Dr. Mihai
Dimian is Associate Professor in Electrical
Engineering and Computer Science Department at “Stefan cel
Mare” University,
His
research in the area of magnetic recording is focused on viable alternatives to
the magnetization reversal, both in traditional longitudinal magnetic media and
in its promising alternatives: perpendicular media and nanoparticulate
media. He offered a rigorous comparison of the main characteristics, such as
critical field and switching time, for damping and precessional
switchings and designed magnetic field pulses for precessional switching by using the direct and inverse
methods He applied perturbation and multi-scale methods for the evaluation of
dissipative effects and relaxation phenomena.
Another direction of his research is the
analysis of nonlinear systems with hysteresis driven
by stochastic processes. The behavior of
hysteretic system affected by thermal fluctuations or noise can be described as
a nonlinear hysteretic transformation of stochastic input. One of his main results in this area was the
spectral analysis of hysteretic systems.
The developed method takes full advantage of the fact that numerous
hysteretic nonlinearities can be constructed trough Preisach
formalism as a weighted superposition of rectangular loop operators that are
individually driven by the same stochastic process. Then the mathematical
theory of stochastic processes on graphs is used to circumvent the difficulties
related to the fact that outputs of hysteretic systems are not Markovian processes. Due to the universality of Preisach model and the general form of the input process,
the method can be applied for the calculation of spectral densities for
hysteretic nonlinearities of various physical origins (such as magnetism,
superconductivity, mechanical structures, and shape-memory alloy)
A special interest in his research is
devoted to the surface effects that have a strong bearing on nanoparticle properties.
In order to describe these contributions, he uses a multi-spin model of
a nanoparticle which is capable of distinguishing
among various atomic environments. The multi-spin dynamics is modeled by
Landau-Lifshitz type equations for each spin while
the effective field is derived from a Dirac-Heisenberg Hamiltonian. He had analyzed the quasi-static and dynamic
properties of magnetic nanoparticles and had
illustrated their dependence on various physical parameters considered in the
problem.
In addition to the above mentioned directions, his research experience
also includes topics related to the landmine detection using hyperspectral images, human detection using infrared
cameras, terahertz-wave technology, and noise and fluctuations in semiconductor
devices.