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Voltage control of magnetism in FeGaB/PIN-PMN-PT multiferroic heterostructures for
high-power and high-temperature applications
Zhongqiang Hu, Tianxiang Nan, Xinjun Wang, Margo Staruch, Yuan Gao, Peter Finkel, and Nian X. Sun
Citation: Applied Physics Letters 106, 022901 (2015); doi: 10.1063/1.4905855
View online: http://dx.doi.org/10.1063/1.4905855
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/106/2?ver=pdfcov
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APPLIED PHYSICS LETTERS 106, 022901 (2015)
Voltage control of magnetism in FeGaB/PIN-PMN-PT multiferroic
heterostructures for high-power and high-temperature applications
Zhongqiang Hu,1 Tianxiang Nan,1 Xinjun Wang,1 Margo Staruch,2 Yuan Gao,1
Peter Finkel,2 and Nian X. Sun1,a)
1
Department of Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts 02115,
USA
2
U.S. Naval Research Laboratory, Washington, DC 20375, USA
(Received 9 December 2014; accepted 31 December 2014; published online 12 January 2015)
We report strong voltage tuning of magnetism in FeGaB deposited on [011]-poled Pb(In1/2Nb1/2)O3Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ternary single crystals to achieve more than 2 times
broader operational range and increased thermal stability as compared to heterostructures based on
binary relaxors. Voltage-induced effective ferromagnetic resonance field shift of 180 Oe for electric
field from 6.7 kV/cm to 11 kV/cm was observed in FeGaB/PIN-PMN-PT heterostructures. This
strong magnetoelectric coupling combined with excellent electric and temperature stability makes
FeGaB/PIN-PMN-PT heterostructures potential candidates for high-power tunable radio frequency/
C 2015 AIP Publishing LLC.
microwave magnetic device applications. V
[http://dx.doi.org/10.1063/1.4905855]
Multiferroic composites with combined ferromagnetic
(FM) and ferroelectric (FE) phases have attracted extensive
attention due to their strong magnetoelectric (ME) coupling at
room temperature.1–4 Specifically in magnetic-piezoelectric
heterostructures, the voltage applied to the piezoelectric layer
produces a mechanical deformation that couples to the magnetic layer, and thus induces a change in the magnetic anisotropy.5–7 The strong ME coupling in the multiferroic
heterostructures exhibits promising applications in tunable radio frequency (RF) microwave devices,8–10 low-power spintronic devices,11–13 and magnetic field sensors.14,15
Recently, large voltage-induced effective FM resonance
(FMR) field has been demonstrated in multiferroic composites using relaxor-based lead magnesium niobate–lead titanate (PMN-PT) and lead zinc niobate–lead titanate (PZNPT) single crystals with high piezoelectric coefficients.16–18
Unlike conventional devices where the Oersted fields generated by large electric current are used for FMR tuning, the
voltage tuning is more power efficient as the bias voltage
applied on single crystals involves minimal electric current.
Therefore, these magnetic-piezoelectric heterostructures
show great potential for the next-generation of compact,
lightweight, and energy-efficient RF microwave devices.
However, the operational electric field (E-field) range has
been limited by the electric coercive field. For example, the
largest tunability is typically achieved between 2 and
6 kV/cm for multiferroic composites based on binary
PMN-PT and PZN-PT due to their low coercive field
(2 kV/cm).17,18 Under high electric field, the devices are
susceptible to failure from corona breakdown induced by
bias fields, which have hindered their applications in highpower devices. Moreover, the low temperature stability of
rhombohedral phase with a rhombohedral to tetragonal
a)
Author to whom correspondence should be addressed. Electronic mail:
[email protected].
0003-6951/2015/106(2)/022901/4/$30.00
transition at TRT 75–95 C would lead to undesirable
changes in performance with temperature.
To expand the operational electric field range and
enhance the temperature stability of piezo-crystal-based multiferroic composites, in this work, the [011]-poled ternary
single crystals lead indium niobate–lead magnesium niobate–lead titanate (PIN-PMN-PT) are used to fabricate FeGaB/
PIN-PMN-PT heterostructures. PIN-PMN-PT single crystals
have much higher dielectric breakdown strength than those
binary piezoelectric crystals due to the large coercive field
(6 kV/cm), while maintaining the excellent piezoelectric
properties with higher temperature operational range with
TRT > 120 C.19–22 Besides, (Fe80Ga20)88B12 films are wellknown magnetostrictive materials with a high piezomagnetic
coefficient of 7 ppm/Oe at low saturation field of 30 Oe.
The FeGaB films also exhibit narrow FMR linewidth of
<20 Oe at X-band (9.5 GHz), which is advantageous in RF
device application comparing to other metallic ferromagnetic
thin films.23 Therefore, large voltage tuning of FMR field is
expected in FeGaB/PIN-PMN-PT heterostructures. With
higher electric coercive field and higher TRT for PIN-PMNPT,19–22 multiferroic FeGaB/PIN-PMN-PT heterostructures
can be potentially useful for high-power tunable RF/microwave devices with wide temperature operational range.
Multiferroic composites FeGaB/PIN-PMN-PT were prepared by co-sputtering of Fe80Ga20 and B targets onto (011)poled PIN-PMN-PT substrates with a base pressure below
1 107 Torr at room temperature. The thickness of FeGaB
film is determined to be 50 nm by fitting the X-ray reflectivity (XRR). 5 nm Cu was then sputtered on top of the FeGaB
as a capping layer. Ferroelectric property of PIN-PMN-PT
was measured by the Radiant Ferroelectric characterization
system. The strain vs E-field curve was measured using a
photonic sensor by sweeping the sinusoidal electric field.
The ferromagnetic resonance spectra were measured using
an X-band electron spin resonance (ESR) spectrometer in
the field sweeping mode with a microwave frequency of
106, 022901-1
C 2015 AIP Publishing LLC
V
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Hu et al.
9.5 GHz and a power of 20 dBm. The magnetic hysteresis loops were measured using a vibrating sample magnetometer (VSM, Lakeshore 7400). During the VSM and FMR
measurements, the DC voltages were applied across the
thickness direction of the PIN-PMN-PT, which was coated
with Au on the back as the bottom electrode and the 5 nm Cu
as the top electrode.
Figure 1 shows the polarization and piezoelectric strain
of (011)-oriented PIN-PMN-PT single crystals as a function
of electric field. The ferroelectric property of PIN-PMN-PT
was characterized at a maximum amplitude of the alternating
electric field of 10 kV/cm and a frequency of 10 Hz. A remanent polarization (Pr) of 25 lC/cm2 was measured for PINPMN-PT, comparable to that of relaxor-based PMN-PT and
PZT-PT.19–22 (011)-oriented PIN-PMN-PT exhibits large inplane piezoelectric coefficients of d31 ¼ 2000 pC/N [100]
and d32 ¼ 1200 pC/N [01–1].19–22 The maximum in-plane
biaxial strain was 0.25% along [01–1] direction.24–26
Given that the FeGaB film is very thin compared to the PINPMN-PT (011) substrate, it would experience the same strain
states as the PIN-PMN-PT under electric field. Therefore,
large voltage-induced in-plane biaxial strain is expected
within the FeGaB film, allowing voltage control of magnetism by strain-mediated magnetoelectric coupling. More
importantly, the electric coercive field of ternary PIN-PMNPT crystal was 6.7 kV/cm, more than triple that of binary
PMN-PT and PZN-PT. This high coercive field would ensure
a larger operational voltage range and better stability, which
is essential for high-power device applications. High-power
here means both high voltage handling capability (due to
high coercive field) and high output power (due to the large
piezoelectric deformation involved).
Figure 2(a) shows the in-plane magnetic hysteresis loops
of the FeGaB/PIN-PMN-PT multiferroic heterostructures
along the [01–1] direction of the PIN-PMN-PT single crystal
at various electric fields. At zero E-field, well-defined magnetic hysteresis loop with a small magnetic coercive field of
15 Oe was observed. When applying electric fields through
the thickness direction of the PIN-PMN-PT substrate, the remanent magnetization of FeGaB decreased with the
FIG. 1. Polarization and piezoelectric strain of (011) oriented PIN-PMN-PT
as a function of electric field, where the electric coercive field was found at
66.7 kV/cm.
Appl. Phys. Lett. 106, 022901 (2015)
FIG. 2. (a) Magnetic hysteresis loops of FeGaB/PIN-PMN-PT heterostructures measured at various electric fields along the [01-1] direction and (b)
Normalized magnetization at a low magnetic bias field (i.e., 5 Oe) as a function of E-field.
magnetic coercive field increased. Figure 2(b) demonstrates
the normalized magnetization M/Ms as a function of E-field
at a low magnetic bias field of 5 Oe. The butterfly shape
(Fig. 2(b)) curve was observed similar to the strain-field
curve in Fig. 1, suggesting a strong strain-driven magnetoelectric coupling between FeGaB and PIN-PMN-PT substrate. The normalized magnetization was varied almost by a
factor of 3 within a range of E-field from 6.7 kV/cm to
11 kV/cm. This is consistent with the results in Fig. 2(a),
implying a large E-field-induced negative effective magnetic
field (Heff) along [01–1] direction.
The field-sweep FMR spectra of the FeGaB/PIN-PMNPT multiferroic composites under different electric fields are
shown in Fig. 3(a). A microwave cavity operating at TE102
mode and X-band (9.5 GHz) was used to perform FMR
measurements of the ferromagnetic/piezoelectric multiferroic heterostructures. The external bias magnetic field was
applied along the in-plane direction of the FeGaB film and
along the PIN-PMN-PT [100] (Fig. 3(a)) or [01–1] direction
(Fig. 4(a)). Clearly, strong ME interaction was observed in
FeGaB/PIN-PMN-PT, which resulted in a large shift of the
effective FMR field from 891 Oe to 1033 Oe, when the
applied electric field was changed from 6.7 kVcm to 11
kVcm. A butterfly-like curve of the effective FMR field
(Heff) as a function of electric field was observed, as shown
in Fig. 3(b), having a maximum Heff tunability of 142 Oe.
The effective magnetic field as a function of E-field shares a
similar shape with that of the piezoelectric strain (r) of
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Hu et al.
Appl. Phys. Lett. 106, 022901 (2015)
FIG. 3. (a) FMR spectra of FeGaB/PIN-PMN-PT at various E-fields with
the external magnetic fields along [100] direction of PIN-PMN-PT and (b)
Effective FMR field as a function of E-field.
PIN-PMN-PT, which has a sudden jump at the electric coercive field of >6.7 kV/cm. This link between the Heff-E and
r-E curves demonstrates the control of the effective magnetic field by E-field via strain mediated mechanism.
Although the screening charges induced by ferroelectric
polarization may exist at the interface of FeGaB and PINPMN-PT, the interfacial charge mediated ME coupling is
negligible because the FeGaB has a thickness of 50 nm.17,18
Thus, pure strain mediated magnetoelectric coupling was
controlled by the electric field applied on the PIN-PMN-PT
due to the piezoelectric effect.
According to Kittel equation, the in-plane FMR frequency can be expressed as17
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
f ¼ c ðH þ Hef f ÞðH þ Hef f þ 4pMs Þ;
(1)
where c is the gyromagnetic ratio (2.8 MHz/Oe), H is the
external magnetic field, and 4pMs is the magnetization of
FeGaB (1.5 T). The voltage-induced effective FMR field Heff
is
Hef f ¼ 3krE =Ms ;
(2)
in which k is the saturation magnetostriction constant of
FeGaB (70 ppm), and rE is E-field-induced biaxial stress
(compressive along [100] and tensile along [01–1]). It can be
concluded from Eqs. (1) and (2) that the effective FMR field
can be shifted upward or downward, depending on whether
FIG. 4. (a) FMR spectra of FeGaB/PIN-PMN-PT at various E-field with
external magnetic fields along [01-1] direction and (b) Effective FMR field
as a function of E-field for [100] and [01-1] directions.
the external magnetic fields are in the direction of in-plane
[100] or [01–1] of the (011)-cut PIN-PMN-PT.17,18 As
shown in Fig. 3(a), increased FMR fields were observed
when the external magnetic field was applied along [100]
direction. In contrast, when the external field was along
[01–1], the FMR fields were reduced, as shown in Fig. 4(a).
The total FMR field shift was 180 Oe when the external magnetic field was applied parallel to [100] or [01–1] direction
(Fig. 4(b)). This large FMR field shift is comparable to that
of the heterostructures based on PMN-PT and PZN-PT, indicating strong mechanical coupling at the interface between
FeGaB and PIN-PMN-PT, and also constitutes a simple but
effective approach for achieving larger FMR tunability.
From Figs. 3(b) and 4(b), we can see that the operational
E-field range is 6.7–11 kV/cm, almost double the range for
PMN-PT and PZN-PT-based multiferroic composites, as
shown in Table I. Meanwhile, the FMR linewidth of the
FeGaB film, which is a critical parameter for microwave
magnetic materials, stays under 120 6 20 Oe at different electric fields. The ratio between the total tunable magnetic field
and the FMR linewidth is as high as 150%, indicating an
excellent figure of merit for tunable microwave devices.
Please note that the critical working temperature range of single crystal-based device would be determined and limited
by rhombohedral–tetragonal transition temperature (TRT),
i.e., for binaries 75 C, for ternaries 120 C. At this temperature range, it is unlikely that magnetic layer would be a
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Appl. Phys. Lett. 106, 022901 (2015)
TABLE I. Comparison of the key attributes of FeGaB/PMN-PT, FeGaB/PZN-PT, and FeGaB/PIN-PMN-PT multiferroic composites.
Multiferroic composites
FeGaB/PMN-PT27
FeGaB/PZN-PT28
FeGaB/PIN-PMN-PT [this work]
Converse ME
FMR linewidth
Tunable
DH/linewidth
E-field
coupling coefficient
(Oe)
magnetic field DH (Oe)
(%)
range (kV/cm)
(Oe cm/kV)
TRT of piezocrystal ( C)
20
50
120
28
750
180
problem because: (a) 120 C is much lower than the Curie
temperature of FeGaB (Tc > 350 C);29 (b) a proper capping
layer can prevent the magnetic layer from being oxidized;
and (c) thermal annealing experiment shows that small Hc
and minimum FMR linewidth can still be maintained in
FeGaB films treated at 180 C.30 Therefore, the potential
application temperature range could be 25–120 C for
FeGaB/PMNPT.
In summary, we have demonstrated large FMR tunability
through voltage induced, strain mediated ME coupling in
FeGaB/PIN-PMN-PT multiferroic heterostructures. A large
effective magnetic anisotropy field change of 180 Oe was
obtained, comparable to that of the composites based on
PMN-PT and PZN-PT single crystals. The operational E-field
range is 6.7–11 kV/cm, more than double the range for
PMN-PT and PZN-PT-based multiferroic heterostructures.
With a high phase transition temperature TRT > 120 C for
PIN-PMN-PT, FeGaB/PIN-PMN-PT heterostructures have
shown great potential for high-power tunable RF/microwave
device applications with wider temperature operational range.
The work was supported by AFRL through FA8650-14C-5705, Winchester Technologies, LLC, and National
Natural Science Foundation of China (NSFC) 51328203.
Funding for author P.F. was provided by the Office of Naval
Research (ONR) through the Naval Research Laboratory’s
Basic Research Program. M.S. was supported in part by the
National Research Council under the Research Associateship
Program.
1
W. Eerenstein, N. D. Mathur, and J. F. Scott, Nature 442, 759 (2006).
N. A. Spaldin and R. Ramesh, MRS Bull. 33, 1047 (2008).
C. W. Nan, M. I. Bichurin, S. X. Dong, D. Viehland, and G. Srinivasan,
J. Appl. Phys. 103, 031101 (2008).
4
S. X. Dong, J. Zhai, J. Li, and D. Viehland, Appl. Phys. Lett. 89, 252904
(2006).
5
G. Subramanyam, M. W. Cole, N. X. Sun, T. S. Kalkur, N. M. Sbrockey,
G. S. Tompa, X. Guo, C. Chen, S. P. Alpay, G. A. Rossetti, K. Dayal, L.Q. Chen, and D. G. Schlom, J. Appl. Phys. 114, 191301 (2013).
2
3
140
1500
150
2–6
0–8
6.7–11
3.5
94
10.2
75–95
75–95
>120
6
N. X. Sun and G. Srinivasan, SPIN 2, 1240004 (2012).
M. Liu and N. X. Sun, Philos. Trans. R. Soc., A 372, 20120439 (2014).
8
X. Yang, J. Wu, Y. Gao, T. Nan, Z. Zhou, S. Beguhn, M. Liu, and N. X.
Sun, IEEE Trans. Magn. 49, 3882 (2013).
9
A. B. Ustinov, G. Srinivasan, and B. A. Kalinikos, Appl. Phys. Lett. 90,
031913 (2007).
10
J. Das, Y.-Y. Song, N. Mo, P. Krivosik, and C. E. Patton, Adv. Mater. 21,
2045–2049 (2009).
11
J. Hu, Z. Li, L.-Q. Chen, and C.-W. Nan, Nat. Commun. 2, 553 (2011).
12
T. Nan, Z. Zhou, J. Lou, M. Liu, X. Yang, Y. Gao, S. Rand, and N. X.
Sun, Appl. Phys. Lett. 100, 132409 (2012).
13
E. Y. Tsymbal, Nat. Mater. 11, 12–13 (2011).
14
T. Nan, Y. Hui, M. Rinaldi, and N. X. Sun, Sci. Rep. 3, 1985 (2013).
15
J. Zhai, Z. Xing, S. Dong, J. Li, and D. Viehland, Appl. Phys. Lett. 88,
062510 (2006).
16
M. Liu, O. Obi, J. Lou, Y. Chen, Z. Cai, S. Stoute, M. Espanol, M. Lew,
X. Situ, K. S. Ziemer, V. G. Harris, and N. X. Sun, Adv. Funct. Mater.
19(11), 1826–1831 (2009).
17
M. Liu, Z. Zhou, T. Nan, B. M. Howe, G. J. Brown, and N. X. Sun, Adv.
Mater. 25(10), 1435–1439 (2013).
18
T. Nan, Z. Zhou, M. Liu, X. Yang, Y. Gao, B. A. Assaf, H. Lin, S. Velu,
X. Wang, H. Luo, J. Chen, S. Akhtar, E. Hu, R. Rajiv, K. Krishnan, S.
Sreedhar, D. Heiman, B. M. Howe, G. J. Brown, and N. X. Sun, Sci. Rep.
4, 3688 (2014).
19
J. Tian, P. Han, X. Huang, H. Pan, J. F. Carroll, and D. A. Payne, Appl.
Phys. Lett. 91, 222903 (2007).
20
S. Zhang, J. Luo, W. Hackenberger, and T. R. Shrout, J. Appl. Phys. 104,
064106 (2008).
21
E. Sun, S. Zhang, J. Luo, T. R. Shrout, and W. Cao, Appl. Phys. Lett. 97,
032902 (2010).
22
P. Finkel, C. J. Murphy, J. Stace, K. Bussmann, A. Heitmann, and A.
Amin, Appl. Phys. Lett. 102, 182903 (2013).
23
J. Lou, R. E. Insignares, Z. Cai, K. S. Ziemer, M. Liu, and N. X. Sun,
Appl. Phys. Lett. 91, 182504 (2007).
24
P. Finkel, K. Benjamin, and A. Amin, Appl. Phys. Lett. 98, 192902 (2011).
25
P. Finkel, A. Amin, S. Lofland, J. Yao, and D. Viehland, Phys. Status
Solidi A 209, 2108–2113 (2012).
26
M. Staruch, J. F. Li, Y. Wang, D. Viehland, and P. Finkel, Appl. Phys.
Lett. 105, 152902 (2014).
27
J. Lou, D. Reed, C. Pettiford, M. Liu, P. Han, S. Dong, and N. X. Sun,
Appl. Phys. Lett. 92, 262502 (2008).
28
J. Lou, M. Liu, D. Reed, Y. Ren, and N. X. Sun, Adv. Mater. 21(46),
4711–4715 (2009).
29
K. Fukamichi, T. Satoh, and T. Masumoto, J. Magn. Magn. Mater. 31,
1589 (1983).
30
L. R. Shah, X. Fan, X. Kou, W. G. Wang, Y. P. Zhang, J. Lou, N. X. Sun,
and J. Q. Xiao, J. Appl. Phys. 107, 09D909 (2010).
7
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