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Magnetoelectricity in polyurethane films loaded with different magnetic particles
Materials Letters 63 (2009) 611–613
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Magnetoelectricity in polyurethane films loaded with different magnetic particles D. Guyomar, D.F. Matei, B. Guiffard ⁎, Q. Le, R. Belouadah Laboratory of Electrical Engineering and Ferroelectricity, LGEF, INSA-Lyon, 8 rue de la Physique, 69621 Villeurbanne Cedex, France
a r t i c l e
i n f o
Article history: Received 11 July 2008 Accepted 28 November 2008 Available online 9 December 2008 Keywords: Magnetoelectric effect Polymers Magnetic particles Composites Films
a b s t r a c t Particulate polymer composites consisting of Terfenol-D/Polyurethane, Fe3O4/Polyurethane, Nickel/Polyurethane and particulate composite layers were prepared by using a simple solution cast method. Magnetoelectric (ME) effect is characterized by measuring the amplitude of the magnetoelectric current versus different input parameters that appear in the theoretical current expression. The results yield two conclusions: 1.Whatever the filler type (Terfenol-D, Fe3O4 or Nickel), the microcomposites show a magnetoelectric effect. 2. The magnetostrictive property of the material does not have a direct influence on the ME effect since ME sensitivity is dc field independent and the magnetoelectric coefficient αp has close values in ac field for all types of polymer fillers. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
The ME effect is defined as the dielectric polarization induced by an applied magnetic field or an induced magnetization in an external electric field [1]. Here, ME effect represents the coupling between an applied magnetic field and a change in electric polarization in a solid. Intensive research have been devoted to the ME effect during the last decade because of the interesting transduction properties the magnetoelectric materials may present. The first observation of the ME effect [2,3] triggered a lot of excitement because of the obvious potential of the crosscorrelation between the magnetic and electric properties of matter for technical applications [4]. It is also interesting to note that – to the best of our knowledge – only theoretical results about ME effect in monolayered two-phase particulate polymer composites have been published [5]. On a general manner, the electric response to an applied H field on a magnetic particles/non piezoelectric polymer composites is not well known. That is the reason why in this letter, we present a comparison between different particulate composites made of highly magnetostrictive Terfenol-D (hard magnetic) or less magnetostrictive Fe3O4 (hard magnetic), Nickel (soft magnetic) and polyurethane elastomer. Our materials are based on a simple mixture of the inorganic filler with a polyurethane matrix.
The chosen polyurethane (PU) is the Polyether-type thermoplastic TPU5888 from Noveon Company. Polymer films were prepared using the solution cast method. PU granules were first predissolved in N,N-dimethylformamide at ∼ 75 °C for one hour. Then 2 wt.% of amorphous Fe3O4, Nickel micropowder (Aldrich, average particle size: 200 µm) or Terfenol-D (Etrema Products, Inc., Ames, IA) micropowder were added to the mechanically stirred solution. One filler content (2 wt.% ) has been tested for the three different filler types (Terfenol-D, Fe3O4 and Nickel). In the following, the filled microcomposites films will be designed as PU/TeD, PU/Fe3O4 or PU/ Ni for the Terfenol-D, Fe3O4 and Nickel filled PU respectively. Pure PU is defined as unloaded polyurethane. At constant temperature, the stirring time varies between 1.5 h and 2.5 h, which allow obtaining precise film thickness. Then, the mixed solution was poured onto a glass plate, degassed to eliminate voids and dried at 70 °C. Composite films were cut into rectangular pieces (∼ 280 micronsthick, 40 mm-length and 10 mm- width) and these samples were gold-sputtered on the two faces (∼ 200 Å-thick, 36 mm — length and 8 mm — width). The films were vertically suspended in air and the top of the specimen was clamped in a sample holder (Fig. 1) [6]. The microcomposite beam was placed between the poles of an electromagnet composed of toloidal Fe–Silicium FA30 magnets surrounded by copper coils (104 turns) thus allowing appliance of ac magnetic field perpendicular to the sample axis through a low bandwidth voltage amplifier (Agilent 33220A). Superimposed parallel dc field is provided by two permanents magnets (Ferrite GSF-30). In brief, the applied field H is a combination of the alternative field hac and bias magnetic
⁎ Corresponding author. E-mail address: [email protected] (B. Guiffard). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.11.058
612
D. Guyomar et al. / Materials Letters 63 (2009) 611–613
Fig. 1. Schematic diagram of the ME measurement system.
field Hdc, and it can be expressed as H = hac + Hdc [8] with hac = Hac × ejωt, j2 = −1 and ω = 2πf, where ω is the angular frequency, f the ac field frequency and Hac the ac field amplitude. We propose different types of current measurements in order to demonstrate the behaviour of the magnetoelectric coefficient in different filled
polymers starting from the fundamental equation of the ME effect given by Dzyaloshinskii [2,7]: D = eE + α P H
ð1Þ
where D is the electric displacement, E is the electric field, ε is the permittivity and αp is the magnetoelectric coefficient. Thus, the ME current is given by: iME = S
dD dt
ð2Þ
where S is the electrodes surface of the sample.
Fig. 2. RMS value of magnetoelectric current IME of pure PU and composites as a function of bias field at 120 Hz, Hac = 20 Oe and at 1 kHz, Hac = 1 Oe. The solid lines serve as guides to the eye.
Fig. 4. RMS value of magnetoelectric current IME of pure PU and composites as a function of the frequency for Hac = 20 Oe in [0 Hz–200 Hz] range and Hac = 1 Oe in [0.2 kHz–5 kHz]; Hdc is null. The solid lines serve as guides to the eye.
Fig. 3. RMS value of magnetoelectric current IME of pure PU and composites as a function of ac field amplitude Hac at 120 Hz and 1 kHz, Hdc is null. The solid lines serve as guides to the eye.
Fig. 5. RMS value of magnetoelectric coefficient αp of pure PU and composites as a function of the frequency for Hac = 1 Oe; Hdc is null. Full lines are plotted to guide the eye.
D. Guyomar et al. / Materials Letters 63 (2009) 611–613 Table 1 Magnetoelectric coefficient values of pure and filled films αp (C/m2.Oe)
PU 2%Ni
PU 2%Fe3O4
PU 2%TeD
f1 = 120 Hz f2 = 1 kHz
6.2 × 10− 11 5.3 × 10− 10
1.2 × 10− 10 6.15 × 10− 10
4 × 10− 11 2.2 × 10− 10
Frequency: f1 = 120 Hz; f2 = 1 kHz.
A short-circuit condition (E = 0) is chosen because it is easier to realize than a perfect open circuit one since the latter is strongly dependent upon the impedance of the sample. IME current amplitude was measured at room temperature with a current amplifier (Keithley 617) combined with a lock-in amplifier (SR 830 Stanford Research Systems) tuned to the ac field frequency f. The following equation results: iME = jα p Sω hac
ð3Þ
This letter shows the influence of the frequency, Hdc and ac field amplitude on the output magnetoelectric current of the microcomposites. 3. Results and discussion Fig. 2 shows the amplitude of the magnetoelectric current IME at 120 Hz for Hac = 20 Oe and 1 kHz for Hac = 1 Oe as a function of bias magnetic field. In order to keep the same magnetic induction B in the electromagnet in high frequencies range, it is necessary to increase the power supply of the electromagnet, but it also makes the magnetic losses increase and Hac = 20 Oe cannot be maintained anymore. That is the reason why applied Hac = 1 Oe at 1 kHz. Even we find in the literature that due to the magnetostriction it should be found an optimal value Hdc bias magnetic field yielding an optimal piezomagnetic coefficient and consequently a peak of IME value [9], it can be clearly observed that with increasing the bias magnetic field, IME remains roughly constant (Fig. 2). This strongly suggests that the magnetostrictive properties of the material do not influence the magnetoelectric effect. In fact, ME coupling does not originate from magnetostriction but rather linear elastic interaction between the particles aggregates and/or agglomerates and the highly polar microdomains of semi-crystalline polymer PU [10,11]. The current response of the studied films to the appliance of both Hdc and Hac could be attributed directly to a ME effect but a part of the output current originates from the parasitic voltage vinduced induced in the loop of the set up closed by the sample via Faraday and B Lenz's Laws: vinduced = − dΦ where ФB is the magnetic flux through the experimental dt loop. Pure PU electrical response is attributed to the parasitic effect. Obviously, the same parasitic effect occurs in the filled microcomposites films also but it has been extracted from the output current of composites as recently explained [12]. The ME current IME is also measured as a function of Hac amplitude (Fig. 3). The measurements are made for f = 120 Hz and f = 1 kHz, Hdc is null. With increasing the alternative field amplitude, IME increases linearly, showing a good agreement with Eq. (3). The frequency dependence of the current has also been studied. Owing to the saturation of the electromagnet explained above, two frequency ranges were
613
considered: 1) [0 Hz–200 Hz] with a constant alternative field amplitude Hac= 20 Oe; 2) [0.2 kHz–5 kHz] with a constant alternative field amplitude Hac = 1 Oe. Fig. 4 shows that the current amplitude roughly exhibits a linear variation as a function of the frequency, in the absence of DC bias field. Thus, it is still in agreement with Eq (3). In this case, the current linearity implies a frequency independent αp coefficient. However, the slight evolution of αp versus frequency can be evaluated from current measurements. It is found that αp values increase as a function of frequency (Fig. 5). A magnetoelectric current is strongly suggested, induced by a linear displacement change of the sample, independent upon DC bias field as observed. However, Fig. 5 also shows that the frequency dependence of αp is not linear. That may be due to the decrease of thickness change with increasing frequency drive.
4. Conclusions From all the measurements plotted in this letter we can make two important conclusions: 1. It is clearly observed that the pure PU shows lower current values than filled polymer (Terfenol-D, Fe3O4 or Nickel) which allows to conclude that the monolayered PU/TeD, PU/Fe3O4 or PU/Ni composites show a ME effect. The magnitude of magnetoelectric current is independent of the applied dc bias magnetic field and is a linear in function of the ac alternative field or applied frequency. 2. Even it is found in the literature that Terfenol-D shows better magnetostrictive properties (λ = 2200 × 10 − 6 ) [9] that Fe3 O 4 (λ = 90.6 × 10− 6) [13] or Nickel (λ = 21.6 × 10− 6) [14], we can see in this letter that for the ME effects there are no significant differences. Actually, measurement of the amplitude of the magnetoelectric current (Fig. 4) or the magnetoelectric coefficient αp at 120 Hz and 1 kHz (Table 1) revealed that Terfenol-D filled polymer exhibits lower ME sensitivity than Fe3O4 or Nickel filled polymer. That fact leads us to the conclusion that the magnetostriction of the material does not have a direct influence on the ME effect in these microcomposites. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Nan CW. J Appl Phys 2008;103:031103–35. Dzyaloshinskii IE. Sov Phys 1959;10:628–9. Astrov DN. Sov Phys 1969;11:708–12. Fiebig MJ. Appl Phys 2005;38:123–52. Nan CW, Li M, Feng X, Yu S. Appl Phys Lett 2001;78:2527–9. Record P. Sens Actuators B 2007;126:344–9. Makoto T, Takao T, Kenji A. IEEE Trans Circuit Theory 1970;17(3):339–44. Nersessian N, Wing S, Carman GP. IEEE Trans Magnetics 2004;40(4):2646–8. Jiles DC, Ostenson JE, Owen CV, Chang TTJ. Appl Phys 1988;64:5417–8. Li Y, Tong G, Liu J, Linliu K, Desper CR, Chu B. Macromolecules 1992;25:7365–72. Guiffard B, Seveyrat L, Sebald G, Guyomar D. J Appl Phys 2006;39:3053–7. Guyomar D, Guiffard B, Belouadah R, Petit L. J Appl Phys 2008;104:074902–6. Bickford LR, Pappis J, Stull JL. Phys Rev 1955;99(4):1210–4. Smith AB, Jones RV. J Appl Phys 1966;37:3.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Magnetoelectricity in polyurethane films loaded with different magnetic particles D. Guyomar, D.F. Matei, B. Guiffard ⁎, Q. Le, R. Belouadah Laboratory of Electrical Engineering and Ferroelectricity, LGEF, INSA-Lyon, 8 rue de la Physique, 69621 Villeurbanne Cedex, France
a r t i c l e
i n f o
Article history: Received 11 July 2008 Accepted 28 November 2008 Available online 9 December 2008 Keywords: Magnetoelectric effect Polymers Magnetic particles Composites Films
a b s t r a c t Particulate polymer composites consisting of Terfenol-D/Polyurethane, Fe3O4/Polyurethane, Nickel/Polyurethane and particulate composite layers were prepared by using a simple solution cast method. Magnetoelectric (ME) effect is characterized by measuring the amplitude of the magnetoelectric current versus different input parameters that appear in the theoretical current expression. The results yield two conclusions: 1.Whatever the filler type (Terfenol-D, Fe3O4 or Nickel), the microcomposites show a magnetoelectric effect. 2. The magnetostrictive property of the material does not have a direct influence on the ME effect since ME sensitivity is dc field independent and the magnetoelectric coefficient αp has close values in ac field for all types of polymer fillers. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
The ME effect is defined as the dielectric polarization induced by an applied magnetic field or an induced magnetization in an external electric field [1]. Here, ME effect represents the coupling between an applied magnetic field and a change in electric polarization in a solid. Intensive research have been devoted to the ME effect during the last decade because of the interesting transduction properties the magnetoelectric materials may present. The first observation of the ME effect [2,3] triggered a lot of excitement because of the obvious potential of the crosscorrelation between the magnetic and electric properties of matter for technical applications [4]. It is also interesting to note that – to the best of our knowledge – only theoretical results about ME effect in monolayered two-phase particulate polymer composites have been published [5]. On a general manner, the electric response to an applied H field on a magnetic particles/non piezoelectric polymer composites is not well known. That is the reason why in this letter, we present a comparison between different particulate composites made of highly magnetostrictive Terfenol-D (hard magnetic) or less magnetostrictive Fe3O4 (hard magnetic), Nickel (soft magnetic) and polyurethane elastomer. Our materials are based on a simple mixture of the inorganic filler with a polyurethane matrix.
The chosen polyurethane (PU) is the Polyether-type thermoplastic TPU5888 from Noveon Company. Polymer films were prepared using the solution cast method. PU granules were first predissolved in N,N-dimethylformamide at ∼ 75 °C for one hour. Then 2 wt.% of amorphous Fe3O4, Nickel micropowder (Aldrich, average particle size: 200 µm) or Terfenol-D (Etrema Products, Inc., Ames, IA) micropowder were added to the mechanically stirred solution. One filler content (2 wt.% ) has been tested for the three different filler types (Terfenol-D, Fe3O4 and Nickel). In the following, the filled microcomposites films will be designed as PU/TeD, PU/Fe3O4 or PU/ Ni for the Terfenol-D, Fe3O4 and Nickel filled PU respectively. Pure PU is defined as unloaded polyurethane. At constant temperature, the stirring time varies between 1.5 h and 2.5 h, which allow obtaining precise film thickness. Then, the mixed solution was poured onto a glass plate, degassed to eliminate voids and dried at 70 °C. Composite films were cut into rectangular pieces (∼ 280 micronsthick, 40 mm-length and 10 mm- width) and these samples were gold-sputtered on the two faces (∼ 200 Å-thick, 36 mm — length and 8 mm — width). The films were vertically suspended in air and the top of the specimen was clamped in a sample holder (Fig. 1) [6]. The microcomposite beam was placed between the poles of an electromagnet composed of toloidal Fe–Silicium FA30 magnets surrounded by copper coils (104 turns) thus allowing appliance of ac magnetic field perpendicular to the sample axis through a low bandwidth voltage amplifier (Agilent 33220A). Superimposed parallel dc field is provided by two permanents magnets (Ferrite GSF-30). In brief, the applied field H is a combination of the alternative field hac and bias magnetic
⁎ Corresponding author. E-mail address: [email protected] (B. Guiffard). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.11.058
612
D. Guyomar et al. / Materials Letters 63 (2009) 611–613
Fig. 1. Schematic diagram of the ME measurement system.
field Hdc, and it can be expressed as H = hac + Hdc [8] with hac = Hac × ejωt, j2 = −1 and ω = 2πf, where ω is the angular frequency, f the ac field frequency and Hac the ac field amplitude. We propose different types of current measurements in order to demonstrate the behaviour of the magnetoelectric coefficient in different filled
polymers starting from the fundamental equation of the ME effect given by Dzyaloshinskii [2,7]: D = eE + α P H
ð1Þ
where D is the electric displacement, E is the electric field, ε is the permittivity and αp is the magnetoelectric coefficient. Thus, the ME current is given by: iME = S
dD dt
ð2Þ
where S is the electrodes surface of the sample.
Fig. 2. RMS value of magnetoelectric current IME of pure PU and composites as a function of bias field at 120 Hz, Hac = 20 Oe and at 1 kHz, Hac = 1 Oe. The solid lines serve as guides to the eye.
Fig. 4. RMS value of magnetoelectric current IME of pure PU and composites as a function of the frequency for Hac = 20 Oe in [0 Hz–200 Hz] range and Hac = 1 Oe in [0.2 kHz–5 kHz]; Hdc is null. The solid lines serve as guides to the eye.
Fig. 3. RMS value of magnetoelectric current IME of pure PU and composites as a function of ac field amplitude Hac at 120 Hz and 1 kHz, Hdc is null. The solid lines serve as guides to the eye.
Fig. 5. RMS value of magnetoelectric coefficient αp of pure PU and composites as a function of the frequency for Hac = 1 Oe; Hdc is null. Full lines are plotted to guide the eye.
D. Guyomar et al. / Materials Letters 63 (2009) 611–613 Table 1 Magnetoelectric coefficient values of pure and filled films αp (C/m2.Oe)
PU 2%Ni
PU 2%Fe3O4
PU 2%TeD
f1 = 120 Hz f2 = 1 kHz
6.2 × 10− 11 5.3 × 10− 10
1.2 × 10− 10 6.15 × 10− 10
4 × 10− 11 2.2 × 10− 10
Frequency: f1 = 120 Hz; f2 = 1 kHz.
A short-circuit condition (E = 0) is chosen because it is easier to realize than a perfect open circuit one since the latter is strongly dependent upon the impedance of the sample. IME current amplitude was measured at room temperature with a current amplifier (Keithley 617) combined with a lock-in amplifier (SR 830 Stanford Research Systems) tuned to the ac field frequency f. The following equation results: iME = jα p Sω hac
ð3Þ
This letter shows the influence of the frequency, Hdc and ac field amplitude on the output magnetoelectric current of the microcomposites. 3. Results and discussion Fig. 2 shows the amplitude of the magnetoelectric current IME at 120 Hz for Hac = 20 Oe and 1 kHz for Hac = 1 Oe as a function of bias magnetic field. In order to keep the same magnetic induction B in the electromagnet in high frequencies range, it is necessary to increase the power supply of the electromagnet, but it also makes the magnetic losses increase and Hac = 20 Oe cannot be maintained anymore. That is the reason why applied Hac = 1 Oe at 1 kHz. Even we find in the literature that due to the magnetostriction it should be found an optimal value Hdc bias magnetic field yielding an optimal piezomagnetic coefficient and consequently a peak of IME value [9], it can be clearly observed that with increasing the bias magnetic field, IME remains roughly constant (Fig. 2). This strongly suggests that the magnetostrictive properties of the material do not influence the magnetoelectric effect. In fact, ME coupling does not originate from magnetostriction but rather linear elastic interaction between the particles aggregates and/or agglomerates and the highly polar microdomains of semi-crystalline polymer PU [10,11]. The current response of the studied films to the appliance of both Hdc and Hac could be attributed directly to a ME effect but a part of the output current originates from the parasitic voltage vinduced induced in the loop of the set up closed by the sample via Faraday and B Lenz's Laws: vinduced = − dΦ where ФB is the magnetic flux through the experimental dt loop. Pure PU electrical response is attributed to the parasitic effect. Obviously, the same parasitic effect occurs in the filled microcomposites films also but it has been extracted from the output current of composites as recently explained [12]. The ME current IME is also measured as a function of Hac amplitude (Fig. 3). The measurements are made for f = 120 Hz and f = 1 kHz, Hdc is null. With increasing the alternative field amplitude, IME increases linearly, showing a good agreement with Eq. (3). The frequency dependence of the current has also been studied. Owing to the saturation of the electromagnet explained above, two frequency ranges were
613
considered: 1) [0 Hz–200 Hz] with a constant alternative field amplitude Hac= 20 Oe; 2) [0.2 kHz–5 kHz] with a constant alternative field amplitude Hac = 1 Oe. Fig. 4 shows that the current amplitude roughly exhibits a linear variation as a function of the frequency, in the absence of DC bias field. Thus, it is still in agreement with Eq (3). In this case, the current linearity implies a frequency independent αp coefficient. However, the slight evolution of αp versus frequency can be evaluated from current measurements. It is found that αp values increase as a function of frequency (Fig. 5). A magnetoelectric current is strongly suggested, induced by a linear displacement change of the sample, independent upon DC bias field as observed. However, Fig. 5 also shows that the frequency dependence of αp is not linear. That may be due to the decrease of thickness change with increasing frequency drive.
4. Conclusions From all the measurements plotted in this letter we can make two important conclusions: 1. It is clearly observed that the pure PU shows lower current values than filled polymer (Terfenol-D, Fe3O4 or Nickel) which allows to conclude that the monolayered PU/TeD, PU/Fe3O4 or PU/Ni composites show a ME effect. The magnitude of magnetoelectric current is independent of the applied dc bias magnetic field and is a linear in function of the ac alternative field or applied frequency. 2. Even it is found in the literature that Terfenol-D shows better magnetostrictive properties (λ = 2200 × 10 − 6 ) [9] that Fe3 O 4 (λ = 90.6 × 10− 6) [13] or Nickel (λ = 21.6 × 10− 6) [14], we can see in this letter that for the ME effects there are no significant differences. Actually, measurement of the amplitude of the magnetoelectric current (Fig. 4) or the magnetoelectric coefficient αp at 120 Hz and 1 kHz (Table 1) revealed that Terfenol-D filled polymer exhibits lower ME sensitivity than Fe3O4 or Nickel filled polymer. That fact leads us to the conclusion that the magnetostriction of the material does not have a direct influence on the ME effect in these microcomposites. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Nan CW. J Appl Phys 2008;103:031103–35. Dzyaloshinskii IE. Sov Phys 1959;10:628–9. Astrov DN. Sov Phys 1969;11:708–12. Fiebig MJ. Appl Phys 2005;38:123–52. Nan CW, Li M, Feng X, Yu S. Appl Phys Lett 2001;78:2527–9. Record P. Sens Actuators B 2007;126:344–9. Makoto T, Takao T, Kenji A. IEEE Trans Circuit Theory 1970;17(3):339–44. Nersessian N, Wing S, Carman GP. IEEE Trans Magnetics 2004;40(4):2646–8. Jiles DC, Ostenson JE, Owen CV, Chang TTJ. Appl Phys 1988;64:5417–8. Li Y, Tong G, Liu J, Linliu K, Desper CR, Chu B. Macromolecules 1992;25:7365–72. Guiffard B, Seveyrat L, Sebald G, Guyomar D. J Appl Phys 2006;39:3053–7. Guyomar D, Guiffard B, Belouadah R, Petit L. J Appl Phys 2008;104:074902–6. Bickford LR, Pappis J, Stull JL. Phys Rev 1955;99(4):1210–4. Smith AB, Jones RV. J Appl Phys 1966;37:3.