[Paper Review] Muon-spin-relaxation study of the Cu-spin dynamics in electron-doped high-T_c_ superconductor Pr_0.86_LaCe_0.14_Cu_1-y_Zn_y_O_4_

Risdiana Risdiana, Tadashi Adachi+4 more|arXiv (Cornell University)|Jul 9, 2010

Physics of Superconductivity and Magnetism5 citations

TL;DR

This study investigates Cu-spin dynamics in electron-doped high-Tc superconductor Pr0.86LaCe0.14Cu1-yZnyO4+α-δ using zero-field muon-spin-relaxation (μSR) to examine nonmagnetic Zn impurity effects. Despite Pr3+ moments inducing spin fluctuations below 30 K, no Zn-induced slowing down of Cu-spin fluctuations was observed—contrasting sharply with hole-doped systems—suggesting the absence of dynamical stripe correlations in electron-doped cuprates or stronger influence from Pr3+ moments than Zn impurities.

ABSTRACT

Muon-spin-relaxation (muSR) measurements have been performed for the partially Zn-substituted electron-doped high-T_c_ superconductor Pr_0.86_LaCe_0.14_Cu_1-y_Zn_y_O_4+alpha-delta_ with y=0-0.05 and the reduced oxygen content delta=0-0.09, in order to investigate nonmagnetic Zn-impurity effects on the Cu-spin dynamics. For all the measured samples with delta=0.01-0.09, it has been found that a fast depolarization of muon spins is observed below 100 K due to the effect of Pr^3+^ moments and that the muSR time spectrum in the long-time region above 5 mu-sec increases with decreasing temperature at low temperatures below 30 K possibly due to slowing down of the Cu-spin fluctuations assisted by Pr^3+^ moments. No Zn-induced slowing down of the Cu-spin fluctuations has been observed for moderately oxygen-reduced samples with delta=0.04-0.09, which is very different from the muSR results of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_. The possible reason may be that there are no dynamical stripe correlations of spins and electrons in the electron-doped high-T_c_ cuprates or that the effect of Pr^3+^ moments on the muSR spectra is stronger than that of a small amount of Zn impurities.

Motivation & Objective

• To investigate the influence of nonmagnetic Zn impurities on Cu-spin dynamics in electron-doped high-Tc superconductors.
• To test whether the pinning of dynamical stripe correlations by Zn, observed in hole-doped cuprates, also occurs in electron-doped systems.
• To examine the role of Pr3+ moments in modulating local spin dynamics and their interplay with Zn doping and oxygen non-stoichiometry.
• To compare Zn-impurity effects in electron-doped and hole-doped cuprates using μSR spectroscopy.
• To determine whether Cu-spin fluctuations are affected by Zn substitution under varying oxygen deficiency (δ) and Zn concentration (y).

Proposed method

• Perfected zero-field (ZF) and longitudinal-field (LF) μSR measurements on polycrystalline samples of Pr0.86LaCe0.14Cu1-yZnyO4+α-δ with y = 0–0.05 and δ = 0–0.09.
• Conducted measurements down to 0.3 K at the RIKEN-RAL Muon Facility to probe spin dynamics on timescales of 10−6 to 10−11 seconds.
• Used electrical resistivity and DC magnetic susceptibility to confirm superconducting transition temperatures and sample quality.
• Analyzed μSR time spectra to extract relaxation rates (λ) and asymmetry parameters (σ), identifying contributions from dynamic spin fluctuations and static magnetic moments.
• Employed post-annealing in Ar to control oxygen deficiency (δ), with δ estimated from weight changes.
• Correlated spectral features with temperature to identify transitions in spin dynamics, including depolarization and long-time spectral growth.

Experimental results

Research questions

• RQ1 Does Zn substitution induce slowing down of Cu-spin fluctuations in electron-doped Pr0.86LaCe0.14Cu1-yZnyO4+α-δ, as seen in hole-doped systems?
• RQ2 How do Pr3+ moments influence the local spin environment and μSR spectra in the absence of Zn?
• RQ3 Is the absence of Zn-induced effects on spin dynamics due to the lack of dynamical stripe correlations in electron-doped cuprates?
• RQ4 To what extent do Pr3+ moments mask or dominate over Zn-impurity effects in μSR spectra?
• RQ5 How does oxygen deficiency (δ) modulate the interplay between static magnetism and dynamic spin fluctuations?

Key findings

• A fast depolarization of muon spins below 100 K was observed due to static random magnetism from Pr3+ moments.
• The μSR time spectrum in the long-time region (>5 μs) increased with decreasing temperature below 30 K, indicating possible slowing down of Cu-spin fluctuations.
• This low-temperature spectral growth was observed even in Zn-free samples, suggesting enhancement of Cu-spin correlation due to Pr3+ moment assistance.
• No significant change in relaxation rate (λ) or asymmetry (σ) was observed with increasing Zn concentration (y ≤ 0.05), indicating no Zn-induced slowing down of Cu-spin fluctuations.
• For moderately oxygen-reduced samples (0.04 ≤ δ ≤ 0.09), the absence of Zn-induced effects persisted, contrasting sharply with hole-doped La2-xSrxCu1-yZnyO4 where such effects were prominent.
• The results suggest either the absence of dynamical stripe correlations in electron-doped cuprates or that Pr3+ moment effects dominate over Zn impurity effects in μSR response.