Interval identification of FMR parameters for spin reorientation transition in (Ga,Mn)As

In this work we report results of ferromagnetic resonance studies of a 6% 15 nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were performed with in-plane oriented magnetic field, in the temperature range between 5K and 120K. We observe a temperature induced reorientation of the effective in-plane easy axis from [-110] to [110] direction close to the Curie temperature. The behavior of magnetization is described by anisotropy fields, H_{eff} (= 4\piM -H_{2\perp}), H_{2\parallel}, and H_{4\parallel}. In order to precisely investigate this reorientation, numerical values of anisotropy fields have been determined using powerful - but still largely unknown - interval calculations. In simulation mode this approach makes possible to find all the resonance fields for arbitrarily oriented sample, which is generally intractable analytically. In 'fitting' mode we effectively utilize full experimental information, not only those measurements performed in special, distinguished directions, to reliably estimate the values of important physical parameters as well as their uncertainties and correlations.Comment: 3 pages, 3 figures. Presented at The European Conference "Physics of Magnetism 2011" (PM'11), June 27 - July 1, 2011, Poznan, Polan

Quantitative Determination of the Adiabatic Condition Using Force-Detected Nuclear Magnetic Resonance

The adiabatic condition governing cyclic adiabatic inversion of proton spins in a micron-sized ammonium chloride crystal was studied using room temperature nuclear magnetic resonance force microscopy. A systematic degradation of signal-to-noise was observed as the adiabatic condition became violated. A theory of adiabatic following applicable to cyclic adiabatic inversion is reviewed and implemented to quantitatively determine an adiabaticity threshold $(\gamma H_1)^2/(\omega_{osc}\Omega) = 6.0$ from our experimental results.Comment: 5 pages, 3 fig

Balanced Dissipative Controllers for Flexible Structures

A balanced approach to shaping the closed-loop properties of the dissipative controllers for flexible structures is presented. In the balanced representation the properties of flexible structures are introduced, and a simple method of designing of the dissipative controllers is obtained. It relates the controller gains with the closed-loop pole locations. The examples illustrate the accuracy of the design method

Comments on Response Errors of Non-proportionally Lightly Damped Structures

Letters to the editor authors repl

Thickness dependence of magnetic properties of (Ga,Mn)As

We report on a monotonic reduction of Curie temperature in dilute ferromagnetic semiconductor (Ga,Mn)As upon a well controlled chemical-etching/oxidizing thinning from 15 nm down to complete removal of the ferro- magnetic response. The effect already starts at the very beginning of the thinning process and is accompanied by the spin reorientation transition of the in-plane uniaxial anisotropy. We postulate that a negative gradient along the growth direction of self-compensating defects (Mn interstitial) and the presence of surface donor traps gives quantitative account on these effects within the p-d mean field Zener model with adequate mod- ifications to take a nonuniform distribution of holes and Mn cations into account. The described here effects are of practical importance for employing thin and ultrathin layers of (Ga,Mn)As or relative compounds in concept spintronics devices, like resonant tunneling devices in particular.Comment: 4 pages, 4 figures and supplementary information 2 pages, 1 figur

Seeding supermassive black holes with a nonvortical dark-matter subcomponent

Article / Letter to editorLeids Instituut Onderzoek Natuurkund