Semimagnetic Semiconductors Research Articles

Pressure Induced Phase Transition in Sn1−xMn x Te*

We have investigated the pressure induced phase transition (B1 M B2) and other related properties of semimagnetic semiconductor (SMS) Sn 1 m x Mn x Te (0 h x h 0.70), using the three-body potential (TBP) approach. The lattice energy, according to this approach, consists of the long range Coulomb as well as three-body interaction and short range (SR) van der Waals (vdW) due to dipole-dipole interactions, and overlap repulsive interactions, effective up to the next nearest neighbours. The calculated phase transition pressure shows linear decrease as a function of Mn composition ( x ).

Parameters Measurements of Semimagnetic Semiconductors by Means of the Electron Paramagnetic Resonance Method

Parameters Measurements of Semimagnetic Semiconductors by Means of the Electron Paramagnetic Resonance Method

Optical identification of impurity levels in strongly phosphorus‐doped wide‐gap II–VI bulk semimagnetic semiconductors

AbstractZn1–xMnxTe and Cd1–xMnxTe crystals doped with phosphorus have been investigated by means of the measurement of Hall effect, photoluminescence and reflectance. By annealing under high pressure of nitrogen (up to 4 MPa) at T = 800 °C for a week, a free hole density as high as 5 × 1018 cm–3 was achieved in Zn0.95Mn0.05Te, while in Cd0.99Mn0.01Te it was only 8 × 1016 cm–3. The phosphorus acceptor binding energy in Zn0.975Mn0.025Te and Cd0.99Mn0.01Te was found to be (0.036 ± 0.002) eV and (0.054 ± 0.002) eV, respectively.

Spin and size-dependent effects in semimagnetic semiconductor nanostructures

The technique of pulsed laser deposition has been applied for growth of Cd1−xMnxTe thin films and CdTe/Cd1−xMnxTe quantum well structures. Different materials (silicon, glass, sapphire) have been used as substrates which where heated to 300 °C during deposition process. X-ray diffraction, scanning electron microscopy, optical absorption and Faraday rotation spectroscopy have been used to characterize the obtained thin films and quantum structures. The observation of exciton peaks in the absorption spectra at low temperatures demonstrates the high quality of the deposited layers. The Faraday rotation spectra of the thin films exhibit peculiarities typical for bulk semimagnetic semiconductors because of strong spin-exchange interaction between band carriers and magnetic ions. For the superlattice structures of CdTe/Cd1−xMnxTe, the peak value of the Faraday rotation increases and its position moves toward higher energies with decreasing barrier thickness because of exciton confinement effect.

Spin-filter diode based on ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures

We propose and demonstrate a spin-filter diode based on semimagnetic semiconductor ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures. It is found that the degree of spin polarization greatly depends on the electric field direction and its magnitude. There is significant difference of the spin polarization between under forward bias and under reverse bias. It is also found that the spin polarization will reverse under relatively small magnetic field, which is originated from resonant enhancement effect for spin-up electrons tunneling through effective steplike potential of the corresponding structure.

Nonlinear magneto-optic Kerr effect in semiconductor microcavities

The photo-induced modifications of the strong magneto-optic Kerr effect have been studied in a semimagnetic semiconductor microcavity operated in the strong coupling regime. These are traced to the saturation and many body interaction blue shift of the exciton transition frequency, which result in a photo-induced reduction of the effective exciton–cavity coupling. Its impact is most striking in the case of initially tuned microcavity, where a modification of the exciton–cavity coupling results in photo-induced polarization rotations of about 30 degrees for laser fluences as low as 1 μJ/cm 2 and magnetic field intensities of 0.2 T.

Magnetic contribution to the specific heat ofPb1−xMnxTe

Temperature dependence of magnetic specific heat and magnetic susceptibility has been studied experimentally and theoretically in the semimagnetic semiconductor ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ for $x=0.024$ and $x=0.056,$ over the temperature range from 0.5 to 15 K, in magnetic fields up to 4 T. There was usually a maximum in the magnetic specific heat around 1 K in zero and low magnetic fields; the maximum shifted toward higher temperatures with increasing magnetic field. The experimental data have been analyzed in the framework of magnetic cluster models. An analysis of the influence of local lattice distortions and $\mathrm{sp}\ensuremath{-}d$ exchange coupling has been performed.

Nonlinear surface polaritons in semimagnetic semiconductor

The paper develops the theory of s-polarized nonlinear surface polaritons in the semimagnetic semiconductor placed in the external static magnetic field. A model of a uniaxial nonlinear medium for the semimagnetic semiconductor is considered. Rigorous criteria of existence of different new types of nonlinear surface polaritons are formulated. It is shown that the new polaritons may exhibit monotonic and nonmonotonic fall of the field in a nonlinear medium. We suggest the method of estimation of the antiferromagnetic resonance frequency in the semimagnetic semiconductors due to the nonlinear surface polariton excitation by the attenuated total reflection method.

Correlation between exciton decay time and Stokes shift in digital magnetic heterostructures

The exciton recombination time and the exciton photoluminescence Stokes shift are systematically investigated in a set of CdTe/Cd 1 - x Mg x Te quantum-well samples containing MnTe layers with the thickness below or equal to 1 ML. Similar to diluted magnetic semiconductors, these digital magnetic heterostructures exhibit strongly magnetic-field-dependent photoluminescence lines which are inhomogeneously broadened. Both quantities under investigation depend on the Mn content, on the details of the Mn distribution within the quantum wells, and on the energy of detection. Three sets of samples are investigated: digital magnetic heterostructures containing four MnTe layers with equidistant spacing and various thickness of the MnTe layers, quantum wells containing 1-ML MnTe at various positions in the quantum well, and quantum wells containing in total 1-ML MnTe but distributed in the quantum well in different ways. For all samples, the exciton recombination time is strongly correlated to the Stokes shift. This correlation is caused by exciton localization, leading to a mixing of radiatively decaying states with small momentum with nonradiative states with large momentum. In our experiment, however, a linear dependence between the exciton decay time and the Stokes shift is observed, which is not yet explained by theory, to our knowledge. Although, the luminescence properties in semimagnetic semiconductors are affected by exchange interactions leading to the formation of magnetic polarons, this process can be ruled out as the origin of the observed correlation.

Spin-phonon dynamics in doped magnetic quantum wells

A review of our recent experiments on the studies of spin-lattice relaxation in semimagnetic semiconductor quantum wells (QWs) is given. Three series of magnetic nanostructures are studied: undoped (Cd,Mn)Te/(Cd,Mg)Te QWs; n-doped (Cd,Mn)Te/(Cd,Mg)Te QWs with two-dimensional electron gas; p-doped (Cd,Mn)Te/(Cd,Mg,Zn)Te QWs with two-dimensional hole gas. In the experiments, we use a technique which combines an injection of nonequilibrium phonons and an optical detection of the induced changes via the exciton photoluminescence. We observe that doping induces a significant acceleration of the spin-lattice relaxation process, which is due to spin-flip transitions between Mn ions and free carriers. We demonstrate experimentally that it is possible to tune the value of spin-lattice relaxation time by changing the intensity of the laser excitation in the doped QWs.

Determining the Antiferromagnetic Resonance Frequency in Semimagnetic Semiconductors by Means of Surface Polaritons

In the articles surface polaritons are investigated in semimagnetic semiconductors in a phase of antiferromagnetic ordering. The influence of the external static magnetic field and the electron concentration on the dispersion properties of the surface polaritons is determined. It is shown that the surface polaritons can have a negative dispersion, independent of the direction of propagation in the Voigt geometry. A new method based on excitation of the surface polaritons in the semimagnetic semiconductors is proposed for determination of the antiferromagnetic resonance frequency.

Determining the Antiferomagnetic Resonance Frequency in Semimagnetic Semiconductors by Means of Surface Polaritons

Determining the Antiferomagnetic Resonance Frequency in Semimagnetic Semiconductors by Means of Surface Polaritons

Spin Conserving Tunneling in Asymmetric Double Quantum Well Structures

We present cw studies of exciton tunneling performed on CdTe-based asymmetric double quantum well structure. With the use of a semimagnetic semiconductor QW in magnetic field, we are able to align the carriers' spins before the tunneling. Using a polarization resolved photoluminescence excitation technique we obtain information on the efficiency of the transfer as well as its polarization memory. We record a transfer of spin polarization between quantum wells accounting for a 10% degree of polarization of photoluminescence.

Spin Conserving Tunneling in Asymmetric Double Quantum Well Structures

We present cw studies of exciton tunneling performed on CdTe-based asymmetric double quantum well structure. With the use of a semimagnetic semiconductor QW in magnetic field, we are able to align the carriers' spins before the tunneling. Using a polarization resolved photoluminescence excitation technique we obtain information on the efficiency of the transfer as well as its polarization memory. We record a transfer of spin polarization between quantum wells accounting for a 10% degree of polarization of photoluminescence.

Semimagnetic ZnMnSe/CdSe Fractional Monolayer Superlattice as an Injector of Spin‐Polarized Carriers

We report on effective injection of spin-oriented carriers from a semimagnetic semiconductor structure to a non-magnetic ZnCdSe/ZnSe quantum well (QW). A short-period ZnMnSe/CdSe fractional monolayer superlattice was used as a spin injector. The carriers are photo-generated in the semimagnetic region, spin-polarized via the effect of giant Zeeman splitting and then injected into the non-magnetic QW. The spin injection efficiency was estimated by circular polarization measurements of recombination emission from the QW. The maximal detected degree of the spin polarization is about 25%.

Origin of spin-glass behavior of Zn1-xMnxO

Alternating current susceptibility has been studied for polycrystalline Zn1 − x Mn x O. Stoichiometric samples demonstrate Curie–Weiss behavior, which indicates mostly antiferromagnetic interactions. Magnetic susceptibility can be described by a diluted Heisenberg magnet model developed for semimagnetic semiconductors. High-pressure oxygen annealing induces spin-glass like behavior in Zn1 − x Mn x O by precipitation of ZnMnO3 in the paramagnetic matrix.

Low-Dimensional Structures of Diluted Magnetic (Semimagnetic) Semiconductors - a Subjective Review

A review on selected areas of research on low-dimensional structures consisting of diluted magnetic (semimagnetic) semiconductors is attempted. In the introductory part, after short historical preliminaries, we describe some early ideas and speculations concerning properties of such structures and we confront them with real results obtained in the course of their experimental investigations. Several issues are addressed to but, in view of the richness of the field, the review is by no means not pretending to be an exhaustive one. We begin with early studies of metal-insulator-semiconductor structures and progress to structures grown by molecular beam epitaxy. We discuss, in particular, the idea of a spin superlattice, type-I-to-type-II transition, wave functions mapping, and detailed determination of the profiles of realistic quantum wells. We put special emphasis on digital growth and, specifically, parabolic and half-parabolic quantum wells, use of tunable g-factor in studies of trions, self-assembled quantum dots, spin injection and, finally, on hybrid structures of ferromagnets and diluted magnetic semiconductor structures. The focus of the present paper is on work clone in the Institute of Physics of the Polish Academy of Sciences, mostly in the Laboratory of Growth and Physics of Low-Dimensional Crystals.

Electron paramagnetic spin-wave effects on the transport current through a semimagnetic semiconductor layer

The relation between the electronic current through a magnetic heterostructure and propagating spin waves in the paramagnetic electron leads is studied. For a typical single magnetic barrier, an optimal regime is shown to exist for which the current intensity is fairly sensitive to transverse oscillations in the applied magnetic field, yielding the potential for a transistorlike device that can be used to study spin waves and the electron interactions in such materials.

Magnetooptical characterization of magnetic photorefractive semiconductors

Optical absorption, Faraday rotation and Voigt phase difference in doped Cd 1-x Mn x Te:V and Cd 1-y Hg y Te:Mn, V have been studied. Introducing the V dopant increases the absorption coefficient in tail part of spectra and codoping with Mn leads to its reduction. Faraday rotation spectrum of Cd 1 -x Mn x Te:V has features (change of the sign, large value of the Verdet constant) which are due to spin-spin-exchange interaction and is not affected by the V doping. The Voigt phase difference as a function of wavelength shows similarity to the spectral dependence of the Verdet constant because of their common nature in the studied semimagnetic semiconductors. However, significant enhancement of the Voigt effect was found more as the temperature was decreased.

Coupling effects of layers on spin transport in ZnSe/Zn 1 - x Mn x Se heterostructures

By use of the scattering matrix method, we investigate the coupling effects of layers on spin-polarized transport through semimagnetic semiconductor heterostructures with triple paramagnetic layers. Due to the coupling between double non-magnetic layers or among triple paramagnetic layers, spin tunneling exhibits interesting and complex features, which are determined by the structural configuration, the external fields as well as the spin orientations. It is shown that for electrons with either spin orientation tunneling through the symmetric or asymmetric heterostructures with triple paramagnetic layers, transmission resonances can approach the optimum under several biases. Moreover, for asymmetric structures, the resonant enhancement can occur under both several positive and negative biases. The spin-dependent resonant enhancement is also clearly reflected in the current density. In addition, for spin electrons traversing the multilayer heterostructure, the resonant splitting occurs in the transmission, which shows rich variations with the bias. These interesting results may be helpful to the development of spintronic devices.