Electromagnetic radiation emanating from the molecular nanomagnet<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Fe</mml:mtext></mml:mrow><mml:mn>8</mml:mn></mml:msub></mml:mrow></mml:math>

Shafir, Oren; Keren, Amit

doi:10.1103/physrevb.79.180404

Cited by 12 publications

(10 citation statements)

References 28 publications

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“…With this experiment we can not detect photon emission and can not reproduce the results that were reported previously 1 . We conclude that energy is released after tunneling in Fe 8 only in the form of thermal energy.…”

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Testing the radiation emanating from the molecular nanomagnetFe8during magnetization reversals

et al. 2014

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In the molecular nanomagnet Fe8 tunneling can occur from a metastable state to an excited state followed by a transition to the ground state. This transition is accompanied by an energy release of 115.6 GHz. We constructed an experimental setup to measure whether this energy is released in the form of thermal or electromagnetic energy. Contrary to a previous publication we find no evidence for release of electromagnetic radiation. Our results for transitions between the first and second excited states to the ground state are consistent with a release of only thermal energy. This energy release extends for a longer time for the second excited state than for the first excited state.While investigating the Fe 8 mononuclear magnet Shafir and Keren 1 made a serendipitous observation; tunneling events where accompanied by a jump in the temperature of a thermometer placed far from the sample and attached directly to the mixing chamber of a dilution refrigerator (DR). When the line of site between the thermometer and sample was blocked, the tunneling signal remained, but the temperature jumps disappeared. This led to the conclusion that energy bursts accompany the tunneling event and arrive at the thermometer in the form of electromagnetic radiation. In order to block the line of site the DR had to warm up and cool down again. Therefore, the test experiment was not done simultaneously with main experiment. Here we revisit the same phenomena, but with an experimental setup designed to detect photons in the microwave range, and with a test experiment done simultaneously with the photon detection.At low temperature, the molecules are described by the Hamiltonian H = −DS 2 z + gµ B S z H + H where S = 10 is the spin, D = 0.292K is the anisotropy parameter, H is the applied magnetic field, µ B is the Bohr magneton, g ≈ 2 is the gyromagnetic factor, and H does not commute with S z and is responsible for tunneling between spin projection states m 2,3 . When the field is strong (∼ ∓1 T) only the m = ±S are populated. When the field is swept across zero and changes sign, the m = ±S state becomes metastable. At matching fields, which are separated by 0.225 T 4,5 , quantum tunneling of magnetization (QTM) can take place from m = ±S to an m = ∓(S − n) state, where n = 0, 1, 2 . . . is an excited state index. For n > 0, the excited m state decays spontaneously to the ground state ∓S and energy is emitted. For n = 1 this energy corresponds to a frequency of 115.6 GHz or wavelength of 2.6 mm and for n = 2 it corresponds to a frequency of 219 GHz. Interestingly, we found (see below) that the heat is released for a longer time from the second excited (n = 2) state than from the first one (n = 1).The experiment is preformed below 0.2 K in order to have temperature independent quantum tunneling 4,5 .

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Testing the radiation emanating from the molecular nanomagnetFe8during magnetization reversals

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“…Intense bursts of radiation have indeed been detected experimentally during magnetic avalanches. There has been much speculation that this could be Dicke superradiance, but experiments have been inconclusive on this very interesting issue [48][49][50][51][52][53].…”

Section: Cold Deflagrationmentioning

confidence: 99%

Magnetic Avalanches in Molecular Magnets

Sarachik

2014

NanoScience and Technology

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Abstract. The reversal of the magnetization of crystals of molecular magnets that have a large spin and high anisotropy barrier generally proceeds below the blocking temperature by quantum tunneling. This is manifested as a series of controlled steps in the hysteresis loops at resonant values of the magnetic field where energy levels on opposite sides of the barrier cross. An abrupt reversal of the magnetic moment of the entire crystal can occur instead by a process commonly referred to as a magnetic avalanche, where the molecular spins reverse along a deflagration front that travels through the sample at subsonic speed. In this chapter, we review experimental results obtained to date for magnetic deflagration in molecular nanomagnets.

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“…There is a direct similarity between the effective dipole interactions caused by the dipole vector potential (19) and the dipole [5][6][7][8][9][10][11] and hyperfine interactions [9][10][11]41,42] in spin systems, these interactions being treated as stochastic fluctuations playing destructive role by dephasing collective motion. While the effective pseudospin interactions, induced by the radiation potential (18) in quantum dots, are equivalent to the effective interactions produced by the resonator feedback field in spin systems [9][10][11].…”

Section: Stochastic Mean-field Approximationmentioning

confidence: 99%

Dynamics of quantum dot superradiance

Yukalov

Yukalova

2010

Phys. Rev. B

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The possibility of realizing the superradiant regime of electromagnetic emission by the assembly of quantum dots is considered. The overall dynamical process is analyzed in detail. It is shown that there can occur several qualitatively different stages of evolution. The process starts with dipolar waves triggering the spontaneous radiation of individual dots. This corresponds to the fluctuation stage, when the dots are not yet noticeably correlated with each other. The second is the quantum stage, when the dot interactions through the common radiation field become more important, but the coherence is not yet developed. The third is the coherent stage, when the dots radiate coherently, emitting a superradiant pulse. After the superradiant pulse, the system of dots relaxes to an incoherent state in the relaxation stage. If there is no external permanent pumping, or the effective dot interactions are weak, the system tends to a stationary state during the last stationary stage, when coherence dies out to a low, practically negligible, level. In the case of permanent pumping, there exists the sixth stage of pulsing superradiance, when the system of dots emits separate coherent pulses.

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Electromagnetic radiation emanating from the molecular nanomagnetFe8

Cited by 12 publications

References 28 publications

Testing the radiation emanating from the molecular nanomagnetFe8during magnetization reversals

Testing the radiation emanating from the molecular nanomagnetFe8during magnetization reversals

Magnetic Avalanches in Molecular Magnets

Dynamics of quantum dot superradiance

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