239 research outputs found
Atomistic spin dynamic method with both damping and moment of inertia effects included from first principles
We consider spin dynamics for implementation in an atomistic framework and we
address the feasibility of capturing processes in the femtosecond regime by
inclusion of moment of inertia. In the spirit of an {\it s-d} -like interaction
between the magnetization and electron spin, we derive a generalized equation
of motion for the magnetization dynamics in the semi-classical limit, which is
non-local in both space and time. Using this result we retain a generalized
Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and
demonstrate how the exchange interaction, damping, and moment of inertia, all
can be calculated from first principles.Comment: 5 pages, 1 figur
Current driven magnetization dynamics in helical spin density waves
A mechanism is proposed for manipulating the magnetic state of a helical spin
density wave using a current. In this paper, we show that a current through a
bulk system with a helical spin density wave induces a spin transfer torque,
giving rise to a rotation of the order parameter.The use of spin transfer
torque to manipulate the magnetization in bulk systems does not suffer from the
obstacles seen for magnetization reversal using interface spin transfer torque
in multilayered systems. We demonstrate the effect by a quantitative
calculation of the current induced magnetization dynamics of Erbium. Finally we
propose a setup for experimental verification.Comment: In the previous version of this paper was a small numerical mistake
made when evaluating equation 3 and 9. The number of digits given in the
calculation of the torque current tensor is reduced to better represent the
accuracy of the calculation. A slightly modified paper have been published in
Phys. Rev. Lett. 96, 256601 (2006) 4 pages 3 figure
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The two-year impact of first generation protease inhibitor based antiretroviral therapy (PI-ART) on health-related quality of life
BACKGROUND: Protease inhibitor based antiretroviral therapy (PI-ART) was introduced in 1996 and has greatly reduced the incidence of HIV-related morbidity and mortality in the industrialised world. PI-ART would thus be expected to have a positive effect on health-related quality of life (HRQL). On the other hand, HRQL might be negatively affected by strict adherence requirements as well as by short and long-term adverse effects. The aim of this study was to assess the influence of two years of first generation PI-ART on HRQL in patients with a relatively advanced state of HIV-infection. Furthermore, we wanted to investigate the relation between developments in HRQL and viral response, self-reported adherence and subjective experience of adverse effects in patients with PI-ART. METHODS: HRQL was measured by the Swedish Health-Related Quality of Life Questionnaire (SWED-QUAL). Sixty-three items from the SWED-QUAL forms two single-item and 11 multi-item dimension scales. For this study, two summary SWED-QUAL scores (physical HRQL composite score and emotional HRQL composite score) were created through a data reduction procedure. At the 2-year follow-up measurement (see below), items were added to measure adherence and subjective experience of adverse effects. Demographic and medical data were obtained from specific items in the questionnaires and from the medical files. Seventy-two patients who were among the first to receive PI-ART (indinavir or ritonavir based) responded to the questionnaire before the start of PI-ART. Of these, 54 responded to the same instrument after two years of treatment (13 had died, four had changed clinic and one did not receive the questionnaire). RESULTS: The main findings were that the emotional HRQL deteriorated during two years of PI-ART, while the physical HRQL remained stable. Multiple linear regression analyses showed that experience of adverse effects contributed most to the deterioration of emotional HRQL. CONCLUSION: In this sample of patients with relatively advanced state of HIV-infection, our data suggested that a negative development of physical HRQL had been interrupted by the treatment and that the emotional dimension of HRQL deteriorated during two years after start of PI-ART. Subjective experience of adverse effects made a major contribution to the decrease in emotional HRQL. The results underline the importance of including HRQL measures in the evaluation of new life prolonging therapies
Multipole decomposition of LDA+ energy and its application to actinides compounds
A general reformulation of the exchange energy of -shell is applied in
the analysis of the magnetic structure of various actinides compounds in the
framework of LDA+U method. The calculations are performed in an efficient
scheme with essentially only one free parameter, the screening length. The
results are analysed in terms of different polarisation channels, due to
different multipoles. Generally it is found that the spin-orbital polarisation
is dominating. This can be viewed as a strong enhancement of the spin-orbit
coupling in these systems. This leads to a drastic decrease in spin
polarisation, in accordance with experiments. The calculations are able to
correctly differentiate magnetic and non-magnetic Pu system. Finally, in all
magnetic systems a new multipolar order is observed, whose polarisation energy
is often larger in magnitude than that of spin polarisation.Comment: Fixed some references and picture
Exchange energy dominated by large orbital spin-currents in -Pu
The electronic structure of the anomalous -phase of Pu is analyzed by
a general and exact reformulation of the exchange energy of the -shell. It
is found that the dominating contribution to the exchange energy is a
polarization of orbital spin-currents that preserves the time reversal
symmetry, hence a non-magnetic solution in accordance with experiments. The
analysis brings a unifying picture of the role of exchange in the -shell
with its relatively strong spin-orbit coupling. The results are in good
accordance with recent measurements of the branching ratio for the to
transition in the actinides.Comment: 6 pages, 1 figure, 2 table
Itinerant magnetic multipole moments of rank five, triakontadipoles, as the hidden order in URuSi
A broken symmetry ground state without any magnetic moments has been
calculated by means of local-density-approximation to density functional theory
plus a local exchange term, the so-called LDA+ approach, for
URuSi. The solution is analysed in terms of a multipole tensor
expansion of the itinerant density matrix and is found to be a non-trivial
magnetic multipole. Analysis and further calculations show that this type of
multipole enters naturally in time reversal breaking in presence of large
effective spin-orbit coupling and co-exists with magnetic moments for most
magnetic actinidesComment: 5 pages, 3 figure
The Fermi Surface Effect on Magnetic Interlayer Coupling
The oscillating magnetic interlayer coupling of Fe over spacer layers
consisting of CuPd alloys is investigated by first principles
density functional theory. The amplitude, period and phase of the coupling, as
well as the disorder-induced decay, are analyzed in detail and the consistency
to the Ruderman-Kittel-Kasuya-Yoshida (RKKY) theory is discussed. For the first
time an effect of the Fermi surface nesting strength on the amplitude is
established from first principles calculations. An unexpected variation of the
phase and disorder-induced decay is obtained and the results are discussed in
terms of asymptotics
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