Ferromagnetism in ZnO-and GaN-based diluted magnetic semiconductors: Achievements and challenges

Proceedings of the IEEE

Volumn 98, Issue 7, 2010, Pages 1288-1301

  Avrutin, Vitaliy ^a   Izyumskaya, Natalia ^a   Ozgur, Ümit ^a   Silversmith, Donald J ^b   Morkoç, Hadis ^a  

^a Virginia Commonwealth University   (United States)

^b AIR FORCE OFFICE OF SCIENTIFIC RESEARCH   (United States)

Author keywords

Defects; Diluted magnetic oxides; Diluted magnetic semiconductors (DMSs); GaN; Local structure; Spintronics; ZnO

Indexed keywords

DEFECTS; DILUTED MAGNETIC SEMICONDUCTORS; FERROMAGNETISM; GALLIUM NITRIDE; II-VI SEMICONDUCTORS; III-V SEMICONDUCTORS; OPTICAL PROPERTIES; OXIDE SEMICONDUCTORS; SPINTRONICS; ZINC OXIDE;

CHARACTERIZATION TECHNIQUES; DILUTED MAGNETIC OXIDE; DILUTED MAGNETIC SEMICONDUCTORS (DMSS); DILUTED SEMICONDUCTORS; FERROMAGNETIC ORDERINGS; LOCAL STRUCTURE; MAGNETIC AND OPTICAL PROPERTIES; STRUCTURAL AND MAGNETIC PROPERTIES;

WIDE BAND GAP SEMICONDUCTORS;

EID: 77953683139     PISSN: 00189219     EISSN: None     Source Type: Journal    
DOI: 10.1109/JPROC.2010.2044966     Document Type: Conference Paper

References (161)

1. T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, "Zener model description of ferromagnetism in zinc-blende magnetic semiconductors" Science, vol.287, no.5455, pp. 1019-1022, Feb. 2000.
2. K. Sato and H. Katayama-Yoshida, "Stabilization of ferromagnetic states by electron doping in Fe-, Co-or Ni-doped ZnO" Jpn. J. Appl. Phys., vol. 40, no. 4A, pp. L334-L336, Apr. 2001.
3. G. P. Das, B. K. Rao, and P. Jena, "Ferromagnetism in Cr-doped GaN: A first-principles calculation," Phys. Rev. B, Condens. Matter, vol.69, no.21, pp. 214422-1-214422-6, Jun. 2004.
4. Theodoropoulou, A. F. Hebard, M. E. Overberg, C. R. Abernathy, S. J. Pearton, S. N. G. Chu, and R. G.WIilson, "Magnetic and structural properties of Mn-implanted GaN," Appl. Phys. Lett., vol.78, no.22, pp. 3475-3477, May 2001.
5. S. Dhar, T. Kammermeier, A. Ney, L. Pérez, K. H. Ploog, A. Melnikov, and A. D. Wieck, "Ferromagnetism and colossal magnetic moment in Gd-focused ion-beam-implanted GaN," Appl. Phys. Lett., vol.89, no.6, pp. 062503-1-062503-3, Aug. 2006.
6. T. Sasaki, S. Sonoda, Y. Yamamoto, K. Suga, S. Shimizu, K. Kindo, and H. Hori, "Magnetic and transport characteristics on high Curie temperature ferromagnet of Mn-doped GaN," J. Appl. Phys., vol.91, no.10, pp. 7911-7913, May 2002.
7. S. Sonoda, S. Shimizu, T. Sasaki, Y. Yamamoto, and H. Hori, "Molecular beam epitaxy of wurtzite (Ga,Mn)N films on sapphire(0 0 0 1) showing the ferromagnetic behaviour at room temperature," J. Cryst. Growth, vol.237, pt. 2, pp. 1358-1362, Apr. 2002.
8. M. E. Overberg, C. R. Abernathy, S. J. Pearton, N. A. Theodoropoulou, K. T. Mccarthy, and A. F. Herard, "Indication of ferromagnetism in molecular-beam-epitaxy-derived N-type GaMnN," Appl. Phys. Lett., vol.79, no.9, pp. 1312-1314, Aug. 2001.
9. M. C. Park, K. S. Kuh, J. M. Myong, J. M. Lee, J. Y. Chang, K. I. Lee, S. H. Han, and W. Y. Lee, "Room temperature ferromagnetic (Ga,Mn)N epitaxial films with low Mn concentration grown by plasma-enhanced molecular beam epitaxy," Solid State Commun., vol.124, no.1-2, pp. 11-14, Sep. 2002.
10. S. Kimura, S. Emura, Y. Yamauchi, Y. K. Zhou, S. Hasegawa, and H. Asahi, "Low temperature molecular beam epitaxy growth of cubic GaCrN," J. Cryst. Growth, vol.310, no.1, pp. 40-46, Jan. 2008.
11. M. H. Kane, M. Strassburg, W. E. Fenwick, A. Asghar, A. M. Payne, S. Gupta, Q. Song, Z. J. Zhang, N. Dietz, C. J. Summers, and I. T. Ferguson, "Correlation of the structural and ferromagnetic properties of Ga1-xMnxN grown by metalorganic chemical vapor deposition," J. Cryst. Growth, vol.287, no.2, pp. 591-595, Jan. 2006.
12. M. Strassburg, M. H. Kane, A. Asghar, Q. Song, Z. J. Zhang, J. Senawiratne, M. Alevli, N. Dietz, C. J. Summers, and I. T. Ferguson, "The Fermi level dependence of the optical and magnetic properties of Ga1-xMnxN grown by metal-organic chemical vapour deposition," J. Phys., Condens. Matter, vol.18, no.9, pp. 2615-2622, Mar. 2006.
13. M. H. Kane, S. Gupta, W. E. Fenwick, N. Li, E.-H. Park,M. Strassburg, and I. T. Ferguson, "Comparative study of Mn and Fe incorporation into GaN by metalorganic chemical vapor deposition," Phys. Stat. Sol. (A), vol.204, no.1, pp. 61-71, Jan. 2007. (Pubitemid 46144774)
14. S. Gupta, W. E. Fenwick, A. Melton, T. Zaidi, H. Yu, V. Rengarajan, J. Nause, A. Ougazzaden, and I. T. Ferguson, "MOVPE growth of transition-metal-doped GaN and ZnO for spintronic applications," J. Cryst. Growth, vol.310, no.23, pp. 5032-5038, Nov. 2008.
15. L. S. Dorneles, D. O'Mahony, C. B. Fitzgerald, F. McGee, M. Venkatesan, I. Stanca, J. G. Lunney, and J. M. D. Coey, "Structural and compositional analysis of transition-metal-doped ZnO and GaN PLD thin films," Appl. Surf. Sci., vol.248, no.1-4, pp. 406-410, Jul. 2005.
16. M. Zajac, J. Gosk, E. Grzanka, S. Stelmakh, M. Palczewska, A. Wysmoaek, K. Korona, M. Kaminska, and A. Twardowski, "Ammonothermal synthesis of GaN doped with transition metal ions (Mn, Fe, Cr)," J. Alloys Compounds, vol.456, no.1-2, pp. 324-338, May 2008.
17. M. Zajac, J. Gosk, E. Grzanka, M. Kaminska, A. Twardowski, B. Strojek, T. Szyszko, and S. Podsiadlo, "Possible origin of ferromagnetism in (Ga,Mn)N," J. Appl. Phys., vol.93, no.8, pp. 4715-4717, Apr. 2003.
18. K. Ando, "Magneto-optical studies of s,p-d exchange interactions in GaN: Mn with room-temperature ferromagnetism," Appl. Phys. Lett., vol.82, no.1, pp. 100-102, Jan. 2003.
19. S. Dhar, O. Brandt, A. Trampert, L. Daweritz, K. J. Friedland, K. H. Ploog, J. Keller, B. Beschoten, and G. Güntherodt, "Origin of high-temperature ferromagnetism in (Ga,Mn)N layers grown on 4H-SiC(0001) by reactive molecular-beam epitaxy," Appl.Phys. Lett., vol.82, no.13, pp. 2077-2079, Mar. 2003.
20. K. H. Ploog, S. Dhar, and A. Trampert, "Structural and magnetic properties of (Ga,Mn)N layers grown on SiC by reactive molecular beam epitaxy," J. Vac. Sci. Technol. B, vol.21, no.4, pp. 1756-1759, Jul./Aug. 2003.
21. T. Dietl, "Self-organized growth controlled by charge states of magnetic impurities," Nature Mater., vol.5, no.9, p. 673-673, Sep. 2006.
22. A. Bonanni, "Ferromagnetic nitride-based semiconductors doped with transition metals and rare earths," Semicond. Sci. Technol., vol.22, no.9, pp. R41-R56, Sep. 2007.
23. C. Liu, F. Yun, and H. Morkoc, "Ferromagnetism of ZnO and GaN: A Review," J. Mater. Sci., Mater. Electron., vol.16, no.9, pp. 555-597, Sep. 2005.
24. H. X. Liu, S. Y. Wu, R. K. Singh, L. Gu, D. J. Smith, N. Newman, N. R. Dilley, L. Montes, and M. B. Simmonds, "Observation of ferromagnetism above 900 K in Cr-GaN and Cr-AlN," Appl. Phys. Lett., vol.85, no.18, pp. 4076-4078, Nov. 2004.
25. S. E. Park, H.-J. Lee, Y. C. Cho, S.-Y. Jeong, C. R. Cho, and S. Cho, "Room-temperature ferromagnetism in Cr-doped GaN single crystals," Appl. Phys. Lett., vol.80, no.19, pp. 4187-4189, Jun. 2002.
26. M. Hashimoto, Y.-K. Zhou, M. Kanakura, and H. Asahi, "High temperature (400 K) ferromagnetism in III-V-based diluted magnetic semiconductor GaCrN grown by ECR molecular-beam epitaxy," Solid State Commun., vol.122, no.1-2, pp. 37-39, Apr. 2002.
27. J. S. Lee, J. D. Lim, Z. G. Khim, Y. D. Park, S. J. Pearton, and S. N. G. Chu, "Magnetic and structural properties of Co, Cr, V ion-implanted GaN," J. Appl. Phys., vol.93, no.8, pp. 4512-4516, Apr. 2003.
28. S. Dhara, B. Sundaravel, K. G. M. Nair, R. Kesavamoorthy, M. C. Valsakumar, T. V. Chandrasekhar Rao, L. C. Chen, and K. H. Chen, "Ferromagnetism in cobalt-doped n-GaN," Appl. Phys. Lett., vol.88, no.17, pp. 173110-1-173110-3, Apr. 2006.
29. Z. Sun, W. Yan, G. Zhang, H. Oyanagi, Z. Wu, Q. Liu, W. Wu, T. Shi, Z. Pan, P. Xu, and S. Wei, "Evidence of substitutional Co ion clusters in Zn1-xCoxO dilute magnetic semiconductors," Phys. Rev. B, Condens. Matter, vol.77, no.24, pp. 245208-1-245208-6, Jun. 2008.
30. W. Kim, H. J. Kang, S. K. Oh, S. Shin, J.-H. Lee, J. Song, S. K. Noh, S. J. Oh, and C. S. Kim, "Magnetic and structural properties of Co ion-implanted GaN," IEEE Trans. Nanotechnol., vol.5, no.2, pp. 149-151, Mar. 2006.
31. V. A. Dinh and H. Katayama-Yoshida, "Ferromagnetism and Curie temperature of vanadium-doped nitrides," J. Electron. Microscopy, vol. 54, no. Suppl. 1, pp. I61-I64, Sep. 2005.
32. A. Bonanni, M. Kiecana, C. Simbrunner, T. Li, M. Sawicki, M. Wegscheider, M. Quast, H. Przybylicska, A. Navarro-Quezada, R. Jakieaa, A. Wolos, W. Jantsch, and T. Dietl, "Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N: The relationship between structural, electronic, and magnetic properties," Phys. Rev. B, Condens. Matter, vol.75, no.12, pp. 125210-1-125210-18, Mar. 2007.
33. W. Kim, H. J. Kang, S. K. Noh, J. Song, and C. S. Kim, "Magnetic and structural properties of Fe ion-implanted GaN," J. Magn. Magn. Mater., vol.316, no.2, pp. e199-e202, Sep. 2007.
34. Y. Shon, Y. H. Kwon, Y. S. Park, S. H. U. Yuldashev, S. J. Lee, C. S. Park, K. J. Chung, S. J. Yoon, H. J. Kim, W. C. Lee, D. J. Fu, T. W. Kang, X. J. Fan, Y. J. Park, and H. T. Oh, "Ferromagnetic behavior of p-type GaN epilayer implanted with Fe\+ ions," J. Appl. Phys., vol.95, no.2, pp. 761-763, Jan. 2004.
35. G. Talut, H. Reuther, S. Zhou, K. Potzger, F. Eichhorn, and F. Stromberg, "Ferromagnetism in GaN induced by Fe ion implantation," J. Appl. Phys., vol.102, no.8, pp. 083909-1-083909-7, Oct. 2007.
36. R.-T. Huang, C.-F. Hsu, J.-J. Kai, F.-R. Chen, and T.-S. Chin, "Room-temperature diluted magnetic semiconductors p-(Ga,Ni)N," Appl. Phys. Lett., vol.87, no.20, pp. 202507-1-202507-3, Nov. 2005.
37. N. Teraguchi, A. Suzuki, Y. Nanishi, Y.-K. Zhou, M. Hashimoto, and H. Asahi, "Room-temperature observation of ferromagnetism in diluted magnetic semiconductor GaGdN grown by RF-molecular beam epitaxy," Solid State Commun., vol.122, no.12, pp. 651-653, Jun. 2002. (Pubitemid 34777171)
38. S. Dhar, O. Brandt, M. Ramsteiner, V. E. Sapega, and K. H. Ploog, "Colossal magnetic moment of Gd in GaN," Phys. Rev. Lett., vol.94, no.3, pp. 037205-1-037205-4, Jan. 2005.
39. V. Avrutin, Ü. Özgür, J. Xie, Y. Fu, F. Yun, H. Morkoç, and V. I. Litvinov, "Gd-implanted GaN as a candidate for spin-injector," Proc. SPIEVInt. Soc. Opt. Eng., Gallium Nitride Mater. Devices, vol. 6121, pp. 61210U-1-61210U-7, Feb. 2006.
40. K. Sato and H. Katayama-Yoshida, "Material design of GaN-based ferromagnetic diluted magnetic semiconductors," Jpn. J. Appl. Phys., vol. 40, no. 5B, pt. 2, pp. L485-L487, May 2001. (Pubitemid 32676995)
41. G. M. Dalpian and S. H. Wei, "Electron-induced stabilization of ferromagnetism in Ga1-xGdxN," Phys. Rev. B, Condens. Matter, vol.72, no.11, pp. 115201-1-115201-5, Sep. 2005.
42. G. M. Dalpian, S.-H. Wei, X. G. Gong, A. J. R. da Silva, and A. Fazzio, "Phenomenological band structure model of magnetic coupling in semiconductors," Solid State Commun., vol.138, no.7, pp. 353-358, May 2006.
43. K. Sato and H. Katayama-Yoshida, "Material design for transparent ferromagnets with ZnO-based magnetic semiconductors," Jpn. J. Appl. Phys., vol. 39, no. 6B, pp. L555-L558, Jun. 2000.
44. N. H. Hong, J. Sakai, N. T. Huong, N. Poirot, and A. Ruyter, "Role of defects in tuning ferromagnetism in diluted magnetic oxide thin films," Phys. Rev. B, Condens. Matter, vol.72, no.4, pp. 045336-1-045336-5, Jul. 2005.
45. H. Liu, X. Zhang, L. Li, Y. X. Wang, K. H. Gao, Z. Q. Li, R. K. Zheng, S. P. Ringer, B. Zhang, and X. X. Zhang, "Role of point defects in room-temperature ferromagnetism of Cr-doped ZnO," Appl. Phys. Lett., vol.91, no.7, pp. 072511-1-072511-3, Aug. 2007.
46. Y. C. Yang, C. F. Zhong, X. H. Wang, B. He, S. Q. Wei, F. Zeng, and F. Pan, "Room temperature multiferroic behavior of Cr-doped ZnO films," J. Appl. Phys., vol.104, no.6, pp. 064102-1-064102-4, Sep. 2008.
47. H. Saeki, H. N. Tabata, and T. Kawai, "Magnetic and electric properties of vanadium doped ZnO films," Solid State Commun., vol.120, no.11, pp. 439-443, Nov. 2001. (Pubitemid 33039372)
48. V. Avrutin, Ü. Özgür, S. Chevtchenko, C. Litton, and H. Morkoç, "Optical and magnetic properties of ZnO:V prepared by ion implantation," J. Electron. Mater., vol. 36, no. 4, pp. 483-487, Apr. 2007.
49. M. Venkatesan, C. B. Fitzgerald, J. G. Lunney, and J. M. D. Coey, "Anisotropic ferromagnetism in substituted zinc oxide," Phys. Rev. Lett., vol.93, no.17, pp. 177206-1-177206-4, Oct. 2004.
50. N. Theodoropoulou, V. Misra, J. Philip, P. LeClair, G. P. Berera, J. S. Moodera, B. Satpati, and T. Som, "High-temperature ferromagnetism in Zn1-xMnxO semiconductor thin films," J. Magn. Magn. Mater., vol.300, no.2, pp. 407-411, May 2006.
51. X. H. Xu, H. J. Blythe, M. Ziese, A. J. Behan, J. R. Neal, A. Mokhtari, R. M. Ibrahim, A. M. Fox, and G. A. Gehring, "Carrier-induced ferromagnetism in n-type ZnMnAlO and ZnCoAlO thin films at room temperature," New J. Phys., vol.8, pp. 135-1-135-11, Aug. 2006.
52. Y. B. Lin, J. P. Xu, W. Q. Zou, L. Y. Lv, Z. H. Lu, F. M. Zhang, Y. W. Du, Z. G. Huang, and J. G. Zheng, "Effects of annealing and hydrogenation on the properties of ZnMnO polycrystalline films synthesized by plasma enhanced chemical vapour deposition," J. Phys. D, Appl. Phys., vol.40, no.12, pp. 3674-3677, Jun. 2007.
53. A. J. Behan, A. Mokhtari, H. J. Blythe, D. Score, X.-H. Xu, J. R. Neal, A.M. Fox, and G. A. Gehring, "Two magnetic regimes in doped ZnO corresponding to a dilute magnetic semiconductor and a dilute magnetic insulator," Phys. Rev. Lett., vol.100, no.4, pp. 047206-1-047206-4, Feb. 2008.
54. C. Song, K. W. Geng, F. Zeng, X. B. Wang, Y. X. Shen, F. Pan, Y. N. Xie, T. Liu, H. T. Zhou, and Z. Fan, "Giant magnetic moment in an anomalous ferromagnetic insulator: Co-doped ZnO," Phys. Rev. B, Condens. Matter, vol.73, no.2, pp. 024405-1-024405-6, Jan. 2006.
55. C. B. Fitzgerald, M. Venkatesan, J. G. Lunney, L. S. Dorneles, and J. M. D. Coey, "Cobalt-doped ZnOVA room temperature dilute magnetic semiconductor," Appl. Surf. Sci., vol.247, no.1-4, pp. 493-496, Jul. 2005.
56. P. V. Radovanovic and D. R. Gamelin, "High temperature ferromagnetism in Ni2\+-doped ZnO aggregates prepared from colloidal diluted magnetic semiconductor quantum dots," Phys. Rev. Lett., vol.91, no.15, pp. 157202-1-157202-4, Oct. 2003.
57. X. Liu, F. Lin, L. Sun, W. Cheng, X. Ma, and W. Shi, "Doping concentration dependence of room-temperature ferromagnetism for Ni-doped ZnO thin films prepared by pulsed-laser deposition," Appl. Phys. Lett., vol.88, no.6, pp. 062508-1-062508-3, Feb. 2006.
58. X. X. Wei, C. Song, K. W. Geng, F. Zeng, B. He, and F. Pan, "Local Fe structure and ferromagnetism in Fe-doped ZnO films," J. Phys., Condens. Matter, vol.18, no.31, pp. 7471-7479, Aug. 2006. (Pubitemid 44121394)
59. D. L. Hou, X. J. Ye, H. J. Meng, H. J. Zhou, X. L. Li, C. M. Zhen, and G. D. Tang, "Magnetic properties of n-type Cu-doped ZnO thin films," Appl. Phys. Lett., vol.90, no.14, pp. 142502-1-142502-3, Apr. 2007.
60. D. B. Buchholz, R. P. H. Chang, J. H. Song, and J. B. Ketterson, "Room temperature ferromagnetism in Cu-doped ZnO films," Appl. Phys. Lett., vol.87, no.8, pp. 082504-1-082504-3, Aug. 2005.
61. S.-J. Han, J. W. Song, C.-H. Yang, S. H. Park, J.-H. Park, Y. H. Jeong, and K. W. Rhie, "A key to room-temperature ferromagnetism in Fe-doped ZnO:Cu," Appl. Phys. Lett., vol.81, no.22, pp. 4212-4214, Nov. 2002.
62. H. Pan, J. B. Yi, L. Shen, R. Q.Wu, J. H. Yang, J. Y. Lin, Y. P. Feng, J. Ding, L. H. Van, and J. H. Yin, "Room-temperature ferromagnetism in carbon-doped ZnO," Phys. Rev. Lett., vol.99, no.12, pp. 127201-1-127201-4, Sep. 2007.
63. K. Ueda, H. Tabata, and T. Kawai, "Magnetic and electric properties of transition-metal-doped ZnO films," Appl. Phys. Lett., vol.79, no.7, pp. 988-990, Aug. 2001. (Pubitemid 33600591)
64. G. Lawes, A. S. Risbud, A. P. Ramirez, and R. Seshadri, "Absence of ferromagnetism in Co and Mn substituted polycrystalline ZnO," Phys. Rev. B, Condens. Matter, vol.71, no.4, pp. 045201-1-045201-5, Jan. 2005.
65. C. N. R. Rao and F. L. Deepak, "Absence of ferromagnetism in Mn-and Co-doped ZnO," J. Mater. Chem., vol.15, no.5, pp. 573-578, Nov. 2005.
66. A. S. Risbud, N. A. Spaldin, Z. Q. Chen, S. Stemmer, and R. Seshadri, "Magnetism in polycrystalline cobalt-substituted zinc oxide," Phys. Rev. B, Condens. Matter, vol.68, no.20, pp. 205202-1-205202-7, Nov. 2003.
67. M. H. Kane, K. Shalini, C. J. Summers, R. Varatharajan, J. Nause, C. R. Vestal, Z. J. Zhang, and I. T. Ferguson, "Magnetic properties of bulk Zn1-xMnxO and Zn1-xCoxO single crystals," J. Appl. Phys., vol.97, no.2, pp. 023906-1-023906-6, Jan. 2005.
68. N. Jedrecy, H. J. von Bardeleben, Y. Zheng, and J.-L. Cantin, "Electron paramagnetic resonance study of Zn1-xCoxO: A predicted high-temperature ferromagnetic semiconductor," Phys. Rev. B, Condens. Matter, vol.69, no.4, pp. 041308-1-041308-4, Jan. 2003.
69. J. H. Park, M. G. Kim, H. M. Jang, and S. Ryu, "Co-metal clustering as the origin of ferromagnetism in Co-doped ZnO thin films," Appl. Phys. Lett., vol.84, no.8, pp. 1338-1340, Feb. 2004.
70. T. Fukumura, Z. W. Jin, M. Kawasaki, T. Shono, T. Hasegawa, S. Koshihara, and H. Koinuma, "Magnetic properties of Mn-doped ZnO," Appl. Phys. Lett., vol.78, no.7, pp. 958-960, Feb. 2001.
71. D. P. Norton, M. E. Overberg, S. J. Pearton, K. Pruessner, J. D. Budai, L. A. Boatner, M. F. Chisholm, J. S. Lee, Z. G. Khim, Y. D. Park, and R. G. Wilson, "Ferromagnetism in cobalt-implanted ZnO," Appl. Phys. Lett., vol.83, no.26, pp. 5488-5490, Dec. 2003.
72. D. J. Keavney, D. B. Buchholz, Q. Ma, and R. P. H. Chang, "Where does the spin reside in ferromagnetic Cu-doped ZnO? Appl. Phys. Lett., vol. 91, no. 1, pp. 012501-1-012501-12503, Jul. 2007.
73. H. Schmidt, M. Diaconu, H. Hochmuth, M. Lorenz, A. Setzer, P. Esquinazi, A. Po ppl, D. Spemann, K.-W. Nielsen, R. Gross, G. Wagner, and M. Grundmann, "Weak ferromagnetism in textured Zn1-xeth TM THORN xO thin films," Superlat. Microstruct., vol.39, no.1-4, pp. 334-339, Jan. 2006.
74. S. Ramachandran, A. Tiwari, J. Narayan, and J. T. Prater, "Epitaxial growth and properties of Zn1-xVxO diluted magnetic semiconductor thin films," Appl. Phys. Lett., vol.87, no.17, pp. 172502-1-172502-3, Oct. 2005.
75. A. C. Mofor, A. El-Shaer, A. Bakin, A. Waag, H. Ahlers, U. Siegner, S. Sievers, M. Albrecht, W. Schoch, N. Izyumskaya, V. Avrutin, S. Sorokin, S. Ivanov, and J. Stoimenos, "Magnetic property investigations on Mn-doped ZnO Layers on sapphire," Appl. Phys. Lett., vol.87, no.6, pp. 062501-1-062501-3, Aug. 2005.
76. P. Sharma, A. Gupta, K. V. Rao, F. J. Owens, R. Sharma, R. Ahuja, J. M. O. Guillen, B. Johansson, and G. A. Gehring, "Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO," Nature Mater., vol.2, no.10, pp. 673-677, Oct. 2003.
77. C. Zener, "Interaction between the d shells in the transition metals," Phys. Rev., vol.81, no.4, pp. 440-444, Feb. 1951.
78. C. Zener, "Interaction between the d-shells in the transition metals. II. Ferromagnetic compounds of manganese with Perovskite structure," Phys. Rev., vol.82, no.3, pp. 403-405, May 1951.
79. V. I. Litvinov and V. K. Dugaev, "Ferromagnetism in magnetically doped III-V semiconductors," Phys. Rev. Lett., vol.86, no.24, pp. 5593-5596, Jun. 2001.
80. A. Kaminski and S. Das Sarma, "Polaron percolation in diluted magnetic semiconductors," Phys. Rev. Lett., vol.88, no.24, pp. 247202-1-247202-4, Jun. 2002.
81. A. C. Durst, R. N. Bhatt, and P. A. Wolff, "Bound magnetic polaron interactions in insulating doped diluted magnetic semiconductors," Phys. Rev. B, Condens. Matter, vol.65, no.23, pp. 235205-1-235205-10, Jun. 2002.
82. T. Dietl and J. Spalek, "Effect of fluctuations of magnetization on the bound magnetic polaron: Comparison with experiment," Phys. Rev. Lett., vol.48, no.5, pp. 355-358, Feb. 1982.
83. J. M. D. Coey, M. Venkatesan, and C. B. Fitzgerald, "Donor impurity band exchange in dilute ferromagnetic oxides," Nature Mater., vol.4, no.2, pp. 173-179, Feb. 2005, Nature Mater.
84. K. Sato and H. Katayama-Yoshida, "First principles materials design for semiconductor spintronics," Semicond. Sci. Technol., vol.17, no.4, pp. 367-376, Apr. 2002.
85. J. M. D. Coey, "Dilute magnetic oxides," Current Opinion Solid State Mater. Sci., vol.10, no.2, pp. 83-92, Apr. 2006.
86. Y. Gohda and A. Oshiyama, "Intrinsic ferromagnetism due to cation vacancies in Gd-doped GaN: First-principles calculations," Phys. Rev. B, Condens. Matter, vol.78, no.16, pp. 161201-1-161201-4, Oct. 2008.
87. L. Liu, P. Y. Yu, Z. Ma, and S. S. Mao, "Ferromagnetism in GaN:Gd: A density functional theory study," Phys. Rev. Lett., vol.100, no.12, pp. 127203-1-127203-3, Mar. 2008.
88. J. S. Hong, "Local magnetic moment induced by Ga vacancy defect in GaN," J. Appl. Phys., vol.103, pp. 063907-1-063907-5, Mar. 2008.
89. J. M. D. Coey and S. A. Chambers, "Oxide dilute magnetic semiconductorsVFact of fiction?" MRS Bull., vol. 33, no. 11, pp. 1053-1058, Nov. 2008.
90. J. M. D. Coey, "d0 ferromagnetism," Solid State Sci., vol.7, no.6, pp. 660-667, Jun. 2005.
91. Y. B. Zhang, Q. Liu, T. Sritharan, C. L. Gan, and S. Li, "Pulsed laser ablation of preferentially orientated ZnO:Co diluted magnetic semiconducting thin films on Si substrates," Appl. Phys. Lett., vol.89, no.4, pp. 042510-1-042510-3, Jul. 2006.
92. H. S. Hsu, J. C. A. Huang, Y. H. Huang, Y. F. Liao, M. Z. Lin, C. H. Lee, J. F. Lee, S. F. Chen, L. Y. Lai, and C. P. Liu, "Evidence of oxygen vacancy enhanced room-temperature ferromagnetism in Co-doped ZnO," Appl. Phys. Lett., vol.88, no.24, pp. 242507-1-242507-3, Jun. 2006.
93. N. Khare, M. J. Kappers, M. Wei, M. G. Blamire, and J. L. MacManus-Driscoll, "Defect-induced ferromagnetism in Co-doped ZnO," Adv. Mater., vol.18, no.11, pp. 1449-1452, Jun. 2006.
94. D. A. Schwartz and D. R. Gamelin, "Reversible 300 K ferromagnetic ordering in a diluted magnetic semiconductor," Adv. Mater., vol.16, no.23-24, pp. 2115-2119, Dec. 2004.
95. M. H. F. Sluiter, Y. Kawazoe, P. Sharma, A. Inoue, A. R. Raju, C. Rout, and U. V. Waghmare, "First principles based design and experimental evidence for a ZnO-based ferromagnet at room temperature," Phys. Rev. Lett., vol.94, no.18, pp. 187204-1-187204-4, May 2005.
96. X. J. Liu, C. Song, F. Zeng, X. B. Wang, and F. Pan, "Influence of annealing on microstructure and magnetic properties of co-sputtered Co-doped ZnO thin films," J. Phys. D, Appl. Phys., vol.40, no.6, pp. 1608-1613, Mar. 2007.
97. M. Gacic, G. Jakob, C. Herbort, H. Adrian, T. Tietze, S. Bruck, and E. Goering, "Magnetism of Co-doped ZnO thin films," Phys. Rev. B, Condens. Matter, vol.75, no.20, pp. 205206-1-205206-8, May 2007.
98. C. Song, S. N. Pan, X. J. Liu, X. W. Li, F. Zeng, W. S. Yan, B. He, and F. Pan, "Evidence of structural defect enhanced room-temperature ferromagnetism in Co-doped ZnO," J. Phys., Condens. Matter, vol.19, no.17, pp. 176229-1-176229-8, May 2007.
99. K. J. Lee, K. H. Kim, F. C. Yu, W. S. Im, C. X. Gao, D. J. Kim, H. J. Kim, and Y. E. Ihm, "Magnetic properties of GaMnN grown via molecular beam epitaxy using a single precursor," Phys. Stat. Sol. (B), vol.241, no.12, pp. 2854-2857, Oct. 2004.
100. X. C. Liu, E. W. Shi, Z. Z. Chen, H.W. Zhang, B. Xiao, and L. X. Song, "High-temperature ferromagnetism in (Co, Al)-codoped ZnO powders," Appl. Phys. Lett., vol.88, no.25, pp. 252503-1-252503-3, Jun. 2006.
101. K. R. Kittilstved, D. A. Schwartz, A. C. Tuan, S. M. Heald, S. A. Chambers, and D. R. Gamelin, "Direct kinetic correlation of carriers and ferromagnetism in Co2\+:ZnO," Phys. Rev. Lett., vol.97, no.3, pp. 037203-1-037203-3, Jul. 2006.
102. X.-L. Li, Z.-L. Wang, X.-F. Qin, H.-S. Wu, X.-H. Xu, and G. A. Gehring, "Enhancement of magnetic moment of Co-doped ZnO films by postannealing in vacuum," J. Appl. Phys., vol.103, no.2, pp. 023911-1-023911-5, Jan. 2008.
103. K. Sato, H. Katayama-Yoshida, and P. Dederichs, "High curie temperature and nano-scale spinodal decomposition phase in dilute magnetic semiconductors," Jpn. J. Appl. Phys., vol.44, no.28-32, pt. 2, pp. L948-L951, 2005.
104. S. Kuroda, N. Nishizawa, K. Takita, M.Mitomo, Y. Bando, K. Osuch, and T. Dietl, "Origin and control of high-temperature ferromagnetism in semiconductors," Nature Mater., vol.6, no.6, pp. 440-446, Jun. 2007.
105. G. Martinez-Criado, A. Somogyi, S. Ramos, J. Campo, R. Tucoulou, M. Salome, J. Susini, M. Hermann, M. Eickhoff, and M. Stutzmann, "Mn-rich clusters in GaN: Hexagonal or cubic symmetry? Appl. Phys. Lett., vol. 86, no. 12, pp. 131927-1-131927-131933, Mar. 2005.
106. H. Katayama-Yoshida, K. Sato, T. Fukushima, M. Toyoda, H. Kizaki, V. A. Dinh, and P. H. Dederichs, "Theory of ferromagnetic semiconductors," Phys. Stat. Sol. (A), vol.204, no.1, pp. 15-32, Jan. 2007.
107. K. Sato, T. Fukushima, and H. Katayama-Yoshida, "Super-paramagnetic blocking phenomena and room-temperature ferromagnetism in wide band-gap dilute magnetic semiconductor (Ga, Mn)N," Jpn. J. Appl. Phys., vol.46, no.25-28, pt. 2, pp. L682-L684, Jul. 2007.
108. J. C. A. Huang and H. S. Hsu, "Inspection of magnetic semiconductor and clustering structure in CoFe-doped ZnO films by bias-dependent impedance spectroscopy," Appl. Phys. Lett., vol.87, no.13, pp. 132503-1-132503-3, Sep. 2005.
109. K. P. Bhatti, S. Kundu, S. Chaudhary, S. C. Kashyap, and D. K. Pandya, "Observation of room temperature ferromagnetism in nanocrystalline ZnO:Co system," J. Phys. D, Appl. Phys., vol.39, no.23, pp. 4909-4914, Dec. 2006.
110. S. J. Pearton, W. H. Heo, M. Ivill, D. P. Norton, and T. Steiner, "Dilute magnetic semiconducting oxides," Semicond. Sci. Technol., vol.19, no.10, pp. R59-R74, Oct. 2004.
111. K. Potzger, S. Zhou, H. Reuther, A. Mücklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdörfer, and T. P. Papageorgiou, "Fe implanted ferromagnetic ZnO," Appl. Phys. Lett., vol.88, no.5, pp. 052508-1-052508-3, Feb. 2006.
112. R. Frazier, G. Thaler, M. Overberg, B. Gila, C. R. Abernathy, and S. J. Pearton, "Indication of hysteresis in AlMnN," Appl. Phys. Lett., vol.83, no.9, pp. 1758-1760, Sep. 2003.
113. K. J. Lee, F. C. Yu, J. A. Kim, D. J. Kim, Y. H. Kang, H. J. Kim, and Y. E. Ihm, "Behavior of precipitates in GaMnN," Phys. Stat. Sol. (B), vol.241, no.7, pp. 1525-1528, Jun. 2004.
114. K. H. Kim, K. J. Lee, D. J. Kim, H. J. Kim, Y. E. Ihm, D. Djayaprawira, M. Takahashi, C. S. Kim, C. G. Kim, and S. H. Yoo, "Magnetotransport of p-type GaMnN assisted by highly conductive precipitates," Appl. Phys. Lett., vol.82, no.11, pp. 1775-1777, Mar. 2003.
115. T. A. Bither and W. H. Cloud, "Magnetic tetragonal- phase in the Mn-Ga binary," J. Appl. Phys., vol.36, no.4, pp. 1501-1502, 1965.
116. L. M. Corliss, N. Elliott, and J. M. Hastings, "Antiferromagnetic structure of CrN," Phys. Rev., vol.117, no.4, pp. 929-935, 1960.
117. Y. Belghazi, G. Schmerber, S. Colis, J. L. Rehspringer, A. Dinia, and A. Berrada, "Extrinsic origin of ferromagnetism in ZnO and Zn0.9Co0.1O magnetic semiconductor films prepared by sol-gel technique," Appl. Phys. Lett., vol.89, no.12, pp. 122504-1-122504-3, Sep. 2006.
118. R. Seshadri, "Zinc oxide-based diluted magnetic semiconductors, " Current Opinion Solid State Mater. Sci., vol.9, no.1-2, pp. 1-7, Feb.-Apr. 2005.
119. D. W. Abraham, M. M. Frank, and S. Guha, "Absence of magnetism in hafnium oxide films," Appl. Phys. Lett., vol.87, no.25, pp. 252502-1-252502-3, Dec. 2005.
120. H. Saito, V. Zayets, S. Yamagata, and K. Ando, "Magneto-optical studies of ferromagnetism in the II-VI diluted magnetic semiconductor Zn1-xCrxTe," Phys. Rev. B, Condens. Matter, vol.66, no.8, pp. 081201(R)-1-081201(R)-4, Aug. 2002.
121. H. Saito, V. Zayets, S. Yamagata, and K. Ando, "Room-temperature ferromagnetism in a II-VI diluted magnetic semiconductor Zn1-xCrxTe," Phys. Rev. Lett., vol.90, no.20, pp. 207202-1-207202-3, May 2003.
122. K. M. Yu, W. Walukiewicz, T. Wojtowicz, I. Kuryliszyn, X. Liu, Y. Sasaki, and J. K. Furdyna, "Effect of the location of Mn sites in ferromagnetic Ga1-xMnxAs on its Curie temperature," Phys. Rev. B, Condens. Matter, vol.65, no.20, pp. 201303(R)-1-201303(R)-4, Apr. 2002.
123. J. Blinowski and P. Kacman, "Spin interactions of interstitial Mn ions in ferromagnetic GaMnAs," Phys. Rev. B, Condens. Matter, vol.67, no.12, pp. 121204(R)-1-121204(R)-4, Mar. 2003.
124. F. Reuss, S. Frank, C. Kirchner, R. Kling, T. Gruber, and A. Waag, "Magnetoresistance in epitaxially grown degenerate ZnO thin films," Appl. Phys. Lett., vol.87, no.11, pp. 112104-1-112104-3, Sep. 2005.
125. M. Johnson, B. R. Bennett, M. J. Yang, M. M. Miller, and B. V. Shanabrook, "Hybrid Hall effect device," Appl. Phys. Lett., vol.71, no.7, pp. 974-976, Aug. 1997.
126. K. Ando, Magneto-Optics, S. Sugano and N. Kojima, Eds. Berlin, Germany: Springer-Verlag, 2000, p. 211.
127. K. Ando, H. Saito, V. Zayets, and M. C. Debnath, "Optical properties and functions of dilute magnetic semiconductors," J. Phys., Condens. Matter, vol.16, no.48, pp. S5 541-S5 548, Dec. 2004.
128. K. Ando, H. Saito, Z. W. Jin, T. Fukumura, M. Kawasaki, Y. Matsumoto, and H. Koinuma, "Magneto-optical properties of ZnO-based diluted magnetic semiconductors," J. Appl. Phys., vol.89 no.11, pp. 7284-7286, Jun. 2001. (Pubitemid 33663147)
129. K. Ando, H. Saito, Z. Jin, T. Fukumura, M. Kawasaki, Y. Matsumoto, and H. Koinuma, "Large magneto-optical effect in an oxide diluted magnetic semiconductor Zn1-xCoxO," Appl. Phys. Lett., vol.78, no.18, pp. 2700-2702, Apr. 2001.
130. A. J. Behan, J. R. Neal, R. M. Ibrahim, A. Mokhtari, M. Ziese, H. J. Blythe, A. M. Fox, and G. A. Gehring, "Magneto-optical and transport studies of ZnO-based dilute magnetic semiconductors," J. Magn. Magn. Mater., vol.310, no.2, pt. 3, pp. 2158-2160, Nov. 2007.
131. E. Przezdziecka, E. Kaminska, M. Kiecana, M. Sawickia, ̀. Kaopotowski, W. Pacuski, and J. Kossut, "Magneto-optical properties of the diluted magnetic semiconductor p-type ZnMnO," Solid State Commun., vol.139, no.10, pp. 541-544, Jul. 2006.
132. M. Tay, Y. H. Wu, G. C. Han, T. C. Chong, Y. K. Zheng, S. J. Wang, Y. B. Chen, and X. Q. Pan, "Ferromagnetism in inhomogeneous Zn1-xCoxO thin films," J. Appl. Phys., vol.100, no.6, pp. 063910-1-063910-9, Sep. 2006.
133. W. Pacuski, D. Ferrand, J. Cibert, C. Deparis, J. A. Gaj, P. Kossacki, and C. Morhain, "Effect of the s,p-d exchange interaction on the excitons in Zn1-xCoxO epilayers," Phys. Rev. B, Condens. Matter, vol.73, no.3, pp. 035214-1-035214-14, Jan. 2006.
134. W. Pacuski, D. Ferrand, J. Cibert, J. A. Gaj, A. Golnik, P. Kossacki, S. Marcet, E. Sarigiannidou, and H. Mariette, "Excitonic giant Zeeman effect in GaN:Mn3+," Phys. Rev. B, Condens. Matter, vol.76, no.16, pp. 165304-1-165304-6, Oct. 2007.
135. W. Pacuski, P. Kossacki, D. Ferrand, A. Golnik, J. Cibert, M. Wegscheider, A. Navarro-Quezada, A. Bonanni, M. Kiecana, M. Sawicki, and T. Dietl, "Observation of strong-coupling effects in a diluted magnetic semiconductor Ga1-xFexN," Phys. Rev. Lett., vol.100, no.3, pp. 037204-1-037204-4, Jan. 2008.
136. J. R. Neal, A. J. Behan, R. M. Ibrahim, H. J. Blythe, M. Ziese, A. M. Fox, and G. A. Gehring, "Room-temperature magneto-optics of ferromagnetic transition-metal-doped ZnO thin films," Phys. Rev. B, Condens. Matter, vol.96, no.19, pp. 197208-1-197208-4, May 2006.
137. R. Fiederling, M. Keim, G. Reuscher, W. Ossau, G. Schmidt, A. Waag, and L. W. Molenkamp, "Injection and detection of a spin-polarized current in a light-emitting diode," Nature, vol.402, no.6763, pp. 787-790, Dec. 1999.
138. Y. Ohno, D. K. Young, B. Beschoten, F. Matsukura, H. Ohno, and D. D. Awschalom, "Electrical spin injection in a ferromagnetic semiconductor heterostructures," Nature, vol.402, no.6763, pp. 790-792, Dec. 1999.
139. W. M. Chen, I. A. Buyanova, K. Nishibayashi, K. Kayanuma, K. Seo, A. Murayama, Y. Oka, G. Thaler, R. Frazier, C. R. Abernathy, F. Ren, S. J. Pearton, C.-C. Pan, G.-T. Chen, and J.-I. Chyi, "Efficient spin relaxation in InGaN/GaN and InGaN/GaMnN quantum wells: An obstacle to spin detection," Appl. Phys. Lett., vol.87, no.19, pp. 192107-1-192107-3, Nov. 2005.
140. I. A. Buyanova, M. Izadifard, W. M. Chen, J. Kim, F. Ren, G. Thaler, C. R. Abernathy, S. J. Pearton, C.-C. Pan, G.-T. Chen, J.-I. Chyi, and J. M. Zavada, "On the origin of spin loss in GaMnN/InGaN light-emitting diodes," Appl. Phys. Lett., vol.84, no.14, pp. 2599-2601, Apr. 2004.
141. S. J. Pearton, D. P. Norton, M. P. Ivill, A. F. Hebard, J. M. Zavada, W. M. Chen, and I. A. Buyanova, "Ferromagnetism in transition-metal doped ZnO," J. Electron. Mater., vol.36, no.4, pp. 462-471, Apr. 2007.
142. S. Ghosh, V. Sih, W. H. Lau, D. D. Awschalom, S.-Y. Bae, S. Wang, S. Vaidya, and G. Chapline, "Room-temperature spin coherence in ZnO," Appl. Phys. Lett., vol.86, p. 232 507, 2005.
143. B. Beschoten, E. Johnston-Halperin, D. K. Young, M. Poggio, J. E. Grimaldi, S. Keller, S. P. DenBaars, U. K. Mishra, E. L. Hu, and D. D. Awschalom, "Spin coherence and dephasing in GaN," Phys. Rev. B, Condens. Matter, vol.63, 2001, 121202
144. R. Ste?pniewski, M. Potemski, A. Wysmoaek, K. Pakuaa, J. M. Baranowski, J. ̀usakowski, I. Grzegory, S. Porowski, G. Martinez, and P. Wyder, "Symmetry of excitons in GaN," Phys. Rev. B, Condens. Matter, vol.60, no.7, pp. 4438-4441, Aug. 1999.
145. A. Tackeuchi, T. Kuroda, A. Shikanai, T. Sota, A. Kuramata, and K. Domen, "No spin polarization of carriers in InGaN," Physica E, vol.7, pp. 1011-1014, 2000.
146. J. Campo, M. Julier, D. Coquillat, J. P. Lascaray, D. Scalbert, and O. Briot, "Zeeman splittings of excitonic transitions at the- point in Wurtzite GaN: A magnetoreflectance investigation," Phys. Rev. B, Condens. Matter, vol.56, 1997, R7108.
147. C. K. Choi, J. B. Lam, G. H. Gainer, S. K. Shee, J. S. Krasinski, J. J. Song, and Y.-C. Chang, "Polarization dependence of the excitonic optical Stark effect in GaN," Phys. Rev. B, Condens. Matter, vol.65, 2002, 155206.
148. M. Julier, J. Campo, B. Gil, and J. P. Lascaray, "Determination of the spin-exchange interaction constant in Wurtzite GaN," Phys. Rev. B, Condens. Matter, vol.57, 1998, R6791.
149. B. Gil and O. Briot, "Internal structure and oscillator strengths of excitons in strained-GaN," Phys. Rev. B, Condens. Matter, vol.55, pp. 2530-2534, 1997.
150. D. W. Langer, R. N. Euwena, K. Era, and T. Koda, "Spin exchange in excitons, the quasicubic model and deformation potentials in II-VI compounds," Phys. Rev. B, Condens. Matter, vol.2, pp. 4005-4022, 1970.
151. B. Gil, A. Lusson, V. Sallet, S. A. Said-Hassani, R. Triboulet, and P. Bigenwald, "Strain-fields effects and reversal of the nature of the fundamental valence band of ZnO epilayers," Jpn. J. Appl. Phys., vol.40, pt. 2, 2001, L1089.
152. B. Gil, "Oscillator strengths of A, ", and C excitons in ZnO films," Phys. Rev. B, Condens. Matter, vol.64, 2001, 201310.
153. D. G. Thomas, "The exciton spectrum of ZnO," J. Phys. Chem. Solids, vol.15, pp. 86-96, 1960.
154. B. J. Skromme, "Optical and magneto-optical characterization of heteroepitaxial gallium nitride," Mater. Sci. Eng. B, vol.50, pp. 117-125, 1997.
155. T. Gruber, G.M. Prinz, C. Kirchner, R. Kling, F. Reuss, W. Limmer, and A. Waag, "Influences of biaxial strains on the vibrational and exciton energies in ZnO," J. Appl. Phys., vol.96, pp. 289-293, 2004.
156. D. D. Awschalom and M. E. Flatte, "Challenges for semiconductor spintronics," Nature Phys., vol.3, no.3, pp. 153-159, Mar. 2007.
157. S. Datta and B. Das, "Electronic analog of the electrooptic modulator," Appl. Phys. Lett., vol.56, no.7, pp. 665-667, Feb. 1990.
158. T. Gruber, M. Keim, R. Fiederling, G. Reuscher, W. Ossau, G. Schmidt, L. W. Molenkamp, and Waag, "Electron spin manipulation using semimagnetic resonant tunneling diodes," Appl. Phys. Lett., vol.78, no.8, pp. 1101-1103, Feb. 2001.
159. F. J. Jedema, A. T. Filip, and V. B. J. Wees, "Electrical spin injection and accumulation at room temperature in an all-metal mesoscopic spin valve," Nature, vol.410, pp. 6826, pp. 345-348, Mar. 2001.
160. R. M. Stroud, A. T. Hanbicki, Y. D. Park, G. Kioseoglou, A. G. Petukhov, B. T. Jonker, G. Itskos, and A. Petrou, "Reduction of spin injection efficiency by interface defect spin scattering in ZnMnSe/AlGaAs-GaAs spin-polarized light-emitting diodes," Phys. Rev. Lett, vol.89, no.16, pp. 166602-1-166602-4, Oct. 2002.
161. M. V. Tsoi, A. G. M. Jansen, and J. Bass, "Search for point-contact giant magnetoresistance in Co/Cu multilayers," J. Appl. Phys., vol.81, no.8, pt. 2B, pp. 5530-5532, Apr. 1997.