First- and second-order transitions of the escape rate in ferrimagnetic or antiferromagnetic particles

Quantum-classical escape-rate transition has been studied for two general forms of magnetic anisotropy in ferrimagnetic or antiferromagnetic particles. It is found that the range of the first-order transition is greatly reduced as the system becomes ferrimagnetic and there is no first-order transition in almost compensated antiferromagnetic particles. These features can be tested experimentally in nanomagnets like molecular magnets.Comment: 11 pages, 3 figures, to appear in Europhys. Let

Chirality tunneling in mesoscopic antiferromagnetic domain walls

We consider a domain wall in the mesoscopic quasi-one-dimensional sample (wire or stripe) of weakly anisotropic two-sublattice antiferromagnet, and estimate the probability of tunneling between two domain wall states with different chirality. Topological effects forbid tunneling for the systems with half-integer spin S of magnetic atoms which consist of odd number of chains N. External magnetic field yields an additional contribution to the Berry phase, resulting in the appearance of two different tunnel splittings in any experimental setup involving a mixture of odd and even N, and in oscillating field dependence of the tunneling rate with the period proportional to 1/N.Comment: 4 pages + 2 figures, references correcte

Macroscopic quantum coherence in mesoscopic ferromagnetic systems

In this paper we study the Macroscopic Quantum Oscillation (MQO) effect in ferromagnetic single domain magnets with a magnetic field applied along the hard anistropy axis. The level splitting for the ground state, derived with the conventional instanton method, oscillates with the external field and is quenched at some field values. A formula for quantum tunneling at excited levels is also obtained. The existence of topological phase accounts for this kind of oscillation and the corresponding thermodynamical quantities exhibit similar interference effects which resembles to some extent the electron quantum phase interference induced by gauge potential in the Aharonov-Bohm effect and the $\Theta$-vacuum in Yang-Mills field theory..Comment: 12 pages, 4 figures, to appear in Phys. Rev.

DEVELOPMENT OF A HARDWARE-SOFTWARE COMPLEX FOR OPTICAL ANALYSIS OF PROBLEM AREAS OF THE SKIN

We have developed a mobile device for the optical analysis of problem areas of the skin to detect cancer. Monitoring identifies patients with suspected cancer, which will enable you to send the patient to a specialized center for effective treatment of cancer at an early stage