Spin dynamics of magnetic nanoparticles: Beyond Brown’s theory

Nowak, Ulrich; Mryasov, O. N.; Wieser, Robert; Guslienko, K. Yu.; Chantrell, R.W.

doi:10.1103/physrevb.72.172410

Cited by 85 publications

(67 citation statements)

References 25 publications

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“…K is the anisotropy energy per atom, i.e., the energy barrier to reversal for a single atom, equal to equal to the quantum threshold given by Eq. (13). Note that this threshold is independent of the number of atoms in the magnetic object.…”

Section: A Effect Of the Longitudinal Anisotropy ( D = 0 E = 0)mentioning

confidence: 96%

“…The development of spin-polarized scanning tunneling microscopy (SP-STM) led to detailed observations of the thermally induced magnetic switch in small ferromagnets, allowing a detailed test of the global rotation of the Néel-Brown view and of its limits. [3][4][5][6][7][8][9][10] In parallel, analyses led to the discussion of other views of the thermally activated magnetization switch, [10][11][12][13][14][15][16][17] for example, spin-wave contributions, nucleation, edge effects, and anisotropy effect. Following earlier works on multilayered materials, 18,19 SP-STM experiments revealed that injection of spin-polarized electrons into a nanoferromagnet could also switch its magnetization.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic reversal of a quantum nanoferromagnet

Gauyacq

Lorente

2013

Phys. Rev. B

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When the external magnetic field applied to a ferromagnetically coupled atomic chain is reversed suddenly, the magnetization of the chain switches, due to the reversal of all the atomic magnetic moments in the chain. The quantum processes underlying the magnetization switching and the time required for the switching are analyzed for model magnetic chains adsorbed on a surface at 0 K. The sudden field reversal brings the chain into an excited state that relaxes towards the system ground state via interactions with the substrate electrons. Different mechanisms are outlined, ranging from the global stepwise rotation of the chain macrospin induced by spin-flip collisions with substrate electrons in the pure Heisenberg chain (Néel-Brown process) to a correlation-mediated direct switching process in the presence of strong magnetic anisotropies in short chains (the global spin of the chain reverses in a single electron interaction). The processes for magnetization switching induced by electrons tunneling from a scanning tunneling microscope tip are also analyzed.

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Section: A Effect Of the Longitudinal Anisotropy ( D = 0 E = 0)mentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Magnetic reversal of a quantum nanoferromagnet

Gauyacq

Lorente

2013

Phys. Rev. B

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“…Two further models that connect to the transport properties, a shift of the chemical potential Similar to micromagnetic models gaining high predictive power and becoming an indispensable tool for nanomagnetism 112 in the last decade, thermal models, meanwhile, reach predictive power for ultrafast experiments. 113 For example, it will be possible to optimize writing asymmetries in all-optical writing experiments to reduce fluence thresholds in the future. The role of spin wave or spin-cluster fluctuations in the characteristic response of the ferromagnet has been suggested in early 2007 in parallel by different groups by atomistic, 114 thermal macrospin, 115,116 or simple micromagnetic spin-fluctuation 117 models.…”

Section: Theoretical Perspectivesmentioning

confidence: 99%

Perspective: Ultrafast magnetism and THz spintronics

Walowski

Münzenberg

2016

Journal of Applied Physics

336

205

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This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now. Published by AIP Publishing. [http://dx

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“…In the former, a suitable simplification of the exchange interaction in a magnetic solid is to express it through the Heisenberg Hamiltonian H xc = − α>β J αβ S α · S β , where the J αβ are exchange constants and S α is the atomic spin on atom α. Using this Hamiltonian to express the exchange field leads to LandauLifshitz-Gilbert equations of motion for the dynamics of atomic moments (see, e.g., [74][75][76]). …”

Section: Exchange Field and Nonlocal Contributionsmentioning

confidence: 99%

Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics

2016

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Starting from the Dirac-Kohn-Sham equation we derive the relativistic equation of motion of spin angular momentum in a magnetic solid under an external electromagnetic field. This equation of motion can be rewritten in the form of the well-known Landau-Lifshitz-Gilbert equation for a harmonic external magnetic field, and leads to a more general magnetization dynamics equation for a general time-dependent magnetic field. In both cases with an electronic spin-relaxation term which stems from the spin-orbit interaction. We thus rigorously derive, from fundamental principles, a general expression for the anisotropic damping tensor which is shown to contain an isotropic Gilbert contribution as well as an anisotropic Ising-like and a chiral, Dzyaloshinskii-Moriya-like contribution. The expression for the spin relaxation tensor comprises furthermore both electronic interband and intraband transitions. We also show that when the externally applied electromagnetic field possesses spin angular momentum, this will lead to an optical spin torque exerted on the spin moment.

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Spin dynamics of magnetic nanoparticles: Beyond Brown’s theory

Cited by 85 publications

References 25 publications

Magnetic reversal of a quantum nanoferromagnet

Magnetic reversal of a quantum nanoferromagnet

Perspective: Ultrafast magnetism and THz spintronics

Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics

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