Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO) nanoparticles in a polyvinylidene fluoride (PVDF) polymer-fibre matrix have been prepared by electrospinning. The average diameter of the electrospun composite fibres is ∼325 nm, independent of the nanoparticle content, and the amount of the crystalline polar β phase is strongly enhanced when compared to pure PVDF polymer fibres. The piezoelectric response of these electroactive nanofibres is modified by an applied magnetic field, thus evidencing the magnetoelectric character of the CFO/PVDF 0-1 composites.This work was supported by FEDER through the COMPETE Program and
by the Portuguese Foundation for Science and Technology (FCT) in the
framework of the Strategic Project PEST C/FIS/UI607/2014 and
PTDC/CTM NAN/112574/2009. R. G., P. M., V. S., G. B. and S. L. M.
acknowledge support from “Matepro – Optimizing Materials and
Processes” (ref. NORTE-07-0124-FEDER-000037), co funded by
“Programa Operacional Regional do Norte” (ON.2 – O Novo Norte,
QREN, FEDER). P. M. and R. Gonçalves acknowledges also support from
FCT (SFRH/BPD/96227/2013 and SFRH/BD/88397/2012 grants
respectively). X. M. acknowledges support from the Ramón y Cajal (RYC)
Programme (Spanish MEC) and the Royal Society.This is the accepted manuscript. The final version is available at http://pubs.rsc.org/en/Content/ArticleLanding/2015/NR/c5nr00453e#!divAbstract

Botelho, G

Ghidini, M

Gonçalves, R

Lanceros-Mendez, S

Martins, P

Mathur, ND

Moya, X

Sencadas, V

R. Gonçalves

P. Martins

X. Moya

M. Ghidini

V. Sencadas

G. Botelho

N. D. Mathur

S. Lanceros-Mendez

Crossref

Nanoscale

Magnetoelectric CoFe<sub>2</sub>O<sub>4</sub>/polyvinylidene fluoride electrospun nanofibres

Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO)
nanoparticles in polyvinylidene fluoride (PVDF) polymerfibre
matrix have been prepared by electrospinning. The
average diameter of the electrospun composite fibres D is ~
325 nm, independently of nanoparticle content, and the
amount of crystalline polar β phase is strongly enhanced
when compared to pure PVDF polymer fibres. The
piezoelectric response of these electroactive nanofibres is
modified by an applied magnetic field, thus evidencing the
magnetoelectric character of the CFO/PVDF 0-1 composites.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST C/FIS/UI607/2014 and PTDC/CTM NAN/112574/2009. R. G., P. M., V. S., G. B. and S. L. M. acknowledge support from “Matepro – Optimizing Materials and Processes” (ref. NORTE-07-0124-FEDER-000037), co funded by “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte, QREN, FEDER). P. M. and R. Gonçalves acknowledges also support from FCT (SFRH/BPD/96227/2013 and SFRH/BD/88397/2012 grants respectively). X. M. acknowledges support from the Ramón y Cajal (RYC) Programme (Spanish MEC) and the Royal Society

Gonçalves, R.

Martins, Pedro Libânio Abreu

Moya, X.

Ghidini, M.

Sencadas, Vítor João Gomes Silva

Botelho, Gabriela

Mathur, N. D.

Lanceros-Méndez, S.

Universidade do Minho: RepositoriUM

Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres

Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO) nanoparticles in a polyvinylidene fluoride (PVDF) polymer-fibre matrix have been prepared by electrospinning. The average diameter of the electrospun composite fibres is ∼325 nm, independent of the nanoparticle content, and the amount of the crystalline polar β phase is strongly enhanced when compared to pure PVDF polymer fibres. The piezoelectric response of these electroactive nanofibres is modified by an applied magnetic field, thus evidencing the magnetoelectric character of the CFO/PVDF 0-1 composites

Gonçalves, R.

Martins, P.

Sencadas, V.

Botelho, G.

Lanceros Mendez, S.

GHIDINI, Massimo

Archivio istituzionale della Ricerca -  Università degli Studi di Parma

Magnetoelectric CoFe<inf>2</inf>O<inf>4</inf>/polyvinylidene fluoride electrospun nanofibres

Goncalves, R

Martins, P M

Sencadas, Vitor

Mathur, N D

Lanceros-Méndez, Senentxu

Research Online

University of Wollongong Research Online Faculty of Engineering and Information Sciences - Papers: Part A Faculty of Engineering and Information Sciences 1-1-2015 Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres R Goncalves Universidade do Minho P M. Martins University of Minho X Moya University of Cambridge, Universitat De Barcelona M Ghidini University of Cambridge Vitor Sencadas University of Wollongong, victors@uow.edu.au See next page for additional authors Follow this and additional works at: https://ro.uow.edu.au/eispapers  Part of the Engineering Commons, and the Science and Technology Studies Commons Recommended Citation Goncalves, R; Martins, P M.; Moya, X; Ghidini, M; Sencadas, Vitor; Botelho, Gabriela; Mathur, N D.; and Lanceros-Méndez, Senentxu, "Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres" (2015). Faculty of Engineering and Information Sciences - Papers: Part A. 5253. https://ro.uow.edu.au/eispapers/5253 Research Online is the open access institutional repository for the University of Wollongong. For further information contact the UOW Library: research-pubs@uow.edu.au Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres Abstract Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO) nanoparticles in a polyvinylidene fluoride (PVDF) polymer-fibre matrix have been prepared by electrospinning. The average diameter of the electrospun composite fibres is ∼325 nm, independent of the nanoparticle content, and the amount of the crystalline polar β phase is strongly enhanced when compared to pure PVDF polymer fibres. The piezoelectric response of these electroactive nanofibres is modified by an applied magnetic field, thus evidencing the magnetoelectric character of the CFO/PVDF 0-1 composites. Keywords electrospun, fluoride, magnetoelectric, nanofibres, cofe2o4, polyvinylidene Disciplines Engineering | Science and Technology Studies Publication Details Goncalves, R., Martins, P., Moya, X., Ghidini, M., Sencadas, V., Botelho, G., Mathur, N. D. & Lanceros-Méndez, S. (2015). Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres. Nanoscale, 7 (17), 8058-8061. Authors R Goncalves, P M. Martins, X Moya, M Ghidini, Vitor Sencadas, Gabriela Botelho, N D. Mathur, and Senentxu Lanceros-Méndez This journal article is available at Research Online: https://ro.uow.edu.au/eispapers/5253 Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres  R. Gonçalves1,2, P. Martins1,3, X. Moya4,5, M. Ghidini4,6, V. Sencadas1, G. Botelho2,  N. D. Mathur4 and S. Lanceros-Mendez1, 3 1Centro/Departamento de Física, Universidade do Minho, 4710-057, Braga, Portugal 2Centro/Departamento de Química, Universidade do Minho, 4710-057, Braga, Portugal 3INL - International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal 4Department of Materials Science, University of Cambridge, Cambridge, CB2 3QZ, United Kingdom 5Facultat de Física, Departament d’Estructura i Constituents de la Matèria, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Catalonia, Spain 6DiFeST, University of Parma, viale G.P. Usberti 7/A, 43124 Parma, Italy  Abstract Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO) nanoparticles in polyvinylidene fluoride (PVDF) polymer-fibre matrix have been prepared by electrospinning. The average diameter of the electrospun composite fibres ?̅? is ~ 325 nm, independently of nanoparticle content, and the amount of polar crystalline β phase is strongly enhanced when compared to pure PVDF polymer fibres. The piezoelectric response of these electroactive nanofibres is modified by an applied magnetic field, thus evidencing the magnetoelectric character of the CFO/PVDF 0-1 composites.   Introduction Strain-mediated magnetoelectric composites that exhibit large direct magnetoelectric effects have emerged in recent years as promising candidates for e.g. the development of magnetic-field sensors and energy-harvesters, due to their high sensitivity, simple fabrication, low cost, and room temperature operation [1,2]. Giant magnetoelectric voltage coefficients, ~ 300 V cm-1 Oe-1 at the ~50 kHz resonance, have been observed in 2-2 laminate composites of high-magnetic-permeability Fe-Si-Co Metglas and piezoelectric PVDF polymer layers bonded using epoxy resin [3], and larger values, ~ 750 V cm-1 Oe-1 at the ~22 kHz resonance, have been reported in 2-1 laminate composites consisting of piezoelectric Pb(Zr,Ti)O3 fibres bonded between Fe-B-Si-C Metglas layers using epoxy resin [4]. However, these strong magnetoelectric effects are non-linear and occur only at very low magnetic-field bias, such that they are not suitable for use as sensors (or harvesters) of moderate and high magnetic fields, and moreover the performance of these composites is compromised by the relative brittleness of the epoxy bonding.  Magnetoelectric composites comprising magnetic nanoparticles embedded in a ferroelectric polymer matrix can overcome these problems: strain coupling typically does not deteriorate with operation, as the magnetic material is in direct contact with, and completely surrounded by, the ferroelectric material, and magnetoelectric voltage coefficients 0-3 composites comprising magnetic nanoparticles and fluorinated-polymer matrices are relatively large both at moderate [5,6] and high [7,8] magnetic fields. Here we extend the range of geometries available for polymer-based magnetoelectric composites by fabricating 0-1 nanofibres comprising CFO ferromagnetic particles and PVDF matrix, as such one-dimensional structures may permit the development of new magnetoelectric devices [9].   Experimental PVDF powder (Solef 1010) was purchased from Solvay Solexis, CFO nanoparticles (35–55 nm) were purchased from Nanoamor, and pure grade N,N-dimethylformamide (DMF) solvent was purchased from Merck. All materials were used as provided by the suppliers. Composite fibres, with nanoparticle content 5, 10 and 20 wt. %, were prepared using the following procedure: (i) CFO nanoparticles were added to the DMF and the solution was placed in an ultrasonic bath; (ii) PVDF powder was added and the resultant solution was mixed using a Teflon mechanical stirrer and an ultrasonic bath until the polymer was completely dissolved; (iii) the CFO/DMF/PVDF solution was introduced into the electrospinning deposition setup, using a plastic syringe connected to a flux regulator; in order to create a jet, high voltage was applied between the syringe needle and an aluminium foil, where the electrospun fibres are collected, forming a mat; deposition conditions were 20 kV bias, 0.5 mm needle inner diameter, 0.5 ml h-1 flow rate, and 20 cm needle-collector distance.  Size and morphology of the CFO/PVDF nanofibres were studied by scanning electron microscopy (SEM) using a Quanta 650 FEI electron microscope with acceleration voltage of 10 kV. Prior to SEM, the nanofibre mats were coated with gold. SEM image analysis was performed using Image J software.   Volume fraction of electroactive β-phase in the nanofibre PVDF matrix was determined via Fourier transform infrared spectroscopy (FTIR) [6,10], performed using a Jasco FT/IR-4100 type A that was operated in attenuated total reflectance mode, with 2 cm-1 resolution. For each sample, sixty four spectra were averaged, and then values of volume fraction Fβ were obtained as 𝐹β = 𝐴β [(𝐾β 𝐾α⁄ )𝐴α + 𝐴β]⁄ , where Aβ = Tβ-1 = 840 cm-1 and Kβ = 7.7×104 cm2 mol-1 are the absorbance and absorption coefficients for the β phase, and Aα = Tα-1 = 764 cm-1 and Kα = 6.1×104 cm2 mol-1 are the absorbance and absorption coefficients for the α phase [11].  Magnetization loops M(H) were measured up to 10 kOe using an Oxford Instruments vibrating sample magnetometer. Piezoelectric coefficients d33 were determined using a Digital Instruments Dimension 3100 for piezoresponse force microscopy (PFM), with conductive Cr/Pt-coated tips of stiffness 40 N m-1. d33 measurements were performed using a 2 V peak-to-peak ac bias at 13 kHz, with and without a 1 kOe magnetic field that was applied using a permanent magnet. Prior to local measurements of the nanofibres piezoresponse, the cantilever deflection amplitude was calibrated via force-distance measurements.  Results and discussion The studied CFO/PVDF electrospun nanofibres have an average diameter ?̅? ~ 325 nm, and are randomly distributed in the aluminium-foil collector (Figure 1). CFO nanoparticle content has no significant impact on the nanofibre average diameter [Figure 1 (a-d)]. The CFO/PVDF nanofibres show a strong enhancement in the volume fraction of electroactive β phase Fβ [11,12] when compared to pure PVDF electrospun nanofibers [Figure 1(e) and (f)], as the interaction between the negatively charged surface of the CFO nanoparticles (whose zeta potential is -22 mV) and the positively charged polymer CH2 groups promotes nucleation of the polar β phase, as seen in CFO/PVDF films [10]. The increase in β phase volume fraction is also assisted by the low evaporation temperature of the solvent (≤ 60 oC) and the stretching that occurs during jet formation [13].  The magnetization of the nanofibres increases with increasing CFO content (Figure 2), as expected [2,5,6]. The shape of the magnetization loops is determined by the mixture of single-domain and multidomain nanoparticles [14], and the magnetization does not saturate at the maximum applied magnetic field of 10 kOe, due to the strong magnetic anisotropy (> 30 kOe) of the CFO nanoparticles [15].  To establish the magnetoelectric character of the nanofibre composites, we performed piezoresponse force microscopy with and without applied magnetic field [Figure 3(a)]. Piezoelectric coefficient d33 increases with applied magnetic field, due to the strain-mediated coupling between the magnetostrictive CFO nanoparticles and the piezoelectric PVDF matrix, which shows reduced piezoelectric coefficients when compared to bulk polymers, possibly due to clamping by the surrounding material (which may reduce significantly the local deformation of the nanofibers) [6,16,19].  To conclude, we studied the structural, magnetic and piezoelectric properties of low-temperature processed 0-1 nanofibre composites of CFO and PVDF. Magnetic-field-induced changes in the piezoelectric response of the nanofibres demonstrated the magnetoelectric character of these 0-1 composites, which may be useful for the development of micro and nanoscale magnetoelectric devices.  Acknowledgments This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011 and the projects PTDC/CTM/69316/2006 and PTDC/CTM-NAN/112574/2009. R. G., P. M., V. S., G. B. and S. L.-M. acknowledge support from “Matepro – Optimizing Materials and Processes” (ref. NORTE-07-0124-FEDER-000037), co-funded by “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte, QREN, FEDER). P. M. also acknowledges support from FCT (SFRH/BD/45265/2008). X. M. acknowledges support from the Ramón y Cajal (RYC) Programme (Spanish MEC) and the Royal Society.   References [1] J. Ma, J. Hu, Z. Li and C. W. Nan, Advanced Materials 23, 1062 (2011). [2] P. Martins and S. Lanceros-Mendez, Advanced Functional Materials 23, 3371 (2013). [3] J. Zhai, S. Dong, Z. Xing, J. Li and D. Viehland, Applied Physics Letters 89, 083507 (2006). [4] S. Dong, J. Zhai, J. Li and D. Viehland, Applied Physics Letters 89, 252904 (2006). [5] J. X. Zhang, J. Y. Dai, L. C. So, C. L. Sun, C. Y. Lo, S. W. Or and H. L. W. Chan, Journal of Applied Physics 105, 054102 (2009). [6] P. Martins, A. Lasheras, J. Gutierrez, J.M. Barandiaran, I. Orue and S. Lanceros-Mendez, Journal of Physics D: Applied Physics 44, 495303 (2011). [7] P. Martins, X. Moya, L. C. Phillips, S. Kar-Narayan, N. D. Mathur and S. Lanceros-Mendez, Journal of Physics D: Applied Physics 44, 482001 (2011). [8] P. Martins, X. Moya, C. Caparrós, J. Fernandez, N. D. Mathur and S. Lanceros-Mendez, Journal of Nanoparticle Research 15, 1825 (2013). [9] S.-H. Xie, Y.-Y. Liu and J.-Y. Li, Frontiers in Physics 7, 399 (2012). [10] P. Martins, C. M. Costa and S. Lanceros-Mendez, Applied Physics A 103, 233 (2011). [11] P. Martins, A. C. Lopes and S. Lanceros-Mendez, Progress in Polymer Science 39, 683 (2014). [12] P. Martins, C. M. Costa, M. Benelmekki, G. Botelho and S. Lanceros-Mendez, CrystEngComm 14, 2807 (2012). [13] C. Ribeiro, V. Sencadas, J. L. G. Ribelles and S. Lanceros-Mendez, Soft Materials 8, 274 (2010). [14] C. P. Bean, Journal of Applied Physics 26, 1381 (1955). [15] C. N. Chinnasamy, B. Jeyadevan, K. Shinoda, K. Tohji, D. J. Djayaprawira, M. Takahashi, R. J. Joseyphus and A. Narayanasamy, Applied Physics Letters 83, 2862 (2003). [16] A. Baji, Y.-W. Mai, Q. Li and Y. Liu, Nanoscale 3, 3068 (2011). [17] E. M. Sabolsky, S. Trolier-McKinstry and G. L. Messing, Journal of Applied Physics 93, 4072 (2003). [18] T. Jungk, Á. Hoffmann and E. Soergel, Applied Physics A 86, 353 (2007). [19] T. Jungk, Á. Hoffmann and E. Soergel, Applied Physics Letters 91, 253511 (2007). [20] B. Dickens, E. Balizer, A. S. DeReggi and S. C. Roth, Journal of Applied Physics 72, 4258 (1992).               Figure 1. SEM image and corresponding distribution of nanofibre diameter D for CFO/PVDF nanofibres with (a) 5 wt. % CFO, (b) 10 wt. % CFO and (c) 20 wt. % CFO. Red lines are Gaussian fits, which were used to estimate the average diameter ?̅?. (d) Nanofibre average diameter ?̅? as a function of CFO content. (e) FTIR spectra for CFO/PVDF nanofibres, and two pure polymer samples in film (PVDF) and nanofibre (e-PVDF) form. Vertical arrows indicate the traces for the α (766 cm-1) and β (840 cm-1) phases. (f) β-phase volume fraction Fβ as a function of CFO content.    Figure 2. (a) Room-temperature magnetization M(H) of CFO/PVDF nanofibre nanocomposites with different CFO concentration. Magnetization was measured along the out-of-plane direction of the nanofibre mats [complementary in-plane M(H) measurements (not shown) evidenced the isotropic magnetic character of the nanofibre composites]. (b) Magnetization Mmax measured at 10 kOe as a function of CFO content.         Figure 3. (a) Schematic representation of the piezoresponse force microscopy setup in applied magnetic field used to establish the magnetoelectric character of the CFO/PVDF nanofibres. (b) One of such nanofibres, as seen via atomic force microscopy. Displacement as a function of voltage, with and without magnetic field, for CFO/PVDF nanofibres with (c) 5 wt. % CFO, (d) 10 wt. % CFO and (e) 20 wt. % CFO. The maximum electric field applied was ~30 MV m-1, which is smaller than the coercive field of PVDF films (~50-120 MV m-1) [20]. (f) Piezoelectric coefficient d33 as a function of CFO content and magnetic field.  

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Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres.

Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres.

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