Disordered magnetism in superconducting KFe2As2 single crystals. Issue 3 (18th January 2013)

• Record Type: Journal Article
• Authors: Grinenko, V.; Drechsler, S.‐L.; Abdel‐Hafiez, M.; Aswartham, S.; Wolter, A. U. B.; Wurmehl, S.; Hess, C.; Nenkov, K.; Fuchs, G.; Efremov, D. V.; Holzapfel, B.; van den Brink, J.; Büchner, B.
• Is Part Of: Physica status solidi. Volume 250:Issue 3(2013:Mar.)
• Page Start: 593
• Page End: 598
• Publication Date: 2013-01-18
• Subjects: Solid state physics -- Periodicals; Solids -- Periodicals; Atomic structure -- Periodicals; 530.41
• DOI: 10.1002/pssb.201200805
• Languages: English
• ISSNs: 0370-1972

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>High‐quality KFe<sub>2</sub>As<sub>2</sub> (K122) single crystals synthesized by different techniques have been studied by magnetization and specific heat (SH) measurements. The adopted phenomenological analysis of the normal state properties shows that there are two types of samples both affected by disordered magnetic phases: (i) cluster‐glass (CG) like or (ii) Griffiths phase (G) like. For (i) at low applied magnetic fields the <italic>T</italic>‐dependence of the zero‐field‐cooled (ZFC) linear susceptibility <italic>χ</italic><sub>l</sub> exhibits an anomaly with an irreversible behavior in ZFC and field‐cooled (FC) data. This anomaly is related to the freezing temperature <italic>T</italic><sub>f</sub> of a CG. For the investigated samples the extrapolated <italic>T</italic><sub>f</sub> to <italic>B</italic> = 0 varies between 56 and 90 K. Below <italic>T</italic><sub>f</sub> we observed a magnetic hysteresis in the field dependence of the isothermal magnetization <italic>M</italic>(<italic>B</italic>). The frequency shift of the freezing temperature <tex-math notation="tex"><![CDATA[$\delta T_{{\rm f}} = {\rm \Delta }T_{{\rm f}} /[T_{{\rm f}} {\rm \Delta }({\rm ln}\, \nu )]\sim 0.05$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgg1v77t15q" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /> has an intermediate value, which provides evidence for the formation of a CG‐like state in the K122 samples of type (i). The frequency dependence of their <italic>T</italic><sub>f</sub> follows a conventional power‐law divergence of critical slowing down <tex-math notation="tex"><![CDATA[$\tau = \tau _{0} [T_{{\rm f}} (\nu )/T_{{\rm f}} (0)- 1]^{- z\nu '} $]]></tex-math><inline-graphic xlink:href="ark:/27927/pgg1v77t13m" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /> with the critical exponent <italic>zν</italic>′ ≈ 10 and a relatively long characteristic time constant <tex-math notation="tex"><![CDATA[$\tau _{0} \approx 6.9 \times 10^{- 11} \, {\rm s}$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgg1v77t18c" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /> also supporting a CG behavior. The large value of the Sommerfeld coefficient obtained from SH measurements of these samples was related to the magnetic contribution from a CG. Samples from (ii) did not show a hysteresis behavior for <italic>χ</italic><sub>l</sub>(<italic>T</italic>) and <italic>M</italic>(<italic>B</italic>). Below some crossover temperature <italic>T</italic>* ≈ 50–80 K a power‐law dependence in the <tex-math notation="tex"><![CDATA[$\chi _{{\rm l}} \, {\propto} \, T^{\lambda _{{\rm G}} - 1} $]]></tex-math><inline-graphic xlink:href="ark:/27927/pgg1v77t17t" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" />, with a non‐universal <italic>λ</italic><sub>G</sub> was observed, suggesting a quantum G‐like behavior. In this case <italic>χ</italic><sub>l</sub> and <italic>M</italic>(<italic>B</italic>) can be scaled using the scaling function <tex-math notation="tex"><![CDATA[$M_{{\rm s}} (T, B) = B^{1- \lambda _{{\rm G}} } Y(\mu B/k_{{\rm b}} T)$]]></tex-math><inline-graphic xlink:href="ark:/27927/pgg1v77t19x" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /> with the scaling moment <italic>µ</italic> ∼ 3.5 <italic>µ</italic><sub>B</sub>. The same non‐universal exponent was found also in SH measurements, where the magnetic contribution <tex-math notation="tex"><![CDATA[$C/T\, {\propto} \, T^{\lambda _{{\rm G}} - 1} $]]></tex-math><inline-graphic xlink:href="ark:/27927/pgg1v77t1bg" mimetype="image" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" />.</p> </abstract>