Supporting Online Materials for
Electric-field-control of resistance and magnetization switching in multiferroic
Zn0.4Fe2.6O4/0.7Pb(Mg2/3Nb1/3)O3-0.3PbTiO3 epitaxial heterostructures
Yuanjun Yang1, Z. L. Luo1, Haoliang Huang1, Yachun Gao1, J. Bao1, X. G. Li2, Sen
Zhang3, Y. G. Zhao3, Xiangcun Chen1, Guoqiang Pan1, C. Gao1,2,a)
1 National Synchrotron Radiation Laboratory & School of Nuclear Science and
Technology, University of Science and Technology of China, Hefei, Anhui 230026,
China
2 Hefei National Laboratory for Physical Sciences at Microscale & Department of
Physics, University of Science and Technology of China, Hefei, Anhui 230026, China
3 Department of Physics & State Key Laboratory of New Ceramics and Fine
Processing, Tsinghua University, Beijing 100084, China
This file includes:
The sample preparation and structure characterization
The ferroelectric-field effect in our multiferroic ZFO/PMN-PT heteroesturcture.
The estimation of the in-plane compressive strain.
The tunability of resistance at 80 K.
The sample preparation and structure characterization
(001)-PMN-PT piezoelectric single crystal with superior piezoelectric properties [1]
was used as the substrate. Epitaxial ZFO films with high Curie temperature (>400 K,
weakly depends on the strain [2]) and semiconducting properties [3] were deposited on
the PMN-PT substrate by rf-magnetron sputtering. Prior to the measurements,
multiferroic ZFO/PMN-PT epitaxial heterostructure was poled by electric field of +10
kV/cm under 140 oC in silicone oil, and then cooled down to room temperature at +5
kV/cm. Structure characterization was carried out on the U7B beamline at Hefei Light
Source by using XRD technique with wavelength of 0.1539 nm. Thickness of films was
calibrated to be 40 nm by small angle x-ray reflectometry as shown in Fig. S1(a). AFM
image in the upper right inset of Fig. S1(a) shows that the root mean square roughness is
less than 1 nm. High angle x-ray diffraction (θ-2θ) scan indicates that the film is highly
oriented along c axis (out-of-plane direction) and no other impure phases as shown in Fig.
S1(b). Fig. S1(c) shows  scans of the (103) peak of substrate and (206) peak of film,
demonstrating that the film is also highly oriented along the in-plane direction. Therefore,
a)
Author to whom correspondence should be addressed; electronic mail: cgao@ustc.edu.cn
1
the ZFO film is highly epitaxial on the PMN-PT substrate.
Reflectivity (a.u.)
(a)
Thickness ~ 40 nm
2μm
RMS:
0.8 nm
0
0
1
2
2μm
3
4
2 (degree)
Intensity (a.u.)
PMN-PT (001) PMN-PT (002)
10
5
10
4
5
6
(b)
PMN-PT (003)
ZFO (004)
10
3
10
2
10
1
20
40
60
80
2 (degree)
Intensity (a.u.)
Substrate (103)
-50
(c)
ZFO (206)
0
50 100 150 200 250 300 350
(degree)
2
Fig. S1 (a) X-ray reflectivity of ZFO epitaxial film. The inset is an AFM image of the
film. (b) θ-2θ scans of the (001)-ZFO/PMN-PT film. (c)  scans of (103) peak of
substrate (up) and (206) peak of film (down).
The ferroelectric-field effect in our multiferroic ZFO/PMN-PT heteroesturcture.
The characteristic screen length of our multiferroic ZFO/PMN-PT heteroesturcture
is estimated from Debye formula [4] L D  ((ε 0ε r k BT) /  e2 n  )1/ 2 (where ε 0 , ε r , k B , T ,
e and n are the permittivity of vacuum, permittivity of the ZFO films, Boltzmann's
constant, the absolute temperature in kelvins, the elementary charge and the density of
carriers, respectively) is ~ 0.1 nm with conditions of ε r  10 [5], T=296 K , and
n=1.6 1021 / cm3 [6]. It means that the electric field will be screened at the interface and
could not affect the film’s transport property. As the consequence, the ferroelectric
polarization would not lead to a considerable change in the number of the density of
carriers and thus a weak ferroelectric-field effect. Meanwhile, dependence of resistance
modulation on the type of carrier was also investigated. The carrier in the ZFO films has
been proved to be n type [6]. If ferroelectric-field effect had an effective influence on the
major carrier concentration, charge carriers would accumulated (depleted) at the interface
under positive (negative) polarization. Consequently, resistance would be decreased
(increased) when electric field from the gate to film poled positively (negatively) the
PMN-PT substrate. It is contradictory to our experiment that the resistance decreases for
both positive and negative electric field. Therefore, ferroelectric-field effect might be
excluded and the resistance variation can be safely attributed to the strain effect.
The estimation of the in-plane compressive strain
It is reasonable that the in-plane strain 11 and  22 along <100> and <010>
directions are isotropic in the <001>-oriented epitaxial ZFO film. Therefore, the in-plane
compressive strain 11 stored in the film was estimated using the following relation:
11  ((1  ν) / (2ν))ε33 , where ν is the Poisson’s ratio with the value of 0.26 [7]. Here the
Poisson’s ratio of its parent compound Fe3O4 was used to estimate the in-plane strain as
they have similar crystalline. The out-of-plane strain was estimated by
ε33   c  E   c  0  / c(0) , where c  E  and c(0) are the out-of-plane lattice parameter of
ZFO film under E and zero electric field as shown in Fig. 1(d) (circular line).
The tunability of resistance at 80 K
Resistance at low temperature (80 K) has a different behavior as compared with that
3
at 296 K. Fig. S2(a) shows that the resistance was decreased by positive electric field, but
increased by negative electric field. Fig. S2(b) shows the tunability of resistance loop
with a shuttlelike shape which is also different from the high-temperature one. This
behavior
has
been
observed
in
La0.7Ca0.3MnO3/PMN-0.3PT
[8]
and
(Pr1-yLay)0.7Ca0.3MnO3/PMN-0.28PT [9] at low temperature. In our ZFO/PMN-PT
heretostructure, we attributed this result to the drastic change of the coercive field of the
substrate. Hysteresis loop does not saturate even electric field is scanned between +12
kV/cm and -12 kV/cm at 80 K, therefore, the coercive field should be higher than the
applied maximum electric field of 6.7 kV/cm at this temperature. Ferroelectric-field
effect can also be neglected at low temperature as discussed above. The estimated
characteristic screen length L D is about 1.1 nm at 80 K. The only explanation is that the
PMN-PT stays in the initial polarization state and only its degree of compression was
changed by the applied field.
0.1
(a)
0
-1
0.0
0.0
1
-0.1
0
-0.2
0
50
100
150
200
Electric field (kV/cm)
R/R (%)
0.2
250
Time (a.u.)
(b)
R/R ()
2
1
0
-1
-2
-9
-6
-3
0
3
6
9
Electric field (kV/cm)
Fig. S2 (a)The tunability of resistance (dotted line) as a function of time under electric
field (plain line) of +1.0 kV/cm (up, poled with +8.3 kV/cm for 10 mins) and -1.0 kV/cm
(down, poled with -8.3 kV/cm for 10 mins) switched on and off at 80 K. (b) The
4
tunability of resistance loop as functions of bipolar electric field at 80 K.
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