T. M. Pekarek

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 3×10−5 emu/g above the background of 7×10−5 emu/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...

Magnetic measurements on the layered III–VI diluted magnetic semiconductor Ga1−xFexSe

Magnetic properties of single crystalline Ga1−xFexSe have been measured. This material is in the new class of diluted magnetic semiconductors based on the III–VI semiconductors. The magnetization versus field for an x=0.05 sample deviates from the linear response seen previously in Ga1−xMnxSe and Ga1−xMnxS and reaches a maximum of 0.12 emu/g (<7% of the expected saturation value) at 1.8 K in 7 T. Ga1−xFexSe exhibits an anisotropy below 2 T from 5 to 400 K with the hard axis perpendicular to the GaSe planes. Neither the broad peak observed from 119–195 K in Ga1−xMnxSe nor the Curie–Weiss behavior observed above 75 K in Ga1−xMnxS are observed in Ga1−xFexSe. The sharp cusp at 10.9 K in Ga1−xMnxS (characteristic of longer range ordering) is also not observed in Ga1−xFexSe in temperatures down to 1.8 K. In 0.1 T in temperatures between 50 and 400 K, the magnetization drops to a roughly constant 0.004 emu/g. Below 5 K, the magnetization approaches a constant value of approximately 0.12 emu/g. The magnetic behav...

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.

Spin glass or random anisotropy?: The origin of magnetically glassy behavior in nanostructured GdAl2

Initially crystalline GdAl2 was mechanically milled for long times to produce a highly chemically disordered phase with approximately 8‐nm grains. Analysis of dc magnetization measurements using an Arrott plot and the approach to saturation suggest the presence of significant random anisotropy. ac susceptibility measurements showed that the shift in the peak temperature with frequency usually seen in magnetically glassy and superparamagnetic systems was virtually undetectable in the 10–1000‐Hz frequency range. Based on these results, we believe that this material represents an interacting system with random anisotropy, where the anisotropy is the result of surface and interface asymmetries.

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 ∼0.0100 T 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.

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.

Magnetic, electrical, and structural studies on the metal-insulator transition in CuIr2S4−xSex (0⩽x⩽4)

Magnetic transitions and structural transformations have been investigated in CuIr2S4−xSex (0⩽x⩽4). It is found from magnetic, resistivity, and thermopower studies that the transition temperature decreases as the Se concentration is increased. The change in magnetization occurs over a 10–15 K range at lower Se concentration, while it broadens to 30 K for an Se concentration of x=0.5. Low-temperature studies proved that beyond the composition corresponding to x=0.5 the cubic structure is stabilized. The metal-insulator transition beyond the x=0.5 composition arises from the electronic rather than from the lattice contribution.

Spin-glass ordering in the layered III-VI diluted magnetic semiconductor Ga1−xMnxS

Magnetization and ac susceptibility measurements on single crystalline Ga1−xMnxS (x=0.09) have been measured near the spin-glass transition. No other III-VI diluted magnetic semiconductor (DMS) is currently known to exhibit a spin-glass transition for comparison with Ga1−xMnxS. Both the magnetization and ac susceptibility measurements were analyzed according to the appropriate universal scaling function for spin-glass transitions. The nonlinear magnetization scaled with the critical exponent values γ=4.0±1.0 and β=0.8±0.2 for a spin-glass transition temperature Tc=11.2±0.2 K. The analysis of the ac susceptibility’s out-of-phase component χ″(ω,T) yielded the parameter values Tc=10.8±0.3 K, zν=10±1, and β=0.6±0.3. The values of the critical exponents are consistent with those obtained in many DMS and non-DMS insulating spin glasses with different lattice structures and exchange interactions. These results indicate that III-V DMS materials such as Ga1−xMnxS belong in the same three-dimensional short-range He...