Yoyu Nakamichi

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

CU-NQR STUDY OF SUCCESSIVE MAGNETIC PHASE TRANSITION IN ANTIFERROMAGNETIC YBA2(CU1-XTX)3O6 (T=FE, CO AND NI)

Split spectra of Cu nuclear quadrupole resonance (NQR) in the chain (Cu(1)) site of the antiferromagnetic YBa 2 (Cu 1- x T x ) 3 O 6 (T=Fe, Co, and Ni) show that the spin alignment of Cu moments in the CuO 2 plane changes at a critical concentration of the substitution of Cu by T. The spin structure of the low-temperature magnetic phase is discussed.

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.

139La and63Cu-NQR of high-Tc oxide superconductors

Nuclear quadrupole resonances (NQR) of139La in La2−xMxCuO4 (M=Ba, Sr) and63Cu in YBa2CU3O7 have been investigated with substitution of Cu by magnetic impurities. For La-system, the strong enhancement of the nuclear relaxation rate, 1/T1 atTc*≈10 K (suggesting the occurrence of magnetic instability with hole-doping), is suppressed by 3D-antiferromagnetism induced by magnetic impurities. In the superconducting region, fluctuations of Cu moments at low temperatures remain extremely fast as at high temperatures. For Y-system, Fe-ions are substituted for both Cu(1) and Cu(2) sites, But Co-ions are preferentially substituted to Cu1 sites. The peaks in the relaxation rate of Cu indicate the appearance of magnetic ordering without destroying superconductivity for the 0.5%-Fe doped sample.