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Nagata et al.

Appl. Phys. Lett. 110, 052901 (2017)(subtracted loop). The set-up was the same as that in Ref. 20.
The P-E loop was obtained at 10 K after the sample wasrMr
field-cooled under an electric field of 140 V/cm.
sOme NThe quality of the crystal and formation of the charge
9A @F9, 9 C D D@ 9:order were confirmed by X-ray diffraction experiments. We
have found that the significant iron defects (>10%) are foundin the sample prepared from Yb2O3 and Fe2O3 in 1:2 ratio
uthis system had been discussed
ualthough the stoichiometry of18
Almost-stoichiometric samonly
bytheamountofoxygen.
msOXØvacancy) shows peaks as spotsple (no more than 3% of ironlOr
O
while the off-stoichiometricsample showsa helicalmodula(Pr,La)
2CuO
4r
a diffraction signal along (2/3 2/3 l) line” rMh lhrtion. Figure 1 shows
uOat room temperature. The signals were observed as spots, indigpr
cating no more than 3% of iron vacancy, and theorderOcharge
as-grown
c-axis. This pattern
glgP takes place
min the ab-plane and along thenSis similar to that of LuFe2O4 rather than that of YbFe2O4
p ji rS S reported
O in Ref. 21. As the difference between
rYb andmLuris
Fig. 1(a) Crystal structure of T’-structure.
OOonly 0.5% in thepionic radius and the thickness of W-layer, itr
is no wonder that YbFe2O4 shows essentially the same charge
orpOr
Ref. 16. The incomorder as that of LuFe2O4 as mentioned in plgP
mensurate signals are observed around (n/3 n/3 integer)
the ciPpoint
along (6d 6d 0) direction with about 0.05 of d at room
S rpOXrO
temperature. However, this incommensurate
reflection signalr
Oto arise from the long-period modulationis unlikelyr on the mFIG. 2. Nyquist plots at 200 K (a), 150 K (b), and 100 K (c). Blue arrows
Or charge order. The origin
O of the incommensurate modulation
indicate the data points measured at 20 Hz. Only the response from the samr
is associated with the magnetic ordering CuOand R-ion
2 displaceple is observed, free of secondary extrinsic contribution such as electrodes
lgP
ment from a wide range q-space observation, magnetizationg n or electrets.
measurements, and X-ray magnetic circular dichroism experie paper.
lgPments. The details are discussed in anotheruS
Fig. 1(b) Site occupancy of two split Pr sites in Pr2CuO4.
In order to detect the intrinsic electric remanent polariO
Ozation in the P-E loop measurement, impedance analysis wasperformed. Following Ref. 19, the sample intrinsic compoO
nent gives rise on a Nyquist plot to a circle connected to theØOorigin. On the other hand, if extrinsic effects occur (such as
interface, electret, etc., effects), theyRFe
give2O
riseOO
4 to a secondcircle, connected to the intrinsic circle at the opposite endlOmlfrom the origin. That is, the quickest responder to the electricP-E“field is the sample intrinsic component,
and the extrinsic
components respond only at a lower
Sfrequency.
T Therefore r
the P-E loop measurements are carried out at high enoughOcfrequency to detect the response of the electronic ferroelectric sample only.
rFigure 2 shows Nyquist plots at 200 K (a), 150 K (b), andp20 Hz n
100 K (c). The data points measured atare indicatedc
by na blue arrow. The data points belong to the part of the curve
related to the sample itself. Furthermore, the data point ati P temperature.
20 Hz moves toward the origin with a decreasingThis tendency should be kept down
10 K as the permittivityntorr
shows no anomaly below 100 K (see Refs. 22 and 23, formgPexample). So only the sample intrinsic
properties are detected
at 10 K in the electric measurements carried out at 20 Hz.
ØlFigure 3 shows the P-E loop obtained with a 20 Hz electricO
field at 10 K. While the primary loops include all compoFONDERTnnents, the secondary loops include only the permittivity andSrTiPS49 9 9 FIG. 1. Superlattice diffraction spots along the (2/3 2/3 l) line.

”uSusO
r100 r
kO50mgPi
mOrXr
SOLLTn Ls i
TS SlgPO”rrOSmgrrlgPiOr|mOr aslgNpr
Oin lOrS npjlgP
u:1
4- 23. P-E loop obtained( with a 20 Hz electric) field by DWM. As theFIG.
Primary loop contains all components, and Secondary loops contain only theextrinsic components such as conductivity, Subtracted loop contains onlythe intrinsic ferroelectric component. Hysteresis character was observed in
the Subtracted P-E loops.

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