Macrospin behavior and superparamagnetism in (Ga,Mn)As nanodots

Journal of Applied Physics, 2004

Applied Physics Letters, 2010

Molecular-beam epitaxy grown, 5 nm thick annealed Ga 0.95 Mn 0.05 As films demonstrate transition from metallic to insulating state for sheet resistances near resistance quantum, which we connect with the two-dimensional hole localization. Below the metal-insulator transition we found the giant anisotropic magnetoresistance ͑GAMR͒ effect, which depends on the orientation of magnetization to crystallographic axes and demonstrates the twofold symmetry angular dependence. The GAMR manifests itself in positive magnetoresistance near 50% at T = 1.7 K for H//͓110͔ crystallographic direction in contrast to smaller negative magnetoresistance for H / /͓110͔ direction. We connect the GAMR with formation of high-and low-resistance states with different localization due to anisotropic spin-orbit interaction.

Physical Review Letters, 2008

Thin epitaxial films of the diluted magnetic semiconductor (DMS) GaMnAs have been studied by low energy muon spin rotation and relaxation (LE-SR) as well as by transport and magnetization measurement techniques. LE-SR allows measurements of the distribution of magnetic field on the nanometer scale inaccessible to traditional macroscopic techniques. The spatial inhomogeneity of the magnetic field is resolved: although homogeneous above T c , below T c the DMS consists of ferromagnetic and paramagnetic regions of comparable volumes. In the ferromagnetic regions the local field inhomogeneity amounts to 0.03 T.

Intermetallics

Tetragonal Mn 3 Ga thin films were epitaxially grown with and without strain on Cr and Mo crystalline buffer layers, respectively, using rf-magnetron sputtering. Epilayers grown on Cr with a lattice mismatch of 4.16%, exhibit a high magnetization of 220 kAm −1 and high perpendicular magnetic anisotropy. These characteristics are attributed to interfacial strain. Additionally, a soft ferromagnetic component is observed in these films but not in relaxed layers grown on Mo, where Δa/a is −0.1%. These latest films exhibit a low magnetization of 80 kAm −1 and both perpendicular and in-plane magnetic anisotropies. We propose that high spin orbit coupling of Mo-5s 1 4d 5 orbitals from the buffer layer and strong hybridization with Mn 3+ -3d 4 orbitals from the magnetic layer are at the origin of in-plane anisotropy at the interface, while Mn 3 Ga magnetocrystalline anisotropy leads to perpendicular anisotropy on the rest of the film.

Journal of Superconductivity - J SUPERCOND, 2003

We present experimental data obtained from ferromagnetic p-(Ga,Mn)As layers that indicate the collective rotation of ferromagnetically coupled Mn spins by optically generated spin-polarized holes through the p–d exchange interaction. The rotation occurs reversibly between the in-plane and perpendicular directions, causing a large change in perpendicular magnetization without the application of a magnetic field. Pump-and-probe experiments suggest that the rotation of Mn spins take place in the picosecond time domain.

Applied Physics Letters, 2004

The occurrence of ferromagnetism in the metallic phase of ͑Ga,Mn͒N thin layers is studied by Monte Carlo simulation assuming an indirect exchange of the Ruderman-Kittel-Kasuya-Yosida type, via the spin-polarized hole system. We take into account a possible polarization of the hole gas due to the existence of an average magnetization in the magnetic layer. Transition temperatures one order of magnitude higher than in similar ͑Ga,Mn͒As nanostructures are obtained. Two regimes are observed for the dependence of the magnetization on temperature.

Applied Physics Letters, 2005

Journal of Applied Physics, 2013

Canadian Journal of Physics, 2000

A brief summary of underlying principles governing ultrathin film magnetic nanostructures and magnetoelectronics will be presented. The presentation will be based more on physical intuition than on rather complex physical and mathematical models in order to bring this new and rapidly expanding field to a broad audience. The success of this field has been based on the ability to create new structures in which interfaces play a crucial role. Three major phenomena have strongly affected progress in the development of new magnetic materials based on ultrathin films: (a) interface anisotropies; (b) interlayer exchange coupling; and (c) magneto-electron transport. The great progress in the study of ultrathin film multilayers and films patterned with submicrometre lateral geometries has led to a new class of electronic devices whose operation is based upon the spin-polarized character of the electronic carriers. "Magnetoelectronics and spintronics" are terms used to mark the deve...

Journal of Applied Physics, 2011

Nanodots with magnetic vortices have many potential applications, such as magnetic memories (VRAMs) and spin transfer nano-oscillators (STNOs). Adding a perpendicular anisotropy term to the magnetic energy of the nanodot it becomes possible to tune the vortex core properties. This can be obtained, e.g., in Co nanodots by varying the thickness of the Co layer in a Co/Pt stack. Here we discuss the spin configuration of circular and elliptical nanodots for different perpendicular anisotropies; we show for nanodisks that micromagnetic simulations and analytical results agree. Increasing the perpendicular anisotropy, the vortex core radii increase, the phase diagrams are modified and new configurations appear; the knowledge of these phase diagrams is relevant for the choice of optimum nanodot dimensions for applications. MFM measurements on Co/Pt multilayers confirm the trend of the vortex core diameters with varying Co layer thicknesses.