Fe–Pd magneto-electric composites with Fe–Pd thick layer

Fe–Pd magneto-electric composites with Fe–Pd thick layer

Sensors and Actuators A 200 (2013) 11–15 Contents lists available at SciVerse ScienceDirect Sensors and Actuators A: Physical journal homepage: www...

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Sensors and Actuators A 200 (2013) 11–15

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna

Output characteristics in Fe–Pd/PZT/Fe–Pd magneto-electric composites with Fe–Pd thick layer Takeshi Kubota a,∗ , Teiko Okazaki b , Naoto Endo b , Kosuke Mikami b , Yasubumi Furuya b a b

North Japan Research Institute for Sustainable Energy, Hirosaki University, 2-1-3 Matsubara, Aomori 030-0813, Japan Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo, Hirosaki 036-8561, Japan

a r t i c l e

i n f o

Article history: Received 1 June 2012 Received in revised form 1 November 2012 Accepted 12 November 2012 Available online 6 December 2012 Keywords: Multi-ferroic composite Magnetoelectric coupling Rapidly solidified ribbon Magnetostrictive Fe–Pd alloy Pb(Zr Ti)O3 Magnetic sensor

a b s t r a c t Magneto-electric (ME) characteristics of the ferromagnetic/ferroelectric Fe70 Pd30 /PZT/Fe70 Pd30 thin composites were investigated. The ME composites composed of the ferroelectric PZT phase (center layer, t: 260 ␮m) and the ferromagnetic, magnetostrictive Fe70 Pd30 phase (t: 30–90 ␮m) glued on both the surfaces of PZT were fabricated. The rapidly solidified Fe70 Pd30 ribbon mainly consists of fct martensitic phase with a large magnetostriction and fcc austenite (parent) phase. According to the DC bias magnetic field dependency of the output ME voltage (VME ) at an AC magnetic field of 1.0 Oe with an operation frequency of 1 kHz for the composites, the increasing in thickness of magnetostrictive layers showed remarkable improvement of VME values. For the composite with 90 ␮m Fe–Pd layers, maximum VME value of 13.9 mV was obtained at 60 Oe of the DC field, which is about two times higher than that of the composite with 30 ␮m Fe–Pd layers. Additionally the VME value of the serial circuit was monotonically enhanced by the serial circuit connection, and the composites exhibited a very large peak at a resonant frequency of 61–68 kHz. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Multi-ferroic materials have a great potential for any useful applications due to their excellent multi-functionality. Ferromagnetic/ferroelectric composites are drawing attention since they exhibit physical properties with magnetoelectric (ME) response significantly larger than those of single-phase materials. Therefore ME composites are expected to be new magnetic devices such as sensors and actuators. The principle of the ME effect is that magnetic field induced strain (magnetostriction, ) in ferromagnetic component is transferred to a strain (ε) in the piezoelectric component through elastic coupling, resulting in a piezo-induced power generation (voltage). Currently, magnetoelectric couplings in Terfenol-D/PZT [1], Terfenol-D/PVDF-film [2], nickel-ferrite/PZT [3], Fe80 Ga20 /PZT [4] and FeCoV/PZT [5] bulk composites have been reported. Further, the ME effect in sputtered AIM-(TbCo2 /FeCo) thin films [6] and all-thin-filmed (Fe0.7 Ga0.3 /PZT)/Si sensors [7] to apply microelectronic devices have been reported. Most of these ME devices consist of PZT: Pb(Zr1−x Tix )O3 and Terfenol-D; Tb1−x Dyx Fe2−y which exhibits giant magnetostriction of 1600–2000 × 10−6 at room temperature.

∗ Corresponding author. Tel.: +81 17 764 7762; fax: +81 17 735 5411. E-mail address: [email protected] (T. Kubota). 0924-4247/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2012.11.021

However, rather large magnetic field of several kOe is required for exhibiting giant strain on the Terfenol-D [1], and ME sensors limitedly driven by large magnetic field are difficult to apply to microelectronic devices. Ferromagnetic shape memory alloy, Fe–Pd, consisted of fct martensite phase exhibits remarkably large magnetostriction due to the conversion of twin-variants by magnetic field [8]. Single crystal of Fe70 Pd30 [9] exhibited field-induced-strain of 6000 × 10−6 at −17 ◦ C, which is larger than the magnetostriction of Terfenol-D. However, heretofore, both academic and technical reports on ME coupling in Fe–Pd/PZT composite are little. Previously, we have investigated the magnetic properties of fct Fe70 Pd30 ribbon prepared by a rapidly solidification meltspinning method [10,11] and of magnetron sputtered films [12]. The magnetostriction of Fe70 Pd30 films was found to be induced at a low magnetic field below 500 Oe. Recently, we have reported the ME effect in Fe70 Pd30 film/PZT/Fe70 Pd30 film and Fe80 Ga20 film/PZT/Fe80 Ga20 film three-layered composites [13]. From these results, it is found that the ME effect in Fe70 Pd30 film/PZT/Fe70 Pd30 film is five times larger than that in Fe80 Ga20 film/PZT/Fe80 Ga20 film. Furthermore, compared to above composites, more large ME effect can be observed in Fe70 Pd30 ribbon/PZT/Fe70 Pd30 ribbon three-layered composite [14]. In this study, we investigated fundamental properties of the rapidly solidified Fe70 Pd30 ribbon, and the ME effect in

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Fe70 Pd30 /PZT/Fe70 Pd30 laminated composites at driving ac magnetic field of low and high frequency ranges was discussed at the point of view of the ribbon thickness. 2. Experimental procedure PZT substrate (C-62) with 260 ␮m in thickness, 20 mm in length and 10 mm in width was purchased from the Fuji Ceramic Inc., Japan. Both the surfaces of PZT are coated with silver film (electrodes), which is about 5 ␮m in thickness. Magnetostrictive Fe70 Pd30 alloy ribbons (30 and 90 ␮m in thickness and 5 mm in width) were produced by a melt-spinning technique in an Ar atmosphere and were glue to substrates by adhesive bond (Epoxy resin; two-liquid mixed type Araldite® standard) as shown in Fig. 1(a). Prior to manufacturing the composite specimens, the ribbon was annealed at 900 ◦ C for 3.6 ks in order to remove inner stress induced during rapid solidification process. Here the reason of the alloy composition is optimal composition for formation of fct martensite phase at room temperature after quenching process [15]. The structure of rapidly solidified Fe70 Pd30 alloy ribbons was analyzed by X-ray diffraction (XRD) with Cu-k␣ radiation. The magnetostriction, , of the ribbons under steady magnetic field was measured using a strain-gauge attached to a longitudinal direction of the ribbon, and magnetic field was applied to same direction. Fig. 1(b) shows schematic illustrations of an originally designed measurement system and directions of magnetic/dielectric field applying to magnetoelectric composites, which are L–T mode three/five-layer composites. Output ME voltage was measured by using the system composed of a function generator (KENWOOD, FG-281), a bipolar amplifier (KIKUSUI, POW35-5) and a solenoid coil for applying magnetic field of AC sinusoidal wave and DC bias, and a charge amplifier (NEC/Avio, AG3103) and a data logger (Tektronix, TDS2014B) for measuring the output voltage. When the

driving AC magnetic field (HAC ) with frequency range of 0.05 Hz to 80 kHz and DC bias magnetic field (HDC ) were applied along the length bi solenoid coil around the composite, the magnetoelectric charge generated across the specimens was measured using the charge amplifier. Here the gain value of charge amplifier was fixed to 400× (1.25 mV/pC) in whole frequency range. Therefore the ME voltage (VME ) was converted by VME = Voutput /400, where Voutput is obtained output voltage from the charge amplifier.

3. Results and discussion 3.1. Fundamental properties of rapidly solidified Fe70 Pd30 alloy ribbon Fig. 2 shows the XRD profiles for rapidly solidified Fe70 Pd30 alloy ribbon in (a) an as-quenched state and (b) an annealed state. On both the results, the structure consists of fct martensitic, fcc austenite and small amount of bct phases. This result is reasonable, because a few phase transformations at the vicinity of room temperature such as fcc to fct, fct to bct and fcc to bct on cooling process have been confirmed in quenched Fe–Pd alloy with near the composition of Fe70 Pd30 [15], and the temperatures strongly depend on the grain size [17,18]. Furthermore, in as-quenched state (as-Q), inner (thermal) stress should be induced during melt-spinning process, phase transformation temperatures might be fluctuated by the stress. Actually the temperature range for the start of the reverse phase transformation from fct to fcc on a heating process for the as-spun Fe70 Pd30 ribbon was recognized about 22–151 ◦ C in our previous study [10,19]. Based on the result of the annealed specimen, co-existence of all the phase, i.e. fct, fcc and bct still remained although fct peak intensity increased. Therefore formation of bct phase might be originated from the effect of grain size.

Fig. 1. (a) Schematics for the layer structure of three-layered composite and outer appearance and (b) schematic of the measurement system and directions of magnetic/dielectric field around composite specimen.

T. Kubota et al. / Sensors and Actuators A 200 (2013) 11–15

Fig. 2. XRD profiles for rapidly solidified Fe70 Pd30 alloy ribbon in (a) an as-quenched state and (b) an annealed state.

At the point of view of magnetostriction, only the fct martensite phase is efficiency. Comparing both the results, because the annealed specimen consisted of relatively large amount of fct phase with strongly 100-oriented texture, larger magnetostriction might be expected on the annealed specimen. The magnetostriction, , of the rapidly solidified Fe70 Pd30 alloy ribbon as a function of applied magnetic field, H, is shown in Fig. 3. The  value remarkably increased in low magnetic field in the range of less than about 2 kOe and mostly saturated at 4 kOe. The saturation  value is 80 × 10−6 for the as-quenched specimen and 92 × 10−6 for the annealed specimen, respectively. Although hysteresis with increasing and decreasing magnetic field was recognized, these specimens showed good magnetic responsibility. 3.2. Output ME voltage of Fe70 Pd30 /PZT/Fe70 Pd30 composites We investigated ME coupling of Fe70 Pd30 /PZT(C-62, t: 260 ␮m)/Fe70 Pd30 laminate composites, in which rapidly solidified Fe70 Pd30 (30 and 90 ␮m) ribbons were glued to silver-coated PZT substrates. Output ME voltage, VME on the driving ac magnetic field Hac was estimated from magnetoelectric charge generated across the samples using relative dielectric constant ε33 T /ε0 .

Fig. 3. Magnetostriction, , as a function of applied magnetic field, H for rapidly solidified Fe70 Pd30 alloy ribbon in (a) an as-quenched state and (b) an annealed state.

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Fig. 4. VME (mV) as a function of DC bias magnetic field, Hbias at an ac driving field, Hac of ±1 Oe with an operation frequency, f, of 1 kHz for various magneto-electric composites (MEC-s), A: Fe70 Pd30 (30 ␮m)/PZT/Fe70 Pd30 (30 ␮m), B and B’: Fe70 Pd30 (90 ␮m)/PZT/Fe70 Pd30 (90 ␮m), C: parallel connection-typed composite of B and B’, D: serial connection-typed composite of B and B’ and E: five-layered Fe70 Pd30 (90 + 90 ␮m)/PZT/Fe70 Pd30 (90 + 90 ␮m).

Fig. 4 shows the VME (mV) as a function of DC bias magnetic field, Hbias at an ac driving field, Hac of ±1 Oe with an operation frequency, f of 1 kHz. Here, names of all the composites are defined as magnetoelectric composite (MEC)-A for the Fe70 Pd30 (30 ␮m)/PZT/Fe70 Pd30 (30 ␮m), MEC-B and MEC-B’ for the Fe70 Pd30 (90 ␮m)/PZT/Fe70 Pd30 (90 ␮m), MEC-C for the parallel connection-typed composite of B and B’, MEC-D for the serial connection-typed composite of B and B’, and MEC-E for the Fe70 Pd30 (90 + 90 ␮m)/PZT/Fe70 Pd30 (90 + 90 ␮m), i.e. five-layered composite structure. For all the MEC, these VME –Hbias loops exhibited hysteresis and a maximum VME is taken at Hbias of about ±40, ±60, ±90 and ±120 Oe, respectively, on decreasing magnetic field from 200 Oe except for MEC-E. Additionally it was found that a little difference between MEC-B and MEC-B’ of optimal Hbias value, the reason might be originated from some technical error on bonding process. Table 1 summarizes the name, symbol in Figs. 4–6, specifications (ribbon thickness, structure of the composite and connection type), optimal DC bias magnetic field, Hbias and maximum VME value at Hbias . For comparing MEC-A and MEC-B, maximum VME value increased with increasing in the thickness of the Fe70 Pd30 layer, the

Fig. 5. VME for the MEC-A, -B, -C, -D and -E under the AC driving magnetic field, HAC of 0.1 Oe with optimal Hbias (40, 60, 90 and 120 Oe).

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Table 1 Defined name, symbol and specifications (ribbon thickness, structure of the composite and connection type) of MEC-s, and optimal DC bias magnetic field, Hbias and maximum VME value at Hbias for each MEC-s. Specimen Name

Symbol

A B B’ C D E

 䊉    

a

Ribbon thickness

Composite structure

Connection type

Optimal Hbias (Oe)a

VME @ Hbias (mV)a

30 ␮m 90 ␮m 90 ␮m 90 ␮m 90 ␮m 90 + 90 ␮m

Three Three Three Three Three Five

Single Single Single Parallel Serial Single

40 60 90 90 90 120

7.39 13.9 12.9 13.5 25.0 15.2

Under 1.0 Oe and 1 kHz of AC magnetic field.

Fig. 6 shows the VME as a function of frequency for the MEC-B, -C, -D and -E under the HAC of 5.0 Oe with optimal Hbias in low frequency range of 5.0 × 10−2 Hz to 1.0 × 102 Hz. It is found that the VME of all the MEC-s sustained almost constant value at 1.0 Hz with decrease in operation frequency. Particularly the MEC-B exhibited good low frequency characteristics, the VME at 5.0 × 10−2 Hz is 4.2 mV, which is highest value at 5.0 × 10−2 Hz, in this study. For the MEC-C, lower VME value was obtained in whole of the measurement range. As the results, the component structure of the MEC-C, parallel connection-typed MEC, is unbefitting for high efficiency- and/or high power generation-typed MEC. However, it is concluded that a three-layered MEC prepared by thicker Fe–Pd layer is appropriate for wide frequency range magnetic sensor, which can generate high VME . Furthermore above mentioned MEC has a potential applied to the energy harvesting technology.

Fig. 6. VME as a function of frequency for the MEC-B, -C, -D and -E under the HAC of 5.0 Oe with optimal Hbias in low frequency range of 5.0 × 10−2 Hz to 1.0 × 102 Hz.

value of the MEC-B reached to about twice of that of the MEC-A. This tendency coincides with our previous research on the Fe70 Pd30 -film (2, 5, 10 ␮m)/PZT/Fe70 Pd30 -film (2, 5, 10 ␮m) composites prepared by a RF-sputtering technique [16]. However, a maximum VME of the MEC-E was comparable to that of MEC-B. It is considered that the reasons for the behavior of the MEC-E are (i) increasing the demagnetization factor by layer thickening for optimal Hbias field shifted to higher field and (ii) buffer effect by multi-bonding layers. The VME value of the MEC-C (13.5 mV) was also comparable to that of the MEC-B (13.9 mV). While, for MEC-D the VME (25.0 mV) is much higher than all other MEC. For both the MEC-C and MEC-D, a magnetic, inferior, characteristic of MEC-B’ results on optimal Hbias . Variation of maximum VME value is quite reasonable because the terminal voltage of the simple-circuits was measured in this study, quantity survey value of the voltage was detected on the MEC-D. Next, the frequency dependencies of the MEC-s were measured in high frequency range of 1.0–9.0 × 104 Hz. Fig. 5 shows the VME for the MEC-A, -B, -C, -D and -E under the AC driving magnetic field, HAC of 0.1 Oe with optimal Hbias (40, 60, 90 and 120 Oe). The VME as a function of frequency for all the MEC-s gradually increased with a frequency from 1.0 × 104 Hz to 50 × 104 Hz and exhibited a remarkably large peak at each resonant frequency, fr (6.1–6.8 × 104 Hz). The thickness dependency as shown in Fig. 4 also appeared in this measurement, and the MEC-B exhibited three times higher VME value than the MEC-A. Especially the VME of the MEC-D reached to 25.0 mV which is five times higher than that of the MEC-A. On the other hand, the VME of the MEC-C was relatively lower than others as against that of the MEC-B. The reason of this reducing tendency is not clear as of now, thus additional measurements are in operation. Therefore thicker Fe–Pd layer is chosen for Fe–Pd/PZT/Fe–Pd threelayered composite with high output voltage, and serial connected circuit is also chosen, simultaneously.

4. Conclusions Magneto-electric (ME) coupling in multiferroic composites designed using ferromagnetic shape memory Fe70 Pd30 and ferroelectric PZT is expected to be applied to several magnetic devices. Thickness dependency of the Fe70 Pd30 layer and the ME voltage of preparing ME composites were investigated in this study. Obtained results are summarized as follows: 1. The rapidly solidified Fe70 Pd30 alloy ribbon exhibited good magnetic responsibility, large magnetostriction with good linearity could be obtained in the weak magnetic field of less than 2 kOe. 2. The output ME voltage, VME , of magneto-electric composite (MEC)-s increased with thickness of the magnetostrictive Fe70 Pd30 layer, and the parallel connection is also effective for enhancement of the VME . 3. Fe70 Pd30 /PZT/Fe70 Pd30 MEC-s at a driving ac field, Hac with optimal dc bias field, Hbias of 40–120 Oe exhibited a very large peak of VME at a resonant frequency, and were constant in a wide frequency range of 1–100 Hz. Acknowledgment This work was partially supported by the Grant-in-Aid for Basic Researches (A) (21246019) from MEXT. References [1] J. Ryu, A.V. Carazo, K. Uchino, H. Kim, Japanese Journal of Applied Physics 40 (2001) 4948. [2] K. Mori, M. Wuttig, Applied Physics Letters 81 (2002) 100. [3] M.I. Bichurin, D.A. Filippov, V.M. Petrov, V.M. Laletsin, N. Paddubunaya, G. Srinivasan, Physical Review B 68 (2003) 132408. [4] X. Dong, J. Zhai, F. Bai, J.F. Li, D. Viehland, Applied Physics 97 (2005) 103902. [5] D.A. Filippov, U. Laletsin, G. Srinivasan, Journal of Applied Physics 102 (2007) 093901. [6] N. Tiercelin, A. Talbi, V. Preobrazhensky, P. Pemod, V. Mortet, K. Haenen, A. Soltani, Applied Physics Letters 93 (2008) 162902.

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