We review the first decade of extensive optical studies of ferromagnetic, III-Mn-V diluted magnetic semiconductors. Mn introduces holes and local moments to the III–V host, which can result in carrier mediated ferromagnetism in these disordered semiconductors. Spectroscopic experiments provide direct access to the strength and nature of the exchange between holes and local moments; the degree of itineracy of the carriers; and the evolution of the states at the Fermi energy with doping. Taken together, the diversity of optical methods reveal that Mn is an unconventional dopant, in that the metal to insulator transition is governed by the strength of the hybridization between Mn and its p-nictogen neighbor. The interplay between the optical, electronic and magnetic properties of III-Mn-V magnetic semiconductors is of fundamental interest and may enable future spin-optoelectronic devices.

/pdf/optical-properties-of-iii-mn-v-ferromagnetic-semiconductors-45uyols7o0.pdf

Optical Properties of III-Mn-V Ferromagnetic Semiconductors

We discuss advances, advantages and problems of spintronics through the example of a semiconductor laser whose emission intensity and polarization are modulated by the spin orientation of electrons. We show that spin transport should be feasible at room temperature and present possible concepts and first results concerning spin injection at high temperatures. Finally, we describe the coherent dynamics of coupled electron and hole spins in a quantum mechanical picture and measure the magnetic field-induced dynamics of localized excitons in a 3 nm GaAs quantum well. The system is capable of performing a quantum controlled not operation (CNOT), which realizes a basic two-qubit operation of quantum information processing in a semiconductor nanostructure.

https://iopscience.iop.org/article/10.1088/0268-1242/17/4/302/pdf

Spin injection, spin transport and spin coherence

We report on the temperature and angular dependence of ferromagnetic resonances originating from MnAs clusters embedded in a Ga1−xMnxAs host matrix with x≈0.1%. The MnAs clusters were formed in situ during metal-organic vapour-phase epitaxy of (Ga,Mn)As on (0 0 1) and (1 1 1) GaAs substrates. The samples exhibit Curie temperatures of T C ≈330 K which are above room temperature and about 10 K higher than in bulk MnAs and MnAs thin films. From the angular dependence of the ferromagnetic resonances it can be concluded that the crystallographic orientation of the clusters with respect to the matrix is the same for both substrates, i.e. MnAs [0 0 0 1] || GaAs [1 1 1] . We observe only one orientation of the clusters for (1 1 1) and four different orientations for (0 0 1) substrates. The easy axis of magnetisation is perpendicular to the c-axis of the clusters. Only in the case of the (1 1 1) sample, all magnetic moments of the clusters can align parallel to an applied in-plane magnetic field at small fields.

Ferromagnetic resonance studies of (Ga,Mn)As with MnAs clusters

We present a unified interpretation of experimentally observed magnetic circular dichroism (MCD) in the ferromagnetic semiconductor (Ga,Mn)As, based on theoretical arguments, which demonstrates that MCD in this material arises primarily from a difference in the density of spin-up and spin-down states in the valence band brought about by the presence of the Mn impurity band, rather than being primarily due to the Zeeman splitting of electronic states.

/pdf/origin-of-magnetic-circular-dichroism-in-gamnas-giant-zeeman-4hg7sta7ad.pdf

Origin of magnetic circular dichroism in GaMnAs: giant zeeman splitting versus spin dependent density of states.

Granular hybrid structures containing ferromagnetic nanoclusters embedded in a semiconducting matrix are an interesting class of materials as their properties can be tuned in a wide range. Hybrids are a promising alternative to dilute magnetic semiconductors in the field of spintronics and magnetoelectronics, because the nanoclusters can show ferromagnetic behavior even at room temperature. In this review, it is focused on the rather well investigated dilute magnetic semiconductor (Ga,Mn)As with MnAs inclusions. Different preparation methods are presented which were developed over the last two decades in order to obtain MnAs nanoclusters in the semiconducting matrix and to tune the structural and magnetic properties of these clusters. Recent results on the influence of the nanoclusters on the hybrids' transport properties as well as first approaches to use hybrids with a random nanocluster distribution in new spintronic devices are discussed. In addition, the perspective of using single MnAs nanoclusters as well as ordered arrangements of a few nanoclusters in new planar magnetoelectronic devices is illustrated.

Transport Properties of Hybrids with Ferromagnetic MnAs Nanoclusters and Their Potential for New Magnetoelectronic Devices

We report the successful growth of magnetic Ga 1− x Mn x As layers on (1 0 0) GaAs substrates by metal-organic vapour-phase epitaxy. Depending on the growth parameters, two different magnetic phases of Ga 1− x Mn x As can be grown. (i) At low Mn-concentrations, Ga 1− x Mn x As alloys are obtained. These alloys exhibit a paramagnetic behaviour with a strong exchange interaction between the localised magnetic moments of the Mn 2+ ions and the extended excitonic states. (ii) At high Mn-concentrations, Mn(Ga)As clusters are formed within a Ga 1− x Mn x As host. The samples are ferromagnetic even above room temperature. The ferromagnetism has been investigated by SQUID and ESR measurements. The s–d and p–d exchange integrals have been determined independently by combining photoluminescence excitation and spin-flip Raman spectroscopy. A reversal of sign of the valence band exchange integral has been detected along with the transition from the paramagnetic to the ferromagnetic phase.

Monitoring the sign reversal of the valence band exchange integral in (Ga,Mn)As

Overgrowth experiments of ferromagnetic (MnGa)As-cluster layers by MOVPE

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Monitoring the sign reversal of the valence band exchange integral in (Ga,Mn)As

Overgrowth experiments of ferromagnetic (MnGa)As-cluster layers by MOVPE