Ferromagnetic material CdGeP2:Mn for spintronics

Solid solutions Cd_1?x Mn_xGeP₂ (x=0?0.19) have been synthesized and identified. In these solutions, the unit cell parameters decrease with an increase in the manganese content. The solid solution Cd_0.81Mn_0.19GeP₂ is a ferromagnet with the Curie temperature T _C ≈ 311 K. The paramagnetic moment of Mn²⁺ ions equal to 5.8 μ_B, as well as the spontaneous magnetization constituting 76% of the total magnetization of a crystal, has been determined with the use of the Langevin function. The origin of ferromagnetism in CdGeP₂:Mn is exchange mediated by charge carriers (holes). These holes are caused by cationic defects in the structure of chalcopyrite.     

Local tilting angles tau for Fe+ in Cd2+ site and Fe3+ in Si4+ site of CdSiP2 semiconductor

The EPR parameters (g factors, g(parallel), g(perdendicular) and zero-field splitting D) for Fe+ in Cd2+ site and Fe3+ in Si4+ site of CdSiP2 semiconductor are calculated from the distinct high-order perturbation formulas. From the calculations, the local tetragonal distortions and hence the local tilting angles tau (which are different from the corresponding host values) for both paramagnetic centers are estimated. The results are discussed.     

EPR parameters and local geometry for Cr3+ and V2+ ions in HfS2 crystals

From the high-order perturbation formulas of EPR parameters (zero-field splitting D, g factors gparallel, gperpendicular and hyperfine structure constants Aparallel, Aperpendicular) based on the two spin-orbit coupling parameter model for 3d3 ions in trigonal symmetry, the EPR parameters of Cr3+ and V2+ ions in HfS2 crystals are calculated. From the calculations, it is found that the local trigonal distortion angle theta of impurity center in HfS2:Cr3+ is smaller than that in HfS2:V2+. The dominant cause of the small zero-field splitting |D| and g-anisotropy |Deltag|=|gparallel-gperpendicular| in HfS2:Cr3+ (compound to HfS2:V2+) is due to the small local trigonal distortion angle theta rather than to the small impurity-ligand distance R in HfS2:Cr3+.     

Formation of manganese solid solutions in single crystals of ZnGeP2

Process of the solid-phase diffusion of manganese into single crystals ZnGeP² are investigated by electron paramagnetic resonance and X-ray element microanalysis. Conditions for formation of a solid solution with Mn²⁺ concentration of 10¹⁸ cm^-3 were found. A diffusion coefficient of manganese in single crystal of ZnGeP² at a diffusion annealing temperature was determined.     

Theoretical investigation of electron paramagnetic resonance spectra and local structure distortion for Mn2+ ions in CaCO3:Mn2+ system: a simple model for Mn2+ ions in a trigonal ligand field

This paper reports on a novel application of a ligand field model for the detection of the local molecular structure of a coordination complex. By diagonalizing the complete energy matrices of the electron-electron repulsion, the ligand field and the spin-orbit coupling for the d5 configuration ion in a trigonal ligand field, the local distortion structure of the (MnO6)10- coordination complex for Mn2+ ions doped into CaCO3, have been investigated. Both the second-order zero-field splitting parameter b(0)2 and the fourth-order zero-field splitting parameter b(0)4 are taken simultaneously in the structural investigation. From the electron paramagnetic resonance (EPR) calculations, the local structure distortion, DeltaR=-0.169 A to -0.156 A, Deltatheta=0.996 degrees to 1.035 degrees for Mn2+ ions in calcite single crystal, DeltaR=-0.185 A to -0.171 A, Deltatheta=3.139 degrees to 3.184 degrees for Mn2+ ions in travertines, and DeltaR=-0.149 A to -0.102 A, Deltatheta=0.791 degrees to 3.927 degrees for Mn2+ ions in shells are determined, respectively. These results elucidate a microscopic origin of various ligand field parameters which are usually used empirically for the interpretation of EPR and optical absorption experiments. It is found that the theoretical results of the EPR and optical absorption spectra for Mn2+ ions in CaCO3 are in good agreement with the experimental findings. Moreover, to understand the detailed physical and chemical properties of the doped CaCO3, the theoretical values of the fourth-order zero-field splitting parameters b(0)4 for Mn2+ ions in travertines and shells are reported first.     

ESR and optical study of Mn2+ doped ammonium selenate single crystals

ESR and optical absorption studies of manganese doped ammonium selenate single crystals are performed at X-band and room temperature to ascertain the site symmetry and location of impurity ions in the lattice. Manganese ions are expected to enter the lattice interstitially. Various spin Hamiltonian parameters are determined. Optical absorption study is also done and associated distortion in the crystal lattice is estimated.     

Correlation of zero-field splittings and site distortions: Variation of b2 FOR Mn2+ with ligand and coordination number

The intrinsic zero-field splitting parameter $\text{b}$₂ increases monotonically with increasing covalency of the Mn-X bonds, but depends on coordination number and type of metal ion. At least two effects of opposite sign must contribute to this complicated behavior. The trigonal distortions of the MX^4?₆ octahedra in some MX₂ layer compounds are evaluated.     

EPR and optical study of Mn2+ doped ammonium tartrate single crystals

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.     

The neutral exciton model for triplet factor-group splittings in aromatic crystals

The calculation of triplet factor-group splitting in benzene, naphthalene and anthracene crystals has been reexamined. Substantially revised values of the two-centre exchange integrals in the neutral exciton model give much improved agreement with experiment in benzene; the need for refinements such as ion-pair contributions is marginal. In naphthalene and anthracene the new values are little altered. Thus, in benzene and naphthalene the neutral exciton model appears to be adequate; in anthracene the previously noted disagreement with experiment remains.Multicentre intermolecular integrals can be neglected in the examples studied, and are unlikely to be important in other aromatic crystals.     

Zero-field splittings in NiSiF6·6H2O as electron paramagnetic resonance thermometer

The problem of splitting of Ni²⁺ states by the electron-phonon interaction has been studied as a function of temperature. In the high-temperature region the slope of the splitting. ?D/?T = 17.58 G/°K suggests that NiSiF₆·6H₂O can be used as a thermometer.     

New monoacylhydrazidate-coordinated Mn2+ and Pb2+ compounds

By the simple hydrothermal self-assembly, four new monoacylhydrazidate-coordinated compounds [Mn(APTH)(2)(H(2)O)] 1, [Pb(APTH)(2)]·0.25H(2)O 2, [Pb(2)(EPDH)(4)(H(2)O)] 3 and [Pb(MPDH)(2)] 4 (APTH = 3-aminophthalhydrazidate, EPDH = 5-ethylpyridine-2,3-dicarboxylhydrazidate, MPDH = 6-methylpyrinde-2,3-dicarboxylhydrazidate) were obtained. It is noteworthy that APTH was derived from the in situ reduction reaction of NPTH (3-nitrophthalhydrazide) with N(2)H(4)·H(2)O as the reducer, whereas EPDH and MPDH were derived respectively from the in situ acylation reactions of epdca and mpdca (epdca = 5-ethylpyridine-2,3-dicarboxylic acid, mpdca = 6-methylpyridine-2,3-dicarboxylic acid) with N(2)H(4)·H(2)O. The photoluminescence analysis indicates that compounds 3 and 4 possess luminescence properties with maximum emissions at 531 nm for 3, and 600 nm for 4, respectively. The density functional theory (DFT) calculations indicate that the emission for compound 3 can be ascribed to a combination of the intra-ligand and inter-ligand charge transfers, while the emission for compound 4 is assigned to the intra-ligand charge transfer.     

Theoretical investigations of the EPR parameters for Cr3+ and Mn4+ ions in PbTiO3 crystals

The complete high-order perturbation formulas of EPR parameters (g factors g( parallel), g( perpendicular) and zero-field splitting D), containing the crystal-field (CF) mechanism and charge-transfer (CT) mechanism (the latter is omitted in crystal-field theory which is often used to study the EPR parameters), are established from a cluster approach for 3d3 ions in tetragonal octahedral sites. According to the calculations based on these formulas, the EPR parameters g( parallel), g( perpendicular) and zero-field splitting D for Cr3+ and Mn4+ ions in PbTiO3 crystals are explained reasonably. The calculations show that (i) the sign of g-shift Deltag(i)(CT) (=g(i)-g(s), where g(s)=2.0023 is free-electron value and i= parallel and perpendicular) in CT mechanism is opposite to, but that of D(CT) is the same as, the corresponding signs in the CF mechanism and (ii) the relative importance of CT mechanism for the high valence state 3d3 ion (e.g., Mn4+) is large and so the contributions to EPR parameters from CT mechanism should be taken into account. The different sign of splitting D and the different defect structure for Cr3+ and Mn4+ impurity centers in PbTiO3 crystals are also suggested from the calculations. The results are discussed.     

EPR theoretical study of local molecular structure and thermal expansion coefficient for octahedral Mn2+ centers in zinc fluosilicate

A theoretical method for studying the inter-relation between electronic and molecular structure has been proposed by diagonalizing the complete energy matrices for a d(5) configuration ion in a trigonal ligand field and considering the second-order and fourth-order EPR parameters D and (a - F) simultaneously. As for ZnSiF(6).6H(2)O:Mn(2+) and ZnSiF(6).6D(2)O:Mn(2+) complex molecules, the local lattice distortion and local thermal expansion coefficient for the octahedral Mn(2+) centers in zinc fluosilicate have been investigated, respectively. The calculations indicate that the local lattice structure around an octahedral Mn(2+) center has an expansion distortion, whether the Mn(2+) ion is doped in ZnSiF(6).6H(2)O or ZnSiF(6).6D(2)O. Moreover, the total tendency of the local lattice expansion distortion will be more and more obvious with the temperature rising, apart from some slight variations at T = 60 K for the ZnSiF(6).6H(2)O. By simulating the two low-symmetry EPR parameters D and (a - F) simultaneously, the local lattice structure parameters R and theta have been determined to vary from 2.204 Angstroms to 2.256 Angstroms and from 53.417 degrees to 52.710 degrees, respectively, in the temperature range 19-297 K for ZnSiF(6).6H(2)O:Mn(2+) and to vary from 2.215 Angstroms to 2.255 Angstroms and from 53.346 degrees to 52.714 degrees, respectively, in the temperature range 50-300 K for ZnSiF(6).6D(2)O:Mn(2+). Subsequently the dependence of local thermal expansion coefficients on the temperature is studied and the corresponding theoretical values of the local thermal expansion coefficients are reported firstly. Some characteristics of local thermal expansion coefficients of Mn(2+) in ZnSiF(6).6H(2)O:Mn(2+) and ZnSiF(6).6D(2)O:Mn(2+) systems are also analyzed.     

[Mn18]2+ and [Mn21]4+ single-molecule magnets

The synthesis and structural characterization of the two new Mn complexes [Mn₁₈O₁₄(O₂CMe)₁₈(hep)₄(hepH)₂(H₂O)₂](ClO₄)₂ (1) and [Mn₂₁O₁₆(O₂CMe)₁₆(hmp)₆(hmpH)₂(pic)₂(py)(H₂O)](ClO₄)₄ (3) are presented, together with a detailed study of their magnetic properties. Complex 1 possesses a ground-state spin of S=13, and the ground-state spin for 3 is estimated to be S=17/2 or 19/2. Both complexes 1 and 3 are new examples of single-molecule magnets (SMMs), displaying frequency-dependent out-of-phase AC signals, as well as magnetization vs. DC field hysteresis at temperatures below 1 K. Complex 1 straddles the classical/quantum interface by also displaying quantum tunneling of the magnetization (QTM).     

New observations on the luminescence decay lifetime of Mn2+ in Zns: Mn2+ nanoparticles

A fast decay emission peaking at 645 nm with a decay lifetime within the experimental resolution of 0.14 micros is observed in ZnS:Mn2+ nanoparticles. This short-lived signal is also observed in pure ZnS and MgS: Eu3+ nanoparticles, which has nothing to do with Mn(2+)-doped ions but is from the deep trap states of the host materials. The short-lived component decreases in intensity relative to the Mn2+ emission at higher excitation powers, while it increases in intensity at low temperatures and shifts to longer wavelengths at longer time delays. Our observations demonstrated further that the emission of Mn2+ in ZnS: Mn2+ nanoparticles behaves basically the same as in bulk ZnS: Mn2+; the fast decay component is actually from the intrinsic and defect-related emission in sulfide compounds.     

Giant excitonic Zeeman splittings in colloidal Co2+ -doped ZnSe quantum dots

Colloidal Co(2+):ZnSe diluted magnetic semiconductor quantum dots (DMS-QDs) were prepared by the hot injection method and studied spectroscopically. Ligand-field electronic absorption and magnetic circular dichroism (MCD) spectra confirm homogeneous substitutional speciation of Co(2+) in the ZnSe QDs. Absorption spectra collected at various times throughout the syntheses reveal that dopants are absent from the central cores of the QDs but are incorporated at a constant concentration during nanocrystal growth. The undoped cores are associated with dopant exclusion from the ZnSe critical nuclei. Analysis of low-temperature electronic absorption and MCD spectra revealed excitonic Zeeman splitting energies (DeltaE(Zeeman)) of these Co(2+):ZnSe QDs that were substantially smaller than anticipated from bulk Co(2+):ZnSe data. This reduction in DeltaE(Zeeman) is explained quantitatively by the absence of dopants from the QD cores, where dopant-exciton overlap would be greatest. Since dopant exclusion from nucleation appears to be a general phenomenon for DMS-QDs grown by direct chemical methods, we propose that DeltaE(Zeeman) will always be smaller in colloidal DMS-QDs grown by such methods than in the corresponding bulk materials.     

Unprecedented Kinetic Inertness for a Mn2+-Bispidine Chelate: A Novel Structural Entry for Mn2+-Based Imaging Agents

The search for more biocompatible alternatives to Gd³⁺-based MRI agents, and the interest in ⁵²Mn for PET imaging call for ligands that form inert Mn²⁺ chelates. Given the labile nature of Mn²⁺, high inertness is challenging to achieve. The strongly preorganized structure of the 2,4-pyridyl-disubstituted bispidol ligand L₁ endows its Mn²⁺ complex with exceptional kinetic inertness. Indeed, MnL₁ did not show any dissociation for 140 days in the presence of 50 equiv. of Zn²⁺ (37 °C, pH 6), while recently reported potential MRI agents MnPyC3A and MnPC2A-EA have dissociation half-lives of 0.285 h and 54.4 h under similar conditions. In addition, the relaxivity of MnL₁ (4.28 mm ⁻¹ s⁻¹ at 25 °C, 20 MHz) is remarkable for a monohydrated, small Mn²⁺ chelate. In vivo MRI experiments in mice and determination of the tissue Mn content evidence rapid renal clearance of MnL₁. Additionally, L₁ could be radiolabeled with ⁵²Mn and the complex revealed good stability in biological media.     

Mn2+在铝酸盐中的发光

用金属硝酸盐、稀土氧化物和乙酸锰为原料,用燃烧法合成了Ce³⁺、Tb³⁺、Mn²⁺共激活的铝酸盐绿色荧光粉,在Ce³⁺和Tb³⁺共激活的铝酸盐体系中掺入Mn²⁺后,发射峰中出现锰的特征峰.通过对其结构的分析,对Mn²⁺发光和最佳掺杂量给出了合理的解释.同时研究了不同碱金属和碱土金属离子代替Mg²⁺时,对Mn²⁺发光的影响.     

EPR of Mn2+ in [Co(H2O)6] PtCl6 single crystals: Estimation of Co2+ spin-lattice relaxation time

EPR of Mn²⁺ in single crystals of [Co(H₂O)₆]PtCl₆ has been studied from room temperature to 77 K at ∼ 9.35 GHz. Mn²⁺ has been found to substitute for Co²⁺ exhibiting a unique magnetic complex. The observation of resolved Mn²⁺ spectra has been interpreted in terms of a random modulation of the interaction between the Mn²⁺ and Co²⁺ ions by the rapid spin-lattice relaxation of Co²⁺ ions. It has been found that the effective spin-relaxation time T₁αT⁻ⁿ where n = 1.8 for 105 < T< 293 K.     

To dope Mn2+ in a semiconducting nanocrystal

It has been an outstanding problem that a semiconducting host in the bulk form can be doped to a large extent, while the same host in the nanocrystal form is found to resist any appreciable level of doping rather stubbornly, this problem being more acute in the wurtzite form compared to the zinc blende one. In contrast, our results based on the lattice parameter tuning in a Zn(x)Cd(1-x)S alloy nanocrystal system achieves approximately 7.5% Mn(2+) doping in a wurtzite nanocrystal, such a concentration being substantially higher compared to earlier reports even for nanocrystal hosts with the "favorable" zinc-blende structure. These results prove a consequence of local strains due to a size mismatch between the dopant and the host that can be avoided by optimizing the composition of the alloyed host. Additionally, the present approach opens up a new route to dope such nanocrystals to a macroscopic extent as required for many applications. Photophysical studies show that the quantum efficiency per Mn(2+) ion decreases exponentially with the average number of Mn(2+) ions per nanocrystal; en route, a high quantum efficiency of approximately 25% is achieved for a range of compositions.