Pinned Co moments in a polycrystalline permalloy/CoO exchange-biased bilayer

Blackburn, E.; Sánchez-Hanke, Cecilia; Roy, Sujoy; Smith, David J.; Hong, Jung‐Il; Chan, Keith; Berkowitz, A. E.; Sinha, Sunil K.

doi:10.1103/physrevb.78.180408

Cited by 33 publications

(31 citation statements)

References 21 publications

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“…The H EB in Py/MgO is accompanied by a large vertical shift in the magnetic moment, indicating the presence of a substantial number of pinned spins (discussed latter). Both H c and H EB are non-zero even at 400 K, further supporting that T b is above 400 K. In contrast to the present case, Dimitrov and coauthors [19] have reported that both H c and H EB are independent of temperature when Py is interfaced with non-magnetic MgO as compared with the strong temperature dependences measured when Py is interfaced with AFM layers [7][8][9][10][11]. Fig.…”

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confidence: 53%

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Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)

Rao

Prater

et al. 2014

Current Opinion in Solid State and Materials Science

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a b s t r a c tIn magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni 82.5 Fe 17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0). Ó 2014 Elsevier Ltd. All rights reserved.Motivated by the proposed racetrack memory patented [1] by Parkin et al, a great deal of research activity has been devoted to Permalloy (Py) magnetic nanostructures for high frequency applications. Py usually refers to Ni 1Àx Fe x alloys that have a vanishingly small magnetocrystalline anisotropy and magnetostriction but extremely large magnetic permeability. These unique properties make Py one of the most important soft magnets for a variety of applications, such as free layers in spin-valve magnetic-reading heads [2,3]. The Py/MgO combination has been widely used in magnetic tunnel junctions (MTJs) devices. More recently, Py is being extensively used [4,5] to demonstrate electric field control of ferromagnetism (FM) in multiferroic based devices. Hence, exploring and understanding the magnetic properties of Py when interfaced with magnetic/non-magnetic oxide materials is of primary importance.To date, epitaxial Py layers have been deposited [6] on MgO bulk substrates using molecular beam...

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confidence: 53%

“…The magnetic properties of Py have been extensively reported for the case where it is interfaced with anti-ferromagnetic (AFM) materials such as hematite [7], CoO [8], IrMn [9], FeMn [10] and NiO [11]. In addition, some preliminary studies have been reported [6] on the deposition of Py on MgO bulk wafers.…”

Section: Introductionmentioning

confidence: 99%

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)

Rao

Prater

et al. 2014

Current Opinion in Solid State and Materials Science

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“…For instance, in Ref. 4, it has been demonstrated that only 10% of the Co spins at the CoO/Py interface are antiferromagnetically coupled to the (ferromagnetic) Py and it has been argued that a significant amount of unpinned Co spins (follow an applied magnetic field) interacts ferromagnetically with the Py. These contributions is a result of the interface disorder.…”

Section: (C)mentioning

confidence: 99%

“…Although the physical properties of CoO/Py interfaces have been studied in various experimental works, 3,4 an adequate characterization of the structural, electronic, and magnetic properties on an atomic level is missing. Insight can be obtained from first principles calculations based on density functional theory.…”

Section: Mechanism Of Magnetization Enhancement At Coo/permalloy Intementioning

confidence: 99%

“…[9][10][11] For the exchange correlation potential, we use the generalized gradient approximation (GGA). 13 In addition, we employ projector augmented wave pseudopotentials 11,12 with the electronic configurations O 2s 2 2p 4 , Co 3d 8 4s 1 , and Ni 3d 9 4s 1 . We have verified that 15 Å of vacuum is sufficient to avoid artificial interaction across this region and that a plane wave basis set with energies up to 400 eV is accurate.…”

Section: (C)mentioning

confidence: 99%

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Mechanism of magnetization enhancement at CoO/permalloy interfaces

Grytsyuk

Schwingenschlögl

2013

Applied Physics Letters

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We investigate the magnetic properties of CoO(111)/permalloy(111) interfaces by ab-initio calculations. We employ a (5 × 5)CoO/(6 × 6)permalloy supercell, to satisfy the ∼5:6 ratio of the lattice constants, and optimize the atomic density near the interface. While experimentally the interface magnetization is 14% higher than in the bulk, we find for the purely O/Co-terminated interface a decrease/increase by 140%/40%, which enables insight into the real interface with partial O deficiency and atomic intermixing. Intermixing between Fe and Ni significantly lowers the total energy, which promotes Fe accumulation at the interface. Since Co-O bonds are energetically favorable, O diffusion into the permalloy is suppressed.

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