Modulated replica symmetry breaking schemes for antiferrimagnetic spin glasses

The temperature and voltage dependence of spin transport is theoretically investigated in a new type of magnetic tunnel junction, which consists of two ferromagnetic outer electrodes separated by a ferromagnetic barrier and a nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic barrier, which plays an important role at finite temperature, is included by taking the mean-field approximation. It is found that, the tunnel magnetoresistance (TMR) and the electron-spin polarization depend strongly on the temperature and the applied voltage. The TMR and spin polarization at different temperatures show an oscillatory behavior as a function of the NM spacer thickness. Also, the amplitude of these oscillations is regularly reduced when the temperature increases. The maximum TMR value, varies approximately from 270 in reverse bias (at T = 0 K) to 25 in forward bias (at ).Received: 25 June 2004, Published online: 14 December 2004PACS: 72.25.Hg Electrical injection of spin polarized carriers - 73.23.Ad Ballistic transport - 73.40.Gk Tunneling     

A microscopic calculation of dynamic critical exponents for displacive phase transitions

For anO(n)-isotropic lattice dynamicalQ ⁴-model describing displacive phase transitions ind dimensions, we employ a microscopic 1/n-expansion in order to show that over-damped soft-phonon behavior emerges for frequencies smaller than those of the characteristic orderv _c =O(n ^–x ). This is concluded from the fact that the displacement propagatorD(q, v) assumes the time-dependent Ginzburg-Landau (TDGL) form with a damping coefficient=O(n ^–x ), whenv becomes smaller thanv _c . The exponentx is found to bex=4–d for 2<d<3,x=(d–1)/2 for 3<d<5, andx=2 ford>5. The dynamic critical exponents forv _c (q) and forD(0,v) are derived atT=T _c 0 and toO(1/n). Their values are nontrivial for 2<d<4 and, within the TDGL-region, agree with the those appearing already for frequencies ofO(n ⁰) in TDGL-models with nonconserved order parameter andO(n ⁰)-damping coefficient. The latter case was studied by Halperin, Hohenberg, and Ma in 1972. Even in the TDGL-region, the energy conservation does not affect the dynamic exponents for largen(>2, since the specific heat is finite), but an energy diffusion singularity appears in theQ ²-response function which is related to the basic quantity of the 1/n-method, the effective interactionU _eff. By an estimate of order we find that the damping coefficients resulting from the coupling between the relaxation modes contained inU _eff and the critical modes inD are of ordern ^–w withw>x, such that the coupling between weakly damped critical modes is responsible for the crossover to the TDGL-behavior for largen. The exponentz=d/2, known to be generated by the coupling between order parameter and conservedO(n)-densities in TDGL-models, cannot be seen up to the order calculated. We also point out problems of a microscopic-expansion and comment upon differences between microscopic treatments for displacive transitions and those for the Bose condensation.     

Scaling functions of susceptibilities toO(1/n) forn-vector models with axial anisotropy

For an axially anisotropicn-vector model withm = O(n) easy – andn – m = O(n) hard components of the order parameter, we derive the susceptibility r ^–1 along one of the equivalent easy axes and the perpendicular one r ^-1 toO(1/n) of the 1/n-expansion in the disordered phase. The results confirm predictions of the scaling theory, e.g.(g, t)=A t ^– X (B g/t ) and (g, t) =A t ^– X (B g/t ), wheret = T – T _c (g = 0),g is the anisotropy parameter andX, X denote the scaling functions. We evaluate the relevant diagrams toO(1/n) which yield the coefficientsA, A and the critical behaviour of the scaling functions and critical amplitudes explicitly for . The extreme anisotropic case, i.e.m = O(1), is discussed briefly in the large-n limit in comparison with the mean field solution.Parts of this paper were presented at the Frühjahrstagung der Deutschen Physikalischen Gesellschaft in Freudenstadt (May 1974).     

Richtlinien und Bemerkungen der Redaktion und des Verlages zur Abfassung von Manuskripten für die Zeitschrift für anorganische und allgemeine Chemie

Barogram of the System HgI₂? I₂ The barogram of the system HgI₂? I₂ is determined by total pressure measurements. From this is concluded the melting diagram and compared with results of references.     

Der chemische Transport der Phase CoS

The Chemical Transport of the CoS phase The CoS_x Phase can be deposited as single crystals by CTR using iodine, only if x is greater than 1.06. This is due to the sulphur phase equilibrium pressure which otherwise is too small for effecting this transport. HI or GeI₂ can be used as transport agent for specimens with less sulphur contents. Using GeI₂ CTR also yields monocrystals of the Co₉S₈ phase.     

Zustandsbarogramm und thermodynamische Daten für das System Germanium – Tellur

Barogram and Thermodynamic Data of the System Germanium—Tellurium The barogram Ge? Te is constructed by total pressure measurements. From the temperature function of the pressure of GeTe follows the thermodynamic data of sclid and gaseous GeTe and gaseous GeTe₂. The data are proved by chemical transport experiments of Ge with Tellurium.     

Investigation of the phase barograms and diagrams of the GeI4-I2, GeI4-BiI3 and GeI4-HgI2 systems

The phase barograms of the systems GeI₄-I₂, GeI₄-BiI₃ and GeI₄-HgI₂ were determined by total pressure measurements in a membrane zero manometer and the resulting phase diagrams were compared with those obtained by DTA measurements. All the systems were single eutectics.

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Zusammenfassung Durch Gesamtdruckmessungen mittels eines Membrannullmanometers wurden Phasenbarogramme der Systeme GeI₄-I₂, GeI₄-BiI₃ und GeI₄-HgI₂ ermittelt und die resultierenden Phasendiagramme mit den an Hand von DTA-Messungen erhaltenen verglichen. Alle diese Systeme besitzen einen eutektischen Punkt.

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Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60^th birthday

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We express our thanks to Mrs. Dr. U. Stahlberg, who carried out the analyses at the MS 7 in the ZFW Dresden     

Zum Chemischen Transport im System Mn/Mo/O

Chemical Transport Reactions in the System Mn/Mo/O For the ternary system Mn/Mo/O the phasepure preparation of the compounds MnMoO₄ and Mn₂Mo₃O₈ by chemical transport is reported. The deposition from a source of coexisting threephase mixtures give the possibility to prepare single crystals under defined oxygen partial pressure. The influence of different startmixtures and the agents Cl₂, HCl, I₂, HI, TeCl₄ and SeCl₄ on the transport behaviour are described. Results hitherto existing for the single crystals give hints of only very small homogeneity ranges for both phases.     

Gleichgewichtsdruckmessungen im System Se/O/Cl

Equilibrium Measurements in the System Se/O/Cl The evaporation and decomposition behaviour was Studied by total pressure measurements in equilibrium with condensed phases as well as in the unsaturated Vapour. The composition Cl/Se = 4 shows the lowest, the composition Cl/Se = 2 the highest total pressure in the Barogramm of the system Se/Cl. Solid SeCl₄ and liquid Se₂Cl₂ exist as condensed compounds whereas only SeCl₂ exists in the gas. The following data were derived (see ?Inhaltsübersicht”?) from the decomposition sublimation SeCl₄, the decomposition of Se₂Cl₂ and the evaporation and decomposition of SeOCl₂.     

Zum System Zn/Mo/O. I. Phasenbestand und Eigenschaften der ternären Zinkmolybdate; Struktur von Zn3Mo2O9

On the System Zn/Mo/O. I. Phases and Properties of Ternary Zinc Molybdates; Crystal Structure of Zn₃Mo₂O₉ Several ternary compounds are known in the Zn/Mo/O-system. The phases ZnMoO₄, Zn₂Mo₃O₈ and Zn₃Mo₂O₉ are stable at 900°C. The coexistence ranges are shown in the ternary phase diagram. The structure of Zn₃Mo₂O₉ has been determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/m (a = 7,757(1) Å, b = 7,132(1) Å, c = 8,370(2) Å, β = 117,40(1)º, Z = 2).