Comment on "Emergence of a Superconducting State from an Antiferromagnetic Phase in Single Crystals of the Heavy Fermion Compound Ce2PdIn8"

0.19 MB·English

by  K. Uhlirova

Comment on ”Emergence of a Superconducting State from an Antiferromagnetic
Phase in Single Crystals of the Heavy Fermion Compound Ce PdIn ”
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K. Uhl´ıˇrov´a,∗ J. Prokleˇska, and V. Sechovsky´
Charles University, DCMP, Ke Karlovu 5, Praha 2, 121 16, Czech Republic
A recently published Letter [1] has reported on the measured more than 5 different CeIn –free samples of
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antiferromagnetism (AF) and ambient-pressure super- Ce PdIn bymeansofresistivity,heatcapacityandmag-
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conductivity (SC) in a Ce PdIn single crystal with netic susceptibility, and paramagnetic behaviour with
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0 T ∼ 10 K and T = 0.68 K, respectively. Although significant magnetocrystalline anisotropy was observed
N c
1 we very much appreciate the effort exerted to prepare down to a SC temperature [11].
0
2 and characterize this new heavy fermion (HF) supercon- TheSCwithTc =0.7–0.45K(sampledependent)has
ductor(SC),wewouldliketoaddacautionarynotethat been confirmed in our samples. The difference of criti-
n
thereportedN´eeltemperaturecoincidesremarkablywith cal temperature is probably given by structural planar
a
J TN = 10.2 K of CeIn3 [2]. It therefore leads us to con- defects, which were also observed in Ce2RhIn8 [10]. In
5 siders the possible presence of CeIn3 in the samples that agreement with [1], the SC has a HF character and it is
2 were investigated. In other CenTIn3n+2(n = 1,2) com- a bulk property of the compound but it does not emerge
pounds [3–5] the AF is either absent (T=Co, Ir) or re- outofalong-rangeAFstatebelowtheN´eeltemperature
n] markably limited to much lower temperatures (T=Rh). of 10 K because the reported AF was due to presence of
o These compounds form a quasi-two-dimensional tetrag- an impurity phase.
c onal structure with the CeIn3 and TIn2 layers alter-
- nating along the (001) direction. Hence one might ex-
r
p pect that the AF correlations develop within the CeIn
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u layers while the interaction between the layers will be
s weaker as reported for CeRhIn , an incommensurate AF ∗ Electronic address: [email protected]ff.cuni.cz
. 5
at (TN = 3.8 K) [6]. The remarkable agreement of the [1] D. Kaczorowski et al., Phys. Rev. Lett. 103, 027003
m T valuesinthereportedCe PdIn withthewell-known (2009).
N 2 8 [2] J. M. Lawrence et al., Phys. Rev. B 22, 4379 (1980).
- CeIn3 isnotdiscussedintheLetter[1]. Neitherthestrik- [3] G. F. Chen et al., J. Phys. Soc. Jpn 71, 2836 (2002).
d ingdiscrepancybetweentheirownresultsonsinglecrys-
n
tals[1]andpolycrystals(reportedparamagneticdownto
o
0.35K [7]) has been explained. The absence of SC in the
c
[ polycrystallinesampleisexplainedbyanunconventional

couplingsensitivetostructuraldisorder,internalstrains,
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and/ortinychangesinthecomposition,butthedisagree-
v
7 mentinthemagneticgroundstateisnotdiscussedatall.
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Although a detailed phase analysis (X-ray diffraction
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and micro-probe) of the crystals was claimed to have
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. been done [1], we would, however, still like to suggest
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thataCeIn singlecrystalcoveredbyasingle-crystalline
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0 layer of Ce2PdIn8 was in fact that which was investi-
1 gated. From the reported heat capacity data, we esti-
: mate the amount of CeIn to be 15−20%. In such case,
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i a microprobe analysis of the sample’s surface would not
X
be able to detect it. Also, most of the diffraction peaks
r of both compounds interfere, because they have an al-
a
most equal lattice parameter a = 0.4693 nm [9] and
a=0.4689 nm [8] for Ce PdIn and CeIn , respectively.
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Our first magnetization data obtained on crystals
grownanalogouslyto[1]wereinagreementwiththeLet-
ter. A careful microprobe analysis, however, indicated
a presence of CeIn , and element mapping showed that
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Ce PdIn and CeIn form a sandwich-like system with
2 8 3 FIG. 1: EDX element mapping (Ce-red, Pd-green, In-blue)
well-defined regions (see Fig.1). ofatypicalpolishedsample. CeIn (redregion)iscoveredby
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a layer of Ce PdIn and Ce Pd In (thin dark green).
To confirm that the AF originates in CeIn , we have 2 8 1.5 1.5 7
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[4] J. S. Kim et al., Phys. Rev. B 69, 024402 (2004). (2008).
[5] R. Movshovich et al., Phys. Rev. Lett. 86, 5152 (2001). [10] E. G. Moshopoulou et al., Acta Crystallogr. Sect. B 62,
[6] W. Bao et al., Phys. Rev. B 62, R14621 (2000). 173 (2006).
[7] D. Kaczorowski et al., Phys. B 404, 2975 (2009). [11] K. Uhl´ıˇrova´ et al., Intermetallics , To Be Published
[8] I. R. Harris et al., J. Less Comm. Met. 9, 7 (1965). (2010).
[9] D. V. Shtepa et al., Mow. Univ. Chem. Bull. 63, 162