Non ergodic aging in potassium niobo-tantalate crystals

Abstract

We present detailed data and analysis of the effects of Zn substitution on the planar Cu site in YBa2Cu3O6+x (YBCO6+x) as evidenced from our 89 Y NMR measurements on oriented powders. For x 1 we find additional NMR lines which are associated with the Zn substitution. From our data on the intensities and temperature dependence of the shift, width, and spin-lattice relaxation rate of these resonances, we conclude that the spinless Zn 3d 10 state induces local moments on the near-neighbour (nn) Cu atoms. Additionally, we conjecture that the local moments actually extend to the farther Cu atoms with the magnetization alternating in sign at subsequent nn sites. We show that this analysis is compatible with ESR data taken on dilute Gd doped (on the Y site) and on neutron scattering data reported recently on Zn substituted YBCO6+x. For optimally doped compounds 89 Y nn resonances are not detected, but a large T -dependent contribution to the 89 Y NMR linewidth is evidenced and is also attributed to the occurence of a weak induced local moment near the Zn. These results are compatible with macroscopic magnetic measurements performed on YBCO6+x samples prepared specifically in order to minimize the content of impurity phases. We find significant differences between the present results on the underdoped YBCO6+x samples and 27 Al NMR data taken on Al 3+ substituted on the Cu site in optimally doped La2CuO4. Further experimental work is needed to clarify the detailed evolution of the impurity induced magnetism with hole content in the cuprates. PACS. 74.72.Bk Y-based cuprates -74.25.Ha Magnetic properties -76.60.Cq Chemical and Knight shifts a Permanent address:

Frequency dependence of aging, rejuvenation and memory in a disordered ferroelectric

“…The isothermal variation of the complex capacitance C(ω, t) in ktn is a slow decay in time (which also depends on the cooling rate R [24]). This decay can be fitted by a power law (t 0 + t) −η with a small exponent η (typically ≃ 0.05) and t 0 in the range of 10 2 s. For a given plateau temperature T pl and a given plateau duration t w , the total decay of the complex capacitance, δC(ω, t w , T pl ) ≡ C(ω, t = 0 + , T pl )− C(ω, t = t w , T pl ) ≥ 0 is found to obey a negative power law of the frequency f and therefore of ω = 2πf .…”