Quantum ignition of deflagration in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mn>8</mml:mn></mml:msub></mml:math>molecular magnet

Leviant, Tom; Keren, Amit; Zeldov, E.; Myasoedov, Y.

doi:10.1103/physrevb.90.134405

Cited by 5 publications

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“…In a magnetic relaxation process there is a competition between heat produced by the reversing spins and heat diffused throughout the sample and the bath; if the diffusion cannot compensate the reaction term, the process becomes unstable and some magnetic materials [23,27,28] experience a transition between thermal relaxation and a fast-propagating spin-reversal process named magnetic deflagration [19]. Additionally Leviant et al [29] have recently shown that magnetic deflagration might also occur in Fe 8 crystals.…”

Section: Discussionmentioning

confidence: 99%

Spin reversal in Fe₈under fast pulsed magnetic fields

et al. 2015

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We report measurements on magnetization reversal in the Fe 8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s −1 and in the temperature range of 0.6-4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ∼4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability-a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability. ⊥ , does not affect the resonance values nH R .In this letter we investigate the temperature dependence of the magnetization reversal in the Fe 8 molecular magnet under fast pulsed magnetic fields of 1.5 kT s −1 . This fast sweep rate allows observation of quantum tunneling of the magnetic moment at high temperatures up to ∼ 4 K. The measurements of spin dynamics are modeled with thermally-activated quantum tunneling transitions accounting for the self-heating that might result in a magnetic deflagration [19]. Experimental set-upA single crystal of Fe 8 molecular magnet with dimensions approximately 1 × 0.15 × 0.27 mm was used for the present investigation. The sample was embedded in stycast, which was pored in a cylindrical mould (but it did not change its plate-like shape). This process allowed us to align the crystal with the applied magnetic field (minor misalignments, ∼5 degrees, may occur).Pulsed magnetic field measurements of 1.5 kT s −1 were performed at the Pulsed Fields facility of the Katholic University of Leuven, Belgium. A coil with an inductance of 650 μH was used to generate magnetic field pulse. This facility allowed us to go up to 70 T with pulse duration of 20 ms by discharging the capacitor bank through a specially designed magnet coil [20].Magnetization reversal was detected using a compensated coil (see figure 1(a)), which was done by tuning the number of inner and outer windings. The compensated coil was sensitive to the signal coming from the sample and insensitive to the signal coming from the applied pulses. Low temperatures down to 0.6 K were achieved using a He 3 cryostat. The sample holder was made of non-metallic materials and was submerged in liquid He 3 during the measurements. The temperature was varied in the range between 0.6 and 4.1 K by pumping the helium with control through a needle valve.The crystal was initially magnetized to negative saturation at a fix bath temperature. Then we swept the magnetic field at an ultra fast rate of 1.5 kT s −1 , so the Fe 8 crystal is in a non-equilibrium magnetization state, as shown in figure 1(b). We recorded the signals of the compensated coil during the complete field sweep. The magnitude of the peak voltage captured with the coils, V, i...

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Section: Discussionmentioning

confidence: 99%

Spin reversal in Fe₈under fast pulsed magnetic fields

et al. 2015

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“…In Fe 8 , only three transitions are observed. Therefore the effective barrier height is taken as the energy difference between m = −10 to m = −7 for the matching field of the n = 1 transition where deflagration was found, namely U = 10 K. Additionally, v ∼ 1 m/s and κ ∼ 2 × 10 −6 m 2 /s are known from previous measurements on particular samples that happen to show deflagration 6 . This gives T f = 2.5 K, in good agreement with our measurement.…”

Section: Figmentioning

confidence: 99%

“…The inset is raw hysteresis loop data taken from Ref. 6 from which the magnetization jumps are derived.…”

Section: Figmentioning

confidence: 99%

“…The Zeeman term removes the degeneracy between S z = ±m and allows the spins of all molecules to align at sufficiently low temperatures. Upon sweeping of the magnetic field from H 0 to −H 0 , the samples magnetization versus field curve exhibits a staircase hysteresis loop 6 . This is attributed to quantum tunneling between magnetization states, which is only allowed for discrete 'matching fields' corresponding to level crossings [7][8][9][10] .…”

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Temperature changes of the Fe8 molecular magnet during its spin reversal process

Yaari

Keren

2017

Phys. Rev. B

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Tunneling of the spins in the Fe8 molecular magnet from a metastable ground state to an excited state is accompanied by a decay of these spins to the global ground state, and an increase of the crystal temperature. We measured this temperature using two thermometers, one strongly coupled and the other weakly coupled to the thermal bath. We found that the temperature increases to no greater than 2.2 K. This upper limit agrees with the flame temperature derived from deflagration theory and previous measurements. In light of this temperature increase we re-examine the Landau, Zener and Stuckelberg (LZS) theory of spin tunneling in large Fe8 crystals.The Fe 8 single molecular magnet is an exciting system to study since its dynamics are fully quantum mechanical below a temperature of 400 mK1 . This molecule has a spin of S = 10, and accounting for the crystal-field together with the spin-orbit interaction, it is governed by the spin Hamiltonian 2 :where the dominating S 2 z term with D = −0.295 K gives rise to an anisotropy barrier [3][4][5] . The H ⊥ term is responsible for the mixing of spin states and tunneling between them. The Zeeman term removes the degeneracy between S z = ±m and allows the spins of all molecules to align at sufficiently low temperatures. Upon sweeping of the magnetic field from H 0 to −H 0 , the samples magnetization versus field curve exhibits a staircase hysteresis loop 6 . This is attributed to quantum tunneling between magnetization states, which is only allowed for discrete 'matching fields' corresponding to level crossings 7-10 . The matching fields for transitions between the states m to m are given by:where n = m + m 7 . Due to H ⊥ the level crossing is in fact an avoided crossing with a tunnel splitting ∆ mm between the m and m levels. According to the Landau, Zener and Stuckelberg [LZS] solution 11-13 of the time dependent Schrödinger equation for a multistate system, the probability for transition between two states, when the external field is in the vicinity of a matching field is given by:where for an isolated spin However, upon sweeping the field at low temperatures, the transitions occur between a metastable spin state (say m = −10), and either a ground state (m = 10) or an excited state (e.g. m = 9). We name these transitions according to their n value. For n ≥ 1 these transitions are accompanied by a decay to the stable ground state (e.g. 9 → 10), leading to an energy release and a temperature increase. According to the spin Hamiltonian, the lowest energy difference between a metastable state and the ground state is approximately 5 K. Therefore, the decay should lead to substantial heating of the crystal and affect the transition rates. In these circumstances the LZS formula will not be applicable for all transitions other then n = 0, namely ±10 to ∓10. Therefore, to properly account for the tunneling probability of general molecular magnets embedded in a crystal and Fe 8 in particular, it is essential to determine how hot the crystal gets after a tunneling event that is foll...

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“…Magnetic deflagration has only been demonstrated to occur in a small number of systems, such as during spin reversal in highly anisotropic molecule magnets-Mn 12 -ac (see for instance [3,6,7]; see [4] for a review) and Fe 8 [8,9]-, in metamagnetic phase-transitions in manganites-La x Pr y Ca 1-x-y MnO 3 [10]-, and in structural magnetic phase-transitions in intermetallic compounds-Gd 5 Ge 4  [11,12].…”

Section: Introductionmentioning

confidence: 99%

Multiphase magnetic deflagrations in a Nd₅Ge₃single crystal

et al. 2017

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We report magnetic deflagration phenomena ocurring in both antiferromagnetic and ferromagnetic phases in a single crystal of the intermetallic compound Nd 5 Ge 3 . We have investigated, using a trigger heat pulse, the spatial and time-resolved evolution of induced magnetic avalanches as a function of the applied magnetic field. The experimental data fit well with the theory of magnetic deflagration.

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Quantum ignition of deflagration in theFe8molecular magnet

Cited by 5 publications

References 28 publications

Spin reversal in Fe₈under fast pulsed magnetic fields

Spin reversal in Fe₈under fast pulsed magnetic fields

Temperature changes of the Fe8 molecular magnet during its spin reversal process

Multiphase magnetic deflagrations in a Nd₅Ge₃single crystal

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Quantum ignition of deflagration in theFe8molecular magnet

Cited by 5 publications

References 28 publications

Spin reversal in Fe8under fast pulsed magnetic fields

Spin reversal in Fe8under fast pulsed magnetic fields

Temperature changes of the Fe8 molecular magnet during its spin reversal process

Multiphase magnetic deflagrations in a Nd5Ge3single crystal

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Spin reversal in Fe₈under fast pulsed magnetic fields

Spin reversal in Fe₈under fast pulsed magnetic fields

Multiphase magnetic deflagrations in a Nd₅Ge₃single crystal