Influence of spacer layer morphology on the exchange-bias properties of reactively sputtered<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Co</mml:mi><mml:mo>∕</mml:mo><mml:mi mathvariant="normal">Ag</mml:mi></mml:mrow></mml:math>multilayers

Normile, P. S.; Toro, J. A. De; Muñoz, T.; González, Javier; Andrés, J. P.; Muniz, Pablo Rodrigues; Galindo, R. Escobar; Riveiro, José Manuel Suárez

doi:10.1103/physrevb.76.104430

Cited by 25 publications

(20 citation statements)

References 23 publications

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“…27 In general terms, this blocked state is removed by increasing the energy of the system, either by applying a strong field or by increasing the temperature, although the deblocking and spin reorientation process are likely influenced by a small in-plane anisotropy and ferromagnetic-antiferromagnetic exchange bias stabilization phenomena at low temperature. 8,29 Moreover, the ZFC curve at 5 kOe shows that, even at low temperatures, there is no observation of any blocking process at such a high field, and thus an almost complete polarization of the magnetic moments along the direction of the field is hypothesized. Independently of the blocking origin, the issue of this work is to determine if the deblocking process of the spins in these core-shell metal-metal oxide systems at intermediate fields consists of the orientation of the cluster superspins, or if it arises from the thermal activation of the disordered oxide phase, acting with a spin-glass-like behavior at low temperatures.…”

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confidence: 98%

X-ray magnetic circular dichroism study of the blocking process in nanostructured iron-iron oxide core-shell systems

et al. 2011

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Experimental evidence for magnetothermal behavior in iron-iron oxide nanostructured systems has been obtained using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe L 2,3 edges. The purpose of this study is the determination of the blocked state in these spin-glass-like core-shell systems. A first overview of the magnetic species participating in the magnetic response was obtained by analyzing the XMCD at saturating fields. Also, the XAS revealed the existence of an antiferromagnetic FeO phase, likely located at the interface regions. Finally, measurements were performed at low temperature and intermediate field, where a frozen state below the blocking energy is observed. The results show that the oxide phase spins are oriented at low temperature, while the magnetic spins of the metallic core do not contribute to the XMCD, suggesting that the blocking process mainly involves the magnetic particle superspins rather than the oxide coverage phase.

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confidence: 98%

X-ray magnetic circular dichroism study of the blocking process in nanostructured iron-iron oxide core-shell systems

et al. 2011

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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: [58,59].…”

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confidence: 99%

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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“…Firstly, flatness of the ZFC curve in the low temperature range at low fields ( Oe), corresponding to the oxidized sample, respect to the non-oxidized one, can be associated to the effect of the effective pinning exerted by the antiferromagnetic phase on the ferromagnetic particles. At such low temperatures, the Fe spins are pinned by exchange interaction with the antiferromagnetic spins [19] and a slight increase of magnetization occurs only when the blocking temperature of the antiferromagnetic phase is overcome. Peaks of the derivative ZFC curves from the non-intentionally oxidized sample are slightly shifted to higher temperatures.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, another effect that must be taking into account is that this lower degree of oxidation in the non-intentionally oxidized sample can lead to a smaller separation between the iron grains, and thus to stronger interactions (either dipolar or even exchange) between these ferromagnetic particles. These stronger interactions can result in a broadening of these energy barrier distributions [19].…”

Section: Resultsmentioning

confidence: 99%

Core-Shell Magnetic Behavior of Ultrathin Films Prepared by Sputtering at Very Low Temperatures

et al. 2008

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We report a magnetic characterization of iron thin films of 6 nm prepared on Si (001) substrates by sputtering at different substrate temperatures. Magnetization loops and zero field cooling-field cooling measurements were performed to unveil the magnetic features of such systems. Magnetic parameters show that films prepared at very low temperature ( S = 200 K) present features of a core-shell granular systems, formed by ferromagnetic iron grains surrounded by an antiferromagnetic iron oxide phase.Index Terms-Thin films, magnetic materials.

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Influence of spacer layer morphology on the exchange-bias properties of reactively sputteredCo∕Agmultilayers

Cited by 25 publications

References 23 publications

X-ray magnetic circular dichroism study of the blocking process in nanostructured iron-iron oxide core-shell systems

X-ray magnetic circular dichroism study of the blocking process in nanostructured iron-iron oxide core-shell systems

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

Core-Shell Magnetic Behavior of Ultrathin Films Prepared by Sputtering at Very Low Temperatures

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