(BZT-BCT/LSMO/LAO) Devices for Multiferroic Applications

1 Structural, Electronic, and Magnetic Analysis and Device Characterization of Ferroelectric-Ferromagnetic Heterostructure (BZT-BCT/LSMO/LAO) Devices for Multiferroic Applications

Md Abdullah-Al Mamun1,2 Ariful Haque1,3 Anthony Pelton1, Bithi Paul1, and Kartik Ghosh1

Abstract— Ferroelectricity and ferromagnetism have devices, high sensitivity magnetic field sensors, actuators, etc been investigated in a lead-free 0.5Ba(Zr0.2Ti0.8)O3- [2], [3]. Over the years, researchers have been trying to 0.5(Ba0.7Ca0.3)TiO3(BZT-BCT)/La0.7Sr0.3MnO3(LSMO) combine suitable electrical and magnetic properties in a single heterostructure for multiferroic applications. The BZT-BCT thin film has been grown on LSMO/Lanthanum Aluminate, material to yield new MF materials with desirable performance LaAlO3 (LAO) by pulsed laser deposition (PLD). Prior to [4]. Until now, the most reported MF material is BiFeO3(BFO) that, the LSMO layer was deposited on a single-crystal LAO which displays the coexistence of spontaneous electric and substrate by PLD. The epitaxial growth of the (001) oriented magnetic ordering in the same phase at room temperature films was confirmed by X-ray Diffraction (XRD) analysis. The [2], [5]. However, the limitations of BFO, such as high small value of the full width at half maximum of the rocking curve peak (0.1°) performed about (002) plane of the BZT-BCT leakage current and antiferromagnetism at room temperature, film indicates an out-of-plane orientation of the film. The must be overcome for commercial applications. Researchers polarization switching behavior in the heterostructure device have investigated some other materials, including YMnO3[6], ∼ C cm2 was observed with a remnant polarization of 47 µ / TbMnO3[5], DyMnO3[7], and hexaferrites [8] with limited ∼ kV cm and a coercive field of 180 / at an applied voltage of success. Some researchers also doped rare earth (RE) elements 5V. The frequency-dependent relative dielectric constant varies in-between 5100 and 4900 in the frequency range from 1 kHz and transition metal ions into BFO to enhance the MF proper- to 50 kHz during the dielectric measurements of the fabricated ties [9]. But the RE element as a dopant degrades the ferroelec- device. The observed low value of the dielectric loss (0.02) tric properties [10]. In addition, there are several reports on MF confirms the outstanding quality of the ferroelectric device. A properties of composite materials or heterostructure systems M − H well-saturated room temperature curve, with a coercive such as BFO/CoFe [11] and BFO/CoFeB [12]. However, a field of ∼1200 A/m and a remnant magnetization of ∼110 kA/m, was observed in the LSMO/LAO system indicating the system has yet to be experimentally demonstrated that can be ferromagnetic behavior of the film. The temperature-dependent electrically and magnetically tunable. magnetization of the LSMO film exhibits a ferromagnetic In this study, we have used heterostructure of ferroelectric ∼ to paramagnetic transition at 360 K. These results on all lead (Pb)-free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3(BZT- solid-state ferroelectric-ferromagnetic heterostructure using BCT) and ferromagnetic La Sr MnO (LSMO) to investi- BZT-BCT and LSMO open viable possibilities for multiferroic 0.7 0.3 3 applications. gate MF properties. BZT-xBCT is a solid solution of rhombohedral (R3m) BZT and tetragonal (P4mm) BCT near x = 0.5 Index Terms — Dielectric losses, Ferroelectric capacitor, Leak- with a morphotropic phase boundary (MPB). Fig. 1 shows age currents, Magnetoelectric coupling, Polarization switching. the unit cell structure of BZT-xBCT. Recently, Liu and Ren reported that the bulk ceramics of a Pb-free BZT-xBCT system I. INTRODUCTION has a high piezoelectric coefficient (d33 ∼ 620 pC/N) near the ULTIFERROIC (MF) materials simultaneously exhibit MPB [13]. Their reported piezoelectricity is comparable to that Mferroelectricity and ferromagnetism in the same phase, of Lead Zirconate Titanate (PZT) and even it is superior to that and they can provide desired magnetoelectric coupling of existing Pb-free systems. The improved dielectric, piezo- between the order parameters [1]. Materials with these kind of electric and ferroelectric properties are due to the MPB start- properties have applications in different solid-state fields such ing from a tetragonal-cubic-rhombohedral triple point, which as magnetic data storage, solid-state transformers, spintronic flattens the energy barrier for lattice distortion and polarization rotation from (001)T state to (111)R state [14]. On the other 1Department of Physics, Astronomy, and Materials Science, Missouri State hand, the ferromagnetic LSMO is a mixed-valence manganite, University, Springfield, MO 65897, USA which is an optimal source of fully spin-polarized carriers and 2 Department of Electrical Engineering, University of South Carolina it shows a rich physics of magnetic phases and transport mech- Columbia, SC 29208, USA 3Department of Materials Science and Engineering, North Carolina State anisms [15]. The LSMO shows high-spin polarization due to University, Raleigh, NC 27606, USA its half-metallic nature arising from conducting electrons [15]. Digital Object Identifier: 10.1109/TMAG.2018.2873513

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of 248 nm, a pulse duration of 20 ns, was used with 10 Hz rep-rate for the deposition. Thin films were grown at different growth temperatures (600°C to 850°C) and different oxygen pressures (10 N/m2 to 10−2 N/m2). The best quality films were deposited at 800°C under 40 N/m2 oxygen pressure. The base pressure of the chamber was below 1×10−3 N/m2. After the desired number of PLD shots, the deposited film was cooled down to room temperature maintaining the oxygen pressure at 1.1×104 N/m2. In this study, the thicknesses of BZT-BCT and LSMO thin films were ∼ 95 nm and ∼ 89 nm, respectively. The thicknesses were measured by a profilometer (Veeco, Dektak 150).

Fig. 1. The unit cell structure of BZT-xBCT (tetragonal). B. Sample Characterizations The PLD grown thin films were characterized by X-ray Diffractometer (Bruker, D8 Discover) using θ-2θ scan in the The high-spin feature makes LSMO reliable for applications range of 20° to 80° maintaining the Bragg−Brentano reflection in spin-dependent transport devices [16]. We used LAO as a geometry. A CuKα x-ray source with the wavelength of 1.54 substrate for this heterostructure system for its low dielectric Å was used as an excitation source. The vibrational properties loss [17] and small lattice mismatch with LSMO which is only of the samples were characterized by micro-Raman scattering around −2.1% [18]. In this study, the ferroelectric BZT-BCT (Horiba Labram Raman-PL System) with a 532 nm green thin film, grown by pulsed laser deposition (PLD), shows a laser. The measurements were performed in a back-scattering high degree of polarization with low leakage current while the geometry with 15 seconds exposure time, and 20 accumulation ferromagnetic LSMO continues to show its ferromagnetism cycles. The illuminated spot size was approximately 2.5 µm up to 360K. Combination of such magnificent properties in diameter on the thin film. We were aware of the possible of those individual layers makes this heterostructure system damage of the thin film due to the excitation source. During more directly amenable to fabricating high performance MF Raman measurements the laser energy was chosen in such devices for practical applications. The top ferroelectric thin a way that the sample did not get damaged due to the film is attributed to bring desirable changes in the underlayer overheating produced by the continuous solid-state laser beam. ferromagnetic properties. Details of the structural property cor- The data was collected through an NGS Labspec-5 software in relation of the BZT-BCT/LSMO/LAO heterostructure system the range of 100 cm−1 to 1000 cm−1. The data were analyzed and the device characterization will be subsequently discussed by Gaussian-Lorentzian peak fitting using Origin Pro 8.5.1. in the results and discussion section. Temperature and magnetic field dependent magnetization of the films were characterized by a Superconducting Quan- II. EXPERIMENTAL DETAILS tum Interference Device (SQUID) magnetometer (Quantum A. Sample Preparation Design, MPMS 5XL) interfaced through MultiVu software. The temperature was varied from 5K to 370K. The M − The ferroelectric BZT-BCT ceramic target was prepared by H hysteresis loop of the sample was observed by varying a standard solid-state reaction using high purity chemicals, i.e., magnetic field from -400 kA/m to +400 kA/m. The maximum BaCO (99.9%, Inframat Advanced Materials), CaO (99.95%, 3 sensitivity of the magnetometer was 10−12 Am2. Polarization Alfa Aesar), TiO (99.9%, Sigma-Aldrich), and ZrO (99.9%, 2 2 measurement was carried out by Sawyer-Tower technique. Au- Inframat Advanced Materials), in appropriate proportions. Ti top electrodes were deposited onto the thin film by thermal The agglomeration of the powder particles was prevented by evaporation using a physical mask. The diameter of the elec- adding Polyvinyl alcohol to the mixture. The final mixer was trodes was 100 to 200 µm. The relative dielectric constant and pressed with a ‘hydraulic press’ to form the target. After the loss tangent were measured using a precision LCZ meter that, the prepared target was calcined at 1350°C and then (Hewlett Packard, 428-4A). The data were analyzed through sintered at 1450°C in the air. On the other hand, a high Origin Pro 8.5.1 software. purity (99.9 %) dense LSMO target was purchased from Kurt J. Lesker Company. A chemical mechanical polished (CMP) III. RESULTS AND DISCUSSION highly oriented (001) LAO substrate was purchased from MTI Corporation. The configuration of the substrate was as follows: A. XRD Analysis surface finish (RMS or Ra): < 8Å with free sub-surface Fig. 2a represents the X-ray diffraction (XRD) patterns damaged, under 1000 class clean room, and in 100 grade of BZT-BCT/LSMO and the LSMO thin films on the LAO plastic bags in a wafer container. substrate. It can be observed that both of the samples exhibit Thin films of LSMO and then BZT-BCT were deposited complete single-phase perovskite structures. There is no evi- on LAO substrates by PLD (Excel Instrument, PLD-STD-18) dence of secondary phases such as Ba3Ca2Ti2O9,andthe technique. A KrF excimer laser (Lambda Physik, COMPEX possibility of such impurity was minimized by sintering at 201) with an energy density of 2×10−4 Jm−2, the wavelength 1100°C for 12 hours [19]. Due to the complete solid solubility 3

Fig. 3. High resolution rocking curve profiles for the (a) BZT-BCT (002), Fig. 2. (a) X-ray diffraction pattern of LSMO (red line) and BZT-BCT/LSMO (b) BZT-BCT (003), and (c) LSMO (002) reflections. The FWHM (θ)ofthe (black line) on LAO substrate. (b) The deconvolution of BZT-BCT (002) peak reflections are 0.10°, 0.15°, and 0.37°, respectively. into (200) and (002) peaks, which is a characteristic of the tetragonal crystal structure.

has no Raman active modes while the tetragonal structure of Ca2+ at Ba-site and Zr4+ at Ti-site, at such high sintering shows some characteristic modes [25]. The phases of ABO temperature, no other secondary phases were observed in the 3 type perovskite crystals are interesting. For example, tetrag- present BZT–BCT ceramics. It should be noted that the highly- onal BaTiO has five atoms, and there are fifteen degrees oriented thin films demonstrate a weak splitting in the 2θ 3 of freedom present in each of the unit cell [26]. It behaves range from 43.5° to 44.5°, which could be induced due to as a ferroelectric crystal below its transition temperature the formation of multiple domains, e.g., a- and c-domains, (T ∼120°C) and the vibrational modes are Raman active analogous to the case of PZT [20]. Such splitting of the t up to T [26]. The Raman spectrum of the tetragonal BZT- XRD peak is a unique characteristic of the tetragonal phase in t BCT thin film shown in Fig. 4 exhibits the following six BZT-BCT. The single (002) plane corresponding to the cubic active optical phonon modes: 2 A (TO), 1 A (LO), 1 E(TO), phase transforms into (200) and (002) crystallographic planes, 1 1 1E(LO),and1B. Each of the A and E modes split into which are the characteristics of a tetragonal structure [21]. 1 1 TO (transverse optical) and LO (longitudinal optical) modes The XRD peak splitting, shown in Fig. 2b, corroborates the due to the presence of long-range electrostatic forces [27]. The presence of tetragonal crystallographic structure in both BZT- signature Raman peaks in the PLD grown BZT-BCT thin film BCTandLSMOthinfilms.Theasymmetryintheshapeofthe are observed at 179.9, 320.5, 543.4, and 748.3 cm−1. The peak peak indicates the coexistence of tetragonal and cubic phases. at 179.9 cm−1 corresponds to the A (TO) mode of vibration, This tetragonal structure might partly be a consequence of 1 which represents the Ti-O phonon vibrations of BZT-BCT. averaging 111 displacements of octahedral Ti4+ (local rhom- [28] Another A (TO) mode at around 543.4 cm−1 represents bohedral structure) [22]. We cannot attribute the splitting of 1 the O-Ti-O symmetric stretching vibrations [29]. The observed the peaks to the presence of CuK or CuK radiation at higher α β peaks are due to the symmetry-forbidden first-order Pm3m angles, as this is predominantly seen in the mentioned 2θ range Raman scattering in the centrosymmetric space group resulting (43.5° to 44.5°). Additionally, the (003) diffraction peak at from the displacement of Ti or Zi atom from its octahedral site 68.7° shows mixed diffraction peaks, which is consistent with [30]. The sharp feature at 543.4 cm−1 indicates the excellent Liu’s results [23]. To further investigate the texture of the films, quality of the thin film. The peak at 320.5 cm−1, attributed we performed XRD rocking curve analyses around BZT-BCT to the B mode, is a characteristic peak for BZT–BCT and (002), BZT-BCT (003), and LSMO (002) planes, which are 1 indicates the asymmetry of the TiO octahedra [31]. This band shown in Fig. 3a, 3b and 3c, respectively. The full width at 6 is considered to be the Raman signature of the tetragonal half maximum (FWHM) (θ) of the rocking curves are around phase. The absence of the A octahedral breathing mode at 0.10°, 0.15°, and 0.37° , respectively. The small values of 1g ∼ 800 cm−1 is an interesting feature in the Raman spectra FWHM imply highly oriented nature of the films. of BZT-BCT thin film, which is usually shown up in their The c-axis lattice constants of LSMO calculated from the bulk counterparts [32]. This breathing mode is associated with XRD analysis of LSMO/LAO and BZT-BCT/LSMO/LAO are more dissimilar ions on B-site of the Raman active perovskite around 3.892 and 3.943 Å, respectively. As the lattice constant [33]. The absence of the breathing mode implies that the Ca2+ of bulk LSMO is 3.889 Å, this induces a tensile strain in the resides on the Ba-site, not on the Ti-site in the as-deposited LSMO layer in both heterostructure systems [24]. However, BZT-BCT thin film. the scenario is critical for the heterostructure system. The The broadening and peak shift of A (LO) vibrational mode BZT-BCT/LSMO/LAO heterostructure experiences two strain 1 at 748.3 cm−1, compared to its bulk counterpart (721.2 cm−1), effects, one incurred from the strain of LSMO/LAO interface is a characteristic feature of the tetragonal phase [21]. The due to the lattice mismatch between the film and the substrate, broadening represents more distortion in the unit cell of and the other from the BZT-BCT/LSMO interface. the thin film compared to the bulk. The blue shift and the broadening of A1(LO) phonon mode are related to the non- B. Raman Spectroscopy centrosymmetricity of the unit cell. The weak intensity of We performed room-temperature micro Raman analysis to some of the vibration bands of the BZT–BCT film denotes investigate the molecular vibrational modes present in BZT- the heavily damped phonons. The peak positions of some of BCT. The cubic perovskite structure of BZT-BCT inherently the modes, such as B1/E(TO) and A1(LO)/E(LO), the shift 4

Fig. 4. Raman spectra of BZT-BCT/LSMO thin ﬁlm on LAO substrate with Gaussian-Lorentzian peak ﬁtting.

TABLE I Fig. 5. Polarization-Electric ﬁeld (P-E) hysteresis loops from Au-Ti/BZT- BCT/LSMO ferroelectric capacitor at different applied voltages. The inset PEAK POSITIONS AND FWHM OF THE CORRESPONDING VIBRATIONAL illustrates the polarization measurement setup of the thin ﬁlm device. The MODES OBTAINED FROM THE GAUSSIAN-LORENTZIAN FITTING PRO- contacts on LSMO layer were made from Indium-Ingot. FILE OF THE RAMAN SPECTRUM ESULTS AND DISCUSSION

ferroelectric nature of the BZT-BCT thin film. The hysteresis loops are almost centered along the y-axis. As the voltage increases, the capacitor starts to show hysteretic characteristics and saturates at a high applied voltage. Table II summarizes the remnant polarization, saturation polarization, and coercive field at different applied voltages measured from the Au-Ti/ BZT-BCT/LSMO ferroelectric capacitor. The P − E hysteresis loops refer to a large remnant and saturation polarization in the BZT-BCT thin film. It shows a towards either the lower or higher frequency region. This 2 maximum remnant polarization (Pr ) of ∼47 µC/cm and a upshift/downshift phenomenon in Raman spectrum indicates coercive field (Ec) of ∼180 kV/cm for the MPB composition the localized chemical environments and strain [26]. As the at an applied voltage of 5V. Such a high remnant polarization BZT-BCT thin films were deposited under the same PLD con- in the PLD grown BZT-BCT thin film implies the uniform ditions, the deviation of chemical composition in the films can distribution of grains, compositional homogeneity, the absence be ruled out, which has also been confirmed by XRD analysis. of domain-wall pinning centers, and low defect density [35], Therefore, the strain originating from both the substrate and [36]. The observed coercive field is also higher than that the LSMO layer is responsible for the shift in Raman modes of the BZT-BCT bulk ceramic (1.68 kV/cm) [37]. The large [34]. In this study, the LSMO thin film yields negligible count coercive field is an outcome of much smaller sized grains in the Raman spectroscopy due to its half-metallic nature. The along with substrate clamping effect [38]. As the average distinct peaks in the Raman spectra imply the high quality of grain size is small in PLD grown thin films compared to the film. Table I represents the peak positions and FWHM their bulk counterpart, the length of the grain boundaries per of the corresponding vibrational modes in the BZT-BCT thin unit volume is larger. Consequently, a high electric field is film. required to orient all the domains along the field direction. The orientation-dependent analysis by Luo et al. reveals that C. Polarization Measurements (001) oriented thin film shows superior ferroelectricity rather Fig. 5 shows the polarization-electric field (P − E) plots of than (110) and (111) oriented thin film [37]. In this work, our an Au-Ti/BZT-BCT/LSMO ferroelectric capacitor at different sample is highly oriented along [001] direction, which upholds applied voltages. The inset of this Fig. represents the schematic the high polarization phenomena in the BZT-BCT structure. of the corresponding device. The time integration of the current response is used to determine the polarization values, D. Dielectric Measurements which can be expressed as follow- The dielectric properties of the BZT-BCT thin film were Q I (t)dt P = = characterized at room temperature as a function of frequency A A ranging from 1 kHz to 50 kHz with an exciting voltage of Where I (t) is the switching current, and A is the area of 1V. The measurement setup for this experiment was the same the top electrode on the capacitor. The observed P − E as shown in the inset of Fig. 5. Fig. 6a represents the typical curves show hysteresis loop, which is an indication of the frequency dependent dielectric constant and 6(b) represents 5

TABLE II REMNANT AND SATURATION POLARIZATION WITH COERCIVE FIELD AT DIFFERENT VOLTAGES APPLIED TO THE FERROELECTRIC CAPACITOR

the frequency dependent dielectric loss over a wide range of frequencies. With increasing frequency, the dielectric constant decreases but the loss tangent increases. The measured largest capacitance was found to be 2.8 nF, which yields a high dielectric constant of ∼5100, and a small loss tangent of ∼0.02 at 1kHz. The improved dielectric properties of the film can be attributed to the spontaneous polarization vectors Fig. 6. Frequency dependence of (a) dielectric constant and (b) dielectric loss which coincide with the field direction during the dielectric for BZT–BCT/LSMO thin film on LAO substrate. A wide range of frequencies measurements. The large value of the dielectric constant and was applied from 1KHz to 50KHz. The dielectric loss was plotted against the logarithm of the frequency. (c) Represents the leakage behavior of the device. the smaller loss tangent compared to its bulk counterpart imply excellent device quality [39]. The leakage current and the time-to-breakdown (tBD) are two important parameters for applications in electronics and memory devices. The leakage phenomenon is a gradual loss of energy from a charged capacitor as it slowly discharges the capacitor and tBD is inversely proportional to the leakage current density [40]. Fig. 6c shows the experimental leakage current profile for two different applied excitations. The low leakage current is consistent with the small loss tangent of the device. The observed leakage current in this study is one order of magnitude smaller compared to that of the same film fabricated by a sol-gel Fig. 7. (a) Magnetization-applied field (M-H ) hysteresis loop of LSMO/LAO (red), BZT-BCT/LSMO/LAO (purple) obtained at room temperature, and (b) technique [41]. Such a low leakage current is highly desirable the low field fragments of the hysteresis loops of Fig. a. The inset of Fig. a for high-performance ferroelectric devices. shows the applied field direction.

E. Magnetic properties TABLE III DIFFERENT MAGNETIC PARAMETERS OBTAINED FROM SQUID MEA- Fig. 7a shows the M − H curve of LSMO/LAO thin film SUREMENTS with the field applied perpendicular to the film plane at room temperature. Fig. 7b illustrates the low field fragments of the hysteresis loops. The magnetization was calculated after subtracting the diamagnetic background of the substrate. The magnetization increases with increasing magnetic field until the saturation is reached at ∼40 kA/m. The ferromagnetic nature of the LSMO thin film was confirmed by the well- behaved M-H curve. The magnetic disorder at the surface of the thin film is considerably larger than that of the bulk sample [42]. In perovskite materials, the cubic symmetry lacks Curie temperature (Tc) of the sample. The commencement of at the surface and charge is transferred from the bulk to the a spontaneous magnetization near 360 K indicates the Tc of surface layer, leading to the formation of higher oxidation state the ferromagnetic thin film. Table III summarizes important (Mn3+) [42]. parameters obtained from different magnetic measurements. Fig. 8 shows the temperature dependence of magnetization Different studies have shown different TC of LSMO thin measurement (M −T curve) of the LSMO/LAO sample at two films, ranging from 324K to 360K, on different substrates different magnetic fields, i.e., a high field of 400 kA/m and [43],[44]. TC is dependent on the magnetic spin alignment, a low field of 8 kA/m. The measurements were performed in therefore, the strain in the film and hence the substrate plays a field-cooled condition. Both of the M − T curves reveal the a crucial role in determining Curie temperature. In a previous 6

Fig. 8. The field-cooled temperature dependent magnetization of LSMO/LAO at different applied magnetic fields. study, we have shown that high quality single crystal LSMO Fig. 9. (a) Surface topography of LSMO, (b) MFM phase image of (grown by the floating zone technique) with negligible strain ferromagnetic LSMO thin film on LAO substrate, (c) surface topography of and defect exhibits TC of 354 K which is the intrinsic Curie BZT-BCT thin film, and (d) PFM phase image of ferroelectric BZT-BCT thin film on LAO substrate. temperature of LSMO [45]. So the observed TC (around 360 K in this study) indicates the high structural quality of the film. The magnificent structural quality of the PLD grown LSMO along the lowest energy surface for (001) orientation [47]. films is also verified in the structural characterization section The piezoresponse force microscopy (PFM) phase image for (Raman and XRD analysis). The high structural quality and the BZT-BCT thin film was obtained utilizing commercially high T of LSMO are desirable for different applications such C available conducting tip in contact mode by applying a DC as infrared bolometers operating at room temperature [46] and voltage of 1V between the tip (top electrode) and the bottom room temperature spintronic devices [44]. In our study, the electrode (LSMO). The out-of-plane PFM phase image is LSMO samples show good structural quality and a high T C shown in Fig. 9d. This phase image distinguishes the domains (∼360 K), making them interesting candidates for different of opposite polarization with dark and bright contrast. This room temperature multiferroic applications. is a direct indication of spontaneous polarization. Thus, we can affirm the existence of ferroelectricity in the PLD grown F. Morphology of the Thin Films BZT-BCT thin film at the nanoscale level. The surface morphology (topography) of the LSMO thin film deposited on LAO substrate is shown in Fig. 9a. No IV. CONCLUSIONS unique domain structures and domain walls were observed in the topography. However, the color contrast reveals the The highly oriented ferroelectric-ferromagnetic heterostruc- existence of different domains in the sample. The magnetic ture of BZT-BCT/LSMO/LAO with excellent properties was force microscopy (MFM) phase image is shown in Fig. 9b. The fabricated using PLD. Along with the XRD theta-2theta scan, image contrast of the phase image is a clear indication of the the small FWHM of high-resolution XRD rocking curve magnetic activity present in the sample. The contrast shown by corroborates the oriented nature of the film. The BZT-BCT the MFM image occurs due to the force gradients between the ferroelectric thin film shows polarization switching behavior tip and the ferromagnetic LSMO thin film. The phase image with a large remnant polarization of ∼47 µC/cm2, a high was obtained after topography measurements (tapping mode) coercive field of ∼180 kV/cm, and a large dielectric constant followed by sample surface scanning at a constant height (lift of ∼5100 with a negligible loss (0.02). The M − H hys- mode). According to this procedure, we do not expect to detect teresis loop at room temperature confirms the ferromagnetic any van der Waals force, and any change in the vibration nature of the LSMO thin film with large saturation field amplitude of the cantilever is proportional to the gradient and remnant magnetization. Temperature-dependent magne- of magnetic fields perpendicular to the sample surface. The tization data show a high Curie temperature of ∼360 K. surface morphology (topography) of the BZT-BCT film is Additionally, PFM and MFM analyses of the ferroelectric shown in Fig. 9c. There is no evidence of cracking or defects (BZT-BCT) and ferromagnetic (LSMO) thin films reveal the on the surface. Furthermore, the observed topography is very corresponding domains of the thin films, respectively. These uniform, which is an indication of a homogenous PLD deposi- results and analyses may guide researchers to develop the tion. Moreover, based on the substrate orientation dependence next-generation sensors and actuators by utilizing the excellent of the equilibrium grain shapes of the BZT-BCT thin film electro-mechanical and magneto-electric coupling properties and the Winterbottom construction theory, it can be visualized of the lead-free ferroelectric-ferromagnetic BZT-BCT/LSMO that the BZT-BCT thin film maintains a layer-by-layer growth heterostructure. 7

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[45] K. Ghosh et al., “Critical Phenomena in the Double-Exchange Ferromag- Dr. Ghosh has completed his PhD from Tata Insti- net La0.7Sr0.3MnO3,” Phys.Rev.Lett., vol. 81, no. 21, pp. 4740–4743, tute of Fundamental Research and postdoctoral stud- Nov. 1998. ies from the University of Maryland at College Park [46] F. Yang, L. Méchin, J.-M. Routoure, B. Guillet, and R. A. Chakalov, and Argonne National Laboratory. Currently, he is “Low-noise La0.7Sr0.3MnO3 thermometers for uncooled bolometric a Professor of Physics and Materials Science at applications,” J. Appl. Phys., vol. 99, no. 2, p. 024903, 2006. Missouri State University. Over the last 30 years in [47] H. Zheng et al., “Self-Assembled Growth of BiFeO3–CoFe2O4 Nanos- his research career, he has been developing organic tructures,” Adv. Mater., vol. 18, no. 20, pp. 2747–2752, Oct. 2006. and inorganic thin films, nanomaterials, and their heterostructures for potential applications in the field of spintronics, renewable energy, and nanobiotech- nology and has made important contributions to these fields. He has published over 170 peer-reviewed articles in highly cited journals and has been serving as a reviewer and an editorial board member in many reputed journals. Ariful Haque received his bachelor’s degree in Electrical and Electronic Engineering from Bangladesh University of Engineering & Technol- ogy (BUET) in 2012. Then he went to Missouri State University, United States for his Master of Science (M.S.) degree in Materials Science. He successfully completed his M.S. from MSU in 2015 with the highest honor. He is currently pursuing the Ph.D. degree in Materials Science and Engineering at North Carolina State University, Raleigh, United States. From fall’2013 to spring’2015, he was a Graduate Teaching Assistant with the department of Physics, Astronomy and Materials science at Missouri State University. At present he is working as a graduate research assistant at the National Science Foundation Center for Advanced Materials and Smart Structures in North Carolina State University on the fabrication, structural and device characterization, and applications of carbon and nitride based wide band gap semiconductor materials. He has expertise in thin film fabrication and characterizations, semiconductor heterostructure, semiconductor doping, electron field emission, laser-solid interaction, electrical and magnetic transport properties, photovoltaics, energy, thin film defects, NV center, nanomaterials, diamond, graphene, graphene oxide, core-shell nano particles, and PVD & CVD fabrications. He has published over 25 peer-reviewed articles in highly cited peer reviewed journals and conferences and has been serving as a reviewer and editorial board member in many reputed journals in his field.

Md Abdullah-Al Mamun has received his Bachelor of Science (B.Sc.) degree in Electrical and Electronic Engineering in 2012 from Bangladesh University of Engineering and Technology, Dhaka, Bangladesh. He received his MS (Master of Science) in Material Science in 2017 from Missouri State University, Springﬁeld, Missouri, USA. He is currently pursuing his PhD in Electrical Engineering from The Univer- sity of South Carolina, Columbia, South Carolina, USA. His research interests include wide bandgap semiconductor.

Bithi Paul has completed her both B.Sc and M.Sc degree in Physics from Jagannath University, Dhaka, Bangladesh. After then, she has received her Master of Science degree in Materials Science from Mis- souri State University, Spring Field, Missouri, USA. Currently, Paul is working as a faculty of Ameri- can International University-Bangladesh (AIUB) in Bangladesh. Her research interest lies on the synthesis of nano- bio composite materials for device and bio sensor applications. Bithi also works on synthesis of semiconductor nano materials and analysis their electrical, optical, and magnetic properties.