Overcoming thermal fluctuations

Eisenmenger, Johannes; Schuller, Iván K.

doi:10.1038/nmat934

Cited by 76 publications

(50 citation statements)

References 7 publications

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“…Future advances in fields such as ultrahigh-density recording and medical applications are also promoted by effectively increasing the magnetic stability of nanomagnets. 3,4 A comprehensive description of the effect involves fundamental questions of surface and interface magnetism. [5][6][7][8][9] The most striking feature is the shift of the FM hysteresis loop along the magnetic field axis, which is widely used in today's spintronic devices to pin the magnetization direction of a FM reference layer.…”

Section: Introductionmentioning

confidence: 99%

Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems

et al. 2009

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Exchange bias, referred to the interaction between a ferromagnet ͑FM͒ and an antiferromagnet ͑AFM͒, is a fundamental interfacial magnetic phenomenon, which is key to current and future applications. The effect was discovered half a century ago, and it is well established that the spin structures at the FM/AFM interface play an essential role. However, currently, ad hoc phenomenological anisotropies are often postulated without microscopic justification or sufficient experimental evidence to address magnetization-reversal behavior in exchange-bias systems. We advance toward a detailed microscopic understanding of the magnetic anisotropies in exchange-bias FM/AFM systems by showing that symmetry-breaking anisotropies leave a distinct fingerprint in the asymmetry of the magnetization reversal and we demonstrate how these emerging anisotropies are correlated with the intrinsic anisotropy. Angular and vectorial resolved Kerr hysteresis loops from FM/AFM bilayers with varying degree of ferromagnetic anisotropy reveal a noncollinear anisotropy, which becomes important for ferromagnets with vanishing intrinsic anisotropy. Numerical simulations show that this anisotropy naturally arises from the inevitable spin frustration at an atomically rough FM/AFM interface. As a consequence, we show in detail how the differences observed for different materials during magnetization reversal can be understood in general terms as originating from the interplay between interfacial frustration and intrinsic anisotropies. This understanding will certainly open additional avenues to tailor future advanced magnetic materials.

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Section: Introductionmentioning

confidence: 99%

Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems

et al. 2009

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“…However, with decreasing particle size, the magnetic anisotropy energy per particle responsible for holding the magnetic moment along certain directions becomes comparable to the thermal energy. When this happens, the single-domain particles become non-magnetic (superparamagnetic) at the blocking temperature [8,9]. So, a fundamental question for nanoscale magnetic particles is to research the phase transition from the ferromagnetic to the superparamagnetic.…”

Section: Introductionmentioning

confidence: 99%

Phase transition from the ferromagnetic to superparamagnetic with a loop shift in 5-nm nickel particles

Liu

Huang

Zhou

et al. 2006

Journal of Magnetism and Magnetic Materials

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“…At temperatures above the Curie temperature, T C , the thermal energy, k B T, is sufficient to overcome the coupling forces so that the material becomes thermally unstable and exhibits paramagnetic behavior. [9] Superparamagnetism often observed in sub-20 nm single domain particles is different in that the material experiences random thermal fluctuations already at temperatures below T C . [10] In this work, the sol-gel synthesis of a series of large-pore mesoporous rare-earth iron garnet thin films through polymer templating of hydrated nitrate salt precursors is reported.…”

Section: Introductionmentioning

confidence: 99%

Room Temperature Magnetic Rare-Earth Iron Garnet Thin Films with Ordered Mesoporous Structure

et al. 2013

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Amphiphilic polymers are very attractive as porogens for the preparation of ordered mesoporous thin films and powders with pore sizes ranging from 40 down to a few nanometers in diameter because they are capable of both forming different superstructures and interacting with sol-gel precursors. In the present work, we report for the first time the synthesis of a series of highly crystalline rare-earth iron garnet (RE 3 Fe 5 O 12 , RE = Y, Gd-Dy) thin films with cubic networks of interconnected pores averaging 17 nm in diameter through facile polymer templating of hydrated nitrate salts. Despite intricate crystallization pathways, e.g., Y 3 Fe 5 O 12 via Y 4 Fe 2 O 9 and h-YFeO 3 , the nanoscale architecture of all these materials is only affected to a limited extent by solid-solid conversions at elevated temperatures.We specifically focus on the characterization of the morphology, microstructure and magnetic properties of polymer-templated Y 3 Fe 5 O 12 . This novel mesoporous material is single phase after heating to 900 °C, free of major structural defects and is also well-defined on the atomic level, as evidenced by a combination of in situ and ex situ scattering/diffraction techniques, electron microscopy, Raman and X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The high quality of the nanocrystalline Y 3 Fe 5 O 12 thin films with overall soft magnetic-like characteristics and moderate anisotropy is further confirmed by SQUID magnetometry measurements. The magnetization behavior in the temperature range 5-380 K well describes Bloch's T 3/2 law for a 3D Heisenberg-type ferromagnet.

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Overcoming thermal fluctuations

Cited by 76 publications

References 7 publications

Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems

Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems

Phase transition from the ferromagnetic to superparamagnetic with a loop shift in 5-nm nickel particles

Room Temperature Magnetic Rare-Earth Iron Garnet Thin Films with Ordered Mesoporous Structure

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