Full text of DOI:10.1557/JMR.2002.0392

The effect of doping Ag on the microstructure of
La2/3Sr1/3MnO3 films
Q. Zhan, R. Yu, L.L. He, and D.X. Li
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy
of Sciences, 72 Wenhua Road, Shenyang 110016, Peoples’ Republic of China
J. Li and C.K. Ong
Center for Superconducting and Magnetic Materials and Department of Physics, National University
of Singapore, Singapore 119260
(Received 2 July 2002; accepted 30 July 2002)
The microstructure of Ag-doped La2/3Sr1/3MnO3 (LSMO) thin films deposited on (001)
LaAlO3 single-crystal substrates was systematically investigated in cross section and
plan view by high-resolution electron microscopy and analytical electron microscopy.
The results showed that the films deposited at 750 °C were perfectly epitaxial with or
without Ag-doping. No Ag in the doped film was detected. On the other hand, the
LSMO films deposited at 400 °C were less perfect. With increasing Ag-doping level,
the shape of LSMO grains became irregular, and the grain size increased gradually.
Large polycrystalline clusters consisting of LSMO, AgO, and Ag grains formed in the
doped films, and the amount and size of them increased with increasing Ag-doping
level. Ag existed at the LSMO grain boundaries in its elemental state. A growth
process for the LSMO-Ag system is discussed based on the experimental results.
The enhancement of the magnetic spin disorders at the grain boundaries and
interfaces caused by doping Ag could result in an improvement of low-field
magnetoresistance.
grain boundaries and interfaces is a promising way to
I. INTRODUCTION
Mixed valence manganites with perovskite structure
exhibit two kinds of magnetoresistance (MR): intrinsic or
intragrain MR observed in the vicinity of magnetic tran-
sition temperature Tc and extrinsic or intergrain MR oc-
curring over a wide temperature range below Tc.1,2
The well-known colossal magnetoresistance (CMR),
explained by the double exchange interactions,3 is an
intrinsic effect. However, the sharp drop in resistance
was achieved only in a high magnetic field in the Tesla
range, thus severely limiting the potential applications of
CMR materials. On the contrary, the intergrain magneto-
resistance usually obtained in an applied field of a few
hundred Oersted has attracted special interest.4–7 In par-
ticular, polycrystalline samples have shown the signifi-
cant low-field effect, which becomes increasingly
important at low temperatures. It was shown that low-
field MR is dominated by the grain boundaries.5,6 Spin-
polarized tunneling4 or spin-dependent scattering6
through or at the grain boundaries is believed to be re-
sponsible for it. Researchers explore various methods for
enhancing the low-field MR as highly as possible, such
as polycrystalline bulk,4,8 polycrystalline thin films,5,9
artificially induced grain boundaries,10 and trilayer
tunnel junctions.11 It seems that introducing weak-link
enhance the low-field MR value in manganite films.12
Since the physical properties, in particular the MR effect,
are sensitive to the structure of perovskite-related man-
ganites, it is expected that the extrinsic MR would be
enhanced by doping to modify the microstructure of
materials.
Ag has been widely used as the most suitable dopant to
improve superconducting properties in materials such as
YBa2Cu3O7−␦ (YBCO).13–17 It is well known that the
addition of Ag to YBCO leads to an increase in the
critical current density, which is believed to be caused by
a “catalytic” effect of Ag dispersed at grain boundaries.
Evidence for this was obtained through scanning electron
microscopy (SEM).16 Studies on the addition of Ag to
perovskite manganites, including thin films and bulk
polycrystalline samples, were also reported recently by a
few groups.18–20 They found improvement in several de-
sirable properties, such as the higher ferromagnetic tran-
sition and the metal–insulator transition temperatures or
large MR value at room temperature. However, the mi-
crostructural effects have not been analyzed clearly. In
particular, the existent stage and position of Ag-dopant
are always argued due to lack of detailed microstructural
studies.
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Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
In this work, the changes of microstructure in
(for simplicity, the indexing was referred to the pseudo-
cubic structure), parallel to the interface. Both of the
films exhibit uniform thickness and flat interfaces.
Figure 2 illustrates typical plan-view morphologies of
the films and corresponding electron diffraction patterns
(EDPs) along [001]c zone axis. The cross-sectional and
plan-view single-crystal EDPs indicate that the films are
not only epitaxial well along the c axis (film-normal) but
also in the ab plane for different doping levels of Ag.
The undoped film, HT0/4, consists of rectangularlike
shaped grains, about 50 nm in size [Fig. 2(a)]. This mo-
saiclike grain alignment suggests that the film is formed
by the coalescence of epitaxial islands.23 Distinct bright
contrasts among the LSMO grains where the coalescence
of epitaxial islands meet were left. The HREM im-
age of the intergranular region is shown in Fig. 3. The
plan-view image of HT4/4 predominantly exhibits moire´
fringes and arrays of misfit dislocations. Figure 2(b)
shows a square network of misfit dislocations caused
La2/3Sr1/3MnO3 (LSMO) thin films with different Ag-
doping level were investigated systematically by high-
resolution electron microscopy (HREM) and analytical
electron microscopy (AEM) in cross-section and plan-
view. Direct evidence for the effect of doping Ag on the
microstructure of LSMO films was provided. A growth
process for the LSMO-Ag system is also discussed.
These results could be helpful in understanding the mi-
croscopic transport mechanisms and therefore the extrin-
sic MR effect.
II. EXPERIMENTAL
The ceramic target LSMO was sintered by conven-
tional solid-state reaction. A metal Ag target was adopted
for doping. Co-deposition of LSMO and Ag on (001)
LaAlO3 (LAO) single-crystal substrates was performed
by a dual-beam pulsed laser ablation (PLA) system.21
The laser frequency on the LSMO target was kept at 4 Hz
while that on the Ag target (Ag repeat rate) was adjusted
from 0 to 6 Hz using a chopper. Substrate temperatures
of 750 and 400 °C were chosen for comparison. The
films were kept in situ for 1 h before they were cooled
down slowly. An oxygen pressure of 0.2 mbar was
adopted during the deposition and subsequent annealing
procedure.
Samples with different doping levels of Ag are defined
as HTn/4 and LTn/4, where HT and LT denote substrate
temperatures of 750 °C and 400 °C, respectively; 4 and n
denote the laser repeat rate for LSMO and Ag targets,
respectively. For example, HT0/4 represents a stoichio-
metric LSMO film deposited at 750 °C; while LT6/4
denotes a co-deposited film deposited at 400 °C with Ag
repeat rate of 6 Hz.
The cross section as well as plan view samples suitable
for transmission electron microscopy (TEM) and HREM
studies were prepared by standard techniques described pre-
viously in detail.22 The microstructures of LSMO films
with different Ag-doping levels were characterized by a
JEM 2010 HREM (JEOL Ltd., Tokyo, Japan) with a point-
to-point resolution of 0.19 nm. Composition analysis was
carried out using a HF 2000 cold field-emission-gun TEM
(Hitachi Ltd., Tokyo, Japan) equipped with an Oxford Link
ISIS energy dispersive spectroscopy (EDS) system (Oxford
Instruments, Buckinghamshire, U.K.).
III. RESULTS
A. Films deposited at Ts = 750 °C
Figure 1 shows the cross-sectional morphologies of
the LSMO films deposited at 750 °C with laser frequen-
cies on the Ag target of 0 Hz (HT0/4) and 4 Hz (HT4/4),
respectively. The insets are corresponding selected-area
electron diffraction (SAED) patterns. The direction of
incident electron beam was along [100]c of the substrate
FIG. 1. Cross-sectional morphologies of the (a) undoped HT0/4 and
(b) Ag-doped HT4/4 LSMO films deposited at 750 °C. The insets are
corresponding EDPs, both showing perfect epitaxy along c axis.
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Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
by the lattice mismatch between the LSMO film and
the LAO substrate. It is noted that the intergranular re-
gion present in the undoped film is absent in the Ag-
doped film.
Furthermore, the energy dispersive x-ray analysis in-
dicated that Ag was not detected in the Ag-doped film
(HT4/4).
B. Films deposited at Ts = 400 °C
Figure 4 gives the low-magnification cross-sectional
bright-field images of LSMO films with different doping
levels of Ag and corresponding EDPs. A columnar grain
structure is clearly observed in LT0/4 with an average
width of 10 nm [Fig. 4(a)]. The columnar grains are ba-
sically perpendicular to the LSMO/LAO interface, and
the size is relatively uniform. With increasing the Ag-
doping level, the columnar structure was destroyed
gradually. Especially for the film LT6/4 with the highest
Ag-doping level, the columnar grains cannot be clearly
resolved, and the growth direction is not completely per-
pendicular to the LSMO/LAO interface. Composite elec-
tron diffraction patterns of the cross-sectional samples
were taken from areas including both the LSMO film and
the LAO substrate. The slightly elongated diffraction
spots along arcs [Figs. 4(b), 4(d), and 4(f)] suggest the
decrease of epitaxial property in the LSMO films depos-
ited at 400 °C in contrast to the high-quality epitaxy for
those deposited at 750 °C. It is known that the substrate
temperature had to be high enough (around Ts ס 600 °C
and above) to obtain good epitaxial growth using pulsed
laser deposition (PLD).24 Moreover, it is worthwhile to
note the presence of additional diffraction spots for the
Ag-doped films that are absent in the undoped ones, such
FIG. 2. Plan-view morphologies of (a) HT0/4 and (b) HT4/4 depos-
ited at 750 °C. The insets are corresponding EDPs.
¯
as 111LSMO, 111Ag, and 202AgO as indicated in Fig. 4(f).
Figures 5(a) and 5(b) show a plan-view bright-field
image and the corresponding SAED pattern of the stoi-
chiometric LSMO thin film (LT0/4). Typical granular
grains are present in the film. The grain size is about
12 nm in diameter, significantly smaller than that of the
undoped films deposited at 750 °C (50 nm). On the other
hand, the diffraction spots of these plan-view samples
elongated along arcs, indicating that the ab-plane align-
ment was also destroyed when the films were deposited
at 400 °C.
Plan-view morphology and corresponding SAED pat-
terns of Ag-doped films are shown in Figs. 5(c)–5(f). It
can be seen that the most significant change in micro-
structure is that large clusters were formed in the doped
films, with their amount and size increasing with Ag-
doping. The average size of the large clusters in LT6/4 is
around 60 nm in diameter. Moreover, in addition to the
diffraction spots of [001]LSMO zone, diffraction spots of
Ag, AgO, and other zones of LSMO were observed
FIG. 3. HREM image of the intergranular region between LSMO
grains in HT0/4.
in Ag-doped films, such as 111LSMO, 111Ag, and 002AgO
,
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Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
FIG. 4. Low-magnification cross-sectional bright-field images of the LSMO films deposited at 400 °C and the corresponding EDPs: (a,b) LT0/4,
(c,d) LT3/4, (e,f) LT6/4.
as indicated in Fig. 5(f). This demonstrates the presence
of elemental Ag and Ag oxide in the doped films. Mean-
while, the growth directions of some LSMO grains
changed remarkably, giving additional diffraction spots
of LSMO other than the [001]LSMO zone.
Besides the formation of large clusters in the Ag-
doped films, the shape of normal LSMO grains became
irregular, and the grain size increased gradually with Ag-
doping. For LT6/4, the average grain size was around
20 nm and some grains coalesced [Fig. 5(e)].
The microstructure at atomic scale of these films was
obtained by HREM observations. Figure 6(a) shows a
plan-view HREM image of the undoped LSMO films.
Some grains were connected, and low-angle grain bound-
aries were formed. The intergranular region also existed
among the LSMO grains, similar to the undoped film
deposited at 750 °C. For the doped LSMO films, some
elemental Ag grains were found at the normal LSMO
grain boundaries. Figure 6(b) shows such a Ag grain with
its [110] direction perpendicular to the film surface. The
size of the Ag grain is about 8 nm.
The high-magnification morphology of a large cluster
in the Ag-doped film is shown in Fig. 7, as indicated by
an arrow. Clearly, the large cluster consisted of sever-
al grains with irregular shape and different size. These
grains have different orientations and do not exhibit typi-
cal granular morphologies. The polycrystalline clusters
are mainly composed of LSMO and AgO grains.
Figure 8(a) shows a HREM image of a large cluster with
a AgO grain enclosed in LSMO grains. Elemental Ag
grains can also be found at the LSMO grain boundaries,
but less frequently, as shown in Fig. 8(b)
The composition analysis of the Ag-doped films
was carried out by using EDS. Figure 9(a) shows a typi-
cal EDS spectrum of a large cluster. Ag peaks were
clearly visible. Quantitative analysis showed that the
content of Ag varied in different clusters, from several
percent (i.e., 3 wt%) to tens of percent (i.e., 40 wt%). In
contrast, no Ag has been detected in normal LSMO
grains, as shown in Fig. 9(b). These compositional re-
sults, combined with the HREM results, demonstrate that
Ag could not substitute into LSMO lattice but mainly
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Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
FIG. 5. Typical plan-view bright-field images of the LSMO films deposited at 400 °C and the corresponding EDPs: (a,b) LT0/4, (c,d) LT3/4,
(e,f) LT6/4.
existed in the large polycrystalline clusters as AgO or
at grain boundaries of normal LSMO grains in its el-
emental state.
According to the data of room-temperature bond en-
thalpies, which give Ag–Ag as approximately 160 and
Ag–O as approximately 220 mJ mol−1,25 it is reasonable
to conclude that Ag tends to oxidize in an oxygen am-
bient during PLD. Pinto et al. have also confirmed the
fact, through optical spectroscopy, that AgO was indeed
generated in the laser plum during PLD of Ag-doped
YBa2Cu3O7−␦ films.26 On the other hand, AgO is un-
stable at elevated temperatures (above 350 °C).26
When AgO arrives at a substrate surface at 750 °C, it
dissociates into Ag and O again during in situ film for-
mation. Not substituting into the LSMO lattice, At atoms
diffuse to sites of lower free energy, typically grain
IV. DISCUSSION
It has been shown that the effect of doping Ag on the
microstructure of the LSMO films depends on the sub-
strate temperature during deposition, and the effect is
significant when the substrate temperature is low (i.e.,
400 °C). A growth process for the LSMO-Ag system and
properties of LSMO films with Ag doping are discussed
in the following.
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Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
boundaries, and segregate as agglomerates. During the
diffusion, the Ag atoms impart their momentum to atoms
of LSMO lattice, increasing the mobility of the latter.
Such an effect is equivalent to an increase in annealing
temperature. As a result, the Ag-doped films deposited at
750 °C are more perfect than the undoped films. The
intergrain regions are eliminated by doping Ag. On the
other hand, the saturated vapor pressure of Ag is fairly
high at high temperatures, i.e., approximately 30 mtorr at
700 °C,17 resulting in the re-evaporation of Ag atoms
during the in situ annealing at 750 °C. Therefore, Ag
could not be detected in the doped films deposited
at 750 °C. This is in agreement with the previous re-
port of x-ray diffraction and x-ray photoelectron spec-
troscopy results on Ag-doped LSMO films deposited
at 750 °C.27
FIG. 6. Plan-view HREM images of the (a) undoped and (b) Ag-
doped LSMO films deposited at 400 °C.
FIG. 8. HREM images of large clusters in the doped LSMO films.
(a) AgO grain enclosed in LSMO grains. (b) Ag particle at the LSMO
grain boundaries.
FIG. 7. High-magnification morphology of a large cluster consisting
of several grains in the doped film.
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Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
a field of only 4 kOe, which is larger by a factor of two
compared with the undoped one.27 This large enhance-
ment could be attributed to the existence of Ag and poly-
crystalline clusters in the doped films. The ferromagnetic
spin alignment would show disordered status to some
extent at the LSMO grain boundaries and AgO-LSMO
interfaces in the polycrystallinelike clusters. Nonmag-
netic metal Ag existing at the LSMO grain boundaries
could also weaken the ferromagnetic interaction between
grains and cause Mn spin disorder at the interfaces. They
serve as a strong scatter centers for the highly spin-
polarized conducting Mn3+ eg electrons and lead to
a high zero-field electrical resistance. Application of a
moderate magnetic field can readily align the spin and
drop the resistivity significantly. As a result, a large MR
value at low magnetic field was obtained.
V. CONCLUSIONS
Cross-section and plan-view observations of changes
in microstructure of LSMO films with different Ag-
doping level were given in detail. The effect of doping
Ag on the microstructure of the LSMO films depended
on the substrate temperature during deposition, and the
effect was significant when the substrate temperature
was low (i.e., 400 °C). With decrease in the substrate
temperature from 750 to 400 °C, epitaxial property of the
LSMO films deteriorated. In the doped LSMO films de-
posited at 400 °C, large polycrystalline clusters consist-
ing of LSMO, AgO, and Ag grains were formed, and Ag
existed at the LSMO grain boundaries in its elemental
state. This modified microstructure due to doping Ag
could lead to an enhanced low-field MR value.
FIG. 9. (a) EDS of a large cluster in the doped film, where Ag peaks were
clearly visible. (b) Nanometer-beam EDS analysis with a spatial resolu-
tion of 2–3 nm inside a LSMO grain, showing the absence of Ag.
When the substrate temperature was 400 °C, the de-
composition of AgO deposited at the substrate surface
could also occur. As discussed above, the decomposed
Ag atoms agglomerated at the LSMO grain boundaries.
At the same time, the diffusion of Ag atoms increased the
mobility of atoms in LSMO grains, leading to the ob-
served larger grain sizes. On the other hand, since the
substrate temperature is not high enough, the decompo-
sition of AgO could be incomplete, with some large AgO
particles kept in the films. Due to the existence of these
large AgO particles, the growth of the subsequent LSMO
grains, especially those lay on the AgO particles, could
not be epitaxial with respect to the LAO substrate. As a
result, LSMO grains with different orientations were
formed, giving the polycrystalline clusters.
ACKNOWLEDGMENT
The authors gratefully acknowledge the support from
the National Natural Science Foundation of China under
Grant No. 50071063.
REFERENCES
The magnetotransport properties were measured at a
low-field of 4 kOe for all of the films.27 The MR values
were similar for the doped and undoped LSMO films
deposited at 750 °C, with a maximum of approximately
3% at the vicinity of Tc and declined with decreasing
temperature. The MR values can even be ignored at
77 K. It is thus clear that the addition of Ag has no
obvious effect on the magnetotransport properties of the
epitaxial films deposited at 750 °C. This may be attrib-
uted to highly aligned grain boundaries in epitaxial films.
However, low-field MR of the Ag-doped LSMO
films grown at Ts ס 400 °C show a large enhancement
compared to the undoped ones. In particular, the MR
value at 77 K for doped films could be as large as 12% in
1. J.M.D. Coey, J. Appl. Phys. 85, 5576 (1999).
2. H.R. Khan, Mater. Sci. Forum 373–376, 93 (2001).
3. C. Zener, Phys. Rev. 82, 403 (1951).
4. H.Y. Hwang, S-W. Cheong, N.P. Ong, and B. Batlogg, Phys. Rev.
Lett. 77, 2041 (1996).
5. A. Gupta, G.Q. Gong, G. Xiao, P.R. Duncombe, P. Lecoeur,
P. Trouilloud, Y.Y. Wang, V.P. Dravid, and J.Z. Sun, Phys.
Rev. B 54, 15629 (1996).
6. X.W. Li, A. Gupta, G. Xiao, and G.Q. Gong, Appl. Phys. Lett. 71,
1124 (1997).
7. J.Y. Gu, C. Kwon, M.C. Robson, Z. Trajanovic, K. Ghosh, and
R.P. Sharma, Appl. Phys. Lett. 70, 1763 (1997).
8. H.L. Ju and H. Sohn, Solid State Commun. 102, 463 (1997).
9. T. Walter, K. Do¨rr, K-H. Mu¨ller, B. Holzapfel, D. Eckert,
M. Wolf, D. Schla¨fer, L. Schultz, and R. Gro¨tzschel, Appl. Phys.
Lett. 74, 2218 (1999).
2718
J. Mater. Res., Vol. 17, No. 10, Oct 2002
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

Q. Zhan et al.: The effect of doping Ag on the microstructure of La2/3Sr1/3MnO3 films
10. N.D. Mathur, G. Burnell, S.P. Isaac, T.J. Jackson, B-S. Teo,
19. T. Tao, Q.Q. Cao, K.M. Gu, H.Y. Xu, S.Y. Zhang, and Y.W. Du,
J.L. MacManus-Driscoll, L.F. Cohen, J.E. Evetts, and M.G. Blamire,
Appl. Phys. Lett. 77, 723 (2000).
Nature 387, 266 (1997).
20. R. Bathe, K.P. Adhi, S.I. Patil, G. Marest, B. Hannoyer, and
S.B. Ogale, Appl. Phys. Lett. 76, 2104 (2000).
21. C.K. Ong, S.Y. Xu, and W.Z. Zhou, Rev. Sci. Instrum. 69, 3659
(1998).
22. Q. Zhan, R. Yu, L.L. He, D.X. Li, and X.N. Guo, Acta Metall.
Sin. 37, 337 (2001).
23. O.I. Lebedev, G. Van Tendeloo, S. Amelinckx, H.L. Ju, and
K.M. Krishnan, Philos. Mag. A 80, 673 (2000).
24. R. Von Helmot, J. Wecker, K. Samwer, L. Haupt, and K. Ba¨rner,
J. Appl. Phys. 76, 6925 (1994).
11. C. Kwon, Q.X. Jia, Y. Fan, M.F. Hundley, D.W. Reagor,
J.Y. Coulter, and D.E. Peterson, Appl. Phys. Lett. 72, 486 (1998).
12. C.J. Lu, Z.L. Wang, G.C. Xiong, and G.J. Lian, J. Mater. Res. 15,
2454 (2000).
13. D. Kumar, M. Sharon, R. Pinto, P.R. Apte, S.P. Pai, S.C. Purandare,
L.C. Gupta, and R. Vijayaraghavan, App. Phys. Lett. 62, 3522
(1993).
14. A.Z. Moshfegh, Y.Q. Wang, Y.Y. Sun, A. Mesarwi, P.H. Hor,
and A. Ignatiev, Physica C 218, 396 (1993).
15. R. Pinto, P.R. Apte, S.P. Pai, and D. Kumar, Physica C 207, 13
(1993).
16. D. Kumar, M. Sharon, P.R. Apte, R. Pinto, S.P. Pai, S.C. Purandare,
C.P. D’Souza, L.C. Gupta, and R. Vijayaraghavan, J. Appl. Phys.
76, 1349 (1994).
25. J.A. Kerr, in CRC Handbook of Chemistry and Physics
1999–2000, edited by D.R. Lide (CRC Press, Boca Raton, FL,
1998).
26. R. Pinto, P.R. Apte, K.P. Adhi, S.B. Ogale, D. Kumar, and
M.S. Hegde, J. Appl. Phys. 78, 5204 (1995).
17. R. Kalyanaraman, S. Oktyabrsky, and J. Narayan, J. Appl. Phys.
27. J. Li, Q. Huang, Z.W. Li, L.P. You, S.Y. Xu, and C.K. Ong,
85, 6636 (1999).
J. Phys.: Condens. Matter 13, 3419 (2001).
18. R. Shreekala, M. Rajeswari, S.P. Pai, S.E. Lofland, V. Smolyaninova,
K. Ghosh, S.B. Ogale, S.M. Bhagat, M.J. Downes, R.L. Greene,
R. Ramesh, and T. Venkatesan, Appl. Phys. Lett. 74, 2857 (1999).
J. Mater. Res., Vol. 17, No. 10, Oct 2002
2719
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