Reorientation, multidomain states and domain walls in diluted magnetic semiconductors

Bogdanov, A. N.; Dragunov, I. E.; Rößler, U.

doi:10.1016/j.jmmm.2007.02.089

Cited by 3 publications

(5 citation statements)

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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%

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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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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Magnetic Anisotropy at Nanoscale

Gutowski

2011

Journal of Nanotechnology

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“…The model from Eq. ( 9) has also proved to be valid for diluted magnetic semiconductors as a novel class of magnetic materials [9,10,11,48]. The invariance of the potential Eq.…”

Section: Reorientation Transitions and Metastable Statesmentioning

confidence: 95%

“…In section II we introduce the phenomenological model and methods; in the next section we derive all possible magnetic configurations in the system, calculate their stability limits, and describe reorientation effects [42,47,48]. These results enable us to calculate the parameters of the multidomain states and analyse the magnetization processes (section IV).…”

Section: Introductionmentioning

confidence: 99%

Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies

Leonov

Rößler

Bogdanov

2008

Journal of Applied Physics

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The interplay between intrinsic and surface/interface-induced magnetic anisotropies strongly influences magnetization processes in nanomagnetic systems. We develop a micromagnetic theory to describe the field-driven reorientation in nanomagnets with cubic and uniaxial anisotropies. Spin configurations in competing phases and parameters of accompanying multidomain states are calculated as functions of the applied field and the magnetic anisotropies. The constructed magnetic phase diagrams allow to classify different types of the magnetization reversal and to provide detailed analysis of the switching processes in magnetic nanostructures. The calculated magnetization profiles of isolated domain walls show that the equilibrium parameters of such walls are extremely sensitive to applied magnetic field and values of the competing anisotropies and can vary in a broad range. For nanolayers with perpendicular anisotropy the geometrical parameters of stripe domains have been calculated as functions of a bias field. The results are applied to analyse the magnetization processes as observed in various nanosystems with competing anisotropies, mainly, in diluted magnetic semiconductor films (Ga,Mn)As. 75.50.Ee,

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“…Application of the presented model will also be relevant when considering electronic circuits where the local magnetic field play a significant role in certain cases [14,15].…”

Section: Implications Of the Modelmentioning

confidence: 99%

Demagnetizing effects in stacked rectangular prisms

Christensen¹,

Nielsen²,

Bahl³

et al. 2011

J. Phys. D: Appl. Phys.

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Abstract.A numerical, magnetostatic model of the internal magnetic field of a rectangular prism is extended to the case of a stack of rectangular prisms. The model enables the calculation of the spatially resolved, three-dimensional internal field in such a stack given any magnetic state function, stack configuration, temperature distribution and applied magnetic field. In this paper the model is applied to the case of a stack of parallel, ferromagnetic rectangular prisms and the resulting internal field is found as a function of the orientation of the applied field, the number of prisms in the stack, the spacing between the prisms and the packing density of the stack. The results show that the resulting internal field is far from being equal to the applied field and that the various stack configurations investigated affect the resulting internal field significantly and non-linearly. The results have a direct impact on the design of, e.g., active magnetic regenerators made of stacked rectangular prisms in terms of optimizing the internal field.PACS numbers: 75.30. Sg,75.60.Ej,41.20.Gz Demagnetizing effects in stacked rectangular prisms 2

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Reorientation, multidomain states and domain walls in diluted magnetic semiconductors

Cited by 3 publications

References 12 publications

Magnetic Anisotropy at Nanoscale

Magnetic Anisotropy at Nanoscale

Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies

Demagnetizing effects in stacked rectangular prisms

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