Spin-spin Exchange Interaction Research Articles

Fluorescence line narrowing-Zeeman spectroscopy of Cr3+-doped Gd3Sc2Al3O12 garnet crystals

This paper discusses line broadening by compositional disorder and by spin-spin exchange interaction between the paramagnetic Cr3+ and Gd3+ ions in antiferromagnetic Gd3Sc2Al3O12 (GSAG) probed using fluorescence line narrowing (FLN) in the absence and presence of a magnetic field. The most intense R1 lines in Cr3+:GSAG, occurring at lambda =691.2 nm and 692.4 nm, have halfwidths of approximately=32 cm-1. The linewidths of the FLN spectra at 1.6 K are respectively 19 cm-1 and 13 cm-1, much larger than the width of the excitation laser beam (<0.2 cm-1): thus the contributions to the R1-line halfwidth from mechanisms of homogeneous and inhomogeneous broadening are approximately equal. In addition, the peaks of the FLN lines are shifted to lower energy from the laser excitation line by approximately=8 cm-1. As the temperature is increased gradually from 1.6 K to 10 K, the FLN peak is shifted to higher energy and is resonant with the excitation above 10 K. In the presence of an external magnetic field the broad FLN spectrum becomes resolvable into three sharp lines with the width of approximately=3 cm-1 at T=1.6 K. The peak of the line with maximum intensity is coincident with the excitation energy. The FLN spectrum at T=10 K and B=3.46 T is similar to that at T=10 K in the absence of a magnetic field. The temperature dependence and magnetic field dependence of the FLN spectra are discussed in terms of spin-spin exchange interaction between Cr3+ and Gd3+ ions in antiferromagnetic GSAG.

Double string and exchange interaction approach to superconductivity

The renormalization factor is calculated for a single-particle state using string excitations of lengths equal to one or two lattice spacings. The wave function renormalization factor of a pair of holes has also been calculated using the intersite tunneling interaction, t, along with the spin-spin exchange interaction, J. The two holes of a pair are at different sites forming a singlet of the same size as the interatomic spacing. The electrons participating in the formation of the double string are attractive forming an antiferromagnetic state. The electron pairs are localized on sites.

ChemInform Abstract: On the Structural Aspects of Magnetism in Transition Metal‐Metalloid Amorphous Alloys

Abstract Transition metal-metalloid amorphous alloys generally have very soft ferromagnetic properties and low electrical conductivity compared to ferromagnetic crystalline alloys. However, the reasons for this are not well understood. The principal difference between a metallic glass and its crystalline counterpart is in the structure and this paper examines the effect of structure on solid-state magnetic interactions like spin-spin coupling, spin-orbit coupling and spin-lattice coupling via the orbital electrons. In the present study, the interaction between the intensely heterogeneous (noncentral) crystal field and the aspherical charge distribution in the paramagnetic ion is seen to introduce large magnetocrystalline anisotropy in crystalline ferromagnets. The width of the domain walls and the magnitude of the hysteresis may be understood on the basis of the magnetic anisotropies in the system and the above mentioned magnetic interactions. In a metallic glass, because of the metastable nature of the structure and the spherically symmetric distribution of material around any atom in the short-range-ordered amorphous clusters, it is argued that the crystal field would be weak, and perhaps central. This would result in an unquenched orbital magnetic moment, a weak orbit-lattice coupling and hence a weak spin-lattice coupling for the paramagnetic ion. The low hysteresis and weak magnetocrystalline anisotropy observed in metallic glasses may be explained on the basis of the above results. In this case, the spin-spin exchange interaction would dominate over the magnetocrystalline anisotropy giving rise to relatively wide and shallow domain walls.

On the structural aspects of magnetism in transition metal-metalloid amorphous alloys

Transition metal-metalloid amorphous alloys generally have very soft ferromagnetic properties and low electrical conductivity compared to ferromagnetic crystalline alloys. However, the reasons for this are not well understood. The principal difference between a metallic glass and its crystalline counterpart is in the structure and this paper examines the effect of structure on solid-state magnetic interactions like spin-spin coupling, spin-orbit coupling and spin-lattice coupling via the orbital electrons. In the present study, the interaction between the intensely heterogeneous (noncentral) crystal field and the aspherical charge distribution in the paramagnetic ion is seen to introduce large magnetocrystalline anisotropy in crystalline ferromagnets. The width of the domain walls and the magnitude of the hysteresis may be understood on the basis of the magnetic anisotropies in the system and the above mentioned magnetic interactions. In a metallic glass, because of the metastable nature of the structure and the spherically symmetric distribution of material around any atom in the short-range-ordered amorphous clusters, it is argued that the crystal field would be weak, and perhaps central. This would result in an unquenched orbital magnetic moment, a weak orbit-lattice coupling and hence a weak spin-lattice coupling for the paramagnetic ion. The low hysteresis and weak magnetocrystalline anisotropy observed in metallic glasses may be explained on the basis of the above results. In this case, the spin-spin exchange interaction would dominate over the magnetocrystalline anisotropy giving rise to relatively wide and shallow domain walls.

Phase transitions in high-Tcsuperconductive oxides

Abstract Superconductivity is stabilized by the opening up of an energy gap at the Fermi Energy E F below the superconductor transition temperature T c ; any other mechanism that opens an energy gap at E F is competitive. In the high-T c bismuth oxides, a charge-density wave (CDW) is competitive; in the high-T c copper oxides the correlation splitting associated with localized electrons is competitive. In each class of oxide, stabilization of superconductivity requires the introduction of mixed valency. It is argued that suppression of a CDW or of localized magnetic moments and long-range magnetic order by the introduction of mixed valency is not a sufficient condition for high-T c superconductivity. A common feature of the superconductive phase in all the p-type high-T c oxides is a Fermi energy that cuts two bands, a [sgrave]∗ band of primarily cationic character (Bi-6s or Cu-3dx2-y2) and a π or π∗ band of primarily anionic character (O-2pπ). The transition from localized copper magnetic moments to Pauli paramagnetism is monitored in the system La2-xSrxCuO4-y; although short-range antiferromagnetic order is retained in the p-type superconductive phase of the copper oxides, a charge-transfer as against a spin-spin exchange interaction appears to be the more probable mechanism for enhancement of the Cooper pairing below T c . The recently discovered n-type superconductivity in Nd2-xCexCuO4 may involve charge transport to the rare-earth 5d bands.

The Faraday effect in magnetic semiconductors (abstract)

In n-type ferromagnetic semiconductors, both bound electrons and free carriers make contributions to the Faraday effect. The spin-orbital interaction of bound electrons, and the spin-spin exchange interaction between bound electrons and between bound electrons and free electrons exist. Thus, the Faraday rotation θ has been deduced as follows: θ=(eμ0/mc)∑∞l=1blλ2lL (He+ν′M)+(eμ0/mc) ∑∞n=1(an/λ2n) L[He+(ν+ν′)M] =θS+θF, where L is the thickness, He the external field, M the magnetization, ν′M the effective field related to the exchange interaction between bound electrons and free electrons, νM the effective field related to the spin-orbital interaction of bound electrons and so on, an and bl the constants related to the concentration N1 of free electrons and the concentration N2 of bound electrons, respectively. While λ&amp;gt;λ0, the wavelength at θ=0, or N1&amp;gt;N0∼1022/m3, θS&amp;gt;θF. Conversely, θS&amp;lt;θF. When θS≪θF, θ∼(a1/λ2+a2/λ4+...). The temperature behavior of θ mainly depends on that of M. θ tends to saturation with M. When θS≫θF, θ∼(b1λ2+b2λ4+⋅⋅⋅). θ is directly proportional to approximately He. The calculations are confirmed by the experimental results in CdCr2S4, etc.

Far-infrared spin resonance in narrow-gap semiconductors

The author reviews far-infrared studies of spin resonance (SR) in narrow-gap semiconductors, with emphasis on SR of the conduction band. While the SR transition is normally electric-dipole-forbidden, it is well known that there exist mechanisms (e.g. 'non-parabolicity' or inversion asymmetry) which relax these selection rules. The author discusses these mechanisms and their relative importance. Although the author concentrates in this review on the Gamma 6-like conduction band of InSb, the author also reviews experimental results on other materials (e.g. HgSe, HgTe, Hg1-xMnxSe). The author discusses the anisotropy of the spin resonance and compares the g factors of free and donor-bound electrons. Furthermore, the author describes certain 'external' effects which influence the observation of SR in semiconductors, e.g. spin-spin exchange interaction in diluted magnetic semiconductors, plasma-shifted SR and uniaxial stress. Special attention is given to the interference of the electric dipole and magnetic dipole matrix elements, which provides a unique opportunity for the determination of the inversion asymmetry parameter (including its sign) in zincblende narrow-gap semiconductors.

Short- and long-range Ca 2+-induced lateral phase separations in ternary mixtures of phosphatidic acid, phosphatidylcholine and phosphatidylethanolamine

Ca 2+-induced lateral phase separation in an equimolar ternary mixture of dipalmitoylphosphatidic acid (DPPA), dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) was investigated by high-sensitivity differential scanning calorimetry. The thermogram showed a merged phase transition of these components in the absence of calcium ions, and the addition of calcium ions induced a change in the thermogram of the ternary mixture in a biphasic fashion. Different features were observed below and above a Ca 2+/DPPA molar ratio of 1. When the ratio was below 1, the transition peak shifted to a higher temperature. Within a range above 1, a major transition peak appeared at a temperature similar to the transition temperature of a binary mixture of DPPC and DMPE. The same tendency was observed in the ternary mixture in which DMPE was replaced with dilauroylphosphatidylethanolamine (DLPE) or dipalmitoylphosphatidylethanolamine (DPPE). The features of these thermograms below and above a Ca 2+/DPPA ratio of 1 could be attributed to Ca 2+-induced lateral phase separations of DPPA molecules in short-range and long-range phase separations, respectively. In order to confirm the short-range phase separation, the Ca 2+ effect on an equimolar ternary mixture of DPPA, DPPC and DMPE was examined using a spin-spin exchange interaction of stearate methyl ester spin probes. The results indicate that the long-range phase separation of phosphatidic acid induced by calcium ions is suppressed in ternary mixtures at low concentrations of Ca 2+.

Interband Faraday effect in Cd1-xMnxSe.

The interband Faraday rotation in the uniaxial diluted magnetic semiconductor ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se, measured with the direction of propagation k^ and the magnetic field H along its optic axis (c^), has been investigated for 0\ensuremath{\le}x&lt;0.5. The Faraday rotation, positive for CdSe, becomes negative and very large when ${\mathrm{Mn}}^{2+}$ replaces ${\mathrm{Cd}}^{2+}$. The sign of the rotation and its dependence on x, H, and temperature T are dominated by the spin-spin exchange interaction between the spins of the 3d electrons of ${\mathrm{Mn}}^{2+}$ and those of the band electrons. The dispersion of the Verdet constant is well described by the excitonic model (single-oscillator model). The antiferromagnetic coupling between ${\mathrm{Mn}}^{2+}$ ions is manifested in the Faraday effect through the phenomenological effective temperature (T+${T}_{\mathrm{AF}}$), as well as with hysteresis effects associated with the formation of a spin-glass phase for high x and low T.

ChemInform Abstract: Semimagnetic Lead Salt Alloys

The magnetic and electronic properties of pseudobinary alloys of the lead compounds (PbTe,PbSe)with Manganese, Europium and Gadolinium are reviewed. These materials have a direct minimum gap at the L-point of the Brillouin zone. The addition of Mn, Eu, or Gd to the diamagnetic hosts causes a rather weak antiferromagnetic exchange interaction. For sufficiently high carrier concentrations (10 2 0 -102 1 cm−3) a ferromagnetic interaction occurs due to RKKY interaction. The spin-spin exchange interaction between the Bloch states and the localized 3d or 4f states is characterized by rather small exchange integrals and the limited applicability of the mean field approximation for the description of energy band parameters like g-factors. Interband transitions in PbMnTe and PbMnS lend support to a zeromagnetic field splitting (“spin-splitting”)of band states which increases linearly with Mn-content up to several meV at temperatures below 4K.

Semimagnetic Lead Salt Alloys

AbstractThe magnetic and electronic properties of pseudobinary alloys of the lead compounds (PbTe,PbSe)with Manganese, Europium and Gadolinium are reviewed. These materials have a direct minimum gap at the L-point of the Brillouin zone. The addition of Mn, Eu, or Gd to the diamagnetic hosts causes a rather weak antiferromagnetic exchange interaction. For sufficiently high carrier concentrations (10 2 0 -102 1 cm−3) a ferromagnetic interaction occurs due to RKKY interaction. The spin-spin exchange interaction between the Bloch states and the localized 3d or 4f states is characterized by rather small exchange integrals and the limited applicability of the mean field approximation for the description of energy band parameters like g-factors. Interband transitions in PbMnTe and PbMnS lend support to a zeromagnetic field splitting (“spin-splitting”)of band states which increases linearly with Mn-content up to several meV at temperatures below 4K.

Far Infrared Magnetoabsorption in Hg1-xMnxTe/HgTe Superlattice

Hg-based superlattices (SL)-e.g., the HgTe/CdTe SL–exhibit interesting and important physical properties. Among these are the tunability of the band gap, achieved by varying the thicknesses of the two constituent materials; and the existence of the vajeqnce band offset, on which the details of the valence bands of the SL largely depen. Recently a new type of Hg-based SL, the Hg1-xMnxTe/HgTe SL, has been successfully prepared. In addition to the ability of varying its band gap by controlling the Mn content, this SL has the advantage that some of its important parameters, including the band offset, can be tuned by an external magnetic field because of the spin-spin exchange interaction in the Hg1-xMnxTe layers. So far, the electronic and optical properties of this type of SL have not been explored.

Shallow centers in diluted magnetic semiconductors

The effect of spin-spin exchange interaction between shallow centers in diluted magnetic semiconductors and localized magnetic moments is reviewed and illustrated by three distinct examples: (1) spin-flip transitions observed on donors in Cd 1−xMn xSe, illustrating the role of exchange as a “magnetic field intensifier;” (2) the bound magnetic polaron, illustrating the effect of exchange on shallow centers in DMS in the absence of an external magnetic field; and (3) the giant magnetoresistance observed in p-type Hg 1−xMn xTe, which arises as a result of exchange-induced “swelling” of the acceptor wave functions with increasing magnetic field.

Electron Spin Resonance and Some Spectral Studies on Coordination Behaviors of Paramagnetic Metal Ions for Chelating Resins

Abstract Coordination behaviors of VO(II), Cr(III), Mn(II), Fe(III), Cu(II), and Gd(III) ions for the iminodiacetato group in the chelating ion-exchange resin Dowex A-1 were studied with the aid of ESR, infrared absorption, and M\ddotossbauer spectroscopies. A comparative investigation also was made with the o-hydroxybenzyliminodiacetato group in the chelating resin Unicellex UR-50. The iminodiacetato group in Dowex A-1 is considered to coordinate as a tridentate ligand and form 1 : 1 chelates with metal ions, whereas the o-hydroxybenzyliminodiacetato group in Unicellex UR-50 coordinates as a quadridentate ligand in alkaline media and forms 1 : 1 chelates. Elucidation of spin-spin exchange interaction has led to a conclusion that the iminodiacetato groups present in the coordination pore of Unicellex UR-50 are closer to one another than those of Dowex A-1. For Fe(III) ions adsorbed in concentrated HCl media, besides the species [FeCl4]−, lower symmetric species are considered to be adsorbed with the anion exchange effect, from results of resin phase ESR and Mössbauer spectra.

Interband magnetoabsorption in semimagnetic semiconductor alloysHg1−kMnkTewith a positive energy gap

Low-temperature infrared magnetoabsorption experiments were carried out on ${\mathrm{Hg}}_{1\ensuremath{-}k}{\mathrm{Mn}}_{k}\mathrm{Te}$ mixed crystals with compositions corresponding to the semiconducting (positive energy gap) range. Measurements were performed in the spectral region 100-350 meV in Voigt and Faraday geometries, using both linear and circular polarizations. The magneto-optical data provide observation of interband ${\ensuremath{\Gamma}}_{8}\ensuremath{\rightarrow}{\ensuremath{\Gamma}}_{6}$ transitions. In addition, transitions from acceptor levels to ${\ensuremath{\Gamma}}_{6}$ Landau levels were observed. The interband magneto-optical transitions are interpreted within the framework of the Pidgeon-Brown model, modified by the contributions of the $s\ensuremath{-}d$ and $p\ensuremath{-}d$ spin-spin exchange interaction between band electrons and localized ${\mathrm{Mn}}^{2+}$ spins. From the theoretical fits of the transition energies to the observed absorption lines, the relative magnetization $A(H,T)$ is deduced at $T=4.2 \mathrm{and} 2$ K for alloys of various Mn content. In contrast with zero-gap ${\mathrm{Hg}}_{1\ensuremath{-}k}{\mathrm{Mn}}_{k}\mathrm{Te}$, in the present case $A(H,T)$ exhibits a nearly linear magnetic field dependence and depends only weakly on temperature. These features are related to the strong antiferromagnetic interactions between the localized magnetic moments. Conduction electrons in crystals in this composition range exhibit large and positive $g$ factors as a consequence of the $s\ensuremath{-}d$ exchange coupling.

A possible role of stimulus-enhanced phosphatidylinositol turnover: Calcium-sparing effect of diacylglycerol in inducing phase separation of phosphatidylcholine/phosphatidylserine mixtures

A physiological role of phosphatidylinositol turnover accelerated by a stimulus was studied using a model system composed of egg yolk phosphatidylcholine (PC), bovine brain phosphatidylserine (PS), yeast phosphatidylinositol (PI) and diacylglycerol (DG) prepared from yeast PI by PI-specific phospholipase C of Bacillus cereus. The effects of PI and DG on Ca2+-induced phase separation of PS were examined using the spin-spin exchange interaction of PC spin probes. DG enhanced Ca2+-induced phase separation in PC/PS mixtures while PI had almost no effect on the phase separation. The results suggest a calcium-sparing effect of DG in inducing phase separation in the PS-containing membranes.

A spin-label study of phosphatidylcholine exchange protein. Regulation of the activity by phosphatidylserine and calcium ion

Exchange of phosphatidylcholine catalyzed by exchange protein has been studied by a new technique using spin-labeled phosphatidylcholine (PC∗). The exchange activity was assayed by the change in electron spin resonance (ESR) spectrum when PC∗ vesicles were incubated with unlabeled phospholipid vesicles. The method utilized decrease in the spin-spin exchange interaction and does not require separation of the donor and acceptor vesicles. 1. (1) The transfer rate, υ, from PC ∗ to phosphatidylcholine vesicles described by υ = k [PC ∗][protein] (1 + K[ PC]) for large excess of a acceptor vesicles where k is the rate constant for association of the protein with PC ∗ vesicles and K the binding constant of the protein with phosphatidylcholine vesicles. The transfer rate at 23°C was 3.2 μ mol · min −1 · ( protein) −1 · ( M PC ∗ ) −1 at [PC] = 14.7 mM, k = 136 mM −1 · min −1, and K = 79 M −1. 2. (2) The exchange activity was inhibited by addition of phosphatidylserine vesicles and also by mixed phosphatidylserine-phosphatidylcholine vesicles. The inhibition was abolished by Ca 2+ and Mg 2+. 3. (3) The ESR spectrum of PC ∗ complexed with exchange protein showed strong immobilization of the lipid alkyl chain, suggesting van der Waals-type binding of the acyl chain to the protein interior. The endogeneous PC ∗ molecule was readily exchanged with phosphatidylcholine but practically inexchangeable with phosphatidylserine in the vesicle membranes. 4. (4) A gel chromatographic analysis indicated weak interaction of the exchange protein with phosphatidylcholine vesicles but strong binding to phosphatidylserine vesicles. The inhibitory effect of the anionic lipid vesicles can be explained by their binding to the protein and incapability of exchange of the endogenous phosphatidylcholine with phosphatidylserine in the anionic membranes. The restoration by Ca 2+ and Mg 2+ may be due to binding of these cations to the anionic lipids, making the protein free from the vesicles. The divalent cations thus act regulatorily for the exchange reaction.

Electron Spin Resonance of LaBe 13 :Er: Evidence for Er spin-spin exchange broadening

The anomalous ESR thermal broadening of Er (5%) in LaBe 13 is attributed to Er spin-spin exchange interaction which induces transitions between the Γ 7 ground state and the low lying excited Γ 8 ( k) levels.

Biosynthesis of spin-labeled peptidoglycan: spin-spin interactions.

Membrane preparations from Gaffkya homari catalyzed the in vitro biosynthesis of soluble uncross-linked spin-labeled peptidoglycan, a uniformly labeled polynitroxide, from the spin-labeled nucleotide UDP-MurNAc-Ala-DGlu-Lys(Nepsilon-2,2,5,5-tetramethyl-1-pyrrolin-1-oxyl-3-carbonyl)-DAla-DAla (I) and UDP-GlcNAc. Soluble spin-labeled peptidoglycan was separated from membrane fragments and its spin-labeled precursor by centrifugation and gel filtration. The molecular weight distribution of the polymer was examined by agarose gel filtration. Spin-labeled [14C]peptidoglycan was polydisperse with a peak of radioactivity corresponding to a molecular weight of 5.0 X 10(5). The electron spin resonance spectrum of spin-labeled peptidoglycan was extensively broadened by spin-spin exchange interactions. These interactions were modified by changes in temperature, reduction by ascorbate, hydrolysis by lysozyme, and complexation with the antibiotic, vancomycin. Spin-spin exchange was reduced or eliminated in spin-labeled peptidoglycan by the random reduction of free radicals by ascorbate. A rotational correlation time of 0.37 ns was calculated for the probe in partially reduced spin-labeled peptidoglycan. This compares to a correlation time of 0.13 ns for the substrate (I). Raising the temperature increases spin-spin exchange line broadening. No transition points were observed for spin-labeled peptidoglycan as measured by this method. Degradati on of spin-labeled peptidoglycan by lysozyme eliminated the observed spin-spin exchange and yielded products with a mobility similar to I. Complexation of spin-labeled peptidoglycan with vancomycin resulted in both pronounced free-radical immobilization and a decrease in spin-spin exchange. The exchange effects are consistent with distance measurements in molecular models for peptidoglycan.

TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF MÖSSBAUER SPECTRA OF REDUCED FERREDOXIN FROM CLOSTRIDIUM PASTEURIANUM

Resume. — Des experiences Mossbauer ont ete faites dans un grand domaine de temperature et de champ magnetique sur du Clostridium Pasteurianum Ferredoxin reduit et sont interpretees en fonction d'un modele expose dans un article publie recemment. Les spectres mesures pour des champs magnetiques intenses et a basses temperatures ont ete calcules par la methode des moindres carres en utilisant l'integrale de transmission. Abstract. — Mossbauer experiments have been performed on reduced Clostridium Pasteurianum Ferredoxin in a wide temperature and magnetic field range and are interpreted in terms of a model, which was developed in an earlier paper. The spectra measured in high magnetic fields and at low temperatures were least squares fitted using the full transmission. 1. Introduction. — Clostridium Pasteurianum Ferre- doxin contains in the active center two clusters of iron and sulfur atoms. In each cluster four sulfur and four iron atoms alternatively occupy the corner of a distorted cube. The iron atoms are co-ordinated with cysteine sulfur atoms of the protein moiety. In an earlier paper (1) a model of the electronic state of the active center of reduced Ferredoxin (Fdred) was developed. Each cluster was described by a wave function 5eff = common to the electrons of all cluster atoms with an effective spin Sefi = \. The two clusters interact weakly via spin-spin coupling and exchange interaction yielding S = 1 and S = 0 states. An external magnetic field breaks the cluster-cluster interaction and each cluster can now be described separately by a wave function corresponding to