Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies

Leonov, A. A.; Rößler, U.; Bogdanov, A. N.

doi:10.1063/1.2996016

Cited by 13 publications

(13 citation statements)

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“…[21][22][23] Surface or interface anisotropies are expected to be significant for thin films, multilayers, and patterned structures, affecting their reversal process and remanent states. 20,24 Therefore, understanding the various contributions to anisotropy as a function of the dimensions of the thin film when it is patterned is the key to obtaining the desired anisotropy, whether it be perpendicular or in plane, in order to use these materials in a range of magnetic devices.…”

Section: Introductionmentioning

confidence: 99%

Shape and strain-induced magnetization reorientation and magnetic anisotropy in thin film Ti/CoCrPt/Ti lines and rings

Navas

Nam²,

Velázquez³

et al. 2010

Phys. Rev. B

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The contributions to the magnetic anisotropy of thin-film rings and lines of width 50 nm and above made from Ti͑5 nm͒ / Co 0.66 Cr 0.22 Pt 0.12 ͑10 and 20 nm͒/Ti ͑3 nm͒ with a perpendicular magnetocrystalline anisotropy are investigated, using magnetic force microscopy to image the ac-demagnetized state. Four regimes of behavior were observed in both lines and rings. Samples with the largest widths ͑Ͼ500 nm͒ showed an out-ofplane maze domain structure typical of unpatterned films with domain widths of ϳ200 nm. As the linewidth decreased, a "bamboo" domain structure forms in which the domain walls lie approximately perpendicular to the linewidth. Further linewidth decreases result in a reorientation to a net in-plane anisotropy perpendicular to the linewidth, and for the narrowest lines, Ͻ200-nm wide, the anisotropy reorients in plane parallel to the line. The evolution of anisotropy is modeled in terms of contributions from magnetocrystalline, shape, and first-and second-order magnetoelastic terms, and good agreement with experiment is obtained, considering both bulk and surface anisotropy contributions.

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Section: Introductionmentioning

confidence: 99%

Shape and strain-induced magnetization reorientation and magnetic anisotropy in thin film Ti/CoCrPt/Ti lines and rings

Navas

Nam²,

Velázquez³

et al. 2010

Phys. Rev. B

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“…INTRODUCTION Magnetization reversal of thin films has been an active research area during the past decades, both in theoretical [1][2][3][4][5][6][7][8][9][10][11][12] and experimental 4,13-57 studies. Hereby, a large number of experimental works have been performed using ultra-thin films of only a few atomic layer thickness 4,18,25,29,43 or multilayers, 37,38,41,47 including magnetically coupled multilayers, for which interesting and relevant collective phenomena occur.…”

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confidence: 99%

Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment

Idigoras

Suszka

Vavassori

et al. 2014

Journal of Applied Physics

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This work studies the influence of crystallographic alignment onto magnetization reversal in partially epitaxial Co films. A reproducible growth sequence was devised that allows for the continuous tuning of grain orientation disorder in Co films with uniaxial in-plane anisotropy by the controlled partial suppression of epitaxy. While all stable or meta-stable magnetization states occurring during a magnetic field cycle exhibit a uniform magnetization for fully epitaxial samples, non-uniform states appear for samples with sufficiently high grain orientation disorder. Simultaneously with the occurrence of stable domain states during the magnetization reversal, we observe a qualitative change of the applied field angle dependence of the coercive field. Upon increasing the grain orientation disorder, we observe a disappearance of transient domain wall propagation as the dominating reversal process, which is characterized by an increase of the coercive field for applied field angles away from the easy axis for well-ordered epitaxial samples. Upon reaching a certain disorder threshold level, we also find an anomalous magnetization reversal, which is characterized by a non-monotonic behavior of the remanent magnetization and coercive field as a function of the applied field angle in the vicinity of the nominal hard axis. This anomaly is a collective reversal mode that is caused by disorder-induced frustration and it can be qualitatively and even quantitatively explained by means of a two Stoner-Wohlfarth particle model. Its predictions are furthermore corroborated by Kerr microscopy and by Brillouin light scattering measurements.

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Section: Discussionmentioning

confidence: 99%

“…Recently many papers are devoted to rippled surfaces of diluted magnetic semiconductors (DMSs), with (Ga, Mn) As being probably the most frequently studied substance in this class [9,10]. The active area of research, both theoretical [11,12] and experimental [13], are competing anisotropies, uniaxial and tetragonal, present in thin layers of this compound.The rippled surfaces were approximated in the literature in many ways, usually as a train of sinusoidal waves as a periodic series of Gaussian-shaped peaks, or as a periodic set of flat islands. Here we propose yet another approach, namely, the rippled surface may be seen as being built by many identical, infinitely long-half cylinders, aligned parallel to each other.…”

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confidence: 99%

Magnetic Anisotropy at Nanoscale

Gutowski

2011

Journal of Nanotechnology

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Nanoscale objects often behave differently than their "normal-sized" counterparts. Sometimes it is enough to be small in just one direction to exhibit unusual features. One example of such a phenomenon is a very specific in-plane magnetic anisotropy observed sometimes in very thin layers of various materials. Here we recall a peculiar form of the free energy functional nicely describing the experimental findings but completely irrelevant and thus never observed in larger objects. Intriguing Experimental ObservationsIn [1] we find the experimentally observed in-plane magnetic anisotropy energy (MAE) diagrams for multilayer structure Cr(4)/Fe(2)/Cr(d Cr )/Fe(4)/Cr(2), where numbers are thicknesses of components, expressed in nm. The thickness of the middle Cr layer, d Cr , was varied in few nm range, and the complete structures were deposited on Si(100) substrate, covered with natural SiO 2 layer 1.5-2.0 nm thick. The substrate was not perfectly flat-as a result of ion beam erosion it was covered with quite well-ordered ripples (see atomic force microscopy (AFM) images of the substrates, Figure 1 in [1]). The metallic layers were deposited using molecular beam epitaxy (MBE) technique. Their transmission electron microscopy (TEM) cross-sections revealed mostly amorphous structure with small inclusions of polycrystalline character. The values of MAE were derived from hysteresis loop area observed while exciting field was oriented along successive in-plane directions.In principle, samples of this kind should not exhibit any in-plane magnetic anisotropy. This is indeed the case when the substrate is flat (see Figure 4(a) in [1]). On the rippled substrate, however, this is no longer true and the sample exhibits peculiar twofold in-plane anisotropy (coercive field, Figure 4(b) in [1], MAE-in Figure 4(c)). It is peculiar since it is not the uniaxial anisotropy: four maxima are visible instead of just two. The Surface Magnetic Anisotropy of a CylinderConsider the static configuration of individual spins located on a surface of a long (ideally: infinitely long), hollow ferromagnetic cylinder. In absence of any external field, one may expect that individual spins may adopt one of the two stable configurations:(i) they all may be aligned with C ∞ symmetry axis of a cylinder. This is the lowest exchange energy configuration; (ii) they all may be oriented perpendicularly to the above symmetry axis. Now the exchange energy is no longer at its global minimum. Nevertheless, such a configuration is stable since it realizes a local minimum of exchange energy.In the second case we may again distinguish two cases: either individual spins are aligned with local C 2 symmetry axis (there are infinitely many of them, each perpendicular to C ∞ ) thus pointing inwards or outwards of a cylinder and being perpendicular to the cylinder's surface, or they can be perpendicular to the local C 2 axis (laying on the cylinder's circumference), making a ring-shaped configuration and producing no net magnetization. It is easy to see that both of thos...

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Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies

Cited by 13 publications

References 77 publications

Shape and strain-induced magnetization reorientation and magnetic anisotropy in thin film Ti/CoCrPt/Ti lines and rings

Shape and strain-induced magnetization reorientation and magnetic anisotropy in thin film Ti/CoCrPt/Ti lines and rings

Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment

Magnetic Anisotropy at Nanoscale

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