Antiferromagnetic Heisenberg Linear Chain Research Articles

Synthesis, coordination modes, structures, and magnetic properties of halogen-substituted 2-hydroxypyridine copper(II) chloride coordination compounds

A family of 6-X-2-hydroxyprydine/pyridone (6-X-2-HOpy/pyridone) Cu(II) compounds, [Cu(6-X-2-HOpy)2Cl2] (1 X = F; 2 X = Cl) and [(6-X-2-pyridone)CuCl(μ-Cl)]2 (3 X = Cl; 4 X = Br), has been prepared. Solution-based infrared spectra displayed a correlation between tautomeric state, primarily driven by halogen identity, and coordination mode with neutral nitrogen coordination mode favored as Br ≪ Cl < F. The tautomeric state of 6-Cl-2-HOpy is influenced by metal ion concentration (M) with lactam concentration increasing as M increases. Compound 1 has F–F contacts less than the sum of the van der Waals radii but falls outside of the typical halogen bonding angle parameters, R–X•••Y = R–Y•••X = 138.2°. Compounds 1 and 2 exhibit weak antiferromagnetic exchanges, fit with a one-dimensional quantum Heisenberg antiferromagnetic linear chain (1D-QHAF) model and J/kB = −1.99(1) K and −0.92(7) K, respectively. Compounds 3 and 4 exhibit a dominating ferromagnetic exchange and an antiferromagnetic exchange and were qualitatively fit to a ferromagnetic linear chain with an interchain interaction model. This model does not accurately represent the physical parameters of the system and was used to show that both exchanges exist and are nontrivial.

One-dimensional molecular solid [I-BzPy-d5][Pt(mnt)2] (I-BzPy-d5+ = 1-N-(4-iodobenzyl)pyridinium-d5, mnt2− = maleonitriledithiolate): Synthesis, crystal structure, magnetic property and variable-temperature infrared spectra

A new one-dimensional molecular solid, [I-BzPy-d5][Pt(mnt)2] (mnt2−=maleonitriledithiolate, I-BzPy-d5+=1-N-(4-iodobenzyl)pyridinium-d5) was synthesized. [I-BzPy-d5][Pt(mnt)2] and its analog [I-BzPy][Pt(mnt)2] are isostructural, crystallized in space group P−1 at ambient temperature. A hysteretic magnetic transition occurs at ca. 80K with 5.6K thermal hysteresis upon cooling. [I-BzPy-d5][Pt(mnt)2] features an alternating S=1/2 Heisenberg antiferromagnetic linear chain magnetic behavior with spin gap of 131K in high-temperature phase, while 306K in low-temperature phase. There is no significant isotope effect of both magnetism and phase transition by comparison of [I-BzPy-d5][Pt(mnt)2] and [I-BzPy][Pt(mnt)2]. The variable-temperature IR spectra in 10–293K revealed the existence of pre-transition phenomenon up until 100K and five intramolecular vibrational modes cooperating with the magnetic phase transition.

Structural, Magnetic, and Computational Correlations of Some Imidazolo‐Fused 1,2,4‐Benzotriazinyl Radicals

1,3,7,8-Tetraphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (5), 8-(4-bromophenyl)-1,3,7-triphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (6), and 8-(4-methoxyphenyl)-1,3,7-triphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (7) were characterized by using X-ray diffraction crystallography, variable-temperature magnetic susceptibility studies, and DFT calculations. Radicals 5-7 pack in 1 D π stacks made of radical pairs with alternate short and long interplanar distances. The magnetic susceptibility (χ vs. T) of radicals 5 and 6 exhibit broad maxima at (50±2) and (50±4) K, respectively, and are interpreted in terms of an alternating antiferromagnetic Heisenberg linear chain model with average exchange-interaction values of J = -31.3 and -35.4 cm(-1) (gsolid = 2.0030 and 2.0028) and an alternation parameter a = 0.15 and 0.38 for 5 and 6, respectively. However, radical 7 forms 1 D columns of radical pairs with alternating distances; one of the interplanar distances is significantly longer than the other, which decreases the magnetic dimensionality and leads to discrete dimers with a ferromagnetic exchange interaction between the radicals (2J = 23.6 cm(-1) , 2zJ' = -2.8 cm(-1) , gsolid = 2.0028). Magnetic exchange-coupling interactions in 1,2,4-benzotriazinyl radicals are sensitive to the degree of slippage and inter-radical separation, and such subtle changes in structure alter the fine balance between ferro- and antiferromagnetic interactions.

Effect of electron doping on the magnetic properties of spin-Peierls like material α′-NaV 2O 5

Na 1+ x V 2O 5 ( x = 0.04 and 0.10) powder were synthesized by solid-state reaction under the condition of excess NaVO 3 with the protection of pure Nitrogen. Both of them showed a typical S = 1/2 one-dimensional (1D) antiferromagnetic Heisenberg linear chain behaviour at high temperature. At low temperature region, Na 1.04V 2O 5 displayed a spin-Peierls like transition at 35 K. The susceptibility of Na 1.10V 2O 5 increased with the decreasing of temperature, without spin-singlet transition. The increase of the susceptibility in Na 1.10V 2O 5 at low temperature results from the isolated V 4+ ions distributed in the nonmagnetic V 5+ chains due to the electron doping. The Curie–Weiss fitting between 4 K and 10 K indicated that the electron doping in α′-NaV 2O 5 induces the Curie term and thus results in the suppression and disappearance of the spin-singlet.

Quantum spin dynamics studied by the nuclear magnetic relaxation of protons in the Haldane-gap system(CH3)4NNi(NO2)3

The nuclear spin-lattice relaxation time ${T}_{1}$ of $^{1}\mathrm{H}$ in the Haldane-gap system $({\mathrm{CH}}_{3}{)}_{4}\mathrm{NNi}({\mathrm{NO}}_{2}{)}_{3}$ has been measured at the temperatures down to $50\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ in the gapped and gapless phases with an external field $H$ up to $8.5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. In the gapless phase for $Hg{H}_{\mathrm{C}1}=2.7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, the relaxation rate ${T}_{1}^{\ensuremath{-}1}$ exhibited, below about $3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a divergent behavior with decreasing temperature. Such a feature is described by an equation, such as ${T}_{1}^{\ensuremath{-}1}\ensuremath{\sim}{T}^{\ensuremath{-}\ensuremath{\alpha}}$ with $\ensuremath{\alpha}=1\ensuremath{-}\ensuremath{\eta}$, where $\ensuremath{\eta}$ is the exponent of the power-law decay for the staggered mode of transverse correlation with respect to the distance in the one-dimensional chain. It has been found that the exponent $\ensuremath{\alpha}$ takes the values around 0.6, which are consistent with the numerical evaluation for $S=1$ Heisenberg antiferromagnetic linear chain (HALC). This yields evidence for the realization of Tomonaga-Luttinger liquid phase. At very low temperatures, ${T}_{1}^{\ensuremath{-}1}$ changes into a remarkable decrease after taking a round peak, accompanying an appreciable broadening in the NMR spectrum, and the temperature for such a peak has a trend to increase with increasing field. In the gapped phase for $Hl{H}_{\mathrm{C}1}$, ${T}_{1}^{\ensuremath{-}1}$ showed an exponential decrease with decreasing temperature. The experimental results were well interpreted in terms of the intrabranch process associated with the scattering of the magnons within each of ${S}_{z}=\ensuremath{-}1$ and $+1$ branches of the first excited state. Anomalous hump of ${T}_{1}^{\ensuremath{-}1}$ appeared at low fields below $1\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ and at low temperatures below $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This was reasonably explained considering the fractional-spin effect in the $S=1$ HALC.

Magnetic Properties of Isostructural BaCoP2O7, BaNiP2O7, and BaCuP2O7 Studied with dc and ac Magnetization and Specific Heat

Magnetic properties of three isostructural compounds BaMP2O7 (M = Co, Ni, and Cu) were investigated by dc and ac magnetization and specific heat measurements. BaCuP2O7 was shown to be an excellent quasi-one-dimensional linear-chain Heisenberg antiferromagnet with an exchange constant (J/kB) of 103.8 K (Hamiltonian H = J Sigma SiS(i+1)) and a temperature for the long-range magnetic order (TN) of 0.81 K giving the ratio kBTN/J = 0.78%. BaCoP2O7 and BaNiP2O7 exhibited long-range antiferromagnetic order at TN = 10.4 and 10.1 K, respectively. BaCoP2O7 and BaNiP2O7 showed a large contribution of the short-range correlation above TN. BaNiP2O7 remained in the antiferromagnetic state up to 90 kOe at 2 K, whereas BaCoP2O7 demonstrated two metamagnetic phase transitions at about 52 and 71 kOe at 2 K if the magnetic field was parallel to the easy direction. BaMP2O7 melted incongruently at 1323 K (M = Co), 1344 K (M = Ni), and 1338 K (M = Cu).

Characterization of quasi-one-dimensional S=1/2 Heisenberg antiferromagnets Sr 2Cu(PO 4) 2 and Ba 2Cu(PO 4) 2 with magnetic susceptibility, specific heat, and thermal analysis

Properties of Sr 2Cu(PO 4) 2 and Ba 2Cu(PO 4) 2 having [Cu(PO 4) 2] ∞ linear chains in their structures with Cu–O–P–O–Cu linkages were studied by magnetic susceptibility ( T=2–400 K, H=100 Oe) and specific heat measurements ( T=0.45–21 K). Magnetic susceptibility versus temperature curves, χ( T), showed broad maxima at T M=92 K for Sr 2Cu(PO 4) 2 and T M=82 K for Ba 2Cu(PO 4) 2 characteristic of quasi-one-dimensional systems. The χ( T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie–Weiss terms) with g=2.153(4) and J/ k B=143.6(2) K for Sr 2Cu(PO 4) 2 and g=2.073(4) and J/ k B=132.16(9) K for Ba 2Cu(PO 4) 2 (Hamiltonian H= JΣS i S i+1 ). The similar J/ k B values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T N, were below 0.45 K. Sr 2Cu(PO 4) 2 and Ba 2Cu(PO 4) 2 are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with k B T N/ J<0.34% together with Sr 2CuO 3 ( k B T N/ J≈0.25%) and γ-LiV 2O 5 ( k B T N/ J<0.16%). Sr 2Cu(PO 4) 2 and Ba 2Cu(PO 4) 2 were stable in air up to 1280 and 1150 K, respectively.

CuSiO3:A quasi-one-dimensionalS=12antiferromagnetic chain system

CuSiO_3, isotypic to the spin - Peierls compound CuGeO_3, was discovered recently as a metastable decomposition product of the silicate mineral dioptase, Cu_6Si_6O_{18}\cdot6H_2O. We investigated the physical properties of CuSiO_3 using susceptibility, magnetization and specific heat measurements on powder samples. The magnetic susceptibility \chi(T) is reproduced very well above T = 8 K by theoretical calculations for an S=1/2 antiferromagnetic Heisenberg linear chain without frustration (\alpha = 0) and a nearest - neighbor exchange coupling constant of J/k_{B} = 21 K, much weaker than in CuGeO_3. Below 8 K the susceptibility exhibits a substantial drop. This feature is identified as a second - order phase transition at T_{0} = 7.9 K by specific heat measurements. The influence of magnetic fields on T_{0} is weak, and ac - magnetization measurements give strong evidence for a spin - flop - phase at \mu_0H_{SF} ~ 3 T. The origin of the magnetic phase transition at T_{0} = 7.9 K is discussed in the context of long - range antiferromagnetic order (AF) versus spin - Peierls(SP)order. Susceptibility and specific heat results support the AF ordered ground state. Additional temperature dependent ^{63,65}Cu nuclear quadrupole resonance experiments have been carried out to probe the Cu^{2+} electronic state and the spin dynamics in CuSiO_3.

Co2+(15-crown-5) Magnetic Supramolecular Cation in [Ni(dmit)2]- π-Spin System

Magnetic cation of Co2+ was incorporated in a monovalent [Ni(dmit)2]- (2-thioxo-1,3-dithiole-4,5-dithiolate) salt by using the supramolecular framework of 15-crown-5. The π-spins of [Ni(dmit)2]- formed a one-dimensional Heisenberg antiferromagnetic linear chain, while the d-spin of Co2+ behaved as a free S = 3/2 spin within the crystal.

One-dimensional antiferromagnetic chain in [Ni(dmit)2]- salts of [K+ or Rb+(4,13-diaza-18-crown-6)] supramolecular cation.

Mixed-stack structures of monovalent [Ni(dmit)2]- and planar M+(4,13-diaza-18-crown-6) (M+ = K+ or Rb+) supramolecular cation were obtained in the isostructural M+(4,13-diaza-18-crown-6)[Ni(dmit)2] salts. The mixed-stack structure decreases the effective π−π overlap of [Ni(dmit)2]- molecules, which results in the one-dimensional Heisenberg antiferromagnetic linear chain of S = 1/2 spins within the crystal.

Cs+(18-crown-6)2e-: A 1D Heisenberg Antiferromagnet with Unusual Phase Transitions

Crystalline Cs+(18-crown-6)2e- was found to be a linear chain Heisenberg antiferromagnet (J/kB = −38.3 K). It undergoes a slow, irreversible transition above ∼230 K from a crystalline low temperature (LT) phase to a disordered Curie−Weiss paramagnetic high temperature (HT) phase. A 100 ppm diamagnetic (more shielded) shift of the 133Cs MAS NMR peak accompanies this transition. EPR studies confirm the transition and are in accord with the conversion of the known crystal structure to a disordered phase. This HT phase undergoes an additional first-order reversible transition upon cooling below ∼220 K (ΔH = 0.33 kJ mol-1 upon rewarming) accompanied by the formation of two peaks in the 133Cs NMR spectrum. Variable-temperature powder X-ray diffraction confirms the disordered or microcrystalline nature of the HT phase(s).

Magnetic Properties of 3-(4-R-Phenyl)-1,5-diphenyl-6-oxo- and -thioxoverdazyl Radical Crystals (R = OCH3, CH3, CN, and NO2)

Magnetic susceptibilities of 8 kinds of 3-(4-R-phenyl)-1,5-diphenyl-6-oxo- and -thioxoverdazyl radical crystals (p-MDpOV (R = OCH3), p-MeDpOV (R = CH3), p-CyDpOV (R = CN), p-NDpOV (R = NO2), p-MDpTV (R = OCH3), p-MeDpTV (R = CH3), p-CyDpTV (R = CN), and p-NDpTV (R = NO2)) were measured between 4.2 and 300 K. The susceptibilities of p-MDpOV, p-CyDpOV, and p-MDpTV can be well explained by a one-dimensional (1D) antiferromagnetic (AFM) Heisenberg linear chain model with exchange interaction of 2 J/k = −27.3, −27.3, and −10.9 K, respectively. The susceptibility of p-MeDpTV can be interpreted in terms of a 1D AFM Heisenberg alternating chain model with 2 J1/k = −92.0 K (alternation parameter α = J2/J1 = 0.7). On the other hand, the susceptibilities of p-MeDpOV, p-NDpOV, and p-CyDpTV follow the Curie−Weiss law with positive Weiss constants of +2.5, +1.5, and +2.9 K, respectively, and the exchange interactions 2 J/k were estimated to be +7.0, +5.0, and +7.0 K, assuming the one-dimensionality for these radical cr...

Magnetic Properties of One-Dimensional Heisenberg Chains with Ferromagnetic-Antiferromagnetic Bond Alternation

We report the results of susceptibility and magnetization measurements on ferromagnetic-antiferromagnetic alternating chain compounds [Cu(TIM)]CuCl 4 (TIM=2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo-1,4,8,11-tetraazatetradecane) and (4-BzpipdH)CuCl 3 (4-BzpipdH=4-benzylpiperidinium). Magnetization curves of both compounds are compared to those calculated for an S =1 linear-chain Heisenberg antiferromagnet. From the fitting of susceptibility data to a numerical formula calculated for an S =1/2 ferromagnetic-antiferromagnetic alternating chain [Inog. Chem. 33 (1994) 5171], we have estimated the antiferromagnetic exchange constant J AF / k B =2.9 K, the ferromagnetic exchange constant | J F |/ k B =4.7 K and the g-value of the magnetic moment g =2.06 for the former and J AF / k B =8.8 K, | J F |/ k B =38.8 K and g =2.17 for the latter, which are different from the values reported previously.

Synthesis, X-ray structures and magnetic properties of linear chain 4-cyanopyridine compounds: [Cu(4-CNpy) 4(H 2O)](ClO 4) 2 and M(4-CNpy) 2Cl 2 (M  Mn, Fe, Co, Ni, Cu)

The synthesis, structures and magnetic properties of linear chain complexes of metal ions with 4-cyanopyridine are reported (4-CNpy=4-cyanopyridine): [Cu(4-CNpy) 4(H 2O)](ClO 4) 2 and M(4-CNpy) 2Cl 2 (MMn, Fe, Co, Ni, Cu). All compounds crystallize in monoclinic systems. Crystallographic data for [Cu(4-CNpy) 4(H 2O)](ClO 4) 2] n ( 1): space group P2 1/ c with a = 13.225(3), b = 10.567(2), c = 20.522(3) A ̊ , β = 99.71(2)°, V = 2826.7(9) A ̊ 3, Z = 4, D calc = 1.640 Mg m −3, μ = 3.430 mm −1 . The compound contains primer CuL 4 units with the ligands bounded to copper ions through the ring nitrogens. These units are weakly linked into chains through semi-coordinated bonds between the nitrile nitrogen and an adjacent copper ion via the axial sites. The magnetic data show only a weak antiferromagnetic interaction ( θ CW = −0.52(1) K). Crystallographic data for [Cu(4-CNpy) 2Cl 2] n ( 2): space group P2 1/ n with a = 3.779(2), b = 25.711(12), c = 7.104(4) A ̊ , β = 95.98(4)°, V = 686.48(4) A ̊ 3, Z = 2, D calc = 1.658 Mg m −3, μ = 5.575 mm −1 . Crystallographic data for [Mn(4-CNpy) 2Cl 2] n ( 6): space group P2 1/ c with a = 3.700(2), b = 7.198(2), c = 26.520(5) A ̊ , β = 92.13(3)°, V = 705.8(4) A ̊ 3, Z = 2, D calc = 1.572 Mg m −3, μ = 1.303 mm −1 . Both dichloride compounds similar structures, consisting of chains of metal ions bibridged by chlorides with the 4-CNpy ligands coordinated to the metal ions in the axial sites through the pyridine nitrogens. The difference in space groups is caused by the different modes of packing the chains into 3D lattices. Infrared spectra and powder X-ray diffraction patterns indicate that the remaining compounds form an isostructural series. The powder magnetic susceptibilities have been measured between 2 and 300 K for all compounds. Antiferromagnetic exchange (Cu, Mn) or ferromagnetic exchange (Ni, Co, Fe) exists within the chains. The Ni, Co and Fe compounds order antiferromagnetically at 7.2(2), 2.1(2) and 4.6(2) K, respectively. Magnetic field induced transitions have been observed in these three compounds below their ordering temperatures. The copper and manganese data have been fit to models for Heisenberg antiferromagnetic linear chain with S = 1 2 and S = 5 2 with exchange constants J Co/ k = −13.7(2) K and J Mn/ k = −0.5 7(1) K, respectively. The nickel and cobalt data have been fit to models for ferromagnetic linear chains, with the nickel compound corresponding to a S = 1 Heisenberg model with exchange constant J/ lk = +4.8(2) K, and the cobalt compound to a S = 1 2 ferromagnetic Ising linear chain with exchange constant J/ k = + 6.6(2) K. The iron data has not been successfully to fit to any model. It is concluded that the total magnetic interaction between the chains has been increased by approximately 50% by the substitution of 4-CNpy for pyridine.

Effect of S= fractional spin on nuclear magnetic relaxation in a S=1 Heisenberg antiferromagnetic linear chain system

The spin-lattice relaxation time ${\mathrm{T}}_{1}$ of proton in NENP was measured at low temperatures and at low fields for a single crystal involving natural defects of 5%, one doped with a nonmagnetic ${\mathrm{Zn}}^{+2}$ ion of 1%, and pure crystal. The magnetization recoveries exhibited exp{-(t/${\mathrm{\ensuremath{\tau}}}_{1}$${)}^{1\mathrm{/}2}$}-type behaviors subsequent to exponential behaviors for initial time, which were qualitatively almost the same in all cases. The absolute values of the corresponding relaxation rates for the former two crystals were much larger than those for the latter. These features were reasonably explained by considering that fractional spins may play the role for thermal reservoir as if a magnetic impurity in a nonmagnetic solid. It is speculated that the spin-lattice relaxation of the fractional spin, the time of which is of the order of nuclear Larmor period, is determined by the collision with low-density Haldane excitations.

Magnetic Susceptibilities ofAV2O5(A=Liand Cs) with Square Pyramidal V(IV)O5

Stoichiometric powder samples of γ-LiV 2 O 5 and CsV 2 O 5 were synthesized and the magnetic susceptibilities were measured in the temperature range from 5 K to 700 K. The magnetic susceptibilities of γ-LiV 2 O 5 and CsV 2 O 5 show good fits to the equations for a S =1/2 one-dimensional Heisenberg antiferromagnetic linear chain model and a S =1/2 dimer model, respectively, although the obtained g -values are rather small (1.8 for both compounds). The ground state of γ-LiV 2 O 5 is neither a spin singlet state nor a magnetically ordered state, while CsV 2 O 5 is in a spin singlet state below 30 K. The results are discussed in comparison with the magnetic properties of α ′ -NaV 2 O 5 and CaV 2 O 5 .

Magnetic Susceptibility of Quasi-One-Dimensional Compoundα'-NaV2O5–Possible Spin-Peierls Compound with High Critical Temperature of 34 K–

Stoichiometric powder samples of α'-NaV 2 O 5 were synthesized and the magnetic susceptibility was measured in the temperature range from 2 K to 700 K. The magnetic susceptibility has a good fit to the equation for an S =1/2 antiferromagnetic Heisenberg linear chain with J / k B =280 K and g =2 above 34 K. Below 34 K the magnetic susceptibility rapidly decreases with decreasing temperature to a constant value of 1.49×10 -4 emu/V 4+ -mol which is reasonable for spin-singlet V 4+ –V 4+ pairs. This rapid reduction of the spin susceptibility below 34 K suggests the existence of a spin-Peierls transition. α'-NaV 2 O 5 is a possible spin-Peierls compound with the highest critical temperature yet observed.

Magnetic properties of a new type of 1,5-diphenyl-6-oxo- and -thioxo-verdazyl radicals

The magnetic susceptibilities of the 3-(4-chlorophenyl)-1,5-diphenyl-6-oxoverdazyl ( p-CD pOV), 3-(4-bromophenyl)-1,5-diphenyl-6-oxoverdazyl ( p-BD pOV), 1,3,5-triphenyl-6-thioxoverdazyl (TTV), and 3-(4-chlorophenyl)-1,5-diphenyl-6-thioxoverdazyl ( p-CD pTV) radicals have been measured between 4.4 and 300 K. The susceptibility of p-CD pOV and p-BD pOV follows the Curie-Weiss law with a positive and negative Weiss constant of +2.5 and −7.7 K, respectively. On the other hand, the susceptibility of TTV and p-CD pTV can be interpreted in terms of an alternating and nonalternating antiferromagnetic Heisenberg linear chain model with an exchange interaction of 2 J 1/ k = −66.0 K (alternation parameter α = J 2/ J 1 = 0.6) and 2 J/ k = −58.5 K, respectively.

Doping induced quantum bound states within the Haldane gap.

Using the approach proposed by Zittartz and M\uller-Hartmann [Z. Phys. 232, 11 (1970)], we show explicitly that quantum bound states at the centre of the Haldane energy gap can be induced by doping in a spin-1 linear chain Heisenberg antiferromagnet. We calculate the dynamic structure factor $S(q,\ensuremath{\omega})$ due to these bound states and use it to interpret the recent neutron scattering experiments on doped ${\mathrm{Y}}_{2}{\mathrm{BaNiO}}_{5}$ [J. F. DiTusa et al., Phys. Rev. Lett. 73, 1857 (1994)].

Electron spin resonance experiments on an [formula omitted] linear chain antiferromagnet in high frequencies and fields

We report the results of electron spin resonance (ESR) measurements on a typical S = 5 2 linear-chain Heisenberg antiferromagnet, (CH 3) 4NMnCl 3 (TMMC) at high frequencies and fields applied along the chain axis. We have observed an ESR signal whose frequency (ν) versus field ( H) relation is expressed by hν = √ g 2 μ B 2 H 2 + C with g = 2.17. This large shift of g value from 2.00 is discussed on the basis of spin wave theory.