arXiv subjects

G. M. Schott

Publications and source records attributed to G. M. Schott.

7 recordsLinked to original sources

arXiv2008

Non-thermal photocoercivity effect in a ferromagnetic semiconductor

We report a photoinduced change of the coercive field, i.e., a photocoercivity effect (PCE), under very low intensity illumination of a low-doped (Ga,Mn)As ferromagnetic semiconductor. We find a strong correlation between the PCE and the sample resistivity. Spatially resolved dynamics of the magnetization reversal rule out any role of thermal heating in the origin of this PCE, and we propose a mechanism based on the light-induced lowering of the domain wall pinning energy. The PCE is local and reversible, allowing writing and erasing of magnetic images using light.

cond-mat.mtrl-sci↗

arXiv2006

Magnetization-Switched Metal-Insulator Transition in a (Ga,Mn)As Tunnel Device

We observe the occurrence of an Efros-Shklovskii gap in (Ga,Mn)As based tunnel junctions. The occurrence of the gap is controlled by the extent of the hole wave-function on the Mn acceptor atoms. Using k.p-type calculations we show that this extent depends crucially on the direction of the magnetization in the (Ga,Mn)As (which has two almost equivalent easy axes). This implies one can reversibly tune the system into the insulating or metallic state by changing the magnetization.

cond-mat.str-el↗

arXiv2006

Current Assisted Magnetization Switching in (Ga,Mn)As Nanodevices

Current induced magnetization switching and resistance associated with domain walls pinned in nanoconstrictions have both been previously reported in (Ga,Mn)As based devices, but using very dissimilar experimental schemes and device geometries . Here we report on the simultaneous observation of both effects in a single nanodevice, which constitutes a significant step forward towards the eventual realization of spintronic devices which make use of domain walls to store, transport, and manipulate information.

cond-mat.mes-hall↗

arXiv2004

1500-fold Tunneling Anisotropic Magnetoresistance in a (Ga,Mn)As stack

We report the discovery of a super-giant tunneling anisotropic magnetoresistance in an epitaxially grown (Ga,Mn)As/GaAs/(Ga,Mn)As structure. The effect arises from a strong dependence of the electronic structure of ferromagnetic semiconductors on the magnetization orientation rather than from a parallel or antiparallel alignment of the contacts. The key novel spintronics features of this effect are: (i) both normal and inverted spin-valve like signals; (ii) a large non-hysteretic magnetoresistance for magnetic fields perpendicular to the interfaces; (iii) magnetization orientations for extremal resistance are, in general, not aligned with the magnetic easy and hard axis. (iv) Enormous amplification of the effect at low bias and temperatures.

cond-mat.mes-hall↗

arXiv2004

Tunneling Anisotropic Magnetoresistance: A spin-valve like tunnel magnetoresistance using a single magnetic layer

We introduce a new class of spintronics devices in which a spin-valve like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets. The effect is observed in a normal-metal/insulator/ferromagnetic-semiconductor tunneling device. This behavior is caused by the interplay of the anisotropic density of states in (Ga,Mn)As with respect to the magnetization direction, and the two-step magnetization reversal process in this material.

cond-mat.mes-hall↗

arXiv2002

Temperature Dependent Magnetic Anisotropy in (Ga,Ma)As Layers

It is demonstrated by SQUID magnetization measurements that (Ga,Mn)As films can exhibit rich characteristics of magnetic anisotropy depending not only to the epitaxial strain but being strongly influenced by the hole and Mn concentration, and temperature. This behavior reflects the spin anisotropy of the valence subbands and corroborates predictions of the mean field Zener model of the carrier mediated ferromagnetism in III-V diluted magnetic semiconductors with Mn. At the same time the existence of in-plane uniaxial anisotropy with [110] the easy axis is evidenced. This is related to the top/bottom symmetry breaking, resulting in the lowering of point symmetry of (Ga,Mn)As to the C_{2v} symmetry group. The latter mechanism coexists with the hole-induced cubic anisotropy, but takes over close to T_C.

cond-mat.mtrl-sci↗

arXiv2001

Lattice constant variation and complex formation in zincblende Gallium Manganese Arsenide

We perform high resolution X-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low temperature molecular beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate temperatures of 220 and 270 degrees C the extrapolated relaxed lattice constant of Zincblende MnAs is 0.590 nm and 0.598 nm respectively. This is in contrast to low temperature GaAs, for which the lattice constant decreases with increasing substrate temperature.

cond-mat.mtrl-sci↗