CALCULATION OF SPIN-REORIENTATION TEMPERATURE IN ND2FE14B

The spin-reorientation phenomenon in Nd2Fe14B has been investigated using an angular dependent free energy approach. A magnetic Hamiltonian which includes the crystal electric field term and the exchange term has been established using realistic band structure results. The temperature dependence of the molecular field is accounted for by introducing the Brillouin function and the magnetic Hamiltonian is diagonalized within the ground state multiplet of the Nd ion. The eigenstates are then used to form the partition function for the free energy. At each temperature, the direction of the molecular field is obtained by searching for the minimum in the angular parameter space of the free energy. Our calculations show that for Nd2Fe14B, the net magnetic anisotropy direction is canted away from the c axis at a temperature close to the experimentally reported spin-reorientation temperature of 150 K. The temperature dependence of the magnetic structure is found to be very sensitive to the size of the second order crystal field parameter B20.

Electronic structure of quantum spheres and quantum wires

The electronic structures of quantum spheres and quantum wires are studied in the framework of the effective-mass theory. The spin-orbital coupling (SOC) effect is taken into account. On the basis of the zero SOC limit and strong SOC limit the hole quantum energy levels as functions of SOC parameter lambda are obtained. There is a fan region in which the ground and low-lying excited states approach those in the strong SOC limit as lambda increases. Besides, some theoretical results on the corrugated superlattices (CSL) are given.

First-principles investigation of the electronic structure and magnetism of eskolaite

The electronic structure and magnetism of eskolaite are studied by using first-principles calculations where the on-site Coulomb interaction and the exchange interaction are taken into account and the LSDA+U method is used.The calculated energies of magnetic configurations are very well fitted by the Heisenberg Hamiltonian with interactions in five neighbour shells; interaction with two nearest neighbours is found to be dominant. The Neel temperature is calculated in the spin-3/2 pair-cluster approximation. It is found that the measurements are in good agreement with for the values of U and J that are close to those obtained within the constrained occupation method.The band gap is of the Mott-Hubbard type.

Spin split cyclotron resonance in GaAs quantum wells

The cyclotron resonance (CR) of electrons in GaAs/AlGaAs quantum wells is investigated theoretically to explain a recent CR experiment, where two CR peaks were observed at high magnetic fields when both spin-up and spin-down states of the lowest Landau level are occupied. Our theoretical model takes into account the conduction band non-parabolicity, the electron bulk longitude-optic-phonon coupling, and the self-consistent subband structure. A good agreement is found.

In-plane stray field induced spin-filtering in a two-dimensional electron gas under the modulation of surface ferromagnetic dual-gate

Based upon a hybrid ferromagnet/semiconductor structure consisting of two-dimensional electron gas and a pair of surface ferromagnetic stripes on top, we have theoretically investigated the effect of in-plane stray field omitted frequently in previous studies on the spin-dependent ballistic transport properties in hybrid structure. It is demonstrated here that, in combination with an external-controllable electrostatic modulation, the concerned structure shows a similar function as a lateral spin-polarized resonant tunneling device, where the strong spin-filtering effect occurs and nearly single-mode polarization is anticipated for the proper modulation. More importantly, the spin polarity of transmission electron can be easily transferred from one extreme to the other by switching the magnetization of stripes, showing the promising application as an efficient spin aligner in the developing semiconductor spintronics.

Spin splitting modulated by uniaxial stress in InAs nanowires

We theoretically study the electronic structure, spin splitting, effective mass, and spin orientation of InAs nanowires with cylindrical symmetry in the presence of an external electric field and uniaxial stress. Using an eight-band k center dot p theoretical model, we deduce a formula for the spin splitting in the system, indicating that the spin splitting under uniaxial stress is a nonlinear function of the momentum and the electric field. The spin splitting can be described by a linear Rashba model when the wavevector and the electric field are sufficiently small. Our numeric results show that the uniaxial stress can modulate the spin splitting. With the increase of wavevector, the uniaxial tensile stress first restrains and then amplifies the spin splitting of the lowest electron state compared to the no strain case. The reverse is true under a compression. Moreover, strong spin splitting can be induced by compression when the top of the valence band is close to the bottom of the conductance band, and the spin orientations of the electron stay almost unchanged before the overlap of the two bands.

Multi-quasiparticle gamma-band structure in neutron-deficient Ce and Nd isotopes

The newly developed multi-quasiparticle triaxial projected shell model approach is employed to study the high-spin band structures in neutron-deficient even-even Ce- and Nd-isotopes. It is observed that gamma-bands are built on each intrinsic configuration of the triaxial mean-field deformation. Due to the fact that a triaxial configuration is a superposition of several K-states, the projection from these states results in several low-lying bands originating from the same intrinsic configuration. This generalizes the well-known concept of the surface gamma-oscillation in deformed nuclei based on the ground-state to gamma-bands built on multi-quasiparticle configurations. This new feature provides an alternative explanation on the observation of two I = 10 aligning states in Ce-134 and both exhibiting a neutron character. (C) 2009 Elsevier B.V. All rights reserved.

Projected shell model description for high-spin states in neutron-rich Fe isotopes

A systematic study of neutron-rich even-even Fe isotopes with a neutron number from 32 to 42 is carried out by using the projected shell model. Calculations are performed up to the spin I=20 state. Irregularities found in the yrast spectra and in B (E2) values are discussed in terms of neutron excitations to the high-j orbital g(9/2). Furthermore, the neutron two-quasiparticle structure of a low-K negative-parity band and the proton two-quasiparticle structure of a high-K positive-parity band are predicted to exist near the yrast region. Our study reveals a soft nature for the ground state of N approximate to 40 isotopes and emphasizes the important role of the neutron g(9/2) orbital in determining the structure properties for both low- and high-spin states in these nuclei.

Structure of upper-g(9/2)-shell nuclei and shape effect in the Ag-94 isomeric states

Using a shell model which is capable of describing the spectra of upper g(9/2)-shell nuclei close to the N = Z line, we study the structure of two isomeric states 7(+) and 21(+) in the odd-odd N = Z nucleus Ag-94. It is found that both isomeric states exhibit a large collectivity. The 7(+) state is oblately deformed, and is suggested to be a shape isomer in nature. The 21(+) state becomes isomeric because of level inversion of the 19(+) and 21(+) states due to core excitations across the N = Z = 50 shell gap. Calculation of spectroscopic quadrupole moment indicates clearly an enhancement in these states due to the core excitations. However, the present shell model calculation that produces the 19(+)-21(+) level inversion cannot accept the large-deformation picture of Mukha et al.

High-spin states in Pt-190

The level structure of Pt-190 has been studied experimentally using the Yb-176 (O-18, 4n) reaction at beam energies of 88 and 95 MeV. gamma-gamma-t coincidence measurements were carried out. Based on the analysis of gamma-gamma coincidence relationships, the level scheme of Pt-190 is extended to high-spin states. A new structure built on the 3413.6 keV 14(+) state has been observed, and the vi(13/2)(-2) vh(9/2)(-1) vj (j = p(3/2) or f(5/2)) configuration is tentatively assigned to it.

Anomaly in the charge radii and nuclear structure

The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of link in the isotope shift at the neutron magic number N = 82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin-orbit coupling interaction and p-n attraction are well described by the relativistic mean field theory.

High-spin states in Au-188: Further evidence for nonaxial shape

The high-spin level structure of Au-188 has been investigated via the Yb-173(F-19,4n gamma) reaction at beam energies of 86 and 90 MeV. The previously reported level scheme has been modified and extended significantly. A new I-pi = 20(+) state associated with pi h(11/2)(-1) circle times nu i(13/2)(-2)h(9/2)(-1) configuration and two new rotational bands, one of which is built on the pi h(9/2) circle times nu i(13/2) configuration, have been identified. The prolate-to-oblate shape transition through triaxial shape has been proposed to occur around Au-188 for the pi h(9/2) circle times nu i(13/2) bands in odd-odd Au isotopes. Evidence for pi h(11/2)(-1) circle times nu i(13/2)(-1) structure of nonaxial shape with gamma < -70 degrees has been obtained by comparison with total Routhian surface and cranked-shell-model calculations.

Medium-spin states in Ge-70 and the role of the g(9/2) orbital

Medium-spin states of Ge-70 have been studied via the Ni-60(C-12,2p gamma)Ge-70 reaction at 45 MeV. The ground-state band and the second 0(+) band have been extended to the 12(+) and 8(+) states, respectively. Two negative-parity bands, one of which has a coupled structure and the other has a decoupled structure, have been observed additionally. Although the latter decoupled structure was known up to the (21(-)) state from a previous experiment, the part of the level scheme up to the 15(-) state has been largely modified by the present experiment. Backbendings observed in the positive- and negative-parity yrast bands have been compared with those of the neighboring even Ge isotopes. The experimental level structure has been compared with the shell-model calculations in the model space (2p(3/2), 1f(5/2), 2(p1/2), 1g(9/2)) employing two kinds of effective interactions, one of which is an extended P + QQ interaction with monopole interactions and the other is developed from a renormalized G matrix. Microscopic structures of the observed bands have been discussed with the help of the shell-model calculations.