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1 Journal of the Korean Magnetics Society, Volume 19, Number 6, December 2009 DOI: /JKMS BaTi 0.5 Co 0.5 Fe 11 O 19 Mx r p Ka- q p ½ Á½ w, œw, w», 12, ( , , y ) Ka (26.5~40 GHz) q Ti-Coƒ ey Mx r p(bati 0.5 Co 0.5 Fe 11 O 19 ) wš, r p-š w» q p w w. Mx r p Ti-Coƒ ey ƒ û. c w» Mx r p» a-b ü» yw» w. œ q Ka q k š, n q p ƒ ƒ w. Ti-Coƒ ey Mx r p w Ka v w k. s ƒ r p/š w (F/R) w w. F/R = 4 w 20 w s 7GHz w Ÿ q p. F/R ƒ ƒw w q w Ì w ù, s. :Mx r p, Ka, q, œ I. m»» w» m C (4~8 GHz) ù Ku (12~18 GHz) q sy k w š q Ka m w ù ƒ ƒ š. Ka 26.5~ 40 GHz q ew ¾ ywš C ù Ku ƒ ù q t w. p m üm, Ÿ m, ITS(Intelligent Transport System) m,, f TV, ü WLAN(Wireless Local Area Network) y. ù ƒ q lq ¾ y j w rp š q ¾ y» k t»» xy w z ƒ f, š q rp Ÿ yƒ q ƒ f», lq q w ƒw. lq» y wš y d q z w lq q» w q š [1, 2]. *Tel: (043) , sskim@chungbuk.ac.kr w q j» w w q s j ù, t q ƒ ƒ w e j, z q y r p(ferrite)ƒ [3-7]. r p q œ q w» yw q ƒ. v r p(spinel ferrite) û» w 1 GHz œ q (natural resonance frequency)ƒ ùkù,» r p(hexagonal ferrite) œ q ƒ 1 GHz ùkù» GHz q ƒ w š š [3, 4]. w r p Mx y c ew» pƒ w w, c w š», q y w» p š q Ka (26.5~40 GHz)»» w. q w,» Fe +3 ƒ ƒ w ù w Ti +4, Ir +4, Ru +4, Sn 4ƒ +4 Co +2, Zn 2ƒ +2 eyw Mx r p y basal plane sww» pƒ ü w w p w w y ƒ q y w w, š q» j š š [8-10]. 203

2 204 lq Ka (26.5~40 GHz) q M-type Ba-ferrite(BaFe 12 2xTi x Co x O 19 ) Ti-Co (x = 0.5) ey g r p-š w wš, r p w y j Ka q p w. WR-28 ƒ q w n / w n q p d w. l v w q w Ì wš, š w. II. x 1. w BaFe 12 2xTi x Co x O 19 (x = 0.5) Mx r p m œ w. BaCO 3, Fe 2 O 3, TiO 2, Co 3 O 4. yw w 250 cc polyethylene» steel ball w 10 ww, powder : :ball 100 : 140 : 200 w. yw z w ³ w e w» w hot plate magnetic stirrer w ww, 50 mesh(300 µm) w ƒ w o C, œ»» 2 w w. þƒ ƒƒ 300 o C/hr ww. w ³ w ³ wš w» w» wš,» (attritor) w w. 100 g» 3mm steel ball 2 kg, š 500 g attritor rod 500 rpm w. w w Mx r p y w» w X- z w. 2. w r Mx r p g š yww w w. r p š (F/R) 3, 4, 5, 6 y g ³ w yww z Ka d w» w ƒ q j» ƒ 7.13 mm, 3.51 mm ƒx xk k z, ƒ v w 0.1 ton/cm 2 10 xw. 3.» š q p eyw Mx r p sy y(m S ) w»wz 19«6y, (H C ) vibrating sample magnetometer(vsm) w d w. w r q p dw» w š n w ƒ v w, d w» w Ka (26.5~40 GHz) ƒ q w /n ( S-parameter ) w d w. d n (S 21 ) (S 11 ) w w, w Hewlett Packard 8722D Vector Network Analyzer WR-28 ƒ q (ƒ = 7.13 mm, = 3.51 mm). III. x š 1. w 1250 C 2 w w Mx r p o (BaFe 12 2xTi x Co x O 19 ) y w» w e yw w Mx r p Ti-Coƒ 0.5 ey w XRD Fig. 1 ùkü. r Fig. 1. X-ray diffraction patterns of M-type hexagonal ferrites (BaFe 12 2x Ti x Co x O 19 ) calcined at 1250 o C: (a) x = 0.0, (b) x = 0.5.

3 BaTi 0.5 Co 0.5 Fe 11 O 19 Mx r p Ka- q p ½ Á½ 205 JCPDS q No Mx r p X- z vj ew. w 850~900 o C Mx r p w, 1200 o C» ewš [11]. 2.» š q p Fig. 2 w Mx r p Ti 4+ -Co 2+ x = 0.5 j ey k VSM d. 5 µb(bohr magneton) Fe 3+ Ti w 4+ Co 2+ (3.75 µb) ey ƒw, w Mx r p sy y emu/g, 2317 Oe ey 0.5 sy y emu/g, 850 Oe ƒ ùkù. Ti-Co ey ƒw w c w» Mx r p Ti-Co ƒ ƒ» a-b plane w ywš, Fig. 3. Material constants of BaFe 12 2x Ti x Co x O 19 composite specimens (F/R = 4): (a) x = 0.0, (b) x = 0.5. Fig. 2. Hysteresis loops of BaTi x Co x Fe 12 2x O 19 hexaferrite powders: (a) x = 0.0, (b) x = 0.5.» w» [11-13]. Fig. 3 w Mx r p Ti 4+ -Co 2+ x = 0.5 j ey k r p/š ƒ 4ƒ yww, Ka 26.5~40 GHz q p. Fig. 3(a) w Mx r p n w(µ r ') 1 ƒ q ƒw w,» x w(µ r '') 0 ƒ ¾ š. w Mx r p œ q ƒ 47.6 GHz[14] w, Ka œ w» ùkù. Ti-Coƒ ey» w x=0.5 œ q Fig. 3(b) Ka (29.5 GHz) ew. Ti-Co ey w œ q w»» w. w (ε r ') 8 š, x w(ε r '') w. Ti-Co ey j yw.

4 v w q p dx q v w (1) t ³ y v Zƒ 1, µ r ', ε r ', µ r '', ε r '', f, š d sww 6ƒ [3]. Z = µ r ---- j 2π tanh c µr ε r f d ε r» µ r n (µ r = µ r ' jµ r "), ε r (ε r = ε r ' jε r "), c Ÿ, f q š d Ì. n w Z =1 w w q w Ì w ùkü v. r n š (1) w v g w e q (1) w»wz 19«6y, w w ù fád l w q w Ì [15-17]. r p/š ƒ 4(F/R = 4) w ƒ w ew y w» w w v v wš Fig. 4 ùkü. w Mx r p, Fig. 4(a) w(ε r ' =8.0) n w» v w ù. Ka (26.5~40 GHz) q Fig. 5(a) 10 db w w. Ti- Co ey 0.5 Fig. 4(b) w(ε r ' =8.2) n w v w û. w n w q» Fig. 5(b) Ÿ q p. Ì 0.7 mm 20 db» s 29~36 Fig. 4. Contour of complex permeability and permittivity of the composite specimens with BaFe 12 2x Ti x Co x O 19 (F/R = 4) in the solution map of impedance matching: (a) x = 0.0, (b) x = 0.5. Fig. 5. Reflection loss determined in BaFe 12 2x Ti x Co x O 19 composite specimens (F/R = 4); (a) x = 0.0, (b) x = 0.5.

5 BaTi 0.5 Co 0.5 Fe 11 O 19 Mx r p Ka- q p ½ Á½ 207 GHz w. 4. r p w q p Fig. 6 r p-š w r p w y w y y w» w Ti-Co ey 0.5 r p š w r p w y n v ùkü. r p w ƒ ƒw w n ƒw» Fig. 6 v w ù q q w. F/R = 3 w q f m = 31.9 GHz F/R = 6 r p w ƒw f m = 28.4 GHz w. w r p w f w n q» s w. Fig. 6 v mw w w Ì w q ƒ ƒ w y w» w Fig. 7 Ti-Co ey x=0.5 r F/R yw 3, 4, 5, 6 yw, w Ì (d m ) q w. r p w ƒw n ƒw» w Ì w (F/R = 3 d m = 0.82 mm, F/R = 6 d m = 0.63 mm). r p w ƒ F/R = 3, 4 w n q û w Ì(ƒƒ 0.8 mm, 0.7 mm) 20 db s 7 GHz w q p ùküš. F/R = 4 r p w n x w Fig. 7. Reflection loss determined in BaFe 12 2x Ti x Co x O 19 (x = 0.5) composite specimens at the first matching thickness. ƒw sww w n x w ù» 20 db s 2 GHz š. s d r p w w. IV. Ka (26.5~40 GHz) q» j q q r r p c w» Mx r p Ti-Co eyz» y q p w. 1. Ti-Coƒ ey Mx r p ey ƒ w ƒ û. c w» Mx r p» a-b yw» w, œ q Ka q k š, n q p ƒ ƒ w. 2. Ti-Coƒ ey Mx r p w Ka v w k. s ƒ r p/š w (F/R) w w. F/R = 4 w 20 db w s 7 GHz w Ÿ q p. Fig. 6. Contour of complex permeability and permittivity of the composite specimens with BaFe 12 2x Ti x Co x O 19 (x = 0.5) in the solution map of impedance matching w w w w.

6 208 š x [1] D. N. Heirman, IEEE 1996 International Symposium on EMC, Santa Clara, August 19-23, 12 (1996). [2] M. Stecher, IEEE 1996 International Symposium on EMC, Santa Clara, August 19-23, 24 (1996). [3] Y. Naito and K. Suetake, IEEE Trans. Micro. Theory and Tech., 19(1), 65 (1971). [4] Y. Naito, J. Phys. IV, 7, C (1997). [5] W. Y. Lim, J. S. Baek, and S. H. Lee, J. Korean Mag. Soc., 14(4), 120 (2004). [6] M. S. Kim, E. H. Min, and J. G. Koh, J. Korean Mag. Soc., 19(2), 62 (2009). [7] H. S. Cho and S. S. Kim, J. Korean Mag. Soc., 18(4), 136 (2008). [8] N. Dishovski, A. Petkev, Iv. Nedkov, and Iv. Razkazov, IEEE Trans. Mag., 30(2), 969 (1994). [9] I. Nedkov, A. Petkov, and V. Karpov, IEEE Trans. Magn., 26(5), 1483 (1990). w»wz 19«6y, [10] A. M. Abo, E. Ata, et al., J. Mag. and Mag. Mat., 204, 36 (1999). [11] M. Sugimoto, Properties of ferroxplana-type hexagonal ferrite, Ferromgnetic Materials, vol. 3, edited by E. P. Wohlfarth, North-Holland Pub. Amsterdam, pp (1982). [12] D. Autissier, A. Podemski, and C. Jacquiod, J. Phys. IV, 7, C (1997). [13] H. Vincent, E. Brando, and B. Sugg, J. of Solid State Chem., 120, 17 (1995). [14] S. Sugimoto, K. Okayama, S. Kondo, H. Ota, M. Kimura, Y. Yoshida, H. Nakamura, D. Book, T. Kagotani, and M. Homma, Mater. Trans., JIM, 39(10), 1080 (1998). [15] J. Y. Shin, Thesis for PhD Degree, Inha University, Korea (1995). [16] H. S. Cho, Thesis for Master Degree, Chungbuk National University, Korea (1999). [17] S. S. Kim, S. B. Jo, K. I. Kwon, K. K. Choi, J. M. Kim, and K. S. Churn, IEEE Trans. Magn., 27(6), 5462 (1991). Microwave Absorbing Properties of M-type Barium Ferrites with BaTi 0.5 Co 0.5 Fe 11 O 19 Composition in Ka-band Frequencies Yong-Jin Kim and Sung-Soo Kim Department of Advanced Materials Engineering, Chungbuk National University, Cheongju , Korea (Received 4 August 2009, Received in final form 10 September 2009, Accepted 21 September 2009) Magnetic and Ka-band absorbing properties have been investigated in Ti-Co substituted M-type barium hexaferrites with BaTi 0.5 Co 0.5 Fe 11 O 19 composition. The ferrite powders were prepared by conventional ceramic processing technique and used as absorbent fillers in ferrite-rubber composites. The magnetic properties were measured by vibrating sample magnetometer. The complex permeability and dielectric constant were measured by using the WR-28 rectangular waveguide and network analyzer in the frequency range 26.5~40 GHz. For the Ti-Co substituted M-hexaferrites, the ferromagnetic resonance is observed at Ka-band (29.4 GHz). The matching frequency and matching thickness are determined by using the solution map of impedance matching. A wide band microwave absorbance is predicted with controlled ferrite volume fraction and absorber thickness. Keywords : M-type barium ferrite, Ka-band, microwave absorbers, ferromagnetic resonance