Large perpendicular magnetic anisotropy in magnetostrictive Fe1−x_{1-x}Gax_x thin films

In this work we report the appearence of a large perpendicular magnetic anisotropy (PMA) in Fe$_{1-x}$Ga$_x$ thin films grown onto ZnSe/GaAs(100). This arising anisotropy is related to the tetragonal metastable phase in as-grown samples recently reported [M. Eddrief {\it et al.}, Phys. Rev. B {\bf 84}, 161410 (2011)]. By means of ferromagnetic resonance studies we measured PMA values up to $\sim$ 5$\times$10$^5$ J/m$^3$. PMA vanishes when the cubic structure is recovered upon annealing at 300$^{\circ}$C. Despite the important values of the magnetoelastic constants measured via the cantilever method, the consequent magnetoelastic contribution to PMA is not enough to explain the observed anisotropy values in the distorted state. {\it Ab initio} calculations show that the chemical ordering plays a crucial role in the appearance of PMA. Through a phenomenological model we are able to explain that an excess of next nearest neighbour Ga pairs (B$_2$-like ordering) along the perpendicular direction arises as the source of PMA in Fe$_{1-x}$Ga$_x$ thin films.Comment: 6 pages, 4 figure

Hole spin polarization in GaAlAs:Mn structures

A self-consistent calculation of the electronic properties of GaAlAs:Mn magnetic semiconductor quantum well structures is performed including the Hartree term and the sp-d exchange interaction with the Mn magnetic moments. The spin polarization density is obtained for several structure configurations. Available experimental results are compared with theory.Comment: 4 page

Bulk Mediated Surface Diffusion: Non Markovian Desorption with Finite First Moment

Here we address a fundamental issue in surface physics: the dynamics of adsorbed molecules. We study this problem when the particle's desorption is characterized by a non Markovian process, while the particle's adsorption and its motion in the bulk are governed by a Markovian dynamics. We study the diffusion of particles in a semi-infinite cubic lattice, and focus on the effective diffusion process at the interface $z = 1$. We calculate analytically the conditional probability to find the particle on the $z=1$ plane as well as the surface dispersion as functions of time. The comparison of these results with Monte Carlo simulations show an excellent agreement.Comment: 16 pages, 7 figs. European Physical Journal B (in press

Nonequilibrium spin distribution in single-electron transistor

Single-electron transistor with ferromagnetic outer electrodes and nonmagnetic island is studied theoretically. Nonequilibrium electron spin distribution in the island is caused by tunneling current. The dependencies of the magnetoresistance ratio $\delta$ on the bias and gate voltages show the dips which are directly related to the induced separation of Fermi levels for electrons with different spins. Inside a dip $\delta$ can become negative.Comment: 11 pages, 2 eps figure

Ferromagnetism and Canted Spin Phase in AlAs/GaMnAs Single Quantum Wells: Monte Carlo Simulation

The magnetic order resulting from a confinement-adapted Ruderman-Kittel-Kasuya-Yosida indirect exchange between magnetic moments in the metallic phase of a AlAs/Ga(1-x)Mn(x)As quantum well is studied by Monte Carlo simulation. This coupling mechanism involves magnetic moments and carriers (holes), both coming from the same Mn(2+) ions. It leads to a paramagnetic, a ferromagnetic, or a canted spin phase, depending on the carrier concentration, and on the magnetic layer width. It is shown that high transition temperatures may be obtained.Comment: 7 figure

Putting Equity Back in Reverse Mortgages: Helping Seniors Retire with Dignity

Policymakers can help some seniors age in place through policies to strengthen private-sector reverse mortgages. In reverse mortgages, individuals who may be “house rich but cash poor” can use their home’s equity to receive regular income or get money through a credit line. Andrew Helman argues that state legislatures can help seniors avoid the “tricks and traps” of reverse mortgages by estab­lishing programs in which lenders who agree to play by rules that ensure the safety and security of such mortgages are placed on a “preferred” list for seniors seeking a loan. He observes that laying the groundwork now can help a larger group of seniors age with dignity

Northern Hardwood Silviculture: Preferences among Family Forest Owners in the Western Upper Peninsula of Michigan

In the northern hardwood forests of the Western Upper Peninsula of Michigan, single-tree selection is the most commonly used silvicultural system. This system provides both a sustained yield of timber and attempts to emulate the windfall disturbance regime that determines the uneven aged structure of northern hardwood forests. However, with concerns about tree species diversity loss and a lack of early successional forests, even-aged regeneration methods are likely to become an increasingly crucial tool in the toolbox for managing northern hardwood forests of the Lake States. The forests of the Western Upper Peninsula are comprised of a mosaic of ownerships, with nearly 40% of the forested land owned by family forest owners. This study assessed family forest owners experience with, perceptions of, and interest in three different silvicultural methods recently implemented as a part of a long-term silviculture study on Michigan Technological University’s Ford Forest. A mailed survey with images and descriptions of clearcut, shelterwood, and single tree selection harvests was sent to family forest owners with at least 20 acres of forestland in the Western Upper Peninsula. The survey also included questions about landowners\u27 use of their forestland, management experience, incentive-program enrollment, and demographics. The findings indicated that family forest owners who rank timber as important reason for owning forestland are the most likely to be accepting of all three methods. Respondents who use their land for hunting are also very likely to implement clearcut and shelterwood methods. Other findings include different preferences for management between absentee and non-absentee landowners. The results of this study suggest that targeting hunting groups and actively managing landowners may have a positive effect on the understanding and acceptance of silviculture among family forest owners

Thermal effects on atomic friction

We model friction acting on the tip of an atomic force microscope as it is dragged across a surface at non-zero temperatures. We find that stick-slip motion occurs and that the average frictional force follows $|\ln v|^{2/3}$, where $v$ is the tip velocity. This compares well to recent experimental work (Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all microscopic parameters. We calculate the scaled form of the average frictional force's dependence on both temperature and tip speed as well as the form of the friction-force distribution function.Comment: Accepted for publication, Physical Review Letter