Haruo Nakajima

Evidence of successive magnetic transition in La2−xBaxCuO4. NQR studies of 139La

Nuclear quadrupole resonance (NQR) of 139 La has been performed to study the electronic and magnetic properties of La 2- x Ba x CuO 4 between 1.5 and 240 K. The temperature dependence of the separation of the double peaks in spectra clearly indicates the magnetic ordering in the small x region. The internal fields at La sites due to magnetic order largely decrease with Ba concentration. The divergence of 1/ T 2 indicates that another phase appears at low temperatures. The electric field gradient changes on passing from the normal to the superconducting states, indicating the apparent influence of superconductivity on the electronic state at La sites in this system.

Strong dependence of the linear-temperature term of heat capacity on Ba- and Sr-doping in the La2CuO4 system

The linear-temperature term, γT, of heat capacity in La2−xMxCuO4 (M = Ba, Sr) is absent in the antiferromagnetically ordered state. The finite γ for x > 0.02 is intrinsic and is attributed to the spin degrees of freedom. In the superconducting (SC) region x > 0.06, γ shows a strong x-dependence. γ is vanishingly small at x = 0.10 for Ba-doping and 0.10 < χ < 0.20 for Sr-doping. An unexpected violent change of the SC transition temperatures with composition is obtained in the Ba-doped system.

NQR studies on magnetic properties of La2−xBaxCuO4

Abstract Nuclear quadrupole resonance (NQR) of 139La has been performed to study magnetic properties of La2-xBaxCuO4 between 1.4 and 250 K. The pronounced enhancement of nuclear relaxation rates of 1/T2 and 1/T1 are obtained for 0.01

139La-NQR study of magnetic phase diagram of La2-xBaxCuO4

We observed the temperature and the x -dependence of the 139 La-NQR spectra in magnetically ordered La 2- x Ba x CuO 4 . The internal field at La nuclei increases discontinuously at T c * , where the nuclear relaxation rate is enhanced and shows its peak. This indicates that a successive magnetic transition occurs at T c * for x <0.02. An asymmetry parameter of the electric quadrupole interaction changes anomalously at the magnetic transition. The magnetic phase diagram of the La-system is discussed.

Nuclear quadrupole resonance of 6365Cu in the 2223 phase of Tl-Ba-Ca-Cu-O and (Bi, Pb)-Sr-Ca-Cu-O

Abstract Nuclear quadrupole resonance (NQR) of 63 65 Cu is observed in the 2223-phase of Tl 2 Ba 2 Ca 2 Cu 2 O 10 ( T c =121 K) and (Bi 1.6 Pb 0.4 )Sr 2 Ca 2 Cu 3 O 10 ( T c =110 K). The electric quadrupole interactions at two Cu sites (in the Cu-O pyramid and in the Cu-O square plane) are distinguished and are compared with those in other T c superconductors.

Helical Spin Resonance and Magntization Measurement in Itinerant Helimagnet FexCo1-xSi(0.3≤x≤0.85)

Measurements of electron spin resonance and magnetization have been performed on the cubic B-20 Fe x Co 1- x Si (0.3≤ x ≤0.85). The magnetization process on Fe 0.8 Co 0.2 Si indicates that this sample is a helimagnet with the cone-ferro-magnetic transition under a low magnetic field. In this sample, the helical spin resonance and the critical field resonance have been observed at 9 GHz at low temperatures, and are similar to those in MnSi observed by Date et al . The helical spin resonance data of Fe 0.8 Co 0.2 Si and MnSi are reasonably explained by the recent magnetic resonance theory for the helical spin structure due to the anti-symmetric exchange interaction existing in the cubic B-20 structure because of the lack of inversion symmetry. In every sample of Fe x Co 1- x Si, ferro- and para- magnetic resonances have been observed at 9 and 24 GHz, and are briefly discussed.

Hyperfine fields and quadrupole frequencies at each Cu site in RBa2Cu3O6 and RBa2Cu3O7 (R: rare earth element)

Abstract Hyperfine field at the Cu(2) site and quadrupole frequencies of both the Cu(1) and Cu(2) sites in RBa 2 Cu 3 O 6 and RBa 2 Cu 3 O 7 (R is a rare earth element) obtained from the Cu-NQR and antiferromagnetic nuclear resonance (AFNMR) are summarized as a function of the rare earth ionic radius.

Heat capacity of the electron-doped Pr2-xCexCuO4

Abstract Low temperature heat capacity was measured as a function of x in Pr 2−x Ce x CuO 4 . The temperature linear term, γT, increases linearly, and the Debye temperature decreases with x. The Einstein contribution to the heat capacity is large and decreases gradually with electron-doping.

Magnetic order at Cu sites in superconducting YBa2(Cu1-xFex)3O7

Abstract Temperature dependence of the nuclear relaxation rate of both Cu(1) and Cu(2) sites indicates the appearance of the magnetic order without destroying superconductivity in the Fe-doped YBa2Cu3O7. The impurity-induced antiferromagnetism of Cu moments is verified also by the observation of the antiferromagnetic Cu NMR around 70–110MHz in this system.

Pressure effects on nuclear spin relaxation anomalies in La2−xBaxCuO4

Nuclear quadrupole resonance (NQR) of 139 La in La 2- x Ba x CuO 4 has revealed an unexpected enhancement of nuclear relaxation rates, 1/ T 1 and 1/ T 2 , with Ba-doping in the low-temperature region, suggesting the occurrence of magnetic instability at T c * ∼10 K. The remarkable pressure dependence of 1/ T 1 below T c * is sharply in contrast to the pressure independence of 1/ T 1 above T c * . At high pressures, the relaxation rates are remarkably enhanced below T c * , increasing proportionally with decreasing temperature.