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Evidence of weak antilocalization in quantum
interference eects of (001) oriented La 0.7 Sr 0.3 MnO
3 –SrRuO 3 superlattices
Roshna Sobhanan Helen, Wilfrid Prellier, Prahallad Padhan
To cite this version:
Roshna Sobhanan Helen, Wilfrid Prellier, Prahallad Padhan. Evidence of weak antilocalization in
quantum interference eects of (001) oriented La 0.7 Sr 0.3 MnO 3 –SrRuO 3 superlattices. Journal
of Applied Physics, American Institute of Physics, 2020, 128 (3), pp.033906. �10.1063/5.0014909�.
�hal-03014244�
J. Appl. Phys. 128, 033906 (2020); https://doi.org/10.1063/5.0014909 128, 033906
© 2020 Author(s).
Evidence of weak antilocalization
in quantum interference effects of
(001) oriented La
0.7
Sr
0.3
MnO
3
–SrRuO
3
superlattices
Cite as: J. Appl. Phys. 128, 033906 (2020); https://doi.org/10.1063/5.0014909
Submitted: 22 May 2020 . Accepted: 02 July 2020 . Published Online: 16 July 2020
Roshna Sobhanan Helen, Wilfrid Prellier, and Prahallad Padhan
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Evidence of weak antilocalization in quantum
interference effects of (001) oriented
La
0.7
Sr
0.3
MnO
3
–SrRuO
3
superlattices
Cite as: J. Appl. Phys. 128, 033906 (2020); doi: 10.1063/5.0014909
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Submitted: 22 May 2020 · Accepted: 2 July 2020 ·
Published Online: 16 July 2020
Roshna Sobhanan Helen,
1
Wilfrid Prellier,
2
and Prahallad Padhan
1,a)
AFFILIATIONS
1
Department of Physics, Indian Institute of Technology Madras, Chennai 600036, Tamilnadu, India
2
Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN, 6 Bd du Marechal Juin, F-14050 Caen Cedex, France
a)
Author to whom correspondence should be addressed: padhan@iitm.ac.in
ABSTRACT
Quantum corrections to conductivity in the ferromagnetic La
0.7
Sr
0.3
MnO
3
(LSMO) and SrRuO
3
(SRO) thin films depend on the structural
mismatches and interfaces accommodating ions and their spins. Here, by making interfaces of LSMO and SRO in the form of artificial
superlattices, we achieve positive magnetoresistance (MR) and weak antilocalization (WAL), although the individual component shows neg-
ative MR and weak localization (WL). The [20 unit cell (u.c.) LSMO/3 u.c. SRO]
×15
superlattice stabilizes in tetragonal symmetry associated
with the rhombohedral and orthorhombic structures and demonstrates the occurrence of the single magnon scattering process. The low-
field MR of the superlattice fit to the Hikami–Larkin–Nagaoka expression yields 595 Å phase coherence length (l
f
) with WAL of carriers.
As the SRO layer thickness in the superlattice increases to 5 u.c., the value of l
f
= 292 Å decreases, and positive MR increases confirm the
manifestation of WAL by SRO. The orthorhombic symmetry of the SRO is preserved in the [20 u.c. SRO/3 u.c. LSMO]
×15
superlattice,
which shows the existence of locally cooperative bond-length fluctuations and conduction due to the scattering of the electron by the Fermi
liquid electrons, bond length, and spin fluctuations. However, as the LSMO layer thickness in the superlattice is increased to 5 u.c., the WL
effect suppresses WAL at the low field. The spin–orbit coupling associated with magnetic anisotropy, i.e., spin and bond length fluctuations,
modifies the WL in the superlattices and leads to WAL, thereby achieving positive MR.
Published under license by AIP Publishing. https://doi.org/10.1063/5.0014909
I. INTRODUCTION
The transport properties of the materials with carriers’ mean
free path larger than the Fermi wavelength are described by the
semiclassical Boltzmann approach. In general, the low-temperature
carriers’ transport in these materials is influenced by the scattering
of carriers through lattice imperfections and carrier–carrier scatter-
ing. In the thin films or heterostructures, as the disorder induced
by the strain or interfaces increases, the mean free path shrinks and
eventually may become comparable to the Fermi wavelength. In
this situation, a fully quantum-mechanical treatment, accounting
for the wavelike nature of the carriers, must be applied to conduc-
tivity. This approach consists of adding some correcting terms to
low-temperature conductivity, the so-called quantum corrections to
conductivity (QCC).
1,2
Recently, QCC in manganites has been
intensively investigated to interpret low-temperature resistivity.
Generally, QCC leads to correction to resistivity from two different
sources: (i) electron–electron interaction and subsequent modifica-
tion of the density of states at the Fermi energy and (ii) weak locali-
zation (WL) effect arising from the self-interference of the wave
pockets as they are backscattered coherently by the impurities or
other defects.
1
These two contributions in the temperature-
dependent conductivity of the 2D systems are of comparable mag-
nitude. However, the contributions in the field dependence of low-
temperature conductivity are radically different, and in principle, it
can unambiguously determine the nature of QCC.
1,3
The external
magnetic field suppressed the WL contribution as the field destroys
the wave coherence, and thus, the self-interference effects are
reduced, and the resistance is decreased, i.e., a negative magnetore-
sistance (MR) is observed. On the other hand, the influence of the
field on the electron–electron scattering contribution leads to a
positive magnetoresistance originated by the spin splitting of elec-
trons in a magnetic field and by the orbital effects.
Journal of
Applied Physics
ARTICLE scitation.org/journal/jap
J. Appl. Phys. 128, 033906 (2020); doi: 10.1063/5.0014909 128, 033906-1
Publ ished under license by AIP Publishing.
The other possible mechanism for the observed positive MR in
the metallic double perovskite oxides is that the external magnetic
field suppresses the long-range antiferromagnetic order to form
short-range antiferromagnetic fluctuations, which enhance electronic
scattering and lead to giant positive MR.
4
In contrast, the application
of the magnetic field on the pero vskite oxides decreases th e local spin
disorder and thus decreases resistivity, which leads to negative MR.
5
Even though the MR of the individual ferromagnetic perovskite oxide
is negative, the positive MR feature is observed due to the structural
or magnetic distortion at the thin film or heterostructure interfaces of
the perovskite oxides. The positive MR 25% at 80 K under 4 T
field obs erved in the Fe
3
O
4
/SrTiO
3
/La
0:7
Sr
0:3
MnO
3
(LSMO) hetero-
structure is attributed to the inverse correlation between the orienta-
tions of the carrier spins (states near the Fermi level) in the two
ferromagnetic layers.
6
The La
0:9
Sr
0:1
MnO
3
/SrNb
0:01
Ti
0:99
O
3
p–n
junctions at 290 K under 0.01 T exhibits 23% MR, which is
explained by the interface induced change on the concentration of
the carriers and the density of state of the electrons at the Fermi
level.
7
The de genera te semiconducting SrT iO
3
single crystals capped
with ultrathin SrTiO
3
/LaAlO
3
bilay ers at a temp er atur e of 2 K and a
magnetic field of 9 T show positive MR of . 30 000% due to the
inhomogeneity of the materials and Lorentz type conduction.
8
The
positive MR is observed in t he antiferromagnetically coupled
La
2/3
Ba
1/3
MnO
3
in the La
2/3
Ba
1/3
MnO
3
/LaNiO
3
superlattices.
9
The low field positive MR has also been observed in the
La
0:7
Sr
0:3
MnO
3
/SrRuO
3
,
10
and SrMnO
3
/SrRuO
3
(SRO),
11
superlat-
tices. In this article, we report the effect of stacking order of
La
0.7
Sr
0.3
MnO
3
(LSMO) and SrRuO
3
(SRO) on the crystal struc-
ture a nd MR of the La
0:7
Sr
0:3
MnO
3
– SrRuO
3
superlattices grown
on the (001) oriented SrTiO
3
(STO).–
II. EXPERIMENTAL METHODS
A multitargeted pulsed laser deposition system was used to
grow the superlattices consisting of LSMO and SRO on (00l) ori-
ented SrTiO
3
using a pulsed KrF excimer laser (λ = 248 nm). These
superlattices were grown at a substrate temperature of 720 °C with
oxygen partial pressure of 300 mTorr followed by cooling to room
temperature in the presence of oxygen. The deposition rates for the
SRO and LSMO layers are calibrated individually for each laser
pulse of energy density 3 J/cm
2
, and it seems to be almost the
same 0:73 A
/pulse. A series of superlattices with [20 u.c. (unit
cell) LSMO/n (=3 and 5) u.c. SRO] and [20 u.c. SRO/n u.c. LSMO]
bilayer configurations were prepared by repeating the bilayer 15
times. A four-circle x-ray diffractometer was used to characterize
the crystal structure of these superlattices. The Raman spectra were
recorded by using a Jobin-Yvon LabRAM HR800UV spectrometer
instrument equipped with a highly efficient thermo-electrically
cooled charge-coupled device. The spectra were recorded at various
temperatures in the backscattering configuration using a 633 nm
emission line of a He–Ne laser. A physical property measurement
system was used to study the electronic transport of the superlattices.
III. RESULTS AND DISCUSSION
The lattice mismatch between the substrate STO (a ¼ 3:905 A
)
and the LSMO (a
pc
¼ 3:88 A
)is0:64%, which is equal and oppo-
site to that of the STO and SRO (a
pc
¼ 3:93 A
). Thus, the (002)
superlattice peak of [20 u:c: LSMO/5 u:c: SRO]
15
appears a t a
higher angle, while that of [20 u:c: SRO/5 u:c: LSMO]
15
appears at a
lower angle as compared to that of the STO [Figs. 1(a) and 1(b)].
The θ−2θ x-ray diffraction (XRD) patterns of different superlattices
show only (00l) peaks of the substrate and the constituents. The
observed (002) Bragg’s reflections with four orders of satellite peaks
[Figs. 1(a) and 1(b)] on either side of the STO peaks are suggesting
the presence of long-range periodicity, epitaxy, and good crystallin-
ity. The broadness of the satellite peaks is due to the merging of
Kiessig fringes.
12
The simulated XRD profile included in Figs. 1(a)
and 1(b) was obtained using the DIFFaX program,
12,13
which is in
good agreement with the measured XRD with respect to the posi-
tion of Bragg’s peaks and their relative diffracted intensity. The sat-
ellite peak positions obtained from the XRD patterns of the
superlattice series are used to calculate the superlattice period (Λ).
The Λ values are in good agreement with the designed thickness
configurations as well as the values obtained from the fit using
DIFFaX.
13
FIG. 1. θ 2θ x-ray diffraction pattern of (a) [20 u:c: LSMO/5 u:c: SRO]
15
and (b) [20 u:c: SRO/5 u:c: LSMO]
15
superlattices. The (002) Bragg’s reflec-
tion of STO, as well as the satellite peaks (0th and ±4th orders), is indicated.
The diffraction profile of these superlattices calculated using the DIFFAX
program is also shown. f scan of the (103) of the (c)
[20 u:c: LSMO/3 u:c: SRO]
15
and (d) [20 u:c: SRO/3 u:c: LSMO]
15
superlattices.
Journal of
Applied Physics
ARTICLE scitation.org/journal/jap
J. Appl. Phys. 128, 033906 (2020); doi: 10.1063/5.0014909 128, 033906-2
Publ ished under license by AIP Publishing.
The f-scan XRD patterns around (103)
pc
of
[20 u:c: LSMO/3 u:c: SRO]
15
and [20 u:c: SRO/3 u:c: LSMO]
15
superlattices show four peaks [Figs. 1(c) and 1(d)]. The 90° separa-
tion between the consecutive peaks in the f-scan confirms that
these superlattices and the substrate are of fourfold symmetry with
the cube-on-cube epitaxial growth. The crystal structures of these
superlattices were further studied from their reciprocal space
mapped along the four
f
-orientations. The Bragg’s reflection mea-
surements consisting of 2θ−ω coupling scans in {103}
pc
for differ-
ent ω values were performed to construct the reciprocal space
mapping (RSM) (Fig. 2).
The [20 u:c: LSMO/3 u:c: SRO]
15
superlattice exhibits the
same q
?
along the h103i
pc
of {103}
pc
with c
pc
¼ 3:851 A
, which is
very close to c
pc
obtained from the h001i
pc
[Figs. 2(a)–2(d)].
However, c
pc
of the [20 u:c: LSMO/3 u:c: SRO]
15
superlattice is
smaller than the c
pc
of the LSMO or SRO along the h001i
pc
; hence,
both LSMO and SRO experience compressive strain. The q
k
along
the h103i
pc
of {103}
pc
of the [20 u:c: LSMO/3 u:c: SRO]
15
super-
lattice is also the same and giving a
pc
¼ 3:968 A
, which is larger
than the lattice parameters of the LSMO and SRO. So, the LSMO
and SRO experience tensile strain along the h001i
pc
. The pseudo-
cubic lattice parameters of the [20 u : c: LSMO/3 u:c: SRO]
15
superlattices extracted from the RSM can be expressed as th e
tetragonal structures with the lattice parameters a
T
¼ 5:611 A
and c
T
¼ 7:702 A
. The RSM studies confirm that the growth of
the [20 u:c: LSMO/3 u:c: SRO]
15
superlattices drives the rhombo-
hedral (R
3m) LSMO and orthorhombic (Pbnm) SRO crystal struc-
tures to the tetragonal I4/mcm structure.
The [20 u:c: SRO/3 u:c: LSMO]
15
superlattice exhibits the
same q
?
along the h103i
pc
of {103}
pc
with c
pc
¼ 3:941 A
, which is
very close to c
pc
obtained from the h001i
pc
[Figs. 2(e)–2(h)].
However, the c
pc
of the [20 u:c: SRO/3 u:c: LSMO]
15
superlattice
is larger than c
pc
of the LSMO or SRO a long the h001i
pc
;thus,
both LSMO and SRO experience tensile strain. The q
k
along
the h103i
pc
of {103}
pc
of the [20u:c: SRO/3 u:c: LSMO]
15
supe rlattice provides a
103
pc
¼ 3:868 A
, a
0
13
pc
¼ 3:861 A
,
a
103
pc
¼ 3:869 A
,anda
013
pc
¼ 3:882 A
, which indicates that the
in-plane lattice parameters a re different but smaller than that o f
the LSMO or SRO. So, the in-plane lattice parameters of
[20 u:c: S RO/3 u:c: LSMO]
15
experience compression with
orthorhombic crystal structures. The orthorhombic lattice
parameters of the [20 u:c: S RO/3 u:c: LSMO]
15
superlattice are
a
O
¼ 5:47 A
, b
O
¼ 5:49 A
,andc
O
¼ 7:882 A
.TheRSMstudies
suggest that the rhombohedral (R
3m) LSMO and orthorhombic
(Pbnm) SRO crysta l structures in the SRO/LSMO superlattices
stabilize as t he distorted orthorhombic structure. The structural
transformation of the LSMO and/or SRO in these superlattices
instigated from the variation of bond length, tilt, and rotation of
the octahedral.
The polarized Raman spectra of the (001) oriented superlatti-
ces with both the stacking order measured at 100 K are shown in
Fig. 3. The first-order Raman scattering because of the cubic phase
of the STO is not observed as the STO transforms into a tetragonal
phase around 110 K.
14
However, the second-order process in
the STO due to two-phonon scattering in the frequency range
of 200 – 500 cm
1
is observed.
15
The Raman spectrum of
[20 u:c: LSMO/3 u:c: SRO]
15
with parallel (HH) polarization of
the incident and scattered light shows peaks centered at around
150, 200, 252, 302, 410, and 431 cm
1
(curve a, Fig. 3).
The peaks that appear in the Raman spectra of the
[20 u:c: LSMO/3 u:c: SRO]
15
superlattice after cross (HV) polari-
zation of th e incident and scattered light are 175, 240, 333, 410,
and 431 cm
1
(curve b, Fig. 3). The peaks at 200 an d 42 7 cm
1
are
pronounced much more strongly with HH polarization as com-
pared to the HV polarization spectrum. The 200 cm
1
has the A
1g
FIG. 2. Reciprocal space mapping around {103}
pc
plane of
[20 u:c: LSMO/3 u:c: SRO]
15
[panels (a) to (d)] and
[20 u:c: SRO/3 u:c: LSMO]
15
[panels (e) to (h)], superlattices grown on (001)
STO.
FIG. 3. Polarized Raman spectra recorded at a temperature of 100 K for the
[20 u:c: LSMO/3 u:c: SRO]
15
(a) and (b) and [20 u:c: SRO/3 u:c: LSMO]
15
(c) and (d) superlattices grown on (001) oriented STO.
Journal of
Applied Physics
ARTICLE scitation.org/journal/jap
J. Appl. Phys. 128, 033906 (2020); doi: 10.1063/5.0014909 128, 033906-3
Publ ished under license by AIP Publishing.
![FIG. 3. Polarized Raman spectra recorded at a temperature of 100 K for the [20 u:c: LSMO/3 u:c: SRO] 15 (a) and (b) and [20 u:c: SRO/3 u:c: LSMO] 15 (c) and (d) superlattices grown on (001) oriented STO.](/figures/fig-3-polarized-raman-spectra-recorded-at-a-temperature-of-3qejhe4n.webp)
![FIG. 2. Reciprocal space mapping around {103} pc plane of [20 u:c: LSMO/3 u:c: SRO] 15 [panels (a) to (d)] and [20 u:c: SRO/3 u:c: LSMO] 15 [panels (e) to (h)], superlattices grown on (001) STO.](/figures/fig-2-reciprocal-space-mapping-around-103-pc-plane-of-20-u-c-2bdfdgkd.webp)
![FIG. 1. θ 2θ x-ray diffraction pattern of (a) [20 u:c: LSMO/5 u:c: SRO] 15 and (b) [20 u:c: SRO/5 u:c: LSMO] 15 superlattices. The (002) Bragg’s reflection of STO, as well as the satellite peaks (0th and ±4th orders), is indicated. The diffraction profile of these superlattices calculated using the DIFFAX program is also shown. f scan of the (103) of the (c) [20 u:c: LSMO/3 u:c: SRO] 15 and (d) [20 u:c: SRO/3 u:c: LSMO] 15 superlattices.](/figures/fig-1-th-2th-x-ray-diffraction-pattern-of-a-20-u-c-lsmo-5-u-22126l5i.webp)
![FIG. 5. Temperature-dependent magnetoresistance at various fields for the (a) [20 u:c: LSMO/3 u:c: SRO] 15 and (b) [20 u:c: SRO/3 u:c: LSMO] 15 superlattices grown on (001) oriented STO. Part of the temperature-dependent resistivity at various fields for [20 u:c: LSMO/3 u:c: SRO] 15 (inset a) and [20 u:c: SRO/3 u:c: LSMO] 15 (inset b) superlattices.](/figures/fig-5-temperature-dependent-magnetoresistance-at-various-45suj0zm.webp)
![FIG. 6. Field-dependent magnetoresistance (a), (b), (e), (f ), and (g) and magnetoconductance (c), (d), and (h) measured at 10 K for the (a) and (c) [20 u:c: LSMO/ 3 u:c: SRO] 15; (b) and (d) [20 u:c: LSMO/5 u:c: SRO] 15; (e), (g), and (h) [20 u:c: SRO/3 u:c: LSMO] 15; and (f ) [20 u:c: SRO/5 u:c: LSMO] 15 superlattices grown on (001) oriented STO. The solid line is the HLN fit to the fielddependent Δσ at the low field in panels (c), (d), and (h). The solid line is the quadratic fit to the field-dependent MR at the low field in panel (g).](/figures/fig-6-field-dependent-magnetoresistance-a-b-e-f-and-g-and-9noa51pr.webp)