arXiv subjects

A. K. Zvezdin

Publications and source records attributed to A. K. Zvezdin.

80 records · Page 5Linked to original sources

arXiv2002

Investigation of a ring single molecular magnet Mn$_6$R$_6$ in megagauss fields

The dependence of the magnetic susceptibility on the magnetic field is investigated for the single molecular magnet [Mn(hfac)$_2$NITPh]$_6$. The spikes of the susceptibility detected in a magnetic field ranging from 90 T to 285 T are interpreted as a manifestation of magnetic quantum jumps under spins reorientation from ferrimagnetic to ferromagnetic structure. The characteristic feature of the single molecular magnet Mn$_6$ R$_6$ is a deficiency of pair Heisenberg exchange interactions for the description of its magnetic properties in high magnetic fields. The comparison of the experimental data with the results of theoretical calculations allows us to prove the existence of strong three-spin interaction in this molecular cluster and to determine the values of exchange constants. For the calculation of the ground state spin structure the modified Lanczos method is used.

cond-mat.str-el↗

arXiv2002

Field - Induced Spin Phase Transitions in the Cobalt Valence Tautomers

Magnetic properties of the Co valence tautomers are considered in wide range of magnetic field and temperature. Particularly, a model of the first order structural phase transition accompanied by a magnetic moment jump is proposed. The phase diagrams of the phase transition on a B-T plane (B is magnetic field and T is temperature) are calculated for four ligand types. Dependence of the critical magnetic field on physical characteristics known from experiments (transition temperature at the absense of magnetic field, entropy change per formula unit, energy difference between two phases) is found. The phase diagram is parametrized for comparison with other phase transitions of this kind.

cond-mat.mtrl-sci↗

arXiv2002

Even-odd effects in magnetoresistance of ferromagnetic domain walls

Difference in density of states for the spin's majority and minority bands in a ferromagnet changes the electrostatic potential along the domains, introducing the discontinuities of the potential at domain boundaries. The value of discontinuity oscillates with number of domains. Discontinuity depends on the positions of domain walls, their motion or collapse of domain walls in applied magnetic field. Large values of magnetoresistance are explained in terms of spin-accumulation. We suggest a new type of domain walls in nanowires of itinerant ferromagnets, in which the magnetization vector changes without rotation. Absence of transverse magnetization components allows considerable spin accumulation assuming the spin relaxation length, L_S, is large enough.

cond-mat.mtrl-sci↗

arXiv2001

Nonlinear Dynamics of Quasiclassical Spin Moment in a Swept Field

Quantum dynamics of anisotropic spin system with large spin moment in a swept magnetic field is theoretically investigated. Magnetic field of this type induces vortex static electrical field, that breaks down the axial symmetry and induces new coherent quantum phenomena: the occurrence of band energy spectrum with continuous spin states, Bloch-type oscillations and interband Zener tunnelling effect. These quantum phenomena display themselves, in particular, in magnetization jumps and susceptibility peaks in the investigated spin system.

cond-mat.mes-hall↗

arXiv2000

First order valence transition in YbInCu_4 in the (B,T) - plane

The puzzling properties of the first order phase transition in YbInCu$_4$ and its alloys in the wide range of magnetic fields and temperatures are perfectly described in terms of a simple entropy transition for free Yb ions. In particular, it turns out that the transition line in the $(B,T)$-plane is very close to the elliptic shape, as it has been observed experimentally. Similar calculations are done, and the experiments are proposed for the $(γ{-}α)$ phase transition in Ce in Megagauss fields. We speculate, that in case of YbInCu$_4$ the first order transition is a Mott transition between a higher temperature phase in which localized moments are stabilized by the entropy terms in the free energy, and a band-like non-magnetic ground state of the $f$-electrons.

cond-mat.str-el↗

arXiv2000

Temperature dependence of the nematic anchoring energy:mean field analysis

In the mean field approximation, we evaluate the temperature dependence of the anchoring energy strength of a nematic liquid crystal in contact with a solid substrate due to thermal fluctuations. Our study is limited to the weak anchoring case, where the microscopic surface energy is small with respect to the mean field energy due to the nematic phase. We assume furthermore that the physical properties of the substrate can be considered temperature independent in the range of the nematic phase. According to the thermodynamical perturbative approach, the macroscopic surface energy is deduced by averaging the microscopic one, with a density matrix containing only the nematic mean field. We show that the thermal renormalization of the anchoring energy coefficients is proportional to the generalized nematic order parameters.

cond-mat.soft↗

arXiv2000

Macroscopic Quantum Oscillations of Antiferromagnetic Nanoclusters in a Swept Magnetic Field

New macroscopic quantum interference effects in the behavior of the antiferromagnetic nanoclusters under action of a swept magnetic field are predicted and theoretically investigated, namely : oscillations of the magnetic susceptibility of nanocluster similar to the electron Bloch oscillations in crystal and the corresponding Stark ladder-like resonances in ac-magnetic field. These effects are related to that of the macroscopic quantum coherence phenomena. The analogy of the antiferromagnetic nanoclusters quantum behavior and Josephson junction with a small capacity was revealed as well.

cond-mat.mes-hall↗

arXiv1998

Quantum Fluctuations in Large-Spin Molecules

A new type of mesoscopic quantum effect in large-spin molecules possessing easy-axis anisotropy, such as Mn12, is predicted. The response of such a system to an external field applied perpendicular to the easy axis is considered. It is shown that the susceptibility of this system exhibits a peculiar peak of purely quantum origin. This effect arises from very general properties of quantum fluctuations in spin systems. We demonstrate that the effect is entirely accessible for contemporary experimental techniques. Our studies show that the many-spin nature of the Mn12 clusters is important for a correct description of this quantum peak.

cond-mat.stat-mech↗