Phys. Rev. B 81, 104507 (2010) [11 pages]
<p>
<b>
Magnetic states of lightly hole-doped cuprates in the clean limit as seen via zero-field muon spin spectroscopy
</b>

<p>
F. Coneri 1, S. Sanna 1,2,*, K. Zheng 1, J. Lord 3, and R. De Renzi1
<i>
<ol>
<li>
Dipartimento di Fisica, Università di Parma, Viale G. Usberti 7A, I-43100 Parma, Italy
<li>Dipartimento di Fisica A. Volta, Università di Pavia, Via Bassi 6, I-27100 Pavia, Italy
<li>ISIS Facility, STFC–Rutherford Appleton Laboratory, HSIC, Didcot OX110QX, United Kingdom
</i>
Received 17 December 2009; published 9 March 2010
<p>
<b>Abstract</b>
<p>
We have performed extensive zero-field &micro;SR experiments on pure YBa<sub>2</sub>Cu<sub>3</sub>O<sub>6+y</sub> and diluted Y-rare-earth substituted Y<sub>0.92</sub>Eu<sub>0.08</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>6+y</sub> and Y<sub>0.925</sub>Nd<sub>0.075</sub>Ba<sub>2</sub>Cu<sub>3</sub>O</sub>6+y</sub> at light hole doping. A common magnetic behavior is detected for all the three families, demonstrating negligible effects of the isovalent Y-substituent disorder. Two distinct regimes are identified, separated by a crossover, whose origin is attributed to the concurrent thermal activation of spin and charge degrees of freedom: a thermally activated and a re-entrant antiferromagnetic regime. The peculiar temperature and hole density dependence of the magnetic moment m(h,T) fit a model with a (spin) activation energy for the crossover between the two regimes throughout the entire investigated range. The magnetic moment is suppressed by a simple dilution mechanism both in the re-entrant regime (0<=h<=0.056) and in the so-called cluster spin glass state coexisting with superconductivity (0.056< h <= 0.08). We argue a common magnetic ground state for these two doping regions and dub it frozen antiferromagnet. Conversely either frustration or finite-size effects prevail in the thermally activated antiferromagnetic state, that vanishes at the same concentration where superconductivity emerges, suggesting the presence of a quantum critical point at hc=0.056(2).

<p>
© 2010 The American Physical Society

<br>
URL:
http://link.aps.org/doi/10.1103/PhysRevB.81.104507
<br>
DOI:
10.1103/PhysRevB.81.104507
<br>PACS:
74.72.-h, 74.25.Ha, 76.75.+i