Yoshiaki Chiba

Electron spin resonance of disordered Sm ions in SmB6

Electron spin resonance (ESR) of disordered Sm ion located at the B 6 -cluster site in SmB 6 is observed. Various valence states such as Sm 3+ , Sm 2+ , Sm 0 , Sm - and Sm 2- are found. It becomes clear that there are two ways of electron trapping on the disorder site. One of them is the 4f-trap where additional electrons occupy the vacant 4f-level of the disordered Sm with the Hund rule. On the other hand, weakly coupled donor electrons exist in addition to the 4f level electrons. Two possibilities of the coupling model are discussed.

Electron spin resonance of Eu and Gd ions in SmB6

Abstract Electron spin resonance (ESR) of the clearly resolved fine structure of Eu 2+ in single crystals of SmB 6 together with the hyperfine structure at various frequencies in low temperature has been observed. The g -shift of the Eu 2+ in SmB 6 is negative and microwave frequency dependent. ESR of Gd 3+ also has been observed and discussed on the difference with Eu 2+ .

Oscillatory High-Field Magnetization in LaP Doped with Ce

A clear de Haas-van Alphen (dHvA) oscillation has been found in LaP doped with 2 atomic percent of Ce under a pulsed field up to 30 Tesla (T) at liquid helium temperature. The oscillation is superimposed on the paramagnetic saturation curve of Ce which does not show the Kondo effect. The Fourier spectrum of the magnetization curves gives an extremal cross-sectional area of the Fermi surface of 0.01 A -2 , which is about a half-value of CeP. The ground state of the Ce atom is investigated by electron spin resonance (ESR) and a nearly isotropic g -value of 1.37 is obtained, in agreement with the theoretical expectation for Γ 7 , while the g -value of field-cooled CeP is 2.93 which is close to that of Γ 8 . The discrepancy is discussed using the neutron diffraction data.

Higher Harmonic Electron Spin Resonance of Eu2+ in SmB6

The second and third harmonic electron spin resonance of Eu 2+ impurities in a cubic site of SmB 6 single crystal are observed in addition to usual Eu 2+ resonances. A motional narrowing effect is found in these harmonic lines and the effect suggests that some dynamical motions such as the dynamical Jahn-Teller effect or valence fluctuation may play an important role on the higher harmonic generation.

Antiferromagnetic resonance in Nd2CuO4

Anomalous electron spin resonance observed in Nd 2 CuO 4 is attributed to antiferromagnetic resonance (AFMR) of Nd spins in the Nd–Cu spin network. The anomaly comes from the staggered field due to Cu spins on the Nd-site. The Cu spins form a tight antiferromagnetic spin network and are almost at rest during the Nd-resonance. The staggered field acts as an additional anisotropy field on the Nd spin. Various magnetic parameters in AFMR are in accord with those determined by the high field magnetization study.

High-Field Faraday Effect of Tb-Doped Glass Above Paramagnetic Saturation

High-field Faraday effect is investigated in Tb-doped glass under a pulsed high magnetic field up to 40 tesla(T). The nonlinear Faraday effect due to saturation of the paramagnetic moment appears below about 20 T at 4.2 K. A considerably large Faraday rotation with the Verdet constant of -45.0 rad. T-1 m-1 is found above the paramagnetic saturation field, and this is explained by the field-induced level mixing in the multiplet levels.

Broadband Buncher Cavity for Beam Transport Line of HiECR Ion Source

A newly developed rf buncher has been installed in the beam transport line of an electron cyclotron resonance (ECR) ion source, HiECR, at the Center for Nuclear Study (CNS) of the University of Tokyo. The rf buncher is a compact cavity having magnetic alloy (MA) cores and operates in the wide frequency range between 18 and 45 MHz without any tuning systems. Bunched beams of H+, O5+, and Ar8+ ions have been produced successfully and measured using a newly designed Faraday cup with good time resolution. In this paper, the design of the MA-loaded buncher cavity and the results of the beam test are presented. A detailed description of the HiECR beam transport line and the design of the new Faraday cup are also given.

Spin-Lattice Relaxation Time of Co2+ Ion in Yttrium Aluminum Garnet

Spin-lattice relaxation times of Co 2+ spins in yttrium aluminum garnet (YAG) are investigated below 100 K. Co 2+ impurities in YAG have the octahedral, tetrahedral and interstitial sites and these spins have considerably different local crystalline electric field symmetries and intensities. The observed relaxation times well reflect the local fields and it is found that the octahedral and interstitial spins show the Orbach relaxation process with the energy gap Δ / k of 280 K and 95 K, respectively, while the tetrahedral spin shows simple direct- and Raman-processes.

Electron spin resonance in CuSO45H2O down to 100 mK

Copper sulfate pentahydrate CuSO 4 5H 2 O is investigated by ESR at 9, 17, 24, 35 and 50 GHz regions down to about 100 mK using a combined cryostat of 3 He and adiabatic demagnetization. The temperature dependent exchange interaction J AB between inequivalent site spins A and B is found. It is about 0.11 K at room temperature and increases with decreasing temperature up to 0.24 K. Temperature dependent resonance shifts are attributed to the exchange shift coming from non-resonant dissimilar spins. Partial order effect below 1 K is discussed.

Electron Spin Resonance of N1-Center in Diamond

Temperature dependence of N 1 -center, a deep donor nitrogen in diamond, is investigated. A clear change in the hyperfine structure of the center is observed around 680 K. The result, explained by the model, is that the self-trapped state with uniaxial symmetry which is stable at low temperatures changes to an isotropic donor state above 680 K.