I. Miotkowski

MAGNETIC MEASUREMENTS ON THE III-VI DILUTED MAGNETIC SEMICONDUCTOR GA1-XMNXSE

We have investigated the magnetic properties of Ga1−xMnxSe, which represent a new class of diluted magnetic semiconductors based on a III-VI semiconductor. These are layered materials; however the local environment is tetrahedral as in the II-VI materials. In contrast to the II-VI semiconductors, the Mn substitutional atoms have direct bonds to three Se atoms and to either a Ga or Mn atom. This leads to a complex temperature dependent magnetization. In fields of 100 G and below, a broad peak is observed in the magnetization centered at 160 K. In addition, a sharp change in magnetization is observed at 119 K. In a field of 100 G, the peak has a magnitude of 3×10−5u2009emu/g above the background of 7×10−5u2009emu/g. With increasing magnetic fields, these features are broadened which is suggestive of some type of short-range antiferromagnetic ordering. At 5 K we observe a magnetization which increases linearly with field up to 6 T similar to the Van Vleck paramagnetic behavior observed in the Fe substituted II-VI se...

The anomalous variation of band gap with alloy composition: cation vs anion substitution in ZnTe

Abstract The energy of the excitonic signature, E g ( x ), in the wavelength modulated reflectivity spectrum of Zn 1− x Mg x Te shows a monotonic increase with x in contrast to a large downward bowing of E g ( x ) in ZnS x Te 1− x and ZnSe x Te 1− x . Free and bound excitonic signatures in the photoluminescence spectra of the same samples provide additional confirmation for these trends. Raman spectra of these ternaries display a remarkable resonance enhancement of the zone center longitudinal optical (LO) phonon and its overtones when the scattered photon energy approaches the free excitonic transition energy: for a fixed exciting photon energy, the intensities of Raman lines with shifts of 1LO, 2LO, 3LO,… are selectively enhanced in sequence as a function of x , but in the reverse order in Zn 1− x Mg x Te as compared to that in ZnSe x Te 1− x , underscoring the monotonic increase of E g ( x ) in the former and a significant downward bowing in the latter.

Explorations of the magnetization of Ga1−xMnxS over a wide range of concentrations, 0.008<x<0.18

Calculations and measurements of the magnetization of Ga1−xMnxS, a III-VI diluted magnetic semiconductor crystal, are reported. Results extend over a wide range of concentrations: x=0.18, 0.13, 0.099, 0.079, 0.062, 0.032, and 0.008. The magnetization was measured at temperatures from 50 to 400 K in magnetic fields up to 7 T. The experimental data are compared with a model of the magnetization that is derived using the energy levels of a singlet Hamiltonian which posits the manganese atoms are not interacting with each other. The Hamiltonian consists of crystal-field, spin-orbit, spin-spin, and Zeeman interactions of the 3d electrons of the Mn+3 substitutional ions. The spin-orbit parameter used in the model was λ=23cm−1, independent of concentration. At smaller values of x the singlet model agreement with the experiment is excellent. For larger values of x and low temperatures the agreement deteriorates somewhat as expected due to the antiferromagnetic coupling of the Mn ions.

Magnetic and transport measurements on the layered III-VI diluted magnetic semiconductor In1−xMnxSe

Magnetic and transport properties of single-crystalline In1−xMnxSe (x=0.01 and 0.10) have been measured. In1−xMnxSe exhibits a prominent magnetization hysteresis between 90 and 290K. In1−xMnxSe is conducting with increasing resistance at low temperatures and a small hysteresis between 90 and 290K with the cooling trace having lower resistivity. The magnetization above and below the hysteresis is consistent with a paramagnetic signal. A Curie–Weiss fit to the data yields a value of Jeff∕kB=−240K. The data are consistent with a saturated component contributing to the hysteresis and a paramagnetic phase that scales with concentration.

Magnetic measurements on ferromagnetic behavior in the bulk II-VI diluted magnetic semiconductor Zn1-xCrxTe

Magnetic measurements on the ferromagnetic behavior in the bulk II–VI diluted magnetic semiconductor Zn1−xCrxTe were made on two x=0.0033 single crystals taken from different regions of the same boule. Ferromagnetism was verified in both samples by an Arrott plot analysis with a transition temperature at 365 K (well above room temperature). For both samples at room temperature, the coercive field is ∼0.0100u2009T and the remanent magnetization is 23% of the saturated value. The similarity in the observed ferromagnetic behavior between the two samples suggests that a stable CryTez or possibly ZnxCryTez precipitate phase is responsible, although a Cr-rich region in the bulk Zn1−xCrxTe itself cannot currently be conclusively ruled out as the source.

The singlet model of the anisotropic magnetization of the III-VI diluted magnetic semiconductor, In1−xMnxS

Results for the anisotropic magnetization of the III-VI diluted magnetic semiconductor (DMS), In1−xMnxS, are presented. The compound has a markedly different crystal structure from previously investigated III-VI crystals. The Hamiltonian includes crystal potential, Zeeman, spin-orbit, and spin-spin terms. The singlet model used assumes that the substitutional Mn are noninteracting which is appropriate when x is small (here 2%). Magnetization versus temperature results are found for several magnetic fields B. The experimental magnetization is compared to our singlet model results with excellent agreement except at low temperatures (⩽20K) where some evidence of possible spin-glass behavior is evident.

The lattice constants of ternary and quaternary alloys in the PbTe-SnTe-MnTe system

Abstract The study of structural properties of quaternary Pb 1− x − y Sn x Mn y Te alloys revealed that they crystallise in a cubic structure of NaCl-type for a wide region of manganese content (up to y =0.16). It was found from X-ray measurements and microprobe analysis that Vegards law is obeyed. The dependencies of the lattice constants on composition for Pb 1− x − y Sn x Mn y , Pb 1− y Mn y Te and Sn 1− y Mn y Te were used to extract the lattice parameter of NaCl-type MnTe phase by extrapolation. The experimental data were also used to obtain an improved estimate of the covalent octahedral radius for Mn.

Strong out-of-plane magnetic anisotropy of Fe adatoms on Bi2Te3

The electronic and magnetic properties of individual Fe atoms adsorbed on the surface of the topological insulator Bi2Te3(111) are investigated. Scanning tunneling microscopy and spectroscopy prove the existence of two distinct types of Fe species, while our first-principles calculations assign them to Fe adatoms in the hcp and fcc hollow sites. The combination of x-ray magnetic circular dichroism measurements and angular dependent magnetization curves reveals out-of-plane anisotropies for both species with anisotropy constants of K-fcc = (10 +/- 4) meV/atom and K-hcp = (8 +/- 4) meV/atom. These values are well in line with the results of calculations.

Thermal hysteresis in the magnetization of the layered III-VI diluted magnetic semiconductor In1−xMnxSe

Magnetic properties of single-crystalline In1−xMnxSe (x=0.10) have been measured. A prominent thermal hysteresis in the magnetization is observed between 90 and 290K. The magnetization is reversible (deviating by only ∼0.8%) from 400 down to ∼120K along the upper branch of the hysteresis. In contrast, the lower branch magnetization is irreversible from 5 up to 290K and deviates by 30% of the 0.010emu∕g hysteresis splitting at 140K. Magnetic-field hysteresis loops at 200K between −7 and +7T demonstrate that changing the magnetic field does not allow movement between the upper and lower branches of the thermal hysteresis. This magnetic behavior is consistent with a charge-density wave. However, the observed ΔT=200K hysteresis in In1−xMnxSe is roughly an order of magnitude larger than other previously reported values of ΔT.

Lattice parameters and optical characterization of Cd1−xMgxSe alloys grown by vertical gradient freezing technique

Single crystals of Cd1−xMgxSe ternaries grown by the vertical gradient freezing technique are characterized by X-ray diffraction and electron probe microanalysis as well as wavelength-modulated reflectivity and photoluminescence to establish their basic structural and optical properties. In the composition range 0<x<0.40, the alloys crystallize in the wurtzite structure with lattice parameters decreasing linearly with increasing Mg concentration (x). X-ray data considered in the context of interatomic distances yield an improved estimate of the tetrahedral covalent radius of Mg. Energy gap as a function of x increases linearly with increasing Mg concentration. The lattice parameters and the energy gap of the end member of the Cd1−xMgxSe wurtzite ternaries, i.e., of MgSe with the wurtzite structure, are deduced from those measurements.