ESR study of some Cu(II)-4-substituted-2-Thiazolylhydrazone complexes

The Cu(II) complexes with 2-N-acetyl-salicylidene-hydrazino-4-chlor-methyl thiazole (L.) and 2-N-acetyl salicylidene-hydrazioo-4-thiazolyl acetic ester (L_II) were prepared and investigated by ESR measurements. The powder ESR spectrum at room temperature of CuL_IICl is quasi-isotropic (g=2.113), while for CuL_IICl is characteristic of monomeric species with axial symmetry (g _II)=2.234,g ₁=2.073). The isotropic ESR spectra of the CuLCl compounds in DMSO solution suggest the presence of pseudo-tetrahedral monomeric species. The anisotropic spectra were obtained for adsorbed CuLCl DMSO solutions on NaY zeolite. The parallel hyperfine structure shows the coexistence of two magnetic nonequivalent monomeric species. The estimation of some LCAO-MO coefficients using Kivelson and Neiman’s approximation reveals a dominant ionic character for copper-ligand bonds.     

Identification of free radicals in irradiated MA-AMPS copolymer

Methacrylamide-2-acrylamido-2-methylpropanesulphonic acid (MA-AMPS) (80:20) is subjected to n -irradiation and the generated free radicals are identified by the electron spin resonance (ESR) technique. The ESR spectrum "obser"ved for MA-AMPS (80:20) has shown a complex line shape, indicating the presence of more than one free radical. Computer simulations are employed to unravel the radicals responsible for the ESR spectrum. Radical "identification has been done with the magnetic parameters employed during computer simulation. The observed ESR spectrum of the copolymer is simulated to be a superposition of component quartet, quintet and singlet spectra. The component spectra are assigned to ～CH 2 - . (CONH 2 )-CH 2 ～ or ～CH 2 - . H-CH 2 ～, . H 3 radicals, "respectively. The possibility of formation of such radicals in the sample material has been discussed.     

Effects of Gd<Superscript>3+</Superscript> doping on structural and dielectric properties of PZT (Zr:Ti = 52:48) piezoceramics

The purpose of this research is to study the effect of doping Gd into Pb(Zr_0.52Ti_0.48)O₃ ceramics prepared by solid state reaction. X-ray diffraction patterns show that all PGZT samples are of tetragonal structure and the highest doping should be no more than 2 mole % Gd at which the unreacted oxides start to appear. The electron spin resonance (ESR) spectra of PGZT's indicate that Gd³⁺ can enter both A site of the perovskite structure instead of only A site as widely believed. The ESR peaks resonance shift towards low fields as the concentration is higher, which is due to the change in crystal field experienced by Gd³⁺ ions. At x =0.001, 0.005 and 0.01 dopings, two sets of powder ESR signals arising from Gd³⁺ (4f⁷, spin 7/2) ions at A site. The first set shows some fine structure having strong absorption peaks centered at 76.26 mT (g = 8.550). The second is a seven-peak spectrum centered at 206.01 mT (g = 3.165), which belongs to the Gd³⁺ ions at B sites. Furthermore, the overlapped ESR strong absorption peaks from 309.17 mT to 314.49 mT (g = 2.2818-2.1087) belong to Gd³⁺ of unreacted Gd₂O₃. The local environments of Gd³⁺ ions were verified from the calculated ESR spectra using appropriate spin Hamiltonian parameter, i.e. gyromagnetic tensor g, zero-field splitting D and hyperfine tensor A.     

Magnetic properties of the low dimensional spin system (VO)PO:ESR and susceptibility

Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)₂P₂O₇. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine J =51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K. Received: 22 December 1997 / Accepted: 17 March 1998     

Magnetic and electric hyperfine interactions of197Au in a paramagnetic molecular complex

Mössbauer spectra measured at low temperature on the paramagnetic compound [Au^II(maleonitrile dithiolate)₂] [(n-C₄H₉)₄N] are discussed in terms of slow electron spin relaxation. Good agreement is obtained using hyperfine interaction parameters derived from ESR measurements.     

Characterization of X-Ray-Irradiated β-Ca3(PO4)2:Dy by means of ESR Spectroscopy

Electron spin resonance (ESR) spectra caused by a stable trapped H atom, a Dy³⁺ ion, and a PO₄ unit were observed in X-ray-irradiated dysprosium-doped β-tricalcium phosphate (β-Ca₃(PO₄)₂:Dy, β-TCP:Dy) phosphor. The ESR spectrum of the H atom in the X-ray-irradiated β-TCP:Dy phosphor was slightly different from that of nondoped X-ray-irradiated β-TCP, suggesting that the Dy³⁺ spin state has a significant effect on the relaxation time of electron spins. The electron spin echo of the H atom was observed in the X-ray-irradiated β-TCP but not in the corresponding X-ray-irradiated β-TCP:Dy phosphor. Authors' address: Kouichi Nakashima, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Aoba-ku, Sendai 980-8577, Japan     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

Novel electron spin resonance spectra of a tetrathiafulvalene salt of copper chloride, (TTF) 2CuCl2

An ESR study has been carried out on electrically conducting (TTF)₂CuCl₂ crystals. The peak-to-peak width W of the ESR spectrum exhibited an unusual angular dependence with respect to the angle θ between the TTF-stack direction and the external field: the W showed a sharp minimum (4.9 G at 300 K) at θ = 0°, a maximum (7.5 G) at 60° (corresponding to 3cos²θ ∼ 1), and another minimum (6.9 G) at 90°. This angular depence has been explained by assuming an anisotropic motional narrowing that may arise from a spin correlation in one-dimensional electroconductive lattices. The temperature dependence of the W showed no anomaly around the temperature of metal-semiconductor transition: the spin relaxation is substantially unchanged by the phase transition.     

纳米FeAl合金的磁共振谱分析

在与晶粒组元相当的包裹纳米FeAl晶粒的无序界面或/和表面组元中,存在Fe-Al-Fe电子的超交换作用或/和Fe-Fe交换作用,使多晶FeAl合金因晶粒纳米化出现非磁性—磁性转变.X波段(频率为9.48GHz)的电子自旋共振(ESR)实验表明多晶FeAl合金没有磁共振信号.纳米晶样品的铁磁共振(FMR)信号是一个线宽ΔH_pp为8×10⁴A/m以上的宽峰.还观测到纳米晶体样品中Fe²⁺离子的ESR精细结构双峰,两峰间隔为1.316×10关键词：     

Investigation of irradiated 1H-Benzo[b]pyrrole by ESR,thermal methods and learning algorithm

1H-Benzo[b]pyrrole samples were irradiated in the air with gamma source at 0.969?kGy per hour at room temperature for 24, 48 and 72?h. After irradiation, electron spin resonance, thermogravimetry analysis (TGA) and differential thermal analysis (DTA) measurements were immediately carried out on the irradiated and unirradiated samples. The ESR measurements were performed between 320 and 400?K. ESR spectra were recorded from the samples irradiated for 48 and 72?h. The obtained spectra were observed to be dependent on temperature. Two radical-type centres were detected on the sample. Detected radiation-induced radicals were attributed to R-^+?NH and R=^?CC₂H₂. The g-values and hyperfine constants were calculated by means of the experimental spectra. It was also determined from TGA spectrum that both the unirradiated and irradiated samples were decomposed at one step with the rising temperature. Moreover, a theoretical study was presented. Success of the machine learning methods was tested. It was found that bagging techniques, which are widely used in the machine learning literature, could optimise prediction accuracy noticeably.     

Excited high spin states of novel π conjugated verdazyl radicals: photoinduced spin alignment utilizing the excited molecular field

This paper reports the excited quartet (S = 3/2) and quintet (S = 2) states arising from the intramolecular radical-triplet pair in the purely organic π conjugated spin systems. A previous paper reported the excited quartet and quintet states of 9-anthracene-(4-phenyliminonitroxide) and 9,10-anthracene-bis(4-phenyliminonitroxide), respectively, in which iminonitroxide radicals are linked to the phenyl- or diphenylanthracene moiety (a spin-coupler) through the π conjugation. The similar excited quartet and quintet states were observed for the 9-anthra-cene-(4-phenylverdazyl) radical (1) and 9,10-anthracene-bis(4-phenylverdazyl) diradical (2) by time resolved electron spin resonance (TRESR). The TRESR spectrum was analysed by the ordinary spin Hamiltonian with the Zeeman and fine structure terms. For the quartet state of 1, the g value, fine structure splitting, and relative population of the Ms sublevels have been determined to be g = 2.0035, D = 0.0230 cm^?1, E = 0.0, P _1/2′ = P _?1/2′ = 0.5 and P _3/2′ = P _?3/2′ = 0.0, respectively, by spectral simulation. The spin Hamiltonian parameters of the quintet state of 2 were determined to be g = 2.0035, D = 0.0128 cm^?1, E = 0.0, P _2′ = P _?2′ = 0.0, P _1′ = P _?1′ = 0.37 and P _0′ = 0.26, respectively. Direct observation of the excited high spin state showed that photoinduced intramolecular spin alignment is realized between the excited triplet state (S = 1) of the phenyl- or diphenylanthracene moiety and the doublet spin (S = 1/2) of the dangling verdazyl radicals. Ab initio MO calculations (DFT) were carried out in order to clarify the mechanism of the photoinduced spin alignment.     

Low-Temperature Phase Transition Detected by ESR in ����-(BEDT-TTF)2IBr2 Single Crystals

Hysteresis of the electron spin resonance (ESR) spectra of localized charge carriers has been observed in ????-(BEDT-TTF)₂IBr₂ single crystals in the temperature range of 15?C30?K. The first-order phase transition has been detected by ESR components. Two lines observed in the ESR spectrum correspond to low-temperature and high-temperature phases.     

Mössbauer study of novel iron(II) complexes synthesized with Schiff bases

Novel [Fe(4-benzyl-2-hydroxyphenyl-propylidene)₂ethylene-diamine], and [Fe (2,4,6-trihydroxy-benzyl-4-metoxiphenyl-methylidene)₂ethylene-diamine] complexes were synthesized by reacting Fe^II salt with the indicated Schiff-base ligands. The compounds were characterized by⁵⁷Fe Mössbauer spectroscopy, FTIR, UV-VIS, TG-DTA-DTG, MS, AFM, XRD, cyclic voltammetry and biological activity measurements. 295 K and 78 K Mössbauer spectra revealed that iron is dominantly in high spin Fe^II state in both complexes while simultaneously a minor low spin Fe^II was also present in both complexes, furthermore a minor high spin Fe^III was observed in [Fe(2,4,6-trihydroxy-benzyl-4-metoxiphenyl- methylidene) ₂ethylene-diamine], too.     

Elementary spin excitations in a Heisenberg S=1/2 antiferromagnet with Skyrmions

The elementary spin excitations in two-dimensional Heisenberg antiferromagnets with spin S=1/2 in a metastable, spatially inhomogeneous state are investigated. The energy spectrum of the excitations, the local order parameter, and the temperature dependence of the spin correlation length are found. It is shown that the results obtained can be used to explain the experimental data on neutron scattering in La₂CuO₄ at temperatures T>T _N. Fiz. Tverd. Tela (St. Petersburg) 39, 656–659 (April 1997)     

二苯甲酮与2-芳基-1,3-二噻烷衍生物光化夺氢反应中产生的活泼自由基的ESR研究

本文用自旋捕捉技术与ESR相结合的方法,研究了九种2-芳基-1,3-二噻烷衍生物与二苯甲酮光化夺氢反应中产生的活泼自由基。结果表明,与硫原子相联的两个碳上的C-H键(即2位和4或6位碳的C-H键),都能发生均裂而生成较稳定的自由基。并均可为ND和TBN捕获而生成两种自由基加合物,其浓度比约为1:1。     

Ground state properties of S = 1 antiferromagnetic chain systems studied by ESR

Electron spin resonance (ESR) was used to study the ground state properties of two kinds of spin (S) one Heisenberg antiferromagnetic chain systems, namely a uniform chain system (HAUC), which is well known as the Haldane system, and a bond alternating chain system (HABA). To investigate and compare the features of the ground state, two nickel chain compounds doped with non-magnetic Zn²⁺ impurities were studied. The HAUC was modelled with Ni(1,3-pn)₂(μ-NO₂)(ClO₄)(1,3-pn = 1,3-propanediamine), abbreviated as NINO, while the HABA was modelled with Ni(333-tet)(μ-NO₂)(ClO₄) (333-tet = bis-(3-aminopropyl)-1,3-propanediamine), abbreviated as NTENP. Both systems have a singlet ground state with an excitation gap. The ground state of NINO approximates well to the valence bond solid state, thus producing S = 1/2 spins at the sites neighbouring the impurities. The angular dependence of the ESR signals of NINO:Zn is explained by the anisotropy of the g tensor for spin 1/2. On the other hand, the ground state of NTENP is expected to be in the singlet dimer phase based on the ratio of alternating bond strengths. In this case, it is expected that the S = 1 spins will appear at the sites neighbouring the impurities without forming the singlet dimer. From ESR studies of NTENP:Zn was observed the triplet state (S = 1), induced by the impurity doping, which is consistent with the above picture.     

Magnetic resonance in pure and diamagnetically diluted spin-Peierls CuGeO3

Magnetic resonance at frequencies 22–75 GHz is investigated in pure single-crystalline CuGeO₃ in the temperature range 1.2–25 K. At temperatures below 4 K the magnetic resonance line splits into four spectral components. The line close to the ESR of the paramagnetic phase is associated with impurities or defects. The other three lines have the same intensity in different samples and are apparently characteristic for pure single crystals at low temperature. An antiferromagnetic resonance with two resonance absorption branches and a spectrum characteristic for an antiferromagnet with easy, average, and hard anisotropy axes was observed and investigated in the Néel compound Cu_0.98Zn_0.02GeO₃ with diamagnetic dilution of the spin subsystem. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 277–282 (25 August 1996)     

Electron spin resonance studies on quantum tunneling in spinel ferrite nanoparticles

The electron spin resonance (ESR) spectrometer, a very sensitive instrument with fast detecting window to explore quantum phase transitions for magnetic nanoparticles, was exploited to study the fascinating interplay between thermal and quantum fluctuations in the vicinity of a quantum critical point. We have measured ESR in ferrofluid samples containing nanosize particles of Fe₂O₃. The evolution of the ESR spectrum with temperature suggests that quantum tunneling of spins occurs in single domain magnetic particles in the low temperature regime. The effects of various microwave fields, particle sizes, and temperatures on the magnetic states of single domain spinel ferrite nanoparticles are investigated. We can consistently explain experimental data assuming that, as the temperature decreases, the spectrum changes from superparamagnetic (SPR) to blocked SPR and finally evolves quantum superparamagnetic behaviour as the temperature lowers down further. A nanoparticle system of a highly anisotropic magnetic material can be qualitatively specified by a simple quantum spin model, or by the Heisenberg model with strong easy-plane anisotropy.Received: 29 August 2003, Published online: 15 October 2003PACS: 76.30.-v Electron paramagnetic resonance and relaxation - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.) - 05.30.-d Quantum statistical mechanics - 75.50.Dd Nonmetallic ferromagnetic materials     

Magnetic properties of the S = 1/2 one-dimensional antiferromagnet MgVO

The magnetic susceptibility and the electron spin resonance in the X-band of the transition metal oxide compound MgVO₃ are reported. We show that this compound, made of weakly coupled infinite chains of VO₅ pyramids, behaves as a S =1/2 one-dimensional Heisenberg antiferromagnet. From the ESR and magnetic experiments we deduce the Néel temperature K, the in-chain coupling constant K and the g-factor values g x = g z =1.972(2), g y =1.946(1) for V⁴⁺ ions in MgVO₃. Received 14 July 1999