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1.
An elastic Ising model for a one-dimensional diatomic spin chain is
proposed to explain the ferroelectricity induced by the collinear
magnetic order with a low-excited energy state. A statistical theory
based on this model is developed to calculate the electrical and
magnetic properties of Ca3CoMnO6, a typical
quasi-one-dimensional diatomic spin chain system. The calculated
ferroelectric polarization and dielectric susceptibility show a good
agreement with recently reported data on Ca3Co2-xMnxO6 (x ≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility
does not coincide well with experiment. We also address the
rationality and deficiency of this model by including a first-order
correction which improves the consistency between the model and
experiment. 相似文献
2.
Kikuchi H. Nagasawa H. Mekata M. Fudamoto Y. Kojima K.M. Luke G.M. Uemura Y.J. Mamiya H. Naka T. 《Hyperfine Interactions》1999,120(1-8):623-627
AgNiO2, a model compound of an S=1/2 triangular lattice, was studied by muon spin relaxation in addition to ac, dc susceptibility,
electrical resistivity and neutron diffraction. The relaxation rate shows a sharp peak at around TN=28 K followed by a sudden decrease of initial asymmetry indicating a magnetic ordering. Three internal fields ranging from
0.2 to 0.3 T were obtained from the muon precession period. However, a neutron diffraction experiment failed to detect any
magnetic order at low temperatures. From these results, it was concluded that magnetic coherence is confined to small domain
compared with the coherence length of neutron diffraction due to spin frustration.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
We describe a method for obtaining the polaron spin-lattice relaxation time T{SL} in pi-conjugated polymers by measuring the optically detected magnetic resonance (ODMR) dynamics as a function of microwave power and laser intensity. The peculiar ODMR dynamics is well described by a spin dependent recombination model where both recombination and spin relaxation rates determine together the response dynamics. We apply this method to the spin 1/2 ODMR in films of pristine 2-methoxy-5-(2{'}-ethylhexyloxy) phenylene vinylene [MEH-PPV] polymer, as well as MEH-PPV doped with various concentrations of radical impurities. We obtained T{SL} approximately 30 micros in pristine MEH-PPV, but substantially shorter when the magnetic impurities are added. 相似文献
4.
T. Hatano Y. Suzuki M. Doyama Y. J. Uemura T. Yamazaki J. H. Brewer 《Hyperfine Interactions》1984,17(1-4):211-217
Positive muon spin relaxation was measured in Al-0.047% Mg quenched from 873 K under zero external magnetic field from 6.3 K to 270 K. The observed spectra were analysed with the calculated muon spin relaxation function which included the static relaxation rates, the trapping rates, the detrapping rates and thet=0 initial trapping fractions. Due to the precise measurements and the realistic expression of spin relaxation function, above four parameters could be determined distinctly. The trapping rates and the distortions around a muon were determined from the values of static relaxation rates at a trapping site. The diffusion features were clearly described by the trapping and detrapping rates. The diffusion process was determined by the temperature dependence of these parameters. 相似文献
5.
Chakhalian JA Kiefl RF Miller R Brewer J Dunsiger SR Morris G MacFarlane WA Sonier JE Eggert S Affleck I Keren A Verdaguer M 《Physical review letters》2003,91(2):027202
We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi-one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with transfer matrix density-matrix renormalization-group numerical simulations. 相似文献
6.
Savici AT Fukaya A Gat-Malureanu IM Ito T Russo PL Uemura YJ Wiebe CR Kyriakou PP MacDougall GJ Rovers MT Luke GM Kojima KM Goto M Uchida S Kadono R Yamada K Tajima S Masui T Eisaki H Kaneko N Greven M Gu GD 《Physical review letters》2005,95(15):157001
Muon spin relaxation measurements in high transverse magnetic fields [FORMULA: SEE TEXT] revealed strong field-induced quasistatic magnetism in the underdoped and Eu-doped (La,Sr)2CuO4 and La1.875Ba0.125CuO4, existing well above Tc and TN. The susceptibility counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards T approximately 25 K. No field-induced magnetism was detected in overdoped La1.81Sr0.19CuO4, optimally doped Bi2212, and Zn-doped YBa2Cu3O7. 相似文献
7.
The static and dynamic magnetic properties of a Prussian blue analogue, molecular magnet Cu^Ⅱ_{3}[Fe^Ⅲ(CN)_6]_2·3NH_3·6H_2O were investigated in detail. The H dependence of the linear AC susceptibility, the irreversibility in the field-cooled (FC)/zero-field-cooled (ZFC) magnetization (M_{FC}/M_{ZFC}) and the relaxation of M_{ZFC} suggest that the magnetic system can be visualized as containing a ferromagnetic cluster of spin below T_C, mixed with small spin-glass clusters formed below temperature T_g less than T_C. The observed magnetic properties are explained with a ferromagnetic-spin-glass phase model. The magnetic ordering of the sample occurs below 19.8K. 相似文献
8.
Effects of exchange interaction and spin-fluctuation on the magnetic and magneto-optic properties of NdF3
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The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -(0.75 + 0.22T) × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones. 相似文献
9.
At low temperature the positively charged muon (μ+) in solid3He is localized in a polaron which, unlike a chemically bound complex, is held together with polarizational attraction (van der Waals force). The dynamic effects in the muon relaxation are determined by the spin exchange of the3He atoms in the polaron. In crystals with large molar volumes (melting pressureP m<60 bar) the rate of magnetic field fluctuations at the muon site is at least one order of magnitude lower than in an unperturbed crystal. In an external electric field the μ+ produces an anisotropic local distortion which reduces the rate of the local3He spin exchange and leads to an increase of the muon spin relaxation rate. 相似文献
10.
We investigated the nature of the freezing in the geometrically frustrated Heisenberg spin glass Y2(Mo2)O(7) by measuring the temperature dependence of the static internal magnetic field distribution above the spin-glass temperature, Tg, using the muon spin relaxation technique. The evolution of the field distribution cannot be explained by changes in the spin susceptibility alone and suggests a lattice deformation. This possibility is addressed by numerical simulations of the Heisenberg Hamiltonian with magnetoelastic coupling at T > 0. 相似文献
11.
Fukaya A. Ohira S. Watanabe I. Hagiwara M. Nagamine K. 《Hyperfine Interactions》1999,120(1-8):619-622
We examined the muon spin relaxation (μSR) of mixed compounds NiC2O4 2⋅(2-methylimidazole)x(H2O)1-x with x=1.0 and 0.49. Although the macroscopic magnetic properties are obviously different from each other, both systems exhibit
similar behavior in the muon spin relaxation. In addition, in the x=0.49 (SG) sample, a critical slowing down of spin dynamics
was not observed in this μSR measurement, though the spin-glass like freezing was observed in the susceptibility measurements.
Qualitative explanation of these anomalous observations is given.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
The structural stability and magnetic properties of the icosahedral Ni13, Ni13^+1 and Ni13^-1 clusters have been obtained by utilizing all-electron density functional theory with the generalized gradient approximations for the exchange-correlation energy. The calculated results show that the ground states of neutral and charged clusters all favour a D3d structure, a distorted icosahedron, due to the Jahn-Teller effect. The radial distortions caused by doping one electron and by doping one hole are opposite to each other. Doping one electron will result in a 1/2 decrease and doping one hole will result in a 1/2 increase of the total spin. Both increasing interatomic spacing and decreasing coordination will lead to an enhancement of the spin magnetic moments for Nil3 clusters. 相似文献
13.
Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect, where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liquid. In this work we report the synthesis and magnetism study of the monocrystalline Mn$_2$Ga$_2$S$_5$, featuring both the van der Waals structure and a bilayered triangular Mn lattice. Magnetic susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature $\theta_{\rm w}\sim-260$ K and a high spin $S=5/2$ Mn$^{2+}$ state. However, no long range magnetic order has been found down to 2 K, and a spin freezing transition is found to occur at around 12 K well below its $\theta_{\rm w}$. This yields a frustration index of $f = -\theta_{\rm w}/T_{\rm f} \approx 22$, an indication that the system is highly frustrated. The absence of a double-peak structure in magnetic specific heat compared with the $TM_2$S$_4$ compounds implies that the spin freezing behavior in Mn$_2$Ga$_2$S$_5$ is a result of the competition between exchange interactions and the 2D crystalline structure. Our results suggest that the layered Mn$_2$Ga$_2$S$_5$ would be an excellent candidate for investigating the physics of 2D magnetism and spin disordered state. 相似文献
14.
Ando K Takahashi S Harii K Sasage K Ieda J Maekawa S Saitoh E 《Physical review letters》2008,101(3):036601
Using the spin Hall effect, magnetization relaxation in a Ni_{81}Fe_{19}/Pt film is manipulated electrically. An electric current applied to the Pt layer exerts spin torque on the entire magnetization of the Ni81Fe19 layer via the macroscopic spin transfer induced by the spin Hall effect and modulates the magnetization relaxation in the Ni81Fe19 layer. This method allows us to tune the magnetization dynamics regardless of the film size without applying electric currents directly to the magnetic layer. 相似文献
15.
E. Sato T. Hatano Y. Suzuki M. Imafuku M. Sunaga M. Doyama Y. Morozumi T. Suzuki K. Nagamine 《Hyperfine Interactions》1984,17(1-4):203-209
The muon spin relaxation in the Al-Mg dilute alloy was measured under the zero external field from 34 to 120 K, and the observed spectra were fitted to the calculated spin relaxation function of the two state model which is taking account of both trapping and detrapping mechanisms. Thus, the muon behavior in Al in the presence of impurity traps were able to be visualized: a muon diffuses in the incoherent hopping process with one phonon assistance, while it is then captured by a trap in a diffusion control process, and detrapped in the thermal activation process. 相似文献
16.
T. N. Mamedov A. S. Baturin V. N. Duginov K. I. Gritsaj R. Khasanov A. Maisuradze A. V. Stoykov 《JETP Letters》2012,95(12):662-665
Polarized negative muons were used to study relaxation mechanisms of shallow acceptors in germanium. In p-type germanium at low temperatures relaxation of the muon spin was observed, indicating that the muonic atom (gallium-like acceptor center) formed via capture of the negative muon by a host atom is in the paramagnetic state and its magnetic moment is relaxing. The relaxation rate of the muon spin was found to depend on temperature and on concentration of gallium impurity. We conclude that to the relaxation of the magnetic moment of the Ga acceptor in Ge there contribute both scattering of phonons and quadrupole interaction between the acceptors. We estimate, for the first time, the hyperfine interaction constant for the gallium acceptor in germanium as 0.11 MHz. 相似文献
17.
NMR and NQR spectra and spin-lattice relaxation measurements carried out in LASCO and YBCO-type crystals are presented and analyzed in order to derive insights on the correlations and spin-dynamics of the Cu2+ ions and on the microscopic mechanisms of high-T c superconductivity. As an illustrative example on how the magnetic correlation length and spin dynamics properties can be extracted from the relaxation rateW, the35Cl NMR data in the two-dimensional Heisenberg system Sr2CuCl2O2, around the paramagnetic-antiferromagnetic (PA-AF) transition are first considered. Then the139La NQR relaxation measurements in La2?xSrxCuO4 are briefly reviewed and it is shown how a simple picture of localized Cu2+ magnetic moments, whose spin fluctuation times are controlled by the charge defects induced by the doping, leads in a direct way to quantitative estimates for the progressive shift, on cooling, of the spectral density of the low-frequency spin excitations towards the high frequency range. This phenomenon can be described in terms of effective spin at the Cu2+ ions, and its similarities with the analogous effect of progressive delocalization in Heavy Fermions systems are pointed out. Thus, the superconducting transition appears to occur in an unconventional Fermi liquid with AF correlations among itinerant pseudoparticles, possibly involving a mechanism not directly related to the magnetic correlated dynamics. In fact, a universal behavior of the relaxation rates as a function of temperature is observed, regardless of the transition temperatureT c. The independence ofT c from the low frequency static and dynamical spin properties is also indicated by89Y Knight shifts and from63Cu relaxation rates in systems like YBa2Cu4O8 (Y124), whereT c can be changed by atomic substitutions and by controlling the oxygen stoichiometry. The effect of an external magnetic field on the correlated spin dynamics of the AF Fermi liquid is investigated and from a comparison of Cu NQR relaxation and NMR relaxation in oriented powder of YBCO and LASCO it is shown that the external field has the small but unambiguous effect of depressing the relaxation rates aboveT c, besides strongly enhancing them in the superconducting phase. A maximum in the ratio \({{W\left( {NQR} \right)} \mathord{\left/ {\vphantom {{W\left( {NQR} \right)} {W\left( {\vec H\left\| {\vec c} \right.} \right)}}} \right. \kern-0em} {W\left( {\vec H\left\| {\vec c} \right.} \right)}}\) is thus observed around 80 K, either in LASCO or in YBCO, again indicating that the transition could be driven by a mechanism not directly involving the spin dynamic properties. To study the role of the fluxions belowT c 89Y NMR shifts and spectra in oriented powders of YBCO are analyzed. Information on the spin susceptibility and on the structure of the vortex lattice is obtained. In addition, from the temperature behavior of the linewidth a motional narrowing related to flux melting is evidenced. The effective correlation time for the vortex motion is derived and it is discussed why μ+SR cannot detect it in view of the different rigid-lattice line broadening. 相似文献
18.
The g-factors of the intra-band states 12,13,14,15 in a magnetic-rotational band built on the 11 state in 82 Rb are measured for the first time by using a transient magnetic field-ion implantation perturbed angular distribution (TMF-IMPAD) method.The magnetic-rotational band in 82 Rb is populated by the 60 Ni(27 Al,4pn) 82 Rb reaction,and the time-integral Larmor precessions are measured after recoil implantation into a polarized Fe foil.The calculation of g-factors is also carried out in terms of a semi-classical model of independent particle angular momentum coupling on the basis of the four-quasiparticle configuration π(g 9/2) 2 π(p 3/2,f 5/2) ν (g 9/2).The measured and calculated g-factors are in good agreement with each other.The g-factors and deduced shear angles decrease with the increase of spin along the band.This clearly illustrates the shear effect of a step-by-step alignment of the valence protons and neutrons in magnetic rotation.The semi-classical calculation also shows that the alignment of the valence neutron angular momentum is faster than that of the valence protons,which results in a decrease of g-factors with increasing spin.The present results provide solid evidence of the shear mechanism of magnetic rotation. 相似文献
19.
We figure out that the ground state of a multiple-spin exchange model applicable to thin films of solid {3}He possesses an octahedral spin nematic order. In the presence of a magnetic field, it is deformed into an antiferroquadrupolar order in the perpendicular spin plane, in which lattice Z{3} rotational symmetry is also broken. Furthermore, this system shows a narrow magnetization plateau at half, m/m{sat}=1/2, which resembles recent magnetization measurements [H. Nema et al., Phys. Rev. Lett. 102, 075301 (2009)]. 相似文献
20.
D. E. Maclaughlin W. G. Clark D. W. Cooke R. H. Heffner 《Hyperfine Interactions》1987,34(1-4):355-367
Nuclear magnetic resonance and relaxation, and the related techniques of muon spin rotation and relaxation, have been used to study local spin polarization and quasiparticle excitations in the heavy-fermion superconductors CeCu2Si2, pure and thoriated UBe13, and UPt3. Measurements of nuclear and positive muon Knight shifts, linewidths, and spinlattice relaxation rates give some hints as to the nature of Cooper pairing in these exotic materials. 相似文献