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Electrochimica Acta 53 (2007) 4–6

Near field and magnetic field generator for thermalassisted magnetic recording

S. Miyanishi ∗, N. Iketani, I. Suzuki, Y. Murakami, K. Kojima, A. TakahashiAdvanced Technology Research Laboratories, SHARP Corporation, 2613-1, Ichinomoto, Tenri, Nara 632-8567, Japan

Received 30 November 2005; received in revised form 16 January 2007; accepted 16 January 2007Available online 30 January 2007

bstract

We fabricated a generator that produces optical near field and magnetic filed in a nanometer area for achievement of thermally assisted magneticecording. The generator consists of an embedded wire with a bottleneck structure on a SiO2 substrate. The magnetic field is mainly generatedround the bottleneck structure by feeding current through the wire. The near field is produced on an edge of the narrow wire by focusing a laser

eam on the bottleneck structure through the backside of the substrate. The generator is anticipated as application to control ordering, chirality,nd phase transition of diamagnetic materials in a nano-area. We confirmed the three-dimentional localization of near field in the nanometer sizeround the bottleneck structure by means of a near field scanning optical microscope.

2007 Elsevier Ltd. All rights reserved.

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eywords: Near field; Magnetic field; Bottleneck structure; Surface plasmon; T

. Introduction

Thermally assisted magnetic recording has attracted atten-ions as a new technology to achieve the areal storage density ofTb/in.2 in magnetic recording [1–3]. It is quite important howmagnetic head incorporates the heat source that enables to

onfine the thermal distribution on a magnetic medium to a 25-m area corresponding to the bit density of 1 Tb/in.2. Recently,n optical near field has been emerging as a possible candi-ate of the nano-sized heat source for the thermally assistedagnetic recording [4,5]. We have reported a near field andagnetic field generator as a new hybridized magnetic head for

he thermally assisted magnetic recording [6]. In the report, thehermally assisted magnetic recording has been accomplishedy means of the near field and magnetic field generator.

The generator is anticipated as application to control orderingnd chirality of diamagnetic materials on a nano-area employingeneration of the magnetic field because the magnetic effect is

seful for processing of many diamagnetic substances includ-ng biological, organic, polymeric, and inorganic materials [7].urthermore, the near field produced by the generator enables to

∗ Corresponding author. Tel.: +81 743 65 4967; fax: +81 743 65 0543.E-mail address: miyanishi.shintaroh@sharp.co.jp (S. Miyanishi).

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013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved.oi:10.1016/j.electacta.2007.01.037

ally assisted magnetic recording

eat up the materials in a nano-area and then to change phase ofaterials. The investigation of the near field confinement is abso-

utely essential in view of acquiring knowledge of applicationo control the nano-sized phase transition of the materials.

In this paper, we report the structure of the generator and char-cterize the three-dimentionally localized optical near field onhe generator by using a near field scanning optical microscopeNSOM).

. Structure of generator

The near field and magnetic field generator consists of anmbedded wire with a bottleneck structure on a quartz (SiO2)ubstrate, and an optical head. Fig. 1 shows an illustration ofhe generator and the optical head located below the generatorn order to irradiate a laser beam on the wire with the bottleneckrom the backside of the SiO2 substrate. The generator wasabricated through a conventional photolithography process.he embedded wire was produced by e-beam deposition after

eactive ion etching of the SiO2 substrate; the wire has a layeredtructure of Au (300 nm)/Ti (50 nm) on the SiO2 substrate. A

rotection layer of SiN with a thickness of about 10 nm covershe top surface of the generator. The curved wire with the bottle-eck part equates to a half-turn coil. The width of the bottleneckire is 1 �m; a curvature radius is 100 nm on the top of the

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nmgenerator as a hybrid magnetic head. We accomplished thermalassisted magnetic recording of a very narrow track width lessthan the optical resolution. In fact, the result suggested that localheating of the magnetic media can be achieved by the localiza-

ig. 1. Schematic diagram of the near field and magnetic field generator and theptical head.

edge of the SiO2 substrate. The magnetic field is mainly gen-rated around the bottleneck wire by feeding current through theire. The embedded wire has also the ledge structure along the

dge on the wire; the height and width of ledges are about 50 nm,espectively (see Fig. 3(a)). The structure locally enhanceshe magnetic field and the near field on the magnetic media6].

We estimate the magnetic field on the surface of the genera-or around the bottleneck wire using the Maxwell equations. Thentensity of the magnetic field, H, around the wire is expresseds follows: H = I/L, where I is an electric current and L is anuter path length of the bottleneck wire. The H of 35.7 kA/m447 Oe) on the surface of the wire was calculated in a casehen the I is 100 mA and the L is 2.8 �m at the bottleneck wire.he magnetic flux can be focused on the center of curvatureround the bottleneck by the configuration of the half-turn coil.he magnetic-field distribution strongly depends on the config-ration of the bottleneck wire. The structure of the embeddedire was also designed to release the heat from the bottleneckire during the current supply.

. NSOM observation

We employed the NSOM to experimentally confirm the local-zation of the near field on the generator. Fig. 2 shows anllustration of a NSOM system and a NSOM image on the sur-ace of the generator. In order to generate the near field, weocused the laser beam with circular polarization on the wirerom the backside of the substrate using an optical head. Thepecifications of the optical head were as follows: wavelength is50 nm, N.A. is 0.65, and a spot diameter (1/e2) is around 1 �m.

A surface plasmon, which is so called the optical near field, isnown to be a collective excitation of the electrons at the inter-

ace between a conductor and an insulator. The laser irradiationxcites a surface plasmon on the metal surface of the bottleneckire and then the surface plasmon is localized and enhanced on

he edge of the bottleneck wire.

ica Acta 53 (2007) 4–6 5

The near field is observed by the detection of the scatteredar field when a tip of an atomic force microscopic (AFM) probehanges the localized near field into the propagating far field. Wean, thus, obtain the three-dimensional distribution of the neareld by the scanning of the probe on the surface of the generator.ince the near field exponentially decreases with the distancerom the metal surface, the near field can be distinguished fromhe far field by the scanning z-height dependence of the scatteredntensity. Fig. 3 shows an AFM image on the surface around theottleneck part of the generator and NSOM images, which areorresponding to the area enclosed by dashed line in Fig. 3(a),canned on two different z-heights. As seen in Fig. 3(b), theear field is locally generated in the 100-nm area around the topf the wedge on the surface of the generator (z = 0 nm), wherehe scattered intensity is designated as bright. The NSOMmage scanned 150-nm above the surface (z = 150 nm) indicatedhat the near field is selectively excited on the ledge structurelong the edge on the wire. Near field localized areas in theSOM images further exceed the optical refraction limit of theptical head.

Fig. 4 shows dependence of the near field intensity on the-height at the center of curvature around the top of the wedgen NSOM measurements. The intensity exponentially decreasesith the scanning z-height of the AFM probe. The z-height at halfaximum of the intensity is about 100 nm. As mentioned above,

he consequences of the NSOM measurement indicate that theear field is three-dimensionally trapped in the 100-nm cubicpace on the top of the wedge of the generator. Furthermore, webtain similar z-height dependence of the near field intensity onhe ledge structure along the edge on the wire.

. Discussion

In the previous report [6], we confirmed the generation of theear field and the magnetic field through the near field assistedagnetic recording employing the near field and magnetic field

Fig. 2. An illustration of a NSOM system.

6 S. Miyanishi et al. / Electrochimica Acta 53 (2007) 4–6

Fig. 3. (a) An AFM image on the surface around the bottleneck part of theg(b

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enerator, and NSOM images (b) on the surface of the generator (z = 0 nm) andc) 150-nm above the surface (z = 150 nm) corresponding to the area enclosedy dashed line in the AFM image.

ion of the near field. The results are consistent with the NSOMeasurement that indicated the three-dimensional nano-sized

onfinement of the near field. The localization of the near fieldnd the magnetic field strongly depends on the configuration of

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ig. 4. Dependence of the near field intensity on z-height at the center of cur-ature around the top of the wedge.

he metal structure. Therefore, a finer configuration of the bot-leneck wire would enables to narrow the region, in which theear field and the magnetic field, on the generator.

. Conclusion

We introduced the structure and the principle of the generatorhat produces the near field and the magnetic field in the nano-rea. The NSOM was employed to experimentally confirm theocalization of the near field on the generator. It was found thathe near field is three-dimensionally localized in the nanome-er size on the generator. The generator holds the promise ofpplication to control ordering, chirality, and phase transitionf many diamagnetic substances including biological, organic,olymeric, and inorganic materials in the nano-area employingeneration of the near field and the magnetic field.

cknowledgements

One of the authors (S.M.) would like to thank K. Innami,. Kitazawa, K. Takayama, T. Ohno, and I. Nakano for usefuliscussions and help.

eferences

1] H. Saga, H. Nemoto, H. Sukeda, M. Takahashi, Jpn. J. Appl. Phys. 38 (3B)(1999) 1839.

2] M. Alex, A. Tselikov, T. McDaniel, N. Deeman, T. Valet, D. Chen, IEEETrans. Magn. 37 (4) (2001) 1244.

3] J.J.M. Ruigrok, J. Magn. Soc. Jpn. 25 (3–2) (2001) 313;T.E. Schlesinger, T. Rausch, A. Itagi, J. Zhu, J.A. Bain, D.D. Stancil, Jpn. J.Appl. Phys.41 (3B) (2002) 1821.

4] T.E. Schlesinger, T. Rausch, A. Itagi, J. Zhu, J.A. Bain, D.D. Stancil, Jpn. J.Appl. Phys. 41 (3B) (2002) 1821.

5] W.A. Challener, T.W. Mcdaniel, C.D. Mihalcea, K.R. Mountfield, K. Pelhos,

I.K. Sendur, Jpn. J. Appl. Phys. 42 (2B) (2003) 981.

6] S. Miyanishi, N. Iketani, K. Takayama, K. Innami, I. Suzuki, T. Kitazawa,Y. Ogimoto, Y. Murakami, K. Kojima, A. Takahashi, IEEE Trans. Magn. 41(10) (2005) 2817.

7] T. Kimura, Polymer J. 35 (2003) 823.