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Disordered magnetism in superconducting KFe2As2 single crystals | | V. Grinenko
; S.-L. Drechsler
; M. Abdel-Hafiez
; S. Aswartham
; A. U. B. Wolter
; S. Wurmehl
; C. Hess
; K. Nenkov
; G. Fuchs
; D. Efremov
; Bernd Holzapfel
; Jeroen van den Brink
; Bernd Buechner
; | | Date: |
17 Oct 2012 | | Abstract: | High-quality KFe2As2 (K122) single crystals synthesized by different
techniques have been studied by magnetization and specific heat (SH)
measurements. There are 2 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 T-dependence of the zero field cooled (ZFC)
linear susceptibility (chi_l) exhibits an anomaly with an irreversible behavior
in ZFC and field cooled (FC) data. This anomaly is related to the freezing
temperature T_f. The extrapolated T_f to B=0 varies between 50 K and 90 K.
Below T_f we observed a magnetic hysteresis in the field dependence of the
isothermal magnetization (M(B)). The frequency shift of the freezing
temperature delta T_f=Delta T_f/[T_fDelta(ln
u)]sim 0.05$ 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 T_f
follows a conventional power-law divergence of critical slowing down: tau=tau_0
[T_f(nu)/T_f(0)-1]^{-z
u^{’}} with the critical exponent z
u^{’}=10(2) and a
relatively long characteristic time constant tau_0 =6.9 x10^{-11}$s also
supporting a CG behavior. The large value of the Sommerfeld coefficient was
related to magnetic contribution from a CG. Samples from (ii) did not show a
hysteresis behavior for chi_l(T) and M(B). Below a crossover temperature T^*
sim 40 K a power-law dependence in the chi_l propto T^[lambda_G-1}], with a
non-universal lambda_G was observed, suggesting a quantum G-like behavior. In
this case chi_l and M(B) can be scaled using the scaling function M_s(T,B)=
B^{1-lambda_{ iny G}}Y(mu B/k_BT) with the scaling moment mu of the order of
3.5mu_b. The same non-universal exponent was found also in SH measurements,
where the magnetic contribution C/T propto T^(lambda_G-1). | | Source: | arXiv, 1210.4590 | | Services: | Forum | Review | PDF | Favorites | |
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