Dynamic correlated Cu(2) magnetic moments in superconductingYBa2(Cu0.96Ni0.04

Abstract

We have examined the magnetic properties of polycrystalline, superconducting YBa2(Cu0.96Ni0.04)3Oy (y ∼7, Tsc ∼75 K) using two local probe techniques: 170 Yb Mössbauer down to 0.1 K and muon spin relaxation (µSR) down to 1.5 K. At 0.1 K, the 170 Yb measurements show the Cu(2) over essentially all the sample volume carry magnetically correlated moments which are static on the time-scale 10 −9 s. The moments show a distribution in size. The correlations are probably short range. As the temperature increases, the correlated moments are observed to fluctuate with measurable rates (in the GHz range) which increase as the temperature increases and which show a wide distribution. The µSR measurements also evidence that the fluctuation rates increase with increasing temperature and there is a distribution. The evidenced fluctuating, correlated Cu(2) moments coexist at an atomic level with superconductivity.

Dynamic correlated Cu(2) magnetic moments in superconducting YBa_2(Cu_0.96Co_0.04)_3O_y (y ~ 7)

“…However, since it is well established that at one end of the phase diagram there is region with magnetically ordered Cu (2) and no superconductivity and that around optimum doping there is a region with superconductivity and no magnetically ordered Cu(2), the two phenomena are usually considered to be mutually exclusive at an atomic level. Previously however 2,3,4,5 , we have shown that this view is not always valid.…”

“…A mechanism has been proposed to explain the magnetically correlated Cu(2) observed in underdoped cuprates 28 , so that this mechanism could play a role here. It is possible however, that a different and so far undefined mechanism, is reponsible for the correlated Cu(2) moments observed both in underdoped (YBa 2 Cu 3 O 7 + Co) cuprates and in optimally doped (YBa 2 Cu 3 O 7 + Ni) cuprates 4 .…”

“…In Ref. 4 (preceding paper), we reported that when Ni is substituted into fully oxidised YBa 2 Cu 3 O y (y ∼7), the Cu (2) in the neighbourhood of each Ni carry magnetic moments which are short range magnetically correlated. For the examined Ni concentration of 4%, essentially all the Cu(2) of the sample were found to carry correlated magnetic moments.…”