Sumiko Noro

MAGNETIC PROPERTIES OF BA2-XKXCU3O4CL2

Abstract Temperature dependence of magnetic susceptibility, specific heat and EPR studies on Ba 2-X K X Cu 3 O 4 Cl 2 for x =0 and 0.02 are reported. Near 320K the value of the line width of EPR signal shows a peak. The other anomaly was observed around 40K in the temperature dependence of susceptibility but not of specific heat. We suppose that there are two sort of Cu ions which order antiferromagnetically at different temperature, at 320K or 40K respectively.

Submillimeter wave AFMR of Ba2Cu3O4Cl2

Antiferromagnetic resonances (AFMR) of Ba 2 Cu 3 O 4 Cl 2 have been studied by submillimeter wave ESR in the frequency region from 90 to 383 GHz using the pulsed magnetic field up to 16 T. The AFMRs observed at 1.8 K clearly showed an easy plane type anisotropy. The temperature dependence of AFMR has been observed from 1.8 K to 265 K and it will be discussed in connection with the characteristic magnetic feature of Ba 2 Cu 3 O 4 Cl 2 . The result of the magnetization measurement is also discussed.

Magnetic properties of Ba2Cu3O4Cl2 single crystals

Abstract The t emperature and angular dependences of the electron spin resonance and magnetic susceptibility of Ba 2 Cu 3 O 4 Cl 2 single crystals are reported. We assume that there are two distinct magnetic systems of Cu A and Cu B spins. It is suggested that the Cu A spins order weakly ferromagnetically below 330 K and that the Cu B spins are paramagnetic down to 40 K but below 40 K show another spin structure, probably a spin glass state.

Far-infrared ESR study of cuprate compounds

Electron spin resonance (ESR) was investigated on the spin-Peierls system CuGeO3 and antiferromagnetic Ba2Cu3O4Cl2 at X-band and far-infrared regions (FIR). The g-values of CuGeO3 were determined to be 2.17, 2.26 and 2.11 for H∥a, H∥b and H∥c-axes, respectively. The temperature dependence of FIR and X-band ESR spectra of CuGeO3 clarified the difference of character among uniform, dimerize and high-field magnetic phases. In the Ba2Cu3O4Cl2 system, the resonance field for H∥c drastically changes around 30K, and antiferromagnetic resonance (AFMR) was observed at 5 K.

Mössbauer study of 57Fe doped LaSrYCu2O6

Abstract The Mossbauer spectra of LaSrYCu 1.97 57 Fe 0.03 O 6 were measured from room temperature to 5K. Room temperature spectrum is a paramagnetic doublet, and IS and QS values suggest that high spin Fe 3+ are in octahedral site provided by a excess oxygen, similar to La 2 SrCu 2 O 6 . Below 210K, Mossbauer spectra become broad, and consist of paramagnetic doublet and magnetic sextet in the wide temperature range. Temperature variation of H hf suggest that the Neel temperature lies above 200K. The irreversibility and field dependence of susceptibility are observed at low temperatures. By combining the results of the Mossbauer spectra and magnetic measurements, these behaviors are explained as superparamgnetism of the antiferro spin clusters, and at low temperatures, clusters freeze to the cluster glass like state.

Crystal structure and resistivity of substituted LaSrYCu2O6

Abstract A series of Y-based 2126 compounds, La 1−x Sr 1+x YCu 2 O 6 (x=0 to 0.5), has been prepared. Crystal structure and cation distribution are determined by Rietveld analysis of X-ray powder diffraction data. Small Y ions occupy (2a) site preferentially. All the studied samples including HIP treated ones are semiconducting and no superconducting transition is observed down to 20K. VRH model is applicable as a transport mechanism at low temperatures.

Charge transfer from Cu in YBa2Cu3O7−δ and Ba2Cu3O4Cl2 crystals determined by Auger electron spectroscopy

A formulation is proposed to estimate the charge transfer ΔqCu from Cu to some anions in metal-oxide crystals, using Auger electron spectroscopy. In the formulation, a parameter, the Auger transition probability ω, is introduced, which is defined as the ratio of Auger intensity due to a certain transition to the total Auger intensity due to other transitions when the same core electrons are primarily excited. By applying the formulation to vacuum-cleaved surfaces of YBa2Cu3O7−δ (YBCO) and Ba2Cu3O4Cl2 (BCOC) crystals, we obtained the following results: (1) YBCO cleaves between CuO2 and BaO layers, and the amount of ΔqCu is 2.3 in units of elementary electric charge. The deviation of ΔqCu from 2.0 suggests the existence of Cu3+-like atoms; (2) for BCOC, ΔqCu varies from 3.3 to 1.7 depending on the Ar ion beam sputtering time.

Magnetic properties of Ba2Cu3−xMxO4Cl2 (M=Ni,Zn)

Abstract Similar to the high temperature superconducting compounds, Ba 2 Cu 3 O 4 Cl 2 has the two dimensional Cu|O plane. We investigated the magnetic properties of this compound. It shows the antiferromagnetic behaviors with a canted spin structure below 335K and another magnetic transition like a spin glass phenomena at 33K. With replacing the Cu ion by a small amount of Ni, the magnetic transition at 335K was depressed.

Mössbauer study of 57Fe-doped La2SrCu2O6

Abstract The Mossbauer spectra of La2SrCu1.9557Fe0.05O6 were measured at various temperatures between 372 and 5 K. The spectrum measured at room temperature consists of two paramagnetic quadrupole doublets with similar Mossbauer parameters. The values of IS and small quadrupole splitting values indicate that high spin Fe3+ ions are in octahedral sites. The spectrum measured at 5 K consists of a broad sextet and a minor paramagnetic component. The distribution function of Hhf shows two peaks of 520 and at 440 kOe. The magnetic susceptibility shows no distinct anomaly in this temperature range. Magnetic ordering seems to take place over a wide range of temperature.