Metal-insulator and magnetic phase transitions: A thermodynamic model

A thermodynamic model of magnetic insulator-to-metal transitions is presented. As the parameters are varied it shows with increasing temperatures; (a) antiferromagnetic insulator → paramagnetic insulator; or (b) antiferromagnetic insulator → metal → paramagnetic insulator; or (c) antiferromagnetic insulator → metal; or (d) metal at all temperatures. Behaviors (b) and (c) are separated by a classical critical point. The model reproduces well the behavior encounted in (V_1-xCr_x)₂O₃ and can be applied to magnetic semiconductors in general.     

Pseudopotential calculations of relaxation and formation energy of a (1/2, 1/2, 1/2) interstitial defect in aluminum

The pseudopotential form factors used previously by the authors to study the vacancy formation in aluminum are employed to calculate the atom displacements around and formation energy of an interstitial aluminum atom placed at the center (1/2, 1/2, 1/2) of the face-centered cubic unit cell with encouraging results.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Hyperfine field at a point interstitial impurity in ferromagnetic nickel

A simple model for the spin polarization around a charged interstitial impurity in ferromagnetic nickel is presented. It is based on screening of the charge by only s-electrons, while d-electrons, considered to be correlated and localized, are responsible, through an exchange mechanism, for the s-electron spin polarization. Agreement with recent experiments on μ⁺ precession in Ni, as well as neutron diffraction data is satisfactory.     

Applied stresses,cyclotron masses and charge-density-waves in silicon inversion layers

The behaviour of cyclotron masses for n-type Si(100)/SiO₂ inversion layers under stress is explained by means of a charge-density-wave model. The model yields: (1) the observed occupied valley degeneracy of two; (2) a cyclotron mass which varies as a function of stress or as a function of electron number density between 0.19 m_e and 0.42 m_e; (3) a charge-density-wave solution only for a restricted range of stresses, with a different paramagnetic solution at each boundary of this range. Of the two tramsitions one is first order and the other second order both as a function of stress and carrier density. The approximations in the calculation are discussed.