longitudinal diffuse scattering ͓Fig. 1͑a͔͒, which clearly indicates strong vertical correlation in the multilayer stack.…”

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confidence: 55%

“…[8][9][10] It is known from related granular Co/ Al 2 O 3 multilayers 11 that the vertical arrangement of the clusters from plane to plane is not random but shows a growthinduced self-organization. Hence, correlated roughness of adjacent layers can be expected in our case-an essential prerequisite for ferromagnetic Néel coupling.3 Indeed, as shown previously for a nonpercolating CoFe/ Al 2 O 3 multilayer, 12 we find close coincidence of x-ray specular small-angle reflectivity and longitudinal diffuse scattering ͓Fig. 1͑a͔͒, which clearly indicates strong vertical correlation in the multilayer stack.…”

supporting

confidence: 50%

“…The FM state of the sample can be recognized by the splitting of the reflectivity edges where R ++ ͑͒ is shifted to higher angles in comparison to R −− ͑͒. 12 The first-order structural superlattice Bragg peak at = 2.45°is dominant in the R −− channel. Its position corresponds to a bilayer thickness d Ϸ 5.4 nm, in agreement with the x-ray results ͑Fig.…”

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confidence: 99%

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Modulated magnetization depth profile in dipolarly coupled magnetic multilayers

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Polarized neutron reflectivity ͑PNR͒ and magnetometry studies have been performed on the metal-insulator multilayer ͓Co 80 Fe 20 ͑1.6 nm͒ /Al 2 O 3 ͑3 nm͔͒ 9 which exhibits dominant dipolar coupling between the ferromagnetic layers. Our PNR measurements at the coercive field reveal a novel and unexpected magnetization state of the sample, exhibiting an oscillating magnetization depth profile from CoFe layer to CoFe layer with a period of five bilayers along the multilayer stack. With the help of micromagnetic simulations we demonstrate that competition between long-and short-ranged dipolar interactions apparently gives rise to this unprecedented phenomenon. DOI: 10.1103/PhysRevB.74.054426 PACS number͑s͒: 75.60.Jk, 61.12.Ha, 73.21.Ac, 78.20.Ls Magnetic multilayers ͑MLs͒ consisting of ferromagnetic ͑FM͒ and nonmagnetic ͑N͒ layers exhibit a large variety of physically interesting properties for both practical applications and fundamental research. In particular, magnetic multilayers comprising 3d ferromagnetic layers interleaved with nonmagnetic spacers exhibit giant magnetoresistance for appropriate thicknesses of the spacer layers.1 Several types of interlayer coupling have been studied theoretically and experimentally ͑e.g., Ref. 2͒. For trilayers consisting of two magnetically saturated, pinhole-free metallic layers separated by a conductive spacer layer, the Ruderman-Kittel-KasuyaYosida ͑RKKY͒ oscillatory exchange provides a major coupling mechanism. In systems with insulating spacer layers and flat interfaces, dipolar interactions are dominant. It favors antiparallel orientation of the intraplanar magnetization between adjacent layers. For rough interfaces the so-called Néel-or orange peel interlayer coupling has to be considered. 3,4 In 1962, Néel 3 pointed out that there should be ferromagnetic coupling between adjacent films due to magnetic dipoles at the interface induced by a correlated morphological corrugation. Finally, if one considers the domain structure within each layer, a magnetostatic interaction could arise between the domain-wall stray fields in a FM / N / FM structure, where N can be a nonmagnetic metallic or insulating layer. Recently Lew et al. 5 have shown that interlayer domain-wall coupling can induce a mirror domain structure in a magnetic trilayer system which can affect the transport properties.In this paper, we report on the observation of a novel magnetization state in a dipolar coupled magnetic metalinsulator multilayer exhibiting an oscillating magnetization depth profile from FM layer to FM layer. The paper is organized as follows: First we argue qualitatively how such unusual magnetization states can be induced by competing dipolar interactions. Then we present the experimental evidence from polarized neutron reflectometry. And, finally, a micromagnetic simulation is presented which underpins the argument that competing interactions can lead to the observed oscillating magnetization depth profile.Dipolar interaction can lead to frustration effects in magnetic multilayers wit...

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Modulated magnetization depth profile in dipolarly coupled magnetic multilayers

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“…For low frequencies (right hand side) one finds a quarter circle, whereas at high f an increasing part with positive curvature appears. These features can be successfully modeled in the framework of the motion of a pinned DW in a random FM exhibiting relaxation, creep, slide and switching [11,27,28,30]. (2) Another strong indication of SFM behavior can be found from analyzing relaxation curves of the thermoremanent magnetic moment, m vs. t. Ulrich et al [31] introduce a universal relaxation behavior for any nanoparticle system according to a decay law of the form…”

Section: Superferromagnetic (Sfm) Orderingmentioning

confidence: 99%

“…This can lead to SFM ordering [10,11,28] (see Fig. 1), where regions of FM correlated particle moments (SFM domains) are found [12,29].…”

Section: Superferromagnetic (Sfm) Orderingmentioning

confidence: 99%

Collective states of interacting ferromagnetic nanoparticles

Petracic

Chen

Bedanta

et al. 2006

Journal of Magnetism and Magnetic Materials

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Discontinuous magnetic multilayers [CoFe/Al 2 O 3 ] are studied by use of magnetometry, susceptometry and numeric simulations. Soft ferromagnetic Co 80 Fe 20 nanoparticles are embedded in a diamagnetic insulating a-Al 2 O 3 matrix and can be considered as homogeneously magnetized superspins exhibiting randomness of size (viz. moment), position and anisotropy. Lacking intra-particle core-surface ordering, generic freezing processes into collective states rather than individual particle blocking are encountered. With increasing particle density one observes first superspin glass and then superferromagnetic domain state behavior. The phase diagram resembles that of a dilute disordered ferromagnet. Criteria for the identification of the individual phases are given.

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Polarized Neutron Reflectivity and Scattering from Magnetic Nanostructures and Spintronic Materials

Zabel

Theis‐Bröhl

Toperverg

2007

Handbook of Magnetism and Advanced Magnetic Materials

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Polarized neutron reflectivity and scattering has established itself as one of the most important experimental methods for the analysis of magnetic nanostructures and spintronic materials. With this method, seminal contributions have been made to the physics of thin magnetic films, interfaces, and superlattices, including collinear and noncollinear exchange coupling. Another rich area is the exchange coupling phenomena between ferromagnetic and antiferromagnetic layers. Presently neutron scattering from laterally patterned magnetic arrays has become very active for the understanding of domain structures, domain reversals, and correlation effects. Established more than 25 years ago, polarized neutron reflectivity was focused mainly on the specularly reflected intensity. With the advent of area detectors and efficient wide‐angle spin analyzers, the off‐specular diffuse scattering could be analyzed, contributing to a more complete picture of the physics of magnetic nanostructures and patterned arrays. In this review a basic introduction into the fundamentals of polarized neutron reflectivity is provided, including specular and off‐specular scattering. For the description of the off‐specular part, the distorted wave Born approximation has rigorously been applied and features missed in the simpler Born approximation are pointed out. The methods are illustrated by a number of examples from research into magnetic thin films, spin valves, magnetic multilayers, exchange bias systems, spintronic materials, and periodic magnetic arrays of islands and stripes.

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Superferromagnetic domain state of a discontinuous metal insulator multilayer

Cited by 34 publications

References 31 publications

Modulated magnetization depth profile in dipolarly coupled magnetic multilayers

Modulated magnetization depth profile in dipolarly coupled magnetic multilayers

Collective states of interacting ferromagnetic nanoparticles

Polarized Neutron Reflectivity and Scattering from Magnetic Nanostructures and Spintronic Materials

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