| 1. |
- Bahrova, O. M., et al.
(författare)
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Cooling of nanomechanical vibrations by Andreev injection
- 2022
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 48:6, s. 476-482
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Tidskriftsartikel (refereegranskat)abstract
- A nanoelectromechanical weak link composed of a carbon nanotube suspended between two normal electrodes in a gap between two superconducting leads is considered. The nanotube is treated as a movable single level quantum dot in which the position-dependent superconducting order parameter is induced due to the Cooper pair tunneling. We show that electron tunneling processes significantly affect the state of the mechanical subsystem. We found that at a given direction of the applied voltage between the electrodes, the stationary state of the mechanical subsystem has a Boltzmann form with an effective temperature dependent on the parameters of the device. As this takes place, the effective temperature can reach significantly small values (cooling effect). We also demonstrate that nanotube fluctuations strongly affect the dc current through the system. The latter can be used to probe the predicted effects in an experiment. Published under an exclusive license by AIP Publishing.
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| 2. |
- Bahrova, O. M., et al.
(författare)
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Entanglement between charge qubit states and coherent states of nanomechanical resonator generated by ac Josephson effect
- 2021
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 47:4, s. 287-293
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Tidskriftsartikel (refereegranskat)abstract
- We considered a nanoelectromechanical system consisting of a movable Cooper-pair box qubit, which is subject to an electrostatic field, and coupled to the two bulk superconductors via tunneling processes. We suggest that qubit dynamics is related to that of a quantum oscillator and demonstrate that a bias voltage applied between superconductors generates states represented by the entanglement of qubit states and coherent states of the oscillator if certain resonant conditions are fulfilled. It is shown that a structure of this entanglement may be controlled by the bias voltage in a way that gives rise to the entanglement incorporating so-called cat-states—the superposition of coherent states. We characterize the formation and development of such states analyzing the entropy of entanglement and corresponding Wigner function. The experimentally feasible detection of the effect by measuring the average current is also considered.
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| 3. |
- Borynskyi, V. Yu, et al.
(författare)
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Thermomagnetic transition in nanoscale synthetic antiferromagnets Py/NiCu/Py
- 2023
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 49:7, s. 863-869
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Tidskriftsartikel (refereegranskat)abstract
- Using the method of SQUID magnetometry, the features of the antiferromagnet-ferromagnet thermomagnetic transition in arrays of the nanosized disks of Py/NiCu/Py synthetic antiferromagnets (SAFs) have been investigated. The effective interlayer interaction in individual SAFs “ferromagnet/diluted ferromagnet/ferromagnet” (F2/f/F1) changes from high-temperature antiferromagnetic to low-temperature ferromagnetic upon the transition at the Curie temperature T C f of the interlayer f. Temperature dependence of the magnetic parameters of individual layers and their effect on the features of the thermomagnetic transition are determined. The observed properties are important for the development of temperature-controlled nanoscale SAFs and multilayer nanostructures based on them.
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| 4. |
- Ilinskaya, O. A., et al.
(författare)
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Polaronic suppression of shuttle vibrations
- 2023
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 49:1, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- A re-entrant behavior of electron shuttling is shown to occur in a nanoelectromechanical transistor made of magnetic material where spin-polarized electrons are injected into a quantum dot with a single electron level split into two by an external magnetic field. A suppression of shuttle vibrations occurs at a certain value of a bias voltage that starts to allow for transport also through the upper energy level of the dot, while for a further increase of the voltage shuttling recovers. The effect is due to a time-dependent polaronic shift of the dot energy level, which results in a reduction of the supply of electric power to the mechanical motion.
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| 5. |
- Ivanov, B. A., et al.
(författare)
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Nonstationary forced motion of domain walls in ferrimagnets near the spin compensation point
- 2020
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 46:8, s. 841-850
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Tidskriftsartikel (refereegranskat)abstract
- The motion of domain walls in ferrimagnets near the sublattice spin compensation point is studied theoretically, when there is an exchange enhancement in the limiting velocity of the wall. Nonlinear regimes of high-velocity nonstationary wall motion are found. A magnet parameter region in which the collective variable approach is invalid, is detected. In this region, the wall motion is accompanied by the periodic appearance of instability with respect to the increase in spin oscillations inside the domain wall.
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| 6. |
- Kulinich, S. I., et al.
(författare)
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Nanomechanical pumping of Cooper pairs through NS junction
- 2023
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Ingår i: Low Temperature Physics. - 1063-777X. ; 49:10, s. 1219-1224
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Tidskriftsartikel (refereegranskat)abstract
- We consider a system consisting of a single-level quantum dot that performs mechanical periodic oscillations between spatially distant normal and superconducting electrodes, approaching them at a distance that allows the exchange of electrons through the vacuum tunnel barrier. Considering that the distance between the electrodes is much greater than the tunneling length, we show that charge pumping occurs in such a nanosystem even when the electrochemical potentials of the electrodes coincide. In this case, the direction of the electron flow is determined by the position of the quantum dot level relative to the electrochemical potential in bulk electrodes. The latter can be controlled by applying a voltage between the ground and the electrodes. It is also shown that the value of the average current is critically sensitive to the strength of the tunnel coupling between the quantum dot and the superconducting electrode, which, in turn, is controlled by the amplitude of mechanical oscillations.
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| 7. |
- Kulyk, Mykola, et al.
(författare)
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Magnetotransport properties of nanogranular composites with low-field positive magnetoresistance
- 2020
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 46:8, s. 792-797
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Tidskriftsartikel (refereegranskat)abstract
- A low-temperature feature is detected in nanogranular magnetic films with perpendicular anisotropy that have a low-field positive magnetoresistance: positive magnetoresistance is observed during the initial magnetization of the demagnetized sample, but is absent when the magnetic field is removed and/or during subsequent magnetizations. This effect is studied using a Co-x(Al2On)(1-x)film withx = 0.60, consisting of Co metal nanogranules in an Al(2)O(n)insulating matrix withnclose to 3. It is found that together with perpendicular anisotropy, the film has local in-plane anisotropy with randomly oriented easy axes, which prevents the reorientation of the granules' magnetic moment projections in the film plane below a certain blocking temperature. The restoration of the local short-range order in the orientation of the magnetic moments of the demagnetized film's neighboring granules, which is optimal for conductivity and is destroyed by the introduction of a magnetic field, is prevented at temperatures below the blocking temperature and is not restored during subsequent cycles of introducing/removing the magnetic field without heating to temperatures above the blocking temperature.
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| 8. |
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| 9. |
- Polishchuk, Dmytr, et al.
(författare)
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Spin-current dissipation in a thin-film bilayer ferromagnet/antiferromagnet
- 2020
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 46:8, s. 813-819
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic resonance in multilayer metal nanostructures containing an antiferromagnetic layer of variable thickness is studied. The contribution to the linewidth of the ferromagnetic resonance that is caused by spin-pumping current dissipation in an exchange-coupled antiferromagnetic/ferromagnetic bilayer is determined. The dissipative processes that occur in the bulk of the antiferromagnet and at the interface between the antiferromagnet (Fe50Mn50) and the ferromagnet (permalloy, Ni81Fe19) are distinguished. The details of how the dissipation transforms when the antiferromagnet Neel vector deviates from the direction of the exchange-pinning field are determined. The proposed method is effective for studying spin scattering in individual layers and at interlayer interfaces in complex magnetic systems.
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| 10. |
- Polishchuk, Dmytr, et al.
(författare)
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Temperature and thickness dependent magnetostatic properties of [Fe/Py]/FeMn/Py multilayers
- 2021
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 47:6, s. 483-487
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of thin-film multilayers [Fe/Py]/FeMn/Py are investigated as a function of temperature and thickness of the antiferromagnetic FeMn spacer using SQUID magnetometry. The observed behavior differs substantially for the structures with 6 nm and 15 nm FeMn spacers. While the 15 nm FeMn structure exhibits exchange pinning of both ferromagnetic layers in the entire measurement temperature interval from 5 to 300 K, the 6 nm FeMn structure becomes exchange de-pinned in the vicinity of room temperature. The depinned state is characterized by a single hysteresis loop centered at zero field and having enhanced magnetic coercivity. The observed properties are explained in terms of finite-size effects and possible ferromagnetic interlayer coupling through the thin antiferromagnetic spacer.
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