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Materials Letters 62 (20

Magnetic and mechanical properties of micro/nano particles prepared bymetallizing rod-shaped bacteria

Xin Liang ⁎, Jianhua Liu, Songmei Li, Yu Mei, Wang Yanqing

School of Materials Science and Engineering, BeiHang University, Beijing 100083, PR China

Received 19 September 2007; accepted 30 January 2008Available online 5 February 2008

Abstract

Ni microparticles composed of nano grains are obtained by microbiological and electroless deposition techniques. Ni nano grains deposit onthe surface of Nocadia, one kind of rod-shaped bacteria. The alignment of the rod-shaped metallized Nocadia under conditions with and withoutan applied magnetic field is investigated. The electromagnetic and mechanical properties of the microparticles are characterized by a networkanalyzer and a nanoindentor. It is found that controlled alignment of the metallized Nocadia is realized under the conditions with and without anapplied magnetic field. The dielectric loss is greater than 4.5. The hardness and the elastic modulus of the specimen are 0.55 GPa and 11.26 GPa,respectively. The mechanical properties are greatly improved compared with the bare bacteria.© 2008 Elsevier B.V. All rights reserved.

Keywords: Magnetic materials; Orientation; Dielectrics; Mechanical properties

1. Introduction

Nano/micro particles of magnetic ferrites have attracted greatresearch interest because of their applications in permanentmagnets, drug delivery, microwave devices and high-densityinformation storage [1–4]. The Ni metal layer has been devel-oped as a prototype metallic system exhibiting a ferromagneticbehavior. The preparation of two dimensions magnetic mate-rials about 1 μm ordered self-assembly is difficult due to extramagnetic interaction among the particles [5–7]. The synthesisand fabrication of metallic micro/nano materials based onbiological templates has become novel and attractive trend.Biological templates such asDNA [8–12], microtubules [13–15],S-layer [16–20] and virus [21–24] have been attractivecandidates for their inherent small size and abundant source.Nocadia, one kind of bacteria with standard rod shape, could be

⁎ Corresponding author. Tel./fax: +86 010 82317103.E-mail addresses: xiaohan999999@126.com, liangxin999999@yahoo.com.cn

(X. Liang), liujh@buaa.edu.cn (J. Liu), songmei_li@buaa.edu.cn (S. Li),yumei@mse.buaa.edu.cn (Y. Mei), kitty@mse.buaa.edu.cn (W. Yanqing).

0167-577X/$ - see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.matlet.2008.01.094

used for preparing magnetic materials by appropriate metalliza-tion methods.

In the previous work, the micro/nano rod shaped hollowmaterial has been prepared by metallizing Nocadia withdeposition of pure Ni [25]. In this paper, the magnetic alignmentbehaviors and the electromagnetism parameters of the materialwere investigated. The mechanical properties were studied tobetter explore the possible applications in broad fields.

2. Experimental

Nocadia was metallized to prepare the micro/nano hollowparticles material by electroless deposition of pure Ni on it aftersensitization-activation and acceleration processes. Nocadiawas cultured in brewis medium and recollected [26]. The opticalmorphology of Nocadia before electroless plating was shown inFig. 1.

The shell thickness of the material with rod shape was about100-150 nm after deposition of Ni [25]. The metallized Nocadiawere collected and dispersed into distilled water with ultrasonicvibration. The solution with the dispersed metallized Nocadiawas dropped on a glass microscope slide. A magnetic field wasapplied parallel to the liquid surface.

Fig. 1. Optical micrograph of Nocadia before deposition. Fig. 3. Consistency (a) and the magnetic movement (b) of the metallized No-cadia → magnetic domains.

3000 X. Liang et al. / Materials Letters 62 (2008) 2999–3002

The sample used in electromagnetic properties measurementwas prepared by homogeneously mixing the metallized Noca-dia with 50 wt.% paraffin wax. The measurements were carriedout by a vector network analyzer (Agilent E8363B) in the rangeof 2–18 GHz. The modulus and hardness of the metallizedNocadia were determined at room temperature throughnanoindentation on the Triboindenter mechanical Test Instru-ment. They were determined from the load–displacement

Fig. 2. Optical micrograph of alignment of metallized Nocadia without (a) andwith (b) an applied magnetic field.

curves by using the Oliver and Pharr method [27]. The loadused for the present nanoindentation evaluation was 2000 μN.

3. Results and discussion

A droplet of the solution containing dispersed metallized Nocadiais laid on a glass slide. Fig. 2(a) exhibits the alignment of the metallized

Fig. 4. Complex permittivity, permeability variation (a) and dielectric andmagnetic loss (b) of sample.

Fig. 5. Load-unload curves of bare Nocadia and metallized Nocadia.

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Nocadia after evaporation of water. The metallized Nocadia arraysalong the same direction which indicated that the magnetic domains ofthe metallized Nocadia are in the same direction during magnetization.

A magnetic field is applied to the metallized Nocadia shown inFig. 2(a) after distilled water is dropped on. The alignment of themetallized Nocadia is exhibited in Fig. 2(b). The material arrays alongthe applied magnetic field direction. In Fig. 2 some metallized Nocadiaare chain-like clusters because of magnetic force, resulting inheterogeneous scale. They can rotate/move to the applied magneticfield direction under magnetic force. Fig. 3 shows the magneticdomains direction, consistency and the magnetic movement of themetallized Nocadia.

Fig. 4(a) shows the real and imaginary parts of the complexpermittivity variation (ε′, ε′′) and permeability variation (μ′, μ′′) of thesample, respectively. ε′′ and ε′ decreases with the measuring frequency.μ′′ decreases with frequency while μ′ increases. Fig. 4(b) presents thedielectric loss (tan(δ)=ε′′ /ε′) and magnetic loss (tan(δ)=μ′′ /μ′). Themagnetic loss is less than 0.2, while the dielectric loss increaseswith frequency, with aminimum of 4.5 at about 5.7 GHz. At the range of17–18 GHz, the dielectric loss shows a sudden increase due toinstability of data at boundary of the experiment. There are two peaksassociated to 7.48 GHz and 9.82 GHz due to synergistic effect ofpolarization loss and conduction loss which was influenced byfrequency. The dominant dipolar polarization, interfacial polarization[28–29] and the associated relaxation phenomena are attributed to theloss mechanisms. It has been shown by [30–32] that the properties ofinterfaces have played an important role in determining dielectricperformance. The conduction loss is caused mainly by the currentforming with free charges which are composed of grain boundaries,lattice distortion and impurities of the Ni layer. The vibration ofelectrons due to the deformation of the electron cloud outside Nickelatomic nucleus and directional shifting of Ni crystal layer electronsunder AC (alternating current) conductivity contribute to the dielectricloss. Furthermore the vibration, reflection and superposition of theelectromagnetic wave interior the Ni layer are also factors of the loss.

The magnetic loss is little owing to the polycrystalline of Ni.Furthermore heterogeneous structure of crystal, relaxation ions andoxide at grain boundary decrease the magnetic loss[28].

Fig. 5 presents load-unload curves of bare Nocaidia and metallizedNocadia. At peak load, the load and displacement are Fmax and hmax,respectively. According to the Oliver and Pharr method of nanoinden-tor, the hardness H=Fmax /A(A is the area function), and the elastic

modulus E ¼ffiffip

pdF

2ffiffiffiA

pdh

dFdh

�is the slope of the unloading curve at maxi-

mum loadÞ. The hardness and elastic modulus of the bare Nocadiaare 0.27 GPa and 9.50 GPa, respectively. Those of the metallizedNocadia are 0.55 GPa and 11.26 GPa, respectively. It appears agreat improvement in the mechanical properties of the metallizedNocadia.

4. Conclusions

(1) After magnetization the metallized Nocadia realizesorientation without an applied magnetic field. Thecontrolled alignment of the metallized Nocadia with rodshape under an applied magnetic field is also realized.

(2) The dielectric loss is greater than 4.4 at the frequencyrange of 2-18 GHz. The magnetic loss is less than 0.2.

(3) The hardness and the elastic modulus of the metallizedNocadia are 0.55 GPa and 11.26 GPa, respectively.

Acknowledgement

The authors gratefully acknowledge the financial supportfrom the National Nature Science Foundation of China(50571003) that made this research possible.

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