Phenomenological theory of Bloch point relaxation

Галкина, Е. Г.; Иванов, Б. А.; Stephanovich, V. A.

doi:10.1016/0304-8853(93)90441-4

Cited by 56 publications

(42 citation statements)

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“…The propagating Bloch point (BP) dissolves simultaneously both the vortex and the antivortex structure. In the continuum theory of micromagnetism, a BP can be defined as a region inside a ferromagnet, where the magnetization collapses to zero [24]. On a shell that encloses the BP, any magnetization direction can be found [23].…”

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confidence: 99%

“…Compared to the typical speed of BPs driven by external fields, this value is unusually high. Because of their vanishing net magnetization, the mobility of BPs is typically very low [24,26]. Here the low BP mobility is compensated by the fact that the BP is driven by the strong exchange field, with typical values on the order of 100 T, resulting in a high BP speed.…”

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Exchange Explosions: Magnetization Dynamics during Vortex-Antivortex Annihilation

2006

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A magnetic vortex and an antivortex can annihilate, resulting in a homogeneous magnetization. A detailed description of the magnetization dynamics of such annihilation processes is obtained by micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. We show that, depending on the relative polarization of the vortex-antivortex pair, the annihilation process is either a continuous transformation of the magnetic structure or it involves the propagation of a micromagnetic singularity (Bloch point) causing a burstlike emission of spin waves. These results provide new insight into a fundamental micromagnetic process that has recently been proposed for a controlled generation of spin waves. DOI: 10.1103/PhysRevLett.97.177202 PACS numbers: 75.40.Gb, 75.40.Mg, 75.75.+a Magnetic vortices in ferromagnets are regions of typically just a few nanometers size, with a core around which the magnetization circulates. Up to a few years ago, such magnetic vortices were considered mainly as a topological detail of magnetic flux-closure patterns [1]. It was found that vortices inevitably occur in singly connected samples with magnetic flux-closure patterns and that they may be located, e.g., at the junctions of magnetic domains [2]. In the wake of the recent dramatic progress in nanomagnetism, static and dynamic properties of submicrometer-sized particles have been extensively studied, and the tiny magnetic vortices and particularly their dynamic properties have moved into the focus of interest [3][4][5][6][7] The counterpart of a magnetic vortex is a magnetic structure with similar properties, known as an antivortex. Both vortex and antivortex have a magnetic core which is magnetized perpendicular to the plane. A vortex and an antivortex can annihilate when they meet [8,9]. Besides the fact that the annihilation is connected with an emission of spin waves [10], not much is known about the magnetization dynamics of a vortex-antivortex annihilation process. We have studied the annihilation of a vortex and an antivortex with finite-element micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. These simulations yield a detailed description of this previously unexplored fundamental magnetization process. The results reveal the process to strongly depend on the relative orientation of the core magnetization of both the vortex and the antivortex. Particularly, if the vortex and antivortex cores are antiparallel to each other, the annihilation process involves the propagation of a Bloch point, which causes a burstlike dissipation of exchange energy (''exchange explosion'') via spin waves. Considering the proposed use of magnetic vortices in data storage and magnetologic approaches [5,11,12], a good control of the dynamic behavior will be mandatory. Understanding the annihilation dynamics of vortices and antivortices is, therefore, an important step towards a precise description of the complicated dynamic magnetization processes involving the temporary formation of vortices.The similarities and differen...

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Exchange Explosions: Magnetization Dynamics during Vortex-Antivortex Annihilation

2006

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“…Its effect on the stationary motion of the BL and BP results in finite values of the mobility of the DW structural inhomogeneities, causing negligibly small additions to their effective masses [1,6,7]. However, in yttrium-iron garnets, where the viscosity is due to an exchange relaxation of the magnetization vector [17], the viscosity can considerably affect the BP dynamics [18]. Therefore, in these materials it is necessary to consider some given factor in the determining of the BP effective mass.…”

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confidence: 99%

A general formalism for the determination of the effective mass of the nanoscale structural inhomogeneities of the domain wall in uniaxial ferromagnets

Shevchenko¹,

Barabash²

2016

Nano Online

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On the basis of the method of gyrotropic Thiele forces, we build a formalism that allows the determination of the effective mass of the nanoscales structural elements of the domain wall (DW): vertical Bloch line and Bloch point in uniaxial ferromagnets. As shown, the effective mass of these magnetic inhomogeneities depends on the value of the gyrotropic domain wall bend that is created by their movement.

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“…The LLBar equations are well suited for description of non-uniform states, like magnetic solitons [14,15] and Bloch points [16], and give the explanation of the reversal effects [17,18]. These equations provide an explanation of recent experiments on magnetization recovery in laserpumped Ni-Ru-Fe heterostructures [19], where the importance of the nonlocal character of the magnetization recovery is established [13].…”

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confidence: 99%

Relaxation of Strongly Suppressed Modulus of Magnetization Following Ultrafast Demagnetization

Yastremsky¹

2016

Metallofiz. Noveishie Tekhnol.

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A longitudinal nonlinear relaxation of magnetization following the ultrafast demagnetization is considered. As demonstrated, the fastest regime occurs for a small deviation of the magnetization from the equilibrium value. However, the relaxation time of strongly suppressed magnetization is substantially increased due to a nonlinearity of magnetic system.Розглянуто поздовжню нелінійну релаксацію намагнетованости після надшвидкого знемагнетування. Найшвидший режим релаксації реалізу-ється за малих відхилів намагнетованости від свого рівноважного стану. Однак характерний час релаксації сильно знемагнетованої системи істот-но збільшується за рахунок нелінійности магнетної системи.Рассмотрена продольная нелинейная релаксация намагниченности после сверхбыстрого размагничивания. Наиболее быстрый режим релаксации реализуется при небольших отклонениях намагниченности от своего рав-новесного состояния. Однако характерное время релаксации сильно раз-магниченной системы существенно увеличивается за счёт нелинейности магнитной системы.

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Phenomenological theory of Bloch point relaxation

Cited by 56 publications

References 2 publications

Exchange Explosions: Magnetization Dynamics during Vortex-Antivortex Annihilation

Exchange Explosions: Magnetization Dynamics during Vortex-Antivortex Annihilation

A general formalism for the determination of the effective mass of the nanoscale structural inhomogeneities of the domain wall in uniaxial ferromagnets

Relaxation of Strongly Suppressed Modulus of Magnetization Following Ultrafast Demagnetization

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