µSR study of annealing and Ce-doping eﬀects on the magnetism in T ′ Pr1.40−x La0.60 Cex CuO4+y [2013A0084]
M. Fujita, K. Tsutsumi1 , K. Sato1 , M. Miyazaki2 , R. Kadono2 , K. Yamada2
Institute for Materials Research, Tohoku University
1
Physics Depertment, Takezono University
2
Institute of Materials Structure Science, High Energy Accelerator Research Organization(KEK)1.

Introduction

It is known that the superconductivity in T ′ structured R2 CuO4 (R: rear earth) appears afteradequate oxygen reduction procedure for moderately Ce(Th)-doped system. The phase diagramof T ′ -R2−x Cex CuO4+δ shows the existence of robust antiferromagnetic (AF) ordered region against
the electron-doping, which is commonly adjacentto the superconducting phase [1]. However, quite
recently, this phase diagram has been challenged
by an evidence of superconductivity in the Cefree T ′ -R2 CuO4 [2, 3]. From a careful study onthin ﬁlm, Naito’s group reported the importanceof heat treatment to realize the stoichiometric T ′ structure without apical oxygen [4]. If the perfect T ′ -structured R2 CuO4 without chemical doping indeed shows superconductivity, the result ofexperimentally studied electron-hole symmetry in
the physical properties should be reconsidered. Furthermore, to understand the role of magnetism inthe mechanism of superconductivity, the true magnetic ground state in the parent compound andthe genuine phase diagram in T ′ -R2−x Cex CuO4 arerequired to be clariﬁed. In order to shade more
light on above issue, we studied the eﬀect of oxygen reduction and Ce substitution on magnetism
in T ′ -Pr1.40−x−y Lay Cex CuO4+δ (PLCCO) by zeroﬁeld muon spin rotation/relazation (µSR) measurements.
2.

Experiment

For the measurement, we prepared three powder samples of Pr1.40−x−y Lay Cex CuO4+δ , that is,as-grown and annealed x=0, and as-grown x=0.16.
From a weight-loss of the sample after the annealing, the relative change in the amount of reduced
oxygen was determined to be ∼0.07 in the x = 0
sample. For each sample, the phase purity waschecked by X-ray diﬀraction measurement. Zeroﬁeld µSR measurement was performed on D2 instrument installed at J-PARC. We measured theµSR time spectrum at the temperatures of 5, 50,75, 100, 125, 150, 175, 200, 250 and 300 K.
3.

Fig.
1:
µSRtimespectrumof
Pr1.40−x−y Lay Cex CuO4+δ at 75 K. Pink, blueand green circles represent the result for theas-grown x = 0, annealed x = 0 and as-grown x= 0.16 samples, respectively. The spectrum forthe later two samples is shifted along the verticaldirection for the clear visualization.

Results and discussion
In Fig. 1, the µSR time-dependence of normal-ized asymmetry at 75K is shown for (a) as-grownx = 0, (b) annealed x = 0, and (c) as-grown x =0.16. The spectrum for the later two samples islifted along the vertical direction. The spectrum
in the all samples exhibits the rotation or fast relaxation components. Therefore, the magnetic order is realized in these samples at low temperature.
To evaluate the magnetic ordering (Néel) temperature TN , we quantitatively analyzed the µSR time
spectrum measured at various temperatures. In theanalysis, we assumed the existence of magnetic order with diﬀerent internal magnetic ﬁelds at the
stopped muon sites.
Figure 2 shows the relaxation rate λ of rotation
components as a function of temperature. In the allsamples, upon cooling, λ increases due to the devel-

Fig. 3: Ce concentration dependence of magneticFig. 2: Temperature dependence of relaxation rateordering (Néel) temperature in the as-grown and
λ for Pr1.40−x−y Lay Cex CuO4+δ , as-grown x = 0
the annealed Pr1.40−x−y Lay Cex CuO4+δ . Open cir(lower ﬁgure), annealed x = 0 (middle ﬁgure) andcles are previously reported results for the annealed
as-grown x = 0.16 (upper ﬁgure).
y=1 system [1].

opment of magnetic order at low temperature. Inthe as-grown x = 0 sample, the λ1 has ﬁnite valueeven at 250 K, indicating a relatively high TN in thissample. It should be noted that the two components
are required to reproduce the time spectrum in theas-grown and annealed x = 0 samples, while thespectrum can be well ﬁtted by a single rotation term
for the as-grown x = 0.16 sample. Thus, the oxygen reduction and the Ce-doping give a diﬀerent impact on the magnetism in the as-grown parent sample, although TN is reduced by both manners. We
also note that there are possible two muon stoppingsites, and the internal magnetic ﬁeld at these sites
calculated from the magnetic structure of Pr2 CuO4
is diﬀerent. This is consistent with the observationof two rotation components in the as-grown parentsample.
From the results shown in Fig. 2, we evaluated
TN , which is deﬁned as the onset temperature forthe appearance of relaxation components. TN forthe as-grown and annealed x = 0 and the as-grownx = 0.16 is 285(15) K, 175(25) K and 125(10) K,respectively. These evaluated TN ′ s are plotted inFig. 3 as a function of Ce concentration. The previously reported results for Pr1−x LaCex CuO4+δ isalso plotted in the ﬁgure. This ﬁgure clearly indicates that the magnetic order is suppressed in awide Ce concentration range by annealing. The ap-pearance of superconductivity in the Ce-doped sample (x = 0.16) after the full suppression of magneticorder by annealing suggests the competitive relation
between magnetic order and the superconductivity.
As mentioned above, we clariﬁed the diﬀerent local magnetism in the oxygen reduced and Ce-dopedsamples. This diﬀerence would be connected with
the necessary condition for the emergence of superconductivity in the T ′ -R2 CuO4+δ Further systematic study on as-grown and annealed sample is important for the full understanding of mechanism ofsuperconductivity in the T ′ -system.
A part of results shown in the report will be published in Key Engineering Materials ((Trans TechPublication) in 2014.
References[1] M. Fujita et al., Phys. Rev. B 67 (2003)
014514.
[2] A. Tsukada et al., Solid State Commun. 133(2005) 427.
[3] T. Takamatsu et al., Applied Phys. Express 5(2012) 073101.
[4] O. Matsumoto et al., Physica C 468 (2008)
1148, ibid 469 (2009) 940, Phys. Rev. B 79
(2009) 100508(R).