Random Distribution Of Mn Research Articles

Distant-Neighbor Exchange Constants in Dilute Magnetic Semiconductors

Several exchange constants ${J}_{i}$ between ${\mathrm{Mn}}^{2+}$ ions which are not nearest neighbors were determined in ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}X$ ( $X\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{S},\mathrm{Se},\mathrm{Te}$) from magnetization steps at 20 mK. When the ${J}_{i}$'s are listed in order of decreasing size, ratios between successive ${J}_{i}$'s are material dependent, and differ from all predictions. The measured ${J}_{i}$'s were identified by comparing the magnetization curves with simulations which assumed a random Mn distribution. Contrary to existing theories the second-largest exchange constant is not ${J}_{2}$ between next-nearest neighbors. The most likely alternative is ${J}_{4}$, between fourth neighbors.

Cu 2(1 − z) Mn zln 2Se 4 alloys; phase diagram and effects of Mn ordering on magnetic behaviour

X-ray powder diffraction, differential thermal analysis and magnetic susceptibility measurements on polycrystalline samples were used to determine the details of the T( z) phase diagram of the alloy system Cu 2(1 − z) Mn z ln 2Se 4. At room temperature, the terminal solid solutions extend over the ranges 0 < z < 0.30 and 0.90 < 1.0. Values of Curie-Weiss θ from magnetic susceptibility data were determined for single phase samples in each range and used to determine the ordering of the Mn in each case. The magnetic data indicate that for 0 < z < 0.30 and T > 200 °C, the Mn is randomly distributed over the cation sublattice, the phase having space group 142d. However, at lower temperatures, for 0.05 < z < 0.30, the Mn atoms order to occupy only the 4a sites resulting in probable antiferromagnetic behaviour. The high z alloys all show a random distribution of Mn on the cation sties, and the compound Mnln 2Se 4 ( z = 1.0) was found to be spinglass, with T g = 2.7 K and θ = −94 K.

Influence of phosphorus substitution on Mn 0.63Cr 0.37As

Mn 0.63Cr 0.37As 1− x P x has been investigated for 0.000 ≤ x≤0.100 by X-ray and neutron diffraction, magnetometric, DTA, DSC and ESR measurements. The results show that there is complete solid solubility throughout the studied composition range with random distribution of Mn, Cr and As, P over the metal and non-metal sublattice, respectively. At and below room temperature the crystal structure is of the MnP type. Phosphorus acts as a positive chemical pressure generator. The characteristic magnetic transitions of Mn 0.63Cr 0.37As on decreasing temperature, para (P) to helimagnetic (H c ) followed by H c to H a , are only maintained at a very low substitution level, x < 0.008. Further increase of the phosphorus content suppresses H c and favours ferromagnetism (F). For x > 0.05 the F mode becomes the only ordered magnetic state. A tentative magnetic phase diagram for Mn 0.63Cr 0.37As 1− x P x (0.00≤ x≤0.10) is advanced. Interesting features of ESR data are presented, and connections to the magnetic phase diagram are proposed.

Electroreflectance and wavelength-modulated reflectivity measurements of Zn1−xMnxTe mixed crystals

Electroreflectance and wavelength-modulated reflectivity data near the fundamental absorption edge of Zn1−xMnxTe solid solutions are presented as a function of temperature and Mn content. From these data the dependence of the energy gap on temperature and composition was determined. The broadening of electroreflectance and wavelength-modulated reflectivity structures is found to depend linearly on [x(1−x)]2 at low temperatures. This indicates that the broadening is produced primarily by the random distribution of Mn and Zn atoms in the lattice.

Magnetic properties of Cu2Zn1-xMnxGeS4: Antiferromagnetic interactions in the wurtz-stannite structure.

Susceptibility and magnetization measurements were carried out on ${\mathrm{Cu}}_{2}$${\mathrm{MnGeS}}_{4}$, and on ${\mathrm{Cu}}_{2}$${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$${\mathrm{GeS}}_{4}$ with 0\ensuremath{\le}x\ensuremath{\le}0.1. These magnetic (or semimagnetic) semiconductors have the wurtz-stannite structure. The data indicate that ${\mathrm{Cu}}_{2}$${\mathrm{MnGeS}}_{4}$ is a low-anisotropy antiferromagnet with a N\'eel temperature ${T}_{N}$=8.25\ifmmode\pm\else\textpm\fi{}0.3 K. The high-field transition from the canted phase to the paramagnetic phase of ${\mathrm{Cu}}_{2}$${\mathrm{MnGeS}}_{4}$ was observed at low temperatures. The transition field gives ${H}_{E}$\ensuremath{\simeq}90 kOe for the intersublattice exchange field at T=0. The anisotropy field ${H}_{A}$ at T=0 is of order 3 kOe. Differences in the magnetic behavior of several ${\mathrm{Cu}}_{2}$${\mathrm{MnGeS}}_{4}$ samples are attributed to differences in the carrier concentration. Values of the Curie constant C for the samples with x\ensuremath{\le}0.1, and also for x=1, are close to those expected theoretically. For x\ensuremath{\le}0.1, the Curie-Weiss temperature FTHETA is approximately equal to ${\mathrm{FTHETA}}_{0}$x, where ${\mathrm{FTHETA}}_{0}$=-32 K. This is consistent with a random Mn distribution over the group-II cation sites. The value of FTHETA for ${\mathrm{Cu}}_{2}$${\mathrm{MnGeS}}_{4}$ (x=1), however, is well below ${\mathrm{FTHETA}}_{0}$, which suggests that the Mn-Mn exchange interactions decrease with increasing x. In all samples, the field required to saturate the magnetization at low temperatures is below 200 kOe. The relatively low saturation field, and the values for the Curie-Weiss temperatures, show that the Mn-Mn antiferromagnetic interactions are much weaker than in the analogous II-VI dilute magnetic semiconductors. This confirms the prediction of Wolff et al. and Heiman et al.

High field magnetization step in Zn1−xMnxTe

Abstract Low temperature and high field magnetization experiments (H ⩽ 19 T) were carried out in diluted Zn1−xMnxTe alloys (x = 0.03). At 1.3 K, the first magnetization step, corresponding to the level crossing for pairs of nearest-neighbours (NN) is observed around H ⋍ 15 T . Magnetization data are analyzed including, within the molecular field approximation (MFA), interactions between Mn ions distributed in small clusters (singles, pairs, triangles) with more distant neighbours than NN. Both the saturation value observed at H ⋍ 10 T and the magnitude of the step agree with a random Mn distribution. Theoretical fits of the magnetization step provide a determination of the NN exchange constant J k = −9.25 ± 0.3 K .

Nearest-neighbor exchange constant and Mn distribution in Zn1-xMnxTe from high-field magnetization step and low-field susceptibility.

Magnetization data in fields up to 210 kOe were obtained on ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te samples with x=0.031 and 0.040. At Tapeq21.4 K, a magnetization step was observed near 150 kOe. This step is attributed to a level crossing for pairs of nearest-neighbor (NN) Mn spins. The magnetic field at the center of the step gives J/${k}_{B}$=-10.0\ifmmode\pm\else\textpm\fi{}0.8 K for the NN exchange constant. This value is slightly higher than that obtained from inelastic neutron scattering. The magnitude of the magnetization step agrees with calculations which assume a random Mn distribution. The technical saturation value for the magnetization at low temperatures also agrees with calculations which assume a random Mn distribution. Low-field susceptibility data, taken at 4\ensuremath{\le}T\ensuremath{\le}350 K, lead to Curie constants which agree with those calculated with S=(5/2) and g=2 for each Mn ion. Assuming NN interactions only, and a random Mn distribution, the Curie-Weiss temperatures give J/${k}_{B}$apeq2-12 K. A detailed theoretical discussion of the NN cluster model, as it applies to the magnetization curve of a dilute magnetic semiconductor at low T, is given. Many of the theoretical results also should apply to a larger class of dilute magnetic materials.

Defect structures in the brannerite-type vanadates. I. Preparation and study of [formula omitted

Phases of the formula Mn 1− x ф x V 2−2 x Mo 2 x O 6 with the brannerite-type (α) structure, where ф represents a vacancy at the Mn 2+ site, have been sythesized and characterized by X-ray diffraction and DTA. The X-ray data are listed for MnV 2O 6 and solid solution with x = 0.40. They indicate the random distribution of V and Mo over the original V sites and the random distribution of Mn and vacancies over the original Mn sites. The monoclinic cell dilates with increasing x, primarily in the direction of the b-axis. The phase diagram of the pseudobinary MnV 2O 6MoO 3 system has been determined. The extent of the stability region for the investigated brannerite solid solution has been established ( x max = 0.45 at 583°C). Other features determined in this system were: (a) little solubility of MoO 3 in the high-temperature (β) modification of MnV 2O 6, (b) a two-phase area of α- and β-type solid solution coexistence, (c) a eutectic point between α-type solid solution and MoO 3 at 583°C and 75 mole% of MoO 3 and (d) phase relationships at the liquidus.

The effect of manganese on olivine-quartz-orthopyroxene stability

The effect of manganese on the stability of ferrosilite relative to fayalite + quartz has been experimentally determined to assess its importance to orthopyroxene barometry. Reaction reversals in a piston-cylinder apparatus were obtained to within 0.1-kbar intervals indicating instability of Fs 95Rh 5 below 10.3, 10.9, 11.4, 12.2, 12.9, 13.7 kbar and Fs 90Rh 10 below 9.8, 10.4, 10.9, 11.6, 12.4 and 13.2 kbar at 750, 800, 850, 900, 950 and 1000°C, respectively. Each mole % MnSiO 3 extends the pyroxene stability by approximately 0.12 kbar relative to FeSiO 3. Electron microprobe analyses of run products indicate a small preference of Mn for pyroxene over olivine with K DMn-Fe opx-oliv = 1.2−1.5, similar to values observed for natural pairs. Mössbauer spectra are consistent with a random distribution of Mn between the M1 and M2 sites in the orthopyroxene. These experimental data allow downward revision of pressure estimates based on the orthopyroxene barometer in areas where Mn is a significant component in orthopyroxene.