Eugene M. Chudnovsky
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Eugene M. Chudnovsky has a total of 4 co-authors. Here are the top co-authors by number of shared publications:
- D. A. Garanin
Institut für Physik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany
2 shared publications - D. A. Garanin
Institut für Theoretische Physik Universität Hamburg Jungiusstr. 9 D-20355 Hamburg Germany
2 shared publications - D. A. Garanin
Department of Physics and Astronomy City University of New York Lehman College Bedford Park Boulevard West 10468-1589 Bronx New York
1 shared publication X. Martinez Hidalgo
Department of Physics and Astronomy City University of New York-Lehman College Bedford Park Boulevard West 10468-1589 Bronx New York
1 shared publication
Latest Publications
- Open Access
Quantum-Classical Escape-Rate Transition of a Biaxial Spin System with a Longitudinal Field: a Perturbative Approach
The quantum-classical transition of the escape rate of the spin model \cal H= -DS_z^2 - H_zS_z + B S_x^2 is investigated by a perturbative approach with respect to B [D. A. Garanin, J. Phys A {\bf 24}, L61 (1991)]. The transition is first order for B<B_c(H_z), the boundary line going to zero as B_c/D ~ 1 - H_z/(2SD) in the strongly biased limit. The range of the first-order transition is thus larger than for the model \cal H = -DS_z^2 - H_zS_z - H_x S_x studied earlier, where in the strongly biased case H_{xc}/(2SD) ~ [1-H_z/(2SD)]^{3/2}. The temperature of the quantum-classical transition, T_0, behaves linearly in the strongly biased case for both models: T_0 ~ 2SD - H_z.
Open AccessQuantum-Classical Escape-Rate Transition of a Biaxial Spin System with a Longitudinal Field: a Perturbative Approach
The quantum-classical transition of the escape rate of the spin model \cal H= -DS_z^2 - H_zS_z + B S_x^2 is investigated by a perturbative approach with respect to B [D. A. Garanin, J. Phys A {\bf 24}, L61 (1991)]. The transition is first order for B<B_c(H_z), the boundary line going to zero as B_c/D ~ 1 - H_z/(2SD) in the strongly biased limit. The range of the first-order transition is thus larger than for the model \cal H = -DS_z^2 - H_zS_z - H_x S_x studied earlier, where in the strongly biased case H_{xc}/(2SD) ~ [1-H_z/(2SD)]^{3/2}. The temperature of the quantum-classical transition, T_0, behaves linearly in the strongly biased case for both models: T_0 ~ 2SD - H_z.
- 1 February 1999
- Published by American Physical Society (APS) in Physical Review B
- Vol. 59 (5) , 3671-3674
Quantum-classical escape-rate transition of a biaxial spin system with a longitudinal field: A perturbative approach
The quantum-classical transition of the escape rate of the spin model is investigated by a perturbative approach with respect to B [D. A. Garanin, J. Phys A 24, L61 (1991)]. The transition is first order for the boundary line going to zero as in the strongly biased limit. The range of the first-order transition is thus larger than for the model studied earlier, where in the strongly biased case The temperature of the quantum-classical transition, behaves linearly in the strongly biased case for both models:- 1 February 1999
- Published by American Physical Society (APS) in Physical Review B
- Vol. 59 (5) , 3671-3674
Quantum-classical escape-rate transition of a biaxial spin system with a longitudinal field: A perturbative approach
The quantum-classical transition of the escape rate of the spin model is investigated by a perturbative approach with respect to B [D. A. Garanin, J. Phys A 24, L61 (1991)]. The transition is first order for the boundary line going to zero as in the strongly biased limit. The range of the first-order transition is thus larger than for the model studied earlier, where in the strongly biased case The temperature of the quantum-classical transition, behaves linearly in the strongly biased case for both models:- Open Access
Quantum-Classical Transition of the Escape Rate of a Uniaxial Spin System in an Arbitrarily Directed Field
The escape rate \Gamma of the large-spin model described by the Hamiltonian H = -DS_z^2 - H_zS_z - H_xS_x is investigated with the help of the mapping onto a particle moving in a double-well potential U(x). The transition-state method yields $\Gamma$ in the moderate-damping case as a Boltzmann average of the quantum transition probabilities. We have shown that the transition from the classical to quantum regimes with lowering temperature is of the first order (d\Gamma/dT discontinuous at the transition temperature T_0) for h_x below the phase boundary line h_x=h_{xc}(h_z), where h_{x,z}\equiv H_{x,z}/(2SD), and of the second order above this line. In the unbiased case (H_z=0) the result is h_{xc}(0)=1/4, i.e., one fourth of the metastability boundary h_{xm}=1, at which the barrier disappears. In the strongly biased limit \delta\equiv 1-h_z << 1, one has h_{xc} \cong (2/3)^{3/4}(\sqrt{3}-\sqrt{2})\delta^{3/2}\cong 0.2345 \delta^{3/2}, which is about one half of the boundary value h_{xm} \cong (2\delta/3)^{3/2} \cong 0.5443 \delta^{3/2}.The latter case is relevant for experiments on small magnetic particles, where the barrier should be lowered to achieve measurable quantum escape rates.Open AccessQuantum-Classical Transition of the Escape Rate of a Uniaxial Spin System in an Arbitrarily Directed Field
The escape rate \Gamma of the large-spin model described by the Hamiltonian H = -DS_z^2 - H_zS_z - H_xS_x is investigated with the help of the mapping onto a particle moving in a double-well potential U(x). The transition-state method yields $\Gamma$ in the moderate-damping case as a Boltzmann average of the quantum transition probabilities. We have shown that the transition from the classical to quantum regimes with lowering temperature is of the first order (d\Gamma/dT discontinuous at the transition temperature T_0) for h_x below the phase boundary line h_x=h_{xc}(h_z), where h_{x,z}\equiv H_{x,z}/(2SD), and of the second order above this line. In the unbiased case (H_z=0) the result is h_{xc}(0)=1/4, i.e., one fourth of the metastability boundary h_{xm}=1, at which the barrier disappears. In the strongly biased limit \delta\equiv 1-h_z << 1, one has h_{xc} \cong (2/3)^{3/4}(\sqrt{3}-\sqrt{2})\delta^{3/2}\cong 0.2345 \delta^{3/2}, which is about one half of the boundary value h_{xm} \cong (2\delta/3)^{3/2} \cong 0.5443 \delta^{3/2}.The latter case is relevant for experiments on small magnetic particles, where the barrier should be lowered to achieve measurable quantum escape rates. - Open Access
First- and Second-Order Transitions between Quantum and Classical Regimes for the Escape Rate of a Spin System
We have found a novel feature of the bistable large-spin model described by the Hamiltonian H = -DS_z^2 - H_xS_x.The crossover from thermal to quantum regime for the escape rate can be either first (H_x<SD/2) or second (SD/2<H_x<2SD) order, that is, sharp or smooth, depending on the strength of the transverse field. This prediction can be tested experimentally in molecular magnets like Mn_12Ac.
Open AccessFirst- and Second-Order Transitions between Quantum and Classical Regimes for the Escape Rate of a Spin System
We have found a novel feature of the bistable large-spin model described by the Hamiltonian H = -DS_z^2 - H_xS_x.The crossover from thermal to quantum regime for the escape rate can be either first (H_x<SD/2) or second (SD/2<H_x<2SD) order, that is, sharp or smooth, depending on the strength of the transverse field. This prediction can be tested experimentally in molecular magnets like Mn_12Ac.
- Open Access
Thermally Activated Resonant Magnetization Tunneling in Molecular Magnets: Mn_12Ac and others
The dynamical theory of thermally activated resonant magnetization tunneling in uniaxially anisotropic magnetic molecules such as Mn_12Ac (S=10) is developed.The observed slow dynamics of the system is described by master equations for the populations of spin levels.The latter are obtained by the adiabatic elimination of fast degrees of freedom from the density matrix equation with the help of the perturbation theory developed earlier for the tunneling level splitting [D. A. Garanin, J. Phys. A, 24, L61 (1991)]. There exists a temperature range (thermally activated tunneling) where the escape rate follows the Arrhenius law, but has a nonmonotonic dependence on the bias field due to tunneling at the top of the barrier. At lower temperatures this regime crosses over to the non-Arrhenius law (thermally assisted tunneling). The transition between the two regimes can be first or second order, depending on the transverse field, which can be tested in experiments. In both regimes the resonant maxima of the rate occur when spin levels in the two potential wells match at certain field values. In the thermally activated regime at low dissipation each resonance has a multitower self-similar structure with progressively narrowing peaks mounting on top of each other.
Open AccessThermally Activated Resonant Magnetization Tunneling in Molecular Magnets: Mn_12Ac and others
The dynamical theory of thermally activated resonant magnetization tunneling in uniaxially anisotropic magnetic molecules such as Mn_12Ac (S=10) is developed.The observed slow dynamics of the system is described by master equations for the populations of spin levels.The latter are obtained by the adiabatic elimination of fast degrees of freedom from the density matrix equation with the help of the perturbation theory developed earlier for the tunneling level splitting [D. A. Garanin, J. Phys. A, 24, L61 (1991)]. There exists a temperature range (thermally activated tunneling) where the escape rate follows the Arrhenius law, but has a nonmonotonic dependence on the bias field due to tunneling at the top of the barrier. At lower temperatures this regime crosses over to the non-Arrhenius law (thermally assisted tunneling). The transition between the two regimes can be first or second order, depending on the transverse field, which can be tested in experiments. In both regimes the resonant maxima of the rate occur when spin levels in the two potential wells match at certain field values. In the thermally activated regime at low dissipation each resonance has a multitower self-similar structure with progressively narrowing peaks mounting on top of each other.
- 8 November 1996
- Published by American Association for the Advancement of Science (AAAS) in Science
- Vol. 274 (5289) , 938-939
Quantum Hysteresis in Molecular Magnets
Magnetic materials normally exhibit a smooth response to external fields, but recent experiments reported in Physical Review Letters yield stepwise response curves. In his Perspective, Chudnovsky discusses the results, which may be evidence for quantum behavior on a macroscopic scale.
- 8 November 1996
- Published by American Association for the Advancement of Science (AAAS) in Science
- Vol. 274 (5289) , 938-939
Quantum Hysteresis in Molecular Magnets
Magnetic materials normally exhibit a smooth response to external fields, but recent experiments reported in Physical Review Letters yield stepwise response curves. In his Perspective, Chudnovsky discusses the results, which may be evidence for quantum behavior on a macroscopic scale.