electric field modulation of magnetic anisotropy and microwave absorption properties in fe50ni50 teflon composite films

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

Electric field modulation of magnetic anisotropy

composite films

Zhenjun Xia,1,2Jun He,1,aXiulong Ou,1Yu Wang,1Shuli He,3

Dongliang Zhao,1and Guanghua Yu2

1Division of Functional Material Research, Central Iron and Steel Research Institute,

Beijing 100081, China

2Department of Materials Physics and Chemistry, University of Science and Technology

Beijing, Beijing 100083, China

3Department of Physics, Capital Normal University, Beijing 100048, China

(Presented 13 January 2016; received 19 October 2015; accepted 2 December 2015;

published online 23 February 2016)

Fe50Ni50 nanoparticle films with the size about 6 nm were deposited by a high energetic cluster deposition source An electric field of about 0 - 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 micro-wave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited

on the dielectric Teflon sheet Then the laminated Fe50Ni50/Teflon composites were used to do 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

fr= γ/2π(4πMsHk)1/2,57the modulation of Hkof magnetic materials with high saturation magne-tization has proven to be an effective approach to enhance the MWA performance

Various techniques had been employed to control Hkof the magnetic films Fu et al controlled the Hkof Fe65Co35/Co films by varying the substrate–target spacing and depositing the films on pre-stressed substrates.8Mayer et al tailored the Hkof Fe films by inclining substrates nanoparti-cles.9Chen et al adopted a magnetic field annealing method to induce the Hkof FeCoB films.10In this article, we are taking a different approach to regulate Hkof the magnetic films, that is, deposit

Fe50Ni50/Teflon composite films under electric field (EF) in high energetic cluster deposition cham-ber 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

Fe50Ni50nanoparticles were prepared by high energetic cluster deposition source.11,12Unlike the regular thin film deposition technique, an EF of about 0 - 40kV was applied on the deposition substrate when the films were manufactured The background pressure of the sputter source is lower than 5 × 10−4Pa During deposition operation, Ar gas with 99.99% purity is continuously intro-duced 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 × 1016Ω·m and permittivity of 1.77 × 10-11F/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 Fe50Ni50nanoparticle 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 6 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 Fe50Ni50films 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, Hkvalue 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 0 to 20 kV step by step, the area monotonically increases When EF is larger than 20 kV, Hkapproaches 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

Fe50Ni50films can be modulated by application of EF

As usual, the magnetic material without dielectric characteristics is difficult to meet electro-magnetic matching requirement In this case, Fe50Ni50nanoparticles 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 1 (a) is bright-field TEM morphology of Fe 50 Ni 50 nanoparticles with the size of about 6nm, the inset is the ED patterns for Fe Ni nanoparticles, (b) is the HRTEM image of Fe Ni nanoparticles.

FIG 2 (a), (b) and (c) are the hysteresis loops of Fe 50 Ni 50 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)| (1)

Zin= Z0(µr/εr)1/2tanhi(2π f d/c)(µrεr)1/2

(2) where Zinis 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)and3(b)are the results of frequency dependence of RL for 5 and 7 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 compos-ites 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 magneti-zation of samples, but also facilitates the increase of Hk Based on the Snoek’s limit,57it 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<-5 dB are exhibited in Fig.4 The 20 kV deposited samples has a considerable contour performance compared with that of 10 kV For example, the 10 kV sample with 3mm thickness exhibits an absorption band from 8 GHz to 17 GHz as marked in Fig.4(a) However, the

FIG 3 (a) and (b) are frequency dependence of RL for Fe 50 Ni 50 /Teflon composites on the different EF assisted deposition condition The inset is the schematic diagram of laminated Fe Ni /Teflon composites.

055905-4 Xia et al. AIP Advances 6, 055905 (2016)

FIG 4 Contour maps of the bandwidth with RL < -5 dB as a function of the composite thickness for samples deposited at

10 kV and 20 kV EF.

20 kV one has a higher absorption band from 11 GHz to the value more than 18GHz, beyond our measuring range This excellent result is an enlightening experience for us that EF assisted deposi-tion is one of the important methods to promote the magnetic anisotropy and the MWA capacity of

Fe50Ni50/Teflon composite films On the other hand, the superior MWA performance is expected to

be obtained only when the composites should have a perfect electromagnetic match In other word, they are in proper thickness as indicated in Fig.4

IV CONCLUSIONS

A series of Fe50Ni50/Teflon composites are synthesized by EF assisted deposition in high energetic cluster deposition system The measurements of the hysteresis loops indicate that EF assisted deposition is an effective method to induce in-plane magnetic anisotropy The reflection loss scan results reveal that the reflection loss peaks shift to higher GHz region with increasing the EF Finally, these results prove that strong in-plane magnetic anisotropy and suitable electro-magnetic matching effect are very important for the Fe50Ni50/Teflon composites to exhibit optimal electromagnetic wave absorption behavior in GHz frequency range

ACKNOWLEDGMENT

This work is supported by the National Natural Science Foundation of China (Grant No 51371055)

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