Discovery of Dicke Superradiation by System of Nuclear Magnetic Moments

Encyclopedia of Magnetic Resonance

2007

Moscow. First involved with NMR related research in 1984, after starting his work at JINR in Dubna, where together with an experimental group he took part in the first observation of pure nuclear spin superradiance. Then developed a microscopic theory of this phenomenon. Received the First Prize of Joint Institute for Nuclear Research for the discovery and theory of nuclear spin superradiance in 2001. Pubslished 250 papers and 4 books. Current research interests: developing the theory of spin superradiance for including novel materials, and for finding new applications.

Section: Transient Superradiancesupporting

confidence: 53%

“…The first observation of pure spin superradiance was accomplished in Dubna 11,12 . A dielectric propanediol C 3 H 8 O 2 , with a paramagnetic admixture of Cr 5+ , was used as an active substance.…”

Section: Experimental Observationmentioning

confidence: 99%

Nuclear Spin Superradiance

Encyclopedia of Magnetic Resonance

2007

“…In resonance experiments, it enhances the NMR signals [16][17][18]. For strongly nonequilibrium systems of polarized nuclei, it leads to fast magnetization reversal [23][24][25][26][27] that has been discovered in experiments [23] and later confirmed in other experimental studies (see references in the review article [4]). …”

Section: Introductionmentioning

confidence: 73%

Optimal conditions for magnetization reversal of nanocluster assemblies with random properties

Kharebov

Henner

Journal of Applied Physics

2013

Magnetization dynamics in the system of magnetic nanoclusters with randomly distributed properties are studied by means of computer simulations. The main attention is paid to the possibility of coherent magnetization reversal from a strongly nonequilibrium state with a mean cluster magnetization directed opposite to an external magnetic field. Magnetic nanoclusters are known to be characterized by large magnetic anisotropy and strong dipole interactions. It is also impossible to produce a number of nanoclusters with identical properties. As a result, any realistic system of nanoclusters is composed of the clusters with randomly varying anisotropies, effective spins, and dipole interactions. Despite this randomness, it is possible to find conditions when the cluster spins move coherently and display fast magnetization reversal due to the feedback action of resonator. By analyzing the influence of different cluster parameters, we find their optimal values providing fast magnetization reversal.

“…Thus, it was observed on proton spins in propanediol C 3 H 8 O 2 , butanol C 4 H 9 OH, and ammonia NH 3 [5][6][7][8] and on 27 Al nuclear spins in ruby Al 2 O 3 [9][10][11]. The characteristic parameters for these experiments with nuclear spins are: the density of spins…”

mentioning

confidence: 99%

“…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 . Among other materials, where spin superradiance could, in principal, be observed, are granular magnets [23] and molecular magnets [24].…”

mentioning

confidence: 99%

Processing Information by Punctuated Spin Superradiance

Yukalova

2002

Phys. Rev. Lett.

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 ...