Nonlinear spin dynamics in ferromagnets with electron-nuclear coupling

2005

Phys. Rev. B

Self Cite

119

A general theory is developed for describing the nonlinear relaxation of spin systems from a strongly nonequilibrium initial state, when, in addition, the sample is coupled to a resonator. Such processes are characterized by nonlinear stochastic differential equations. This makes these strongly nonequilibrium processes principally different from the spin relaxation close to an equilibrium state, which is represented by linear differential equations. The consideration is based on a realistic microscopic Hamiltonian including the Zeeman terms, dipole interactions, exchange interactions, and a single-site anisotropy. The influence of cross correlations between several spin species is investigated. The critically important function of coupling between the spin system and a resonant electric circuit is emphasized. The role of all main relaxation rates is analyzed. The phenomenon of self-organization of transition coherence in spin motion, from the quantum chaotic stage of incoherent fluctuations, is thoroughly described. Local spin fluctuations are found to be the triggering cause for starting the spin relaxation from an incoherent nonequilibrium state. The basic regimes of collective coherent spin relaxation are studied.Comment: Latex file, 31 page

Section: Influence Of Cross Correlationsmentioning

confidence: 99%

Nonlinear spin relaxation in strongly nonequilibrium magnets

2005

Phys. Rev. B

Self Cite

119

“…All this machinery has been thoroughly described in Refs. [56,57] and its use has been demonstrated for studying the dynamics of magnetic systems [58][59][60].…”

Section: Analytical Solutionmentioning

confidence: 99%

Ultrafast polarization switching in ferroelectrics

Yukalova

2019

Phys. Rev. Research

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“…(6) varies between 10 and 100. As has been shown [21,22], if nuclear spins are inside a ferromagnet or ferrimagnet, possessing long-range magnetic order, then the coupling parameter g can be increased by a factor of µ B /µ N ∼ 10 3 , where µ B is the Bohr magneton and µ N is the nuclear magneton. Therefore, the coupling parameter g can be made as large as g ∼ 10 5 .…”

mentioning

confidence: 93%

Processing Information by Punctuated Spin Superradiance

Yukalova

2002

Phys. Rev. Lett.

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The possibility of realizing the regime of punctuated spin superradiance is advanced. In this regime, the number of superradiant pulses and the temporal intervals between them can be regulated. This makes it feasible to compose a kind of the Morse Code alphabet and, hence, to develop a technique of processing information. 76.20.+q, 76.60.Es, 07.55.Yv, 85.90.+h Spin systems can exhibit a phenomenon that is analogous to atomic superradiance [1,2], because of which it is called spin superradiance. To realize this phenomenon, spin systems, similarly to atomic ones, are to be prepared in an inverted state. This is achieved by placing a polarized spin sample in an external magnetic field directed opposite to spin polarization. Contrary to atomic systems, coherent spin motion develops not owing to direct spin correlations but due to the interaction of spins with a resonator feedback field, for which purpose the spin sample has to be coupled with a resonant electric circuit, whose natural frequency is tuned to the Zeeman frequency of spins [3]. More details on similarities and differences between atomic superradiance and spin superradiance can be found in the review [4]. Spin superradiance is the process of coherent spontaneous emission by moving spins. As in the case of atomic systems, one may distinguish two main types of this phenomenon, transient superradiance and pulsing superradiance. Transient spin superradiance occurs when the spin sample is prepared in the inverted state, after which no following pumping is involved. In this case, a single superradiant burst arises, peaked at the delay time. Pulsing spin superradiance is radically different from the transient regime by the occurrence of a series of superradiant pulses, for which the spin sample is to be subject to a permanent pumping supporting the inverted spin polarization. Both regimes of spin superradiance, transient [5][6][7][8] as well as pulsing [9][10][11] were observed in experiments with different materials containing nuclear spins. A microscopic theory of these phenomena, based on realistic spin Hamiltonians, was developed [12][13][14][15], being in good agreement with experiment and with computer modelling [16]. It is worth stressing that only by invoking microscopic Hamiltonians it has become possible to give an accurate description of purely self-organized regimes which cannot be treated by the phenomenological Bloch equations [12][13][14].In the present paper, we advance the possibility of realizing the third type of spin superradiance, which we call punctuated spin superradiance, and which is principally different from the transient and pulsing types. In this regime, unlike the transient case, not a single but many superradiant bursts can be produced. In distinction to the pulsing regime, where the number of pulses and the temporal distance between them are prescribed by a given setup and cannot be varied, in the process of punctuated superradiance both the number of superradiant bursts as well as time intervals between each pair of them can ...