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Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films Zhenjun Xia, Jun He, , Xiulong Ou, Yu Wang, Shuli He, Dongliang Zhao, and Guangh[.]
Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films , Zhenjun Xia, Jun He , Xiulong Ou, Yu Wang, Shuli He, Dongliang Zhao, and Guanghua Yu Citation: AIP Advances 6, 055905 (2016); doi: 10.1063/1.4942957 View online: http://dx.doi.org/10.1063/1.4942957 View Table of Contents: http://aip.scitation.org/toc/adv/6/5 Published by the American Institute of Physics AIP ADVANCES 6, 055905 (2016) Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/ Teflon composite films Zhenjun Xia,1,2 Jun He,1,a Xiulong Ou,1 Yu Wang,1 Shuli He,3 Dongliang Zhao,1 and Guanghua Yu2 Division of Functional Material Research, Central Iron and Steel Research Institute, Beijing 100081, China Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China Department of Physics, Capital Normal University, Beijing 100048, China (Presented 13 January 2016; received 19 October 2015; accepted December 2015; published online 23 February 2016) Fe50Ni50 nanoparticle films with the size about nm were deposited by a high energetic cluster deposition source An electric field of about - 40 kV was applied on the sample platform when the films were prepared The field assisted deposition technique can dramatically induce in-plane magnetic anisotropy To probe the microwave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited on the dielectric Teflon sheet Then the laminated Fe50Ni50/Teflon composites were used to reflection loss scan The results prove that the application of electric field is an effective avenue to improve the GHz microwave absorption performance of our magnetic nanoparticles films expressed by the movement of reflection loss peak to high GHz region for the composites C 2016 Author(s) All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License [http://dx.doi.org/10.1063/1.4942957] I INTRODUCTION Electromagnetic radiation, pollution, and interference are serious issues in terms of safety, environment, and human health Microwave absorption (MWA) material has the potential to solve this problem, and its application in civil and military engineering has been increasing recently.1–3 MWA properties are closely related to magnetic and/or dielectric loss of materials.4 Magnetic materials with high saturation magnetization and large magnetic anisotropy field (Hk) are expected to be the candidates for MWA in GHz range based on the Snoek’s equation f r = γ/2π(4πMs Hk )1/2,5–7 the modulation of Hk of magnetic materials with high saturation magnetization has proven to be an effective approach to enhance the MWA performance Various techniques had been employed to control Hk of the magnetic films Fu et al controlled the Hk of Fe65Co35/Co films by varying the substrate–target spacing and depositing the films on pre-stressed substrates.8 Mayer et al tailored the Hk of Fe films by inclining substrates nanoparticles.9 Chen et al adopted a magnetic field annealing method to induce the Hk of FeCoB films.10 In this article, we are taking a different approach to regulate Hk of the magnetic films, that is, deposit Fe50Ni50/Teflon composite films under electric field (EF) in high energetic cluster deposition chamber The results indicate that EF assisted deposition is a very effective technique to induce the Hk and modify MWA performance in our samples a Corresponding author at: Division of Functional Material Research, Central Iron and Steel Research Institute, No 76 Xueyuan South Road, Haidian District, 100081 Beijing, P.R China Tel.: +86-10-62187570, Fax: +86-10-62187102 E-mail address: hejun@cisri.com.cn (Jun He) 2158-3226/2016/6(5)/055905/4 6, 055905-1 © Author(s) 2016 055905-2 Xia et al AIP Advances 6, 055905 (2016) II EXPERIMENTAL DETAILS Fe50Ni50 nanoparticles were prepared by high energetic cluster deposition source.11,12 Unlike the regular thin film deposition technique, an EF of about - 40kV was applied on the deposition substrate when the films were manufactured The background pressure of the sputter source is lower than × 10−4 Pa During deposition operation, Ar gas with 99.99% purity is continuously introduced into the sputtering chamber through a nozzle, maintaining the sputtering chamber pressure at about 40 - 50 Pa A tank with cooling interlayer in sputtering chamber is used to cool down the sputtered nanoparticles during deposition To probe the electromagnetic wave absorption properties, 0.5 mm thick Teflon sheet, with resistivity of 1.18 × 1016 Ω·m and permittivity of 1.77 × 10-11 F/m in a wide frequency range, was chosen as the functional substrate The Teflon sheets were cut into annular samples with ϕout = 7.00 mm and ϕin = 3.04 mm to match the cavity size of coaxial transmission line 90 nm thick Fe50Ni50 nanoparticle films were then deposited on them to be the Fe50Ni50/Teflon composites The morphology and the size of the nanoparticles were characterized by transmission electron microscope (TEM) JEOL 2010 The magnetic properties were measured by a vibrating sample magnetometer (VSM) at room temperature The coaxial transmission line method was chosen to scan the reflection loss (RL) characteristics by an Agilent N5230C network analyzer III RESULTS AND DISCUSSION Fig 1(a) shows the bright-field TEM morphology of the Fe50Ni50 nanoparticles, the size of the nanoparticles is about nm It has fcc phase structure and confirmed as indexed in the inset Fig 1(b) exhibits a high-resolution TEM (HRTEM) of the nanoparticles The clear lattice spacing as shown in HRTEM corresponds with the standard (200) plane of the γ FeNi phase Room temperature hysteresis loops of the Fe50Ni50 films are measured as shown in Fig 2(a) - 2(c) The strong ferromagnetic characteristics for all of these nanoparticles films are ascribed to the high packing density due to the application of high energy electric field during deposition In this study, Hk value is determined by calculating the area between the in-plane (∥) and out-of-plane (⊥) magnetization curves as shadowed in Fig 2(b) There is little difference between the in-plane and out-of-plane hysteresis loops for zero field deposited sample as shown in Fig 2(a) However, as the EF goes up from to 20 kV step by step, the area monotonically increases When EF is larger than 20 kV, Hk approaches its saturation as shown in Fig 2(d) In fact, EF promoted the packing density of our Fe50Ni50 nanoparticles On the condition of same thickness, the measured samples become more and more difficult to be magnetized in the out-of-plane direction with increasing EF, compared with the in-plane direction Thus, the magnetic measurement indicates that the Hk of Fe50Ni50 films can be modulated by application of EF As usual, the magnetic material without dielectric characteristics is difficult to meet electromagnetic matching requirement In this case, Fe50Ni50 nanoparticles were deposited onto a 0.5 mm thick annular Teflon sheet as a composite The laminated structural Fe50Ni50/Teflon composites as sketched in the inset of Fig 3(a) were used to scan the complex permeability µr and complex permittivity εr According to the transmission-line theory, the reflection loss can be obtained by the FIG (a) is bright-field TEM morphology of Fe50Ni50 nanoparticles with the size of about 6nm, the inset is the ED patterns for Fe50Ni50 nanoparticles, (b) is the HRTEM image of Fe50Ni50 nanoparticles 055905-3 Xia et al AIP Advances 6, 055905 (2016) FIG (a), (b) and (c) are the hysteresis loops of Fe50Ni50 films prepared under 0kV, 10kV, and 20kV applied electric field respectively (d) is the EF dependence of magnetic anisotropy following equations: RL( f ) = 20log10 |(Zin − Z0)/(Zin + Z0)| Zin = Z0(µr /ε r )1/2 i(2π f d/c)(µr ε r )1/2 (1) (2) where Zin is the input impedance of the absorber, c is the velocity of electromagnetic waves in free space, f is the frequency of microwaves, and d is the thickness of the absorber The RL was calculated by equation (1) and (2) Fig 3(a) and 3(b) are the results of frequency dependence of RL for and layers Fe50Ni50/Teflon composites respectively It is clear that the application of EF is very effective in improving the GHz MWA performance Both of the composites exhibit the RL peaks shift to the high GHz region when the EF increases from 10 to 20 kV As introduced in magnetic measurement, the increment of EF, not only modifies the in-plane magnetization of samples, but also facilitates the increase of Hk Based on the Snoek’s limit,5–7 it is obvious that the maximum RL is easy to appear in the higher resonance frequency region To amplify the impression of the MWA capability for our Fe50Ni50/Teflon composites, the RL contour maps were given for samples deposited by 10 kV and 20 kV EF The contour maps of the bandwidth with RL