Formation of magnetic moments in the cuprate superconductor Hg0.8Cu0.2Ba2Ca2Cu308+6 below Tc seen by NQR

• Published in: Physica. C, Superconductivity Superconductivity, 2004-07, Vol.406 (1-2), p.27-36
• Main Authors: Breitzke, H, Eremin, I, Manske, D, Antipov, E V, Luders, K
• Format: Article
• Language: English
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2004.02.183

We report pure zero field nuclear magnetic resonance (NQR) measurements on the optimally doped three layer high Tc-compounds HgBaCaCuO and HgBaCaCuO(F) with Tc = 134 K. Above Tc two Cu NQR line pairs are observed it the spectra corresponding to the two inequivalent Cu lattice sites. Below Tc the Cu NQR spectra show additional line; leading to the extreme broadened Cu NQR spectra at 4.2 K well known for the HgBaCaCuO compounds. The spinlattice relaxation curves follow a triple exponential function with coefficients depend onto the saturation time (number of saturation pulses), whereas the spin-spin relaxation curve is described by a single exponential function. From the spin-lattice relaxation we deduced a complete removal of the Kramers degeneracy of the Cu quadrupole levels indi. cating that the additional lines are due to a Zeemann splitting of the 63/65Cu lines due to the spontaneous formation o magnetic moments within the CuO layers. Below 140 K, the spectra are well fitted by a number of 6 63/61Cu line pairs From the number of the Cu lines, the position of the lines relative to each other and the complete removal of tht Kramers degeneracy we deduced an orientation of the magnetic moments parallel to the c-axis with magnitudes of tht order of 1000 G. We also discuss the possible microscopic origin of the observed internal magnetic fields.