(Nagoya univ.) Yasuharu Kozuka, Asami Horiguchi, Hisanori Shiozawa, Ritsuko Tsuchiya, Hirofumi Yoshikawa, Kunio Awaga(Meijo univ.) Shunji Bandow, Sumio Ijima

Chemical Syntheses of Spherical Hollow Nanomagnets

Single Domain Magnet

· Down Sizing· Shape Control

Top-down

Bottom-up

N

S

N

S

~ 1 m

Bubble Domains in Co thin film

0 0 0 0 0 0 01 1 1 1

S

N

d (< 500 nm)

t (< 50 nm)

Domain Structure ?Thin film Effect ? Quantum Effect ?Catalysis ? Metal and Supercon. ?

Spherical Hollow Nanomagnet

Classification and physical phenomena of thin films

Thick film

Thin film

Thin film

Ultra Thin film Ultra high Thin film

100m

10m

m

m

100nm

10nm

1nm 0.1nm

100pm

～ 1000 atoms layer

～ 100 atoms layer

Particle size ofbulk magnetic material

vertical magnetization particle size, GMR

artificial latticewidth of quantum well

monoatomic layer(angstrom scale)

Elastic strain field of lattice defect, PMA

Macroscopicbulk

Mesoscopic

MicroscopicSuper lattice

Josephson deviceInsulation film

STM scale

Whisker non-transition crystal

HEMT activated layer

Thickness of magnetic wall

m 10–4

10–6

10–9

Å=10–10

diameter

thickness

Polystyrene Beads

Diameter = 100 ~ 1000 nm

Emulsion Polymerization

Water

HC CH2

n

Micelle

SEM

PS bead

Cu(NO3)2

(NH2)2CO（ Thermal decomposition）

Aging at 85 ℃

Cu(CO3)2Cu(OH)2

500 ℃

Cu under H2

CuO in air500 nm

PS + Cu(NO3)2 ＋ CO(NH2)2 ＋ PVP [Cu(OH) ２ CuCO ３ ]85 ℃

（ Poly Vinyl Pyrrolidone ）

8

7

6

5

4

pH

6543210

Ti me (h)

N. Kawahashi, H. Shiho, J. Mater. Chem., 10, 2294 (2000).

Calcination

Homogeneous precipitation of metal hydroxides on PS beads

Concentrations of PS beads, Cu(NO3)2, CO(NH2)2, and PVP

Parameters are

Reaction temperature and time⑥

①

⑤

④③②

d = 460 nm 800 nm

SEM images of PS beads coated with Cu hydroxides

1 m 1 m

Size Effects

PS bead / nm Curie Const. / emu K g-1 Weiss const. / K

300 1.02 x 10-3 - 5.6

460 1.05 x 10-3 - 25

800 3.03 x 10-4 - 32

Surface area / g

m=0 paramagnet

m=7 weak ferromagnet

Cu Cu

O(H)

Cu2(OH)3(n-CmH2m+1COO)

Cu(NO3)2 Co(NO3)2

SEM image of PS beads (600 nm) coated with Co hydroxides

1 m

To get Co magnet

Flow meter

Furnace

Manostat

Vacuum pump

H2 bomb

Apparatus for Calcination

Sample

SEM

TEM

Calcination under H2 at 500 ℃ for 3 hrs PS beads d = 800 nm

850 nm

80 nm

fcc Co

X-ray powder diffraction pattern

T400 ℃

hcp fcc

RT Calcination

Co

Soft ferromagnet Coercive field < 40 Oe

Negligible temp. dependence

Magnetization curve at 2 K

Calcination

in Air

450 ℃6 hrs

500nm

Hollow spherical Co oxides

before after

2 K

Summary

Future works

• Syntheses of various metals and metal oxides hollow spheres

• Synthesis of cobalt hollow spheres in hcp phase

• Single particle magnetic measurements

• Hollow spherical nanomagnet of fcc-cobalt

• Soft magnet