International Journal of Modern Physics B

A mesoscopic field theory for the primitive model of ionic systems with additional, short-range interactions is presented. Generic models in continuum space and with positions of the ions restricted to lattice sites of various lattices are described in detail. We describe briefly the field-theoretic methods and review the foundations of the mesoscopic description. The types of phase diagrams predicted by our theory for different versions of the model are presented and discussed. They all agree with recent simulations. On the quantitative level our theory yields an RPM tricritical-point location on the sc lattice which is in good agreement with the simulation results. Arguments indicating that the critical point in the RPM belongs to the Ising universality class are given.

In terms of the Green's function method we study the energy spectrum of dipolar boson atoms with the dipole-dipole interaction in an optical lattice. The Superfluid-Mott-Insulator phase transition condition of the dipolar bosons is determined from the energy-band structure of the excitation spectrum as a function of interatomic repulsion, dipolar bosons interaction and the tunnel coupling constants. The superfluid phase is explained explicitly from the energy spectrum derived in terms of the Bogoliubov approach as well.

We present a complete Monte Carlo simulation of the transport properties of a Si/SiGe quantum well. The scattering mechanisms, viz. intervalley phonons, acoustic phonons, interface roughness and impurity scattering (including resonant scattering), are considered in detail, and we derive analytic expressions for the scattering rates, in each case properly taking the quantized electron wave functions into account. The numerically obtained distribution function is used to discuss the influence of each scattering mechanism for different electric fields applied parallel to the interfaces and also different temperatures.

We have employed the constrained variational method to study the influence of spin polarization on the ground state properties of liquid ³He. The spin polarized phase, we have found, has stronger correlation with respect to the unpolarized phase. It is shown that the internal energy of liquid ³He increases by increasing polarization with no crossing point between polarized and unpolarized energy curves over the liquid density range. The obtained internal energy curves show a bound state, even in the case of fully spin polarized matter. We have also investigated the validity of using a parabolic formula for calculating the energy of spin polarized liquid ³He. Finally, we have compared our results with other calculations.

First-principles density functional calculation of the total energy as a function of volume has been performed by the TB-LMTO approach for the ordered alloy FeRh in the anti-ferromagnetic state. We find that FeRh undergoes a structural phase transition from NaCl-type to tetragonal-type structure around 20.3 GPa which is in best agreement with the recent experimental observation. The calculations show that the energy of the antiferromagnetic ground state is lower than the one for the ferromagnetic state at ambient conditions.

A series of Al–Mg_x alloys, with x = 0.82, 2.09, 2.28, 2.49 and 4.47 wt.%, respectively were characterized by using positron annihilation lifetime studies (PAL), X-ray diffraction (XRD), and sound velocity and internal friction using a vibrating reed technique (VRT). PAL lifetime values increase linearly as the composition is varied, but texturing or preferential orientation is maximum at an intermediate value of composition (x = 2.49%). The internal friction shows a minimum at the same composition, and the sound velocity changes show the maximum value here too. This means that at this composition the sample is the most ordered and defect free.

The giant magnetoimpedance (GMI) effect has been observed in as-deposited (Fe₈₈Zr₇B₅)_0.97 Cu_0.03 amorphous film prepared by radio frequency sputtering. The maximum magnetoimpedance ratio of 17% was obtained at a frequency of 13 MHz. The field and frequency dependences of magnetoimpedance, magnetoresistance, magnetoreactance and transverse permeability have been investigated in detail. Our results show that a close correlation between longitudinal GMI and transverse permeability exists. Our results indicate that the amorphous (Fe₈₈Zr₇ B₅)_0.97Cu_0.03 films have good soft magnetic properties and remarkable GMI effect even though in the as-deposited state.