High Field ESR Measurements Research Articles

Magnetic Excitation in the S = 1/2 Ising-like Antiferromagnetic Chain CsCoCl3 in Longitudinal Magnetic Fields Studied by High-field ESR Measurements

Magnetic Excitation in the <i>S</i> = 1/2 Ising-like Antiferromagnetic Chain CsCoCl₃ in Longitudinal Magnetic Fields Studied by High-field ESR Measurements

Effect of the Cr5+ ion doping on the quantum transition of the spin-dimer compounds Ba3Mn2−xCrxO8 (x = 0, 0.01, 0.04 and 0.06)

Ba3Mn2O8 has a quantum-disordered paramagnet ground state formed by the singlet, and the excitation states with the triplon and quintuplet. We have investigated the magnetization behaviors of the single crystal samples Ba3Mn2−xCrxO8 (x = 0, 0.01, 0.04 and 0.06) with both the static and pulsed high magnetic field from zero up to 60 T. At the temperature TN, the magnetization decreases rapidly with the decrease of temperature, which is the evidence of the dimerization of spin dimers. The field-induced quantum magnetization plateaus (half of the saturation magnetization) and high-field polarization states show the excited triplet and quintuplet states appear with the change of temperature and the applied magnetic field. The high field magnetization and ESR measurement results confirm that the J0/kB value and the zero-field gap Δ/kB value are close to the reported value, which also indicates that Ba3Mn2−xCrxO8 is not a simple isolated dimer system.

Electric Dipole Active Magnetic Resonance and Nonreciprocal Directional Dichroism in Magnetoelectric Multiferroic Materials in Terahertz and Millimeter Wave Regions

We review electric dipole active magnetic resonance and nonreciprocal directional dichroism in magnetoelectric multiferroic materials in terahertz and millimeter wave regions. Owing to dynamical magnetoelectric coupling generated by the spin-dependent electric polarization, magnetic resonance, which usually occurs owing to magnetic dipole transition, can be induced by the oscillating electric fields of electromagnetic wave. This electric dipole active magnetic resonance can be useful for microscopic investigations of magnetic excitation in unconventional spin systems. The magnetoelectric coupling also induces the nonreciprocal directional dichroism, which provides a novel functionality to materials as an optical diode, in teraheltz and microwave absorption by magnetic resonance. As examples, we describe the results of the high field ESR measurements of the triangular lattice antiferromagnet $$\hbox {CuFeO}_{\mathrm{2}}$$ and the interacting quantum spin dimer systems $$\hbox {TlCuCl}_{\mathrm{3}}$$ and $$\hbox {KCuCl}_{\mathrm{3}}$$ .

21aBD-3 NaCuMoO_4(OH)配向試料の強磁場ESR測定2

21aBD-3 NaCuMoO_4(OH)配向試料の強磁場ESR測定2

THz ESR study of Spinel Compound GeCo2O4

Abstract We performed terahertz ESR measurements of spin frustrated spinel compound GeCo2O4 using pulsed magnetic fields of up to 40 T. A very broad EPR absorption line was observed at 86 K. The g-values at 86 K were estimated to be g=5.26±0.07, 5.16±0.12 and 4.98±0.07 for B//[111], [100] and [110], respectively. High-field ESR measurements revealed complicated phase structures and a field-induced magnetic phase below 3 K. Critical fields of magnetic phases at 1.8 K for B//[111] were observed at 1.8 T, 5.0 T, 8.6 T, 11.0 T and 12.9 T for B//[111]. An energy gap of 300 GHz (=14.4 K=1.24 meV), which was related to the lattice deformation, was observed for B//[111]. The zero field gap of ω 4 mode, which is considered to be a singlet-triplet excitation of the di-tetramer, was estimated to be 1120 GHz.

Size-dependent magnetism in nanocrystals of spin-chain α-CoV2O6

Magnetization and high-field ESR measurements have been performed to study the magnetism of nanocrystals of α-CoV2O6, an Ising spin-chain system without triangular lattice but presenting interesting 1/3 magnetization step. The results demonstrated the antiferromagnetic (AFM) enhancement and gradual suppression of the 1/3 magnetization step in nanoparticle samples. Within the framework of core–shell model consisting of the AFM core spins and the uncompensated/disordered shell spins, the AFM enhancement below TN=13K is a result of enhanced shell disorder with weak ferromagnetism. This AFM enhancement, along with the suppression of saturation magnetization, results in the suppression of 1/3 magnetization step. Furthermore, the paramagnetism of the shell was confirmed by our high-field ESR measurements. The time-dependent magnetization suggests the presence of spin-glass-like freezing. This is expected for nanoparticles with surface shell disorder with ferromagnetic correlations, but is not expected for bulk material of α-CoV2O6 without spin frustration. These findings demonstrate that size tuning is an effective parameter for controlling the ground state of α-CoV2O6.

Development of High-Field ESR System Using SQUID Magnetometer and its Application to Measurement under High Pressure

We have developed a high-field and high-frequency ESR system using a commercially available magnetometer equipped with the superconducting quantum interference device (SQUID). This is magnetization detection type ESR and ESR is observed as a change of the magnetization at the resonance condition under irradiation of the electromagnetic wave. The frequency range is from 70 to 315 GHz and the maximum magnetic field is 5 T. The sensitivity is estimated to be 10 13 spins/G. The advantage of this system is that the high-field ESR measurements can be made very easily and quantitatively. Moreover, this high-field ESR can be applied to the measurements under pressure by using a widely used piston-cylinder pressure cell.

Possible new temperature phase observed in GeCo2O4 spinel by high-field ESR

High-field ESR measurements of cubic spinel GeCo2O4 single crystals have been performed using the pulsed magnetic field up to 16 T in the temperature range from 300 K to 1.8 K. Dynamical resonance shifts due to antiferromagnetic ordering were observed. New AFMR modes appear below 3 K. High-field ESR measurements reveal complicated phase structures and field-induced magnetic phases below TN, suggesting new temperature field phases.

Electromagnon Excitation of the Triangular Lattice Antiferromagnet CuFeO2 in High Magnetic Fields

In this paper, we report results of high field ESR measurements of the triangular lattice antiferromagnet CuFeO2. From polarization measurements for the ESR signals, we show an appearance of the electromagnon excitation in the field-induced 1/5 plateau phase of this compound.

High field ESR measurements of S = 1/2 low dimensional antiferromagnet (2,3-dmpyH)2CuBr4

High field ESR measurements of (2,3-dmpyH)2CuBr4 powder sample have been performed in the frequency range from 60 to 315 GHz using the pulsed magnetic field up to 16 T. Observed temperature range is 1.8 to 265 K. ESR spectrum observed at 265 K shows a typical powder pattern spectrum of Cu2+ ion, and obtained g-values are g// = 2.307 and g⊥ = 2.053. Temperature dependence measurements are also performed at 80, 160 and 315 GHz, and almost no temperature dependence of g-value is observed for all frequencies down to 1.8 K. These results are rather unusual for the low dimensional strongly correlated spin system, and possible mechanisms by spin frustration is suggested.

Quantum disordered phase on the frustrated honeycomb lattice

In the present paper we study the phase diagram of the Heisenberg model on the honeycomb lattice with antiferromagnetic interactions up to third neighbors along the line ${J}_{2}={J}_{3}$ that includes the point ${J}_{2}={J}_{3}={J}_{1}/2$, corresponding to the highly frustrated point where the classical ground state has macroscopic degeneracy. Using the linear spin-wave theory and the Schwinger boson technique followed by a mean field decoupling and exact diagonalization for small systems, we find an intermediate phase with a spin gap and short-range N\'eel correlations in the strong quantum limit $(S=\frac{1}{2})$. All techniques provide consistent results which allow us to predict the existence of a quantum disordered phase, which may have been observed in recent high-field ESR measurements in manganites.

High Field ESR Measurements of S=1/2 Quasi One-Dimensional Antiferromagnet Cu3Mo2O9

S=1/2 one-dimensional chain and dimer system Cu3Mo2O9, in which the super-exchange network forms one-dimensional corner-sharing tetrahedoron of Cu2+ ion, has been investigated by high field ESR measurements using the powder sample and the pulsed magnetic field up to 40 T at 2.0 K. The high field ESR measurements with wide frequency range suggest the existence of the magnetic phase transition at 8 T. Three ESR modes appear above 18 T, which corresponds to the magnetization jump. The ground state of Cu3Mo2O9 will be discuss.

Observation of Elementary Excitations of Quantum Sine-Gordon Spin System KCuGaF6 Under High Magnetic Field

In magnetic field, KCuGaF6 can be mapped onto the quantum sine-Gordon model, for which low-energy elementary excitations are solitons, antisolitons and their bound states breathers. Using high-frequency, high-field ESR measurements, we observed these unusual magnetic excitations.

High-field ESR measurements of S=3/2 honeycomb lattice antiferromagnet Bi3Mn4O12(NO3)

High-field ESR measurements of the novel Mn substance Bi3Mn4O12(NO3), which is a model substance of S=3/2 honeycomb lattice antiferromagnet, have been performed using the pulsed magnetic field up to 16 T. No resonance shift and the gapless behavior are observed in the temperature dependence measurements. Although, very strong antiferromagnetic interactions are expected from the Weiss temperature, there is no evidence of the long-range ordering down to 1.9 K from the magnetic susceptibility, the specific heat and the ESR measurements. Therefore, the existence of the frustration effect in Bi3Mn4O12(NO3) is strongly suggested in spite of the honeycomb lattice structure.

High field ESR measurements of quantum triple chain system Cu3(OH)4SO4

Magnetic properties of Cu3(OH)4SO4, which is a model substance of an S = 1/2 triple chain system, have been investigated by the magnetization and the high field ESR measurements. The magnetization measurements of powder sample have been performed up to 7 T at 2 K. The derivative magnetization curve shows a jump at 1.2 T due to a magnetic phase transition. The high field ESR measurements have been performed using the pulsed magnetic field up to 16 T in the temperature range from 1.8 K to 300 K. The resonance shifts due to low dimensionality are observed below 40 K far from TN = 5.3 K. The frequency-field diagram at 1.8 K below 5 T shows AFMR modes, which can be described by conventional AFMR theory of two sublattice with an uniaxial anisotropy, and the spin flop transition field is estimated to be 1.2 T. The ESR modes above 5 T deviate from the conventional AFMR modes.

High-field and high-pressure ESR measurements of SrCu2(BO3)2

High-field and high-pressure ESR measurements of SrCu2(BO3)2 have been performed at 1.6 K in the field region up to 30 T, the frequency region from 70 to 360 GHz and the pressure region up to 12 kbar. The direct ESR transition mode between the singlet ground state and the triplet excited states was observed at various pressures. We have succeeded in observing the decrease of the spin gap directly upon applying the pressure. The origin of the decrease of the gap energy is discussed.

Field-Induced Order-Disorder Transition in AntiferromagneticBaCo2V2O8Driven by a Softening of Spinon Excitation

High field magnetization and ESR measurements on the quasi-one-dimensional (1D) antiferromagnet BaCo(2)V(2)O(8) have been performed in magnetic fields up to 50 T along the chain. The experimental results are explained well in terms of a 1D S=1/2 antiferromagnetic XXZ model in longitudinal fields. We show that the quantum phase transition from the Néel ordered phase to the spin liquid one in the model is responsible for a peculiar order to disorder transition in BaCo(2)V(2)O(8).

High field ESR studies of layered manganese oxides [formula omitted] (A=Ba, Sr)

High field ESR measurements have been performed on newly synthesized layered manganese oxides A 4 Mn 3 O 10 (A=Ba, Sr) using a pulsed magnetic field up to 16 T. From the temperature and the frequency dependence measurements, it was confirmed that both ground states at low temperature are the antiferromagnetic ordered state. The typical AFMR absorption lines were observed for both compounds and both were well explained by the AFMR theory for a two-sublattice antiferromagnet with orthorhombic magnetic anisotropy. Moreover, we found that the magnetic anisotropy energies in these compounds are very small as compared with their exchange interactions.

High-field ESR measurements on the spin gap system [formula omitted

We have performed high-field/high-frequency ESR measurements on the spin gap system TlCuCl 3 in pulsed magnetic fields up to 55 T. The field dependence of the magnon excitation of TlCuCl 3 is studied above the field-induced quantum critical point at H g ≃ 6 T and up to fields corresponding to half of the magnetic saturation. The observed ESR modes are compared to recent theoretical calculations.

High-field ESR study of one-dimensional [formula omitted] Heisenberg antiferromagnet with next-nearest exchange interaction

High-field ESR measurements of Cu[2-(2-aminomethyl)pyridine]Br 2 (Cu(ampy)Br 2) powder sample, which is a model substance of the S = 1 2 one-dimensional Heisenberg antiferromagnet (1DHAF) with a frustration, have been performed in the frequency region from 40 to 480 GHz using the pulsed magnetic field up to 16 T. The obtained g-values are g / / = 2.06 and g ⊥=2.06, which suggest that the orbital ground state of Cu 2+ in Cu(ampy)Br 2 is the x 2– y 2 orbital state. Distinct frequency dependent g-shift is observed below 4.2 K from the temperature dependence measurements. The possibility of the phase transition below 4.2 K is discussed from the frequency dependence results at 1.7 and 4.2 K.