Measurement of the anisotropy constant of antiferromagnets in metallic polycrystalline exchange biased systems

Vallejo-Fernández, G.; Fernandez-Outon, L.E.; O’Grady, K.

doi:10.1063/1.2817230

Cited by 87 publications

(63 citation statements)

References 14 publications

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“…2͒ 21 ͒ could be ascribed to thermal activation processes occurring during the measurements at high temperatures. 34,35 Interface defects may lower the symmetry of the crystal fields thus leading to enhancement in the anisotropy due to local structural deformations and associated elastic strains. 36 This strain-related interface anisotropy can be up to an order of magnitude larger than the corresponding bulk value for moderate strains.…”

Section: Resultsmentioning

confidence: 99%

Discrimination between coupling and anisotropy fields in exchange-biased bilayers

Geshev

Nicolodi

Silva

et al. 2009

Journal of Applied Physics

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In the framework of models that assume planar domain wall formed at the antiferromagnetic part of the interface of exchange-biased bilayers, one cannot distinguish between the cases of high or low ratios between the coupling and the antiferromagnet's anisotropy fields by using hysteresis loop measurement, ferromagnetic resonance, anisotropic magnetoresistance, or ac susceptibility techniques applied on one and the same sample. The analysis of the experimental data obtained on a series of FeMn/Co films indicated that once the biasing is established the variation in the coercivity with the FeMn layer thickness could be essential for solving this problem. If the coercivity decreases with the thickness then the interlayer exchange coupling is the parameter that varies while the domain-wall energy of the antiferromagnet remains practically constant.

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Section: Resultsmentioning

confidence: 99%

Discrimination between coupling and anisotropy fields in exchange-biased bilayers

Geshev

Nicolodi

Silva

et al. 2009

Journal of Applied Physics

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“…Actually, the AFM component in exchange biased systems is usually composed of nanosized grains, which are prone to superparamagnetic effects [56]. To account for the possible existence of superparamagnetic CoO grains, a reduction coefficient must be applied to H E derived from Equation (1), which does not include thermal activation effects: As a consistency test of our model, the temperature dependence of H E in the Co/CoO-CoO system was re-calculated using the same parameters as above (red line in Figure S3 …”

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High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect

et al. 2015

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Thermal activation tends to destroy the magnetic stability of small magnetic nanoparticles, with crucial implications in ultra-high density recording among other applications. Here we demonstrate that low blocking temperature ferromagnetic (FM) Co nanoparticles (T B <70 K) become magnetically stable above 400 K when embedded in a high Néel temperature antiferromagnetic (AFM) NiO matrix. The origin of this remarkable T B enhancement is due to a magnetic proximity effect between a thin CoO shell (with low Néel temperature, T N ; and high anisotropy, K AFM ) surrounding the Co nanoparticles and the NiO matrix (with high T N but low K AFM ). This proximity effect yields an effective AFM with an apparent T N beyond that of bulk CoO, and an enhanced anisotropy compared to NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations via core-shell exchange-bias coupling, leading to the observed T B increase. Mean-field calculations provide a semi-quantitative understanding of this magnetic-proximity stabilization mechanism. 2The current miniaturization trend in magnetic applications has led to a quest to suppress spontaneous thermal fluctuations (superparamagnetism) in ever-smaller nanostructures [1][2][3][4][5], which is a clear example of the fundamental efforts of condensed matter physics to meet technological challenges [6] (e.g., the continued growth of recording density [7]). Despite the foreseeable change of recording paradigm from continuous to patterned media, where each bit is recorded in an individual nanostructure [7], the key for sustained storage density increase will remain the introduction of progressively more anisotropic (high K) materials [8], which allow for magnetic stability at very small volumes, V (i.e., blocking temperature, T B ∝ KV, above room temperature, RT). Two main strategies are largely investigated to achieve high K (both of them with implications in other active technologies beyond information storage, such as permanent magnets, magnetic hyperthermia or even sensors [5,[9][10][11]): (i) the use of compounds with intrinsically high magnetocrystalline anisotropy (such as FePt [3,8]) and (ii) the design of exchange-coupled nanocomposites [4,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].Unfortunately, most high-K materials require high-temperature annealing processes to obtain the desired phase, which could hamper their implementation in certain structures. Thus, FM-AFM exchange coupling alternatives may be an appealing option. In fact, it has been demonstrated [4] that ferromagnetic-antiferromagnetic (FM-AFM) interfacial exchangecoupling is an effective method, later patented by Seagate [12], to increase the effective K of FM nanoparticles. However, a T B enhancement beyond RT using this approach has been rarely reported [22][23][24][25][26] (where often broad particle size distribution can partly account for the "apparent" T B increase [22][23][24][25]). The reason for this scarcity is that high Néel temperature (T N ) AFMs tend to h...

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“…Thermal activation determines the amount of rotatable and pinned uncompensated magnetic moments in the AF and is therefore strongly connected to the size of H C and EB both increasing with decreasing temperature [35][36][37].…”

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Preparation and characterisation of epitaxial Pt/Cu/FeMn/Co thin films on (100)‐oriented MgO single crystals

Schmidt

Gräfe

Audehm

et al. 2015

Physica Status Solidi (a)

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This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.FeMn/Co thin-films, a purely metallic exchange-bias system, were prepared on (100)-oriented MgO single crystals. The layers were grown by molecular beam epitaxy (MBE). The crystalline and magnetic properties could be tuned by using sputtered Pt buffer layers deposited at variable temperatures. A transition of the crystalline orientation from (111)-terminated layers at lower deposition temperatures to (100)-terminated layers at temperatures higher than 950 K was established and the impact on the magnetic sample properties was investigated. Here, the detailed sample preparation process is shown together with low energy electron diffraction (LEED), medium energy electron diffraction (MEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements revealing the samples structure and composition. The crystalline orientation of Pt was imprinted to the magnetic layer stack and clearly influenced the exchangebias (EB) and coercive field (H C ) as shown by superconducting quantum interference device (SQUID) and magneto-optical Kerr effect (MOKE) measurements. Furthermore, a correlation between the crystallite size and the temperature dependent magnetic properties could be identified.

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Measurement of the anisotropy constant of antiferromagnets in metallic polycrystalline exchange biased systems

Cited by 87 publications

References 14 publications

Discrimination between coupling and anisotropy fields in exchange-biased bilayers

Discrimination between coupling and anisotropy fields in exchange-biased bilayers

High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect

Preparation and characterisation of epitaxial Pt/Cu/FeMn/Co thin films on (100)‐oriented MgO single crystals

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