Strong non-volatile voltage control of magnetism in magnetic/antiferroelectricmagnetoelectric heterostructuresZ. Zhou, X. Y. Zhang, T. F. Xie, T. X. Nan, Y. Gao, X. Yang, X. J. Wang, X. Y. He, P. S. Qiu, N. X. Sun, and D. Z.

Sun Citation: Applied Physics Letters 104, 012905 (2014); doi: 10.1063/1.4861462 View online: http://dx.doi.org/10.1063/1.4861462 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/104/1?ver=pdfcov Published by the AIP Publishing

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Strong non-volatile voltage control of magnetism in magnetic/antiferroelectricmagnetoelectric heterostructures

Z. Zhou,1,a) X. Y. Zhang,2,a) T. F. Xie,2 T. X. Nan,1 Y. Gao,1 X. Yang,1 X. J. Wang,1

X. Y. He,3 P. S. Qiu,3 N. X. Sun,1,b) and D. Z. Sun1,2,b)

1Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Avenue,Boston, Massachusetts 02115, USA2Key Laboratory of Resource Chemistry of Education Ministry, Department of Chemistry,Shanghai Normal University, 100 Guilin Road, Shanghai 200234, China3Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, China

(Received 13 November 2013; accepted 21 December 2013; published online 8 January 2014)

Strong magnetoelectric coupling was demonstrated in magnetic/antiferroelectric heterostructures

of FeGaB/Pb(La,Sn,Zr,Ti)O3, which exhibited a voltage induced coercive field change of 7–10 Oe

and ferromagnetic resonance field shifts by �80 Oe. Nonvolatile voltage induced magnetization

switching and ferromagnetic resonance field shift in FeGaB were realized based on the

ferroelectric-antiferroelectric phase transition in Pb(La,Sn,Zr,Ti)O3. The nonvolatile strong voltage

control of magnetism in magnetic/antiferroelectric heterostructures has great implications in

compact and power efficient spintronics and RF/microwave components. VC 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4861462]

In past decade, attracted by the increasing demand of

compact, fast, and low power consumption RF/microwave

devices and spintronic devices, lots of researchers have

devoted their efforts to realizing electric field (E-field) or

voltage control of magnetism, instead of magnetic field

(H-field).1–25 For instance, state of the art RF/microwave

magnetic devices relies on bulky, noisy, slow, and energy

consuming electromagnets for the tuning, which severely

limits their applications in mobile systems, such as aircrafts,

satellites, radars, and mobile communication systems.

Recently, multiferroic composites with combined ferromag-

netic (FM) and ferroelectric (FE) phases have been widely

studied for achieving E-field or voltage control of magnetism

for spintronics and tunable RF/microwave applications,6–10

including voltage tunable resonators,6 magnetic field

sensors,7 tunable inductors,8 and tunable filters.9,10 The

strain mediated magnetoelectric (ME) coupling allows E-

field control of ferromagnetism.1–17 Most prior works are

focused on ME coupling in FM/FE heterostructures, such

as, NiCr/PZT,11 FeGaB/PZT (Lead zirconate titanate),12

FeGaB/PZNPT (lead zinc niobate-lead titanate),13 FeCoB/

PMNPT (lead magnesium niobate-lead titanate),14 Terfenol-D

(Tb-Dy-Fe)/PZNPT,16 etc. Giant ME coupling coefficient up

to �600 Oe cm/kV was obtained in single crystal FE substrate

based multiferroic heterostructures.16 Nevertheless, the appli-

cations of single crystal FE slabs are limited by their fragility

after hundreds of voltage cycles.

Compared to conventional ferroelectric ceramics, anti-

ferroelectric (AFE) ceramics26–31 have a large piezoelectric

strain up to �300 ppm,27 much higher than that of PZT with

a typical piezoelectric strain of �60 ppm (Refs. 11 and 12)

due to electric-field induced AFE-FE phase transition, where

the atom arrangements in FE phase are more dilute than that

in AFE phase.30,31 Strong magnetoelectric coupling can be

expected in FM/AFM (antiferromagnetic) heterostructures

due to the large achievable strain in AFM ceramics. Besides

magnetoelectric coupling strength, another property of fun-

damental importance in magnetoelectric multiferroic hetero-

structures is non-volatility of the magnetoelectric coupling.

Conventional voltage tunable RF/microwave devices were

demonstrated at constant applied voltage and have not pro-

ven to be non-volatile.6–10

Efforts have been made to achieve non-volatile magne-

toelectric coupling in FM/FE heterostructures.12–14,17 In

(011) oriented PMN-PT slab, for example, by applying

E-field close to the coercive fields back and forth, non-180�

ferroelastic polarization switches induced non-volatile strain

states were observed.14,17 Non-volatile voltage control of

magnetic properties was realized in FeCoB/PMN-PT,14

Ni/PMN-PT,17 and FeGaB/PZT ceramic heterostructure.12

Further, Liu et al. revealed non-volatile tuning in FeGaB/

PZN-PT heterostructure through E-field induced phase tran-

sition in PZN-PT single crystal substrate.13

In this work, we report on strong non-volatile magnetoelec-

tric coupling in a FeGaB/PSZT (La-modified Pb(Sn,Zr,Ti)O3)

FM/AFE heterostructures through voltage induced AFE to FE

phase transition in PSZT. Strong voltage induced ferromagnetic

resonance (FMR) field shift of �80 Oe induced was demon-

strated in FMR field measurements. By introducing E-field

induced anti-ferroelectric/ferroelectric phase transition in PSZT

ceramic into multiferroic system, a non-volatile magnetoelectric

coupling was demonstrated. The strong magnetoelectric cou-

pling with voltage impulse induced non-volatile magnetization

switching in FeGaB/PSZT magnetoelectric/antiferroelectric het-

erostructures constitutes an approach to achieve strong magneto-

electric coupling in FM/AFE heterostructures, which can have

great technological implications.

Magnetic/AFE FeGaB/PSZT heterostructures were pre-

pared by co-sputtering of Fe0.70Ga0.30 and B targets onto

a)Z. Zhou and X. Y. Zhang contributed equally to this work.b)Authors to whom correspondence should be addressed. Electronic

addresses: sundazhi@shnu.edu.cn and nian@ece.neu.edu. Tel.: þ1-(617)-

373 3351.

0003-6951/2014/104(1)/012905/4/$30.00 VC 2014 AIP Publishing LLC104, 012905-1

APPLIED PHYSICS LETTERS 104, 012905 (2014)

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La-modified PSZT ceramic substrates (8 mm� 3 mm� 0.5 mm)

with a base pressure below 1� 10�7 Torr at room temperature.

100 nm amorphous FeGaB films were deposited on the top or

on the side of the PSZT ceramics (Fig. 1(a)), and 5 nm Cr layers

were deposited between them to improve adhesion. The

La-modified PSZT ceramics (with density of 7.0 g/cm3) with

composition of Pb0.96La0.04(Zr0.45Sn0.36Ti0.18)O3 were prepared

by a conventional solid-state reaction process. Raw powders

were mixed with Al2O3 balls in deionized water by ball-milling

for 2 h. The mixtures were calcined at 850 �C for 2 h after

being dried. After ball-milling, the powder was pressed into

disks and the green compacts were sintered at 1340 �C for 2 h

in lead ambiance. The ferroelectric/antiferroelectric and

piezo-strain properties were measured by a P-E hysteresis looper

and a photonic sensor. The magnetization measurements of

FeGaB/PSZT were carried out by using a vibrating sample mag-

netometer (VSM). Field sweep FMR field measurements were

carried out by electron spin resonance (ESR) spectrometer at

X-band. A DC E-field was applied across the thickness direction

of PSZT during VSM and FMR measurements, see Fig. 1(a).

The X-ray diffraction (XRD) pattern of PSZT ceramics

was measured with a Cu Ka source (k¼ 1.541 A), see Fig.

1(b). The polarization vs. applied E-field (P-E) loop shows a

typical antiferroelectric P-E loop,26–28 which indicates the

anti-ferroelectric phase of PSZT ceramic, see Fig. 1(c). As

applied E-field is larger than 20 kV/cm, associated with the

polarization increases from 0 to 18 lC/cm2, the orthorhom-

bic (pseudo-tetragonal)29 anti-ferroelectric phase is changed

into a rhombohedral ferroelectric phase, leading to a large

E-field induced strain change along d33 the side orientation,

see Fig. 1(c).26–32 A large strain was expected due to crystal

elongation along c-axis during the transition. The

antiferroelectric-ferroelectric phase transition in PSZT sub-

strates offers the opportunity to obtain a strong magnetoelec-

tric coupling coefficient due to large strain change,

furthermore, the hysteretic strain dependence of E-field27

also provides the possibility of voltage impulse induced

non-volatile switch.12–14,17 As shown in Fig. 1(c), we applied

E-field from 0 kV/cm to 30 kV/cm and then back to 0 kV/cm,

the strain dependence of E-field follows an identical hyste-

retic behavior due to PSZT ferroelectric/antiferroelectric

phase transition. At applied E-field of 15 kV/cm, two strain

states (see Fig. 1(c), green and blue square) were created

through AFE-FE phase transition, which provides the

non-volatility and voltage impulse controllability. After de-

posited FeGaB thin film, the surface roughness of PSZT top

surface is �15 nm, see Fig. 1(d). The Atomic Force

Microscopy (AFM) image of PSZT side surface is similar to

PSZT top surface due to identical polishing process and dep-

osition method.

Figure 2 shows the magnetic hysteresis (M-H) loops

measured under varied E-fields applied across the thickness

direction of PSZT. The FeGaB layer is either on the top

(Fig. 2(a)) or the side (Fig. 2(b)) of PSZT substrates. We

studied both cases to obtain the optimized tunability and

non-volatility in controlling the magnetization or FMR fields

of FeGaB/PSZT system by using the d31 (Fig. 2(a) for

FeGaB on top) and d33 (Fig. 2(b) for FeGaB on side) of the

PSZT slab. The upper left inset of Fig. 2(a) shows the

enlarged magnetization change under varied E-field around

HC, and the inset of Fig. 2(b) shows remanent magnetization

Mr change under varied E-field. The coercivity HC of the

FeGaB film on top of PSZT, Fig. 2(a), was increased from

35 Oe to 41 Oe by applying an E-field from 0 kV/cm to

30 kV/cm. On the contrary, the HC of the FeGaB film on the

side of PZT (Fig. 2(b)) was decreased from 39 Oe to 27 Oe at

the same condition. Meanwhile, the remanent magnetization

of the FeGaB on side was reduced by 30% at zero magnetic

field. The opposite HC variation trends tuned by E-field are

resulted from opposite d31 (top) and d33 (side) change trends

induced by E-field.28

Further, we examined the non-volatility of these M-H

loops, for FeGaB(top)/PSZT heterostructure, there exists a

significant difference between the two M-H loops measured

FIG. 1. (a) The schematic of FeGaB

film deposited on the top or on the side

of Pb(Sn,Zr,Ti)O3 ceramics. E-field is

applied across PSZT layer. (b) X-ray

diffraction pattern of PSZT ceramics.

(c) Polarization and strain vs. E-field

loop of Pb(Sn,Zr,Ti)O3 ceramic mate-

rial, correspondingly. The colored dots

represent different strain state induced

by varied applied E-field. (d) The

AFM image of PSZT surface (top)

with FeGaB thin film.

012905-2 Zhou et al. Appl. Phys. Lett. 104, 012905 (2014)

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at 15 kV/cm E-field, one(green) is increased from 0 kV/cm,

the other one (blue) is decreased from 30 kV/cm, see Figs.

2(a) and 2(b). This difference of M-H loops at same applied

E-field can be explained by the two strain states at 15 kV/cm

E-field resulting from AFE-FE phase transition, see Fig. 1(c).

With applied bias magnetic field of 40.5 Oe, we switched the

E-field, and the magnetization was changed from 500 G to

�500 G, where DM/M¼ 17%, with non-volatility, see the left

inset of Fig. 2(a). For FeGaB(side)/PSZT heterostructure, see

Fig. 2(b), non-volatile E-field induced M-H loops switching

was also obtained. The largest remanent magnetization switch

back and forth was achieved, corresponding to DM¼ 50 G.

Figs. 2(c) and 2(d) show FMR field spectra of

FeGaB/PSZT multiferroic heterostructure, top and side,

respectively, under varied E-field. The insets of both figures

represent the FMR field dependence of applied E-field.

External magnetic field was applied in plane of FeGaB thin

film (top and side). For FeGaB(top), the maximum FMR field

switch is 32 Oe, from E-field of 0 kV/cm to 30 kV/cm, corre-

sponding to ME coupling coefficient a¼DH/DE¼ 1.1 Oe

cm/kV. For FeGaB(side), the maximum FMR field switch is

81 Oe, leading to large ME coupling coefficient a¼DH/DE

¼ 2.7 Oe cm/kV. The E-field induced in-plane anisotropy field

change can be simulated by piezoelectric and inverse

magneto-elastic equations.11,12 The FMR field Hr dependence

of applied E-field is similar to the hysteric strain dependence

of E-field, see Figs. 1(c) and 1(d) and Figs. 2(c) and 2(d),

which implies non-volatile switch of FMR field. The in-plane

FMR frequency can be expressed by well-known Kittel

equations

f ¼ cffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðHr þ Hk þ Hef f ÞðHr þ Hk þ Hef f þ 4pMSÞ

q; (1)

where c is the gyromagnetic ratio (2.8 MHz/Oe), Hr is the FMR

field, Hk is the in-plane anisotropic field, and 4pMS is the mag-

netization of 1.3 T.13 Heff is compressive and tensile stress

corporately induced internal effective magnetic field. The FMR

field shift DHr can be derived directly from equation

DHr ¼ DHef f ¼3kSeY

MS: (2)

Here, Y is Young’s modulus of 55 GPa and ks is magne-

tostriction of 70 ppm The FMR field shift is directly propor-

tional to the E-field induced effective piezo-strain, where e33

is 0.07% for PSZT slab at applied E-field of 30 kV/cm, see

Figs. 1(c) and 1(d). From Eq. (2), we can calculate effective

magnetic field DHeff¼ 84 Oe for FeGaB(side), which is very

close to our experimental result of 81 Oe. For FeGaB(top), we

have e31� 0.5e33 (Ref. 28) in PSZT ceramics, DHeff¼ 42 Oe,

close to 31 Oe experimental result.

Based on the E-field induced non-volatile switches of

magnetization at bias applied magnetic field and FMR field

in FeGaB/PSZT multiferroic heterostructure, as shown in

Fig. 2, the mechanism of voltage impulse (100 ms) tunable

magnetization and FMR field can be designed. Figs. 3(a) and

3(b) show the voltage impulse tuned FeGaB magnetization

at certain bias magnetic field, by maintaining a constant E-

field of 15 kV/cm, the E-field impulse(<100 ms) with ampli-

tude of �15 kV/cm or 15 kV/cm was applied periodically. In

FeGaB(top)/PSZT heterostructure, see Fig. 3(a), the magnet-

izations were switched between 500 G and �500 G back and

forth at 40.5 Oe applied bias magnetic field. Fig. 3(b) shows

the remanent magnetizations switched back and forth in

FeGaB(side)/PSZT heterostructure induced by voltage

impulses, from 113 G to 50 G. The FMR fields switched by

voltage impulse were also measured. For FeGaB(top)/PSZT

heterostructure, the FMR fields were switched from

�1015 Oe to �995 Oe by voltage impulse, as shown in Fig.

3(c), and the FMR fields were switched from �2094 Oe to

�2043 Oe under the same condition in FeGaB(side)/PSZT

heterostructure, see Fig. 3(d).

FIG. 2. (a) M-H loops under varied E-

field of FeGaB(top)/PSZT multifer-

roics heterostructure. The inset repre-

sents the larged magnetization change

under varied E-field around HC, and

the inset of Fig. 2(b) shows remanent

magnetization Mr change under

varied E-field. (b) M-H loops of

FeGaB(side)/PSZT multiferroics heter-

ostructure. The inset represents rema-

nent magnetization Mr change under

varied E-field. (c) FMR spectra under

varying E-field of FeGaB(top)/PSZT

multiferroics heterostructure. The inset

shows FMR field dependence of E-field.

(d) FMR spectra of FeGaB(side)/PSZT

multiferroics heterostructure. The inset

shows FMR field dependence of E-field.

012905-3 Zhou et al. Appl. Phys. Lett. 104, 012905 (2014)

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In summary, we have demonstrated a strong non-

volatile voltage control of magnetization through E-field-

induced antiferroelectric/ferroelectric phase transition in

PSZT. These magnetic/antiferroelectric heterostructures with

strong non-volatile voltage control of magnetism constitute

great candidates for next-generation voltage-impulse-con-

trolled lightweight, power efficient, spintronics and RF/

microwave devices.

This work was financially supported by AFRL through

UES Subcontract No. S-875-060-018, Semiconductor Research

Corporation, and National Natural Science Foundation of

China (NSFC) Nos. 51328203 and 51132001.

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FIG. 3. (a) Magnetization switch of

FeGaB(top)/PSZT under applied H-

field of 40.5 Oe induced by voltage

impulse. (b) Magnetization switch of

FeGaB(side)/PSZT under zero bias

magnetic field induced by voltage

impulse. (c) FMR field switch of

FeGaB(top)/PSZT induced by voltage

impulse. (d) FMR field switch of

FeGaB(side)/PSZT induced by voltage

impulse.

012905-4 Zhou et al. Appl. Phys. Lett. 104, 012905 (2014)

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