Magnetic interactions of substitutional Mn pairs in GaAs

We employ a kinetic-exchange tight-binding model to calculate the magnetic interaction and anisotropy energies of a pair of substitutional Mn atoms in GaAs as a function of their separation distance and direction. We find that the most energetically stable configuration is usually one in which the spins are ferromagnetically aligned along the vector connecting the Mn atoms. The ferromagnetic configuration is characterized by a splitting of the topmost unoccupied acceptor levels, which is visible in scanning tunneling microscope studies when the pair is close to the surface and is strongly dependent on pair orientation. The largest acceptor splittings occur when the Mn pair is oriented along the symmetry direction, and the smallest when they are oriented along . We show explicitly that the acceptor splitting is not simply related to the effective exchange interaction between the Mn local moments. The exchange interaction constant is instead more directly related to the width of the distribution of all impurity levels -- occupied and unoccupied. When the Mn pair is at the (110) GaAs surface, both acceptor splitting and effective exchange interaction are very small except for the smallest possible Mn separation.Comment: 25 figure

Pathways to longevity - but is it successful?

Non peer reviewe

Chern number spins of Mn acceptor magnets in GaAs

We determine the effective total spin $J$ of local moments formed from acceptor states bound to Mn ions in GaAs by evaluating their magnetic Chern numbers. We find that when individual Mn atoms are close to the sample surface, the total spin changes from $J = 1$ to $J = 2$, due to quenching of the acceptor orbital moment. For Mn pairs in bulk, the total $J$ depends on the pair orientation in the GaAs lattice and on the separation between the Mn atoms. We point out that Berry curvature variation as a function of local moment orientation can profoundly influence the quantum spin dynamics of these magnetic entities.Comment: 4 pages, 3 figure

Magnetic properties of substitutional Mn in (110) GaAs surface and subsurface layers

Motivated by recent STM experiments, we present a theoretical study of the electronic and magnetic properties of the Mn-induced acceptor level obtained by substituting a single Ga atom in the (110) surface layer of GaAs or in one of the atoms layers below the surface. We employ a kinetic-exchange tight-binding model in which the relaxation of the (110) surface is taken into account. The acceptor wave function is strongly anisotropic in space and its detailed features depend on the depth of the sublayer in which the Mn atom is located. The local-density-of-states (LDOS) on the (110) surface associated with the acceptor level is more sensitive to the direction of the Mn magnetic moment when the Mn atom is located further below the surface. We show that the total magnetic anisotropy energy of the system is due almost entirely to the dependence of the acceptor level energy on Mn spin orientation, and that this quantity is strongly dependent on the depth of the Mn atom.Comment: 14 pages, 13 figure

Successful SPRINT hypertension trial does not cover all older patients

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INCIDENT DEMENTIA IN TRIALS OF ANTIHYPERTENSIVE TREATMENTS

Non peer reviewe

Magnetic Anisotropy of Isolated Cobalt Nanoplatelets

Motivated in part by experiments performed by M.H. Pan et al. (nanoletters, v.5, p 83, 2005), we have undertaken a theoretical study of the the magnetic properties of two-monolayer thick Co nanoplatelets with an equilateral triangular shape. The analysis is carried out using a microscopic Slater-Koster tight-binding model with atomic exchange and spin-orbit interactions designed to realistically capture the salient magnetic features of large nanoclusters containing up to 350 atoms. Two different truncations of the FCC lattice are studied, in which the nanoplatelet surface is aligned parallel to the FCC (111) and (001)crystal planes respectively. We find that the higher coordination number in the (111) truncated crystal is more likely to reproduce the perpendicular easy direction found in experiment. Qualitatively, the most important parameter governing the anisotropy of the model is found to be the value of the intra-atomic exchange integral J. If we set the value of J near the bulk value in order to reproduce the experimentally observed magnitude of the magnetic moments, we find both quasi-easy-planes and perpendicular easy directions. At larger values of J we find that the easy-axis of magnetization is perpendicular to the surface, and the value of the magnetic anisotropy energy per atom is larger. The possible role of hybridization with substrate surface states in the experimental systems is discussed.Comment: 15 pages, 13 figure

A tale of two therapies lipid-lowering vs. anti-inflammatory therapy : a false dichotomy?

Non peer reviewe

Self-Perception of Economic Means is Associated with Dietary Choices, Diet Quality and Physical Health in the Oldest Old Men from the Highest Socioeconomic Group

IntroductionSelf-perception of economic means may affect dietary choices, diet quality, and health behavior. We examined these associations in the oldest-old men from the highest socioeconomic class.MethodsThe participants in this cross-sectional analysis were the oldest- old home-dwelling men (n = 314, mean age 87 years, range 82-97 years) from the longitudinal Helsinki Businessmen Study cohort. They responded to a postal health and nutrition questionnaire, whereupon dietary intakes were assessed using 3-day food diaries and two diet quality indices. The questionnaire also included items about health, exercise, falls, and economic means.ResultsHigher self-perception of economic means was linearly associated with higher fish intake (p = 0.021), fruit and vegetable intakes (p = 0.027), use of alcohol (p = 0.003), overall diet quality according to IDQ (p = 0.008), self-perceived physical condition (p = 0.002) and inversely associated with body weight (p = 0.011), weight loss (p = 0.008), blood glucose levels (p = 0.020), and falls (p = 0.029).ConclusionSelf-perception of economic means was associated with dietary choices and physical health even among affluent older men. This information is important, because self-perception of economic means, however real, may affect health and nutrition behavior of older people.Peer reviewe

A tale of two therapies lipid-lowering vs. anti-inflammatory therapy : a false dichotomy?

Non peer reviewe