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The process of magnetization reversal in ferromagnetic Ga(1-x)MnxAs epilayers has been systematically investigated using the planar Hall effect (PHE). Interestingly, we have observed a pronounced asymmetry in the PHE hysteresis when the range of the field scan is restricted to fields below the final magnetization transition. The observed behavior indicates that (a)A multidomain structures are formed as M undergoes a reorientation, (b) the domain landscape formed in this way remains stable even after the magnetic field is switched off, and (c) the reorientation of magnetization directions corresponding to the transition points in PHE takes place separately within each domain. © 2007 The American Physical Society., References: Ohno, H., (2000) Nature (London), 408, p. 944. , NATUAS 0028-0836 10.1038/35050040; Twardowski, A., (2000) Acta Phys. Pol. A, 98, p. 203. , ATPLB6 0587-4246; Koshihara, S., (1997) Phys. Rev. Lett., 78, p. 4617. , PRLTAO 0031-9007 10.1103/PhysRevLett.78.4617; Lee, S., (2003) J. Appl. Phys., 93, p. 8307. , JAPIAU 0021-8979 10.1063/1.1556272; Tang, H.X., (2003) Phys. Rev. Lett., 90, p. 107201. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.107201; Tang, H.X., Roukes, M.L., (2004) Phys. Rev. B, 70, p. 205213. , PRBMDO 0163-1829 10.1103/PhysRevB.70.205213; Moore, G.P., (2003) J. Appl. Phys., 94, p. 4530. , JAPIAU 0021-8979 10.1063/1.1601690; Liu, X., (2003) Phys. Rev. B, 67, p. 205204. , PRBMDO 0163-1829 10.1103/PhysRevB.67.205204; Liu, X., (2005) Phys. Rev. B, 71, p. 035307. , PRBMDO 0163-1829 10.1103/PhysRevB.71.035307; Sawicki, M., (2006) J. Magn. Magn. Mater., 300, p. 1. , JMMMDC 0304-8853 10.1016/j.jmmm.2005.10.020; Sawicki, M., (2004) Phys. Rev. B, 70, p. 245325. , PRBMDO 0163-1829 10.1103/PhysRevB.70.245325; Baxter, D.V., (2002) Phys. Rev. B, 65, p. 212407. , PRBMDO 0163-1829 10.1103/PhysRevB.65.212407; Holleitner, A.W., (2004) Appl. Phys. Lett., 85, p. 5622. , APPLAB 0003-6951 10.1063/1.1829797; Hamaya, K., (2003) IEEE Trans. Magn., 39, p. 2785. , IEMGAQ 0018-9464 10.1109/TMAG.2003.815710; Hamaya, K., (2004) IEEE Trans. Magn., 40, p. 2682. , IEMGAQ 0018-9464 10.1109/TMAG.2004.832667; Wang, K.Y., (2005) Phys. Rev. B, 72, p. 085201. , PRBMDO 0163-1829 10.1103/PhysRevB.72.085201; Tang, H.X., (2004) Nature (London), 431, p. 52. , NATUAS 0028-0836 10.1038/nature02809; Welp, U., (2003) Phys. Rev. Lett., 90, p. 167206. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.167206; Titova, L.V., (2005) Phys. Rev. B, 72, p. 165205. , PRBMDO 0163-1829 10.1103/PhysRevB.72.165205; Okamoto, K., (1983) J. Magn. Magn. Mater., 35, p. 353. , JMMMDC 0304-8853 10.1016/0304-8853(83)90539-5; Yamanouchi, M., (2006) Phys. Rev. Lett., 96, p. 096601. , PRLTAO 0031-9007 10.1103/PhysRevLett.9

A series of GaMnAs epilayers grown on GaInAs buffer layers have been investigated. The concentrations of Mn in the GaMnAs layer and In in the GaInAs layer were varied in the series, for which the tensile strain condition for the GaMnAs layer are systematically changed. The X-ray measurement provided the lattice constants of the layers, from which the stain of the GaMnAs layer was determined. The magneto-transport data revealed in-plane anisotropy in the GaMnAs sample grown on a GaInAs buffer with a low concentration of In. Such in-plan magnetic anisotropy of the GaMnAs layer continuously changed to a vertical magnetic anisotropy when the tensile strain was increased in the sample grown on the GaInAs buffer with a higher In concentration. This experiment clearly demonstrated that the magnetic anisotropy of GaMnAs could be continuously engineered by using the strain introduced by the GaInAs buffer layers., References: Wolf, S.A., Awschalom, D.D., Buhrman, R.A., Daughton, J.M., von MoInár, S., Roukes, M.L., Chtchelkanova, A.Y., Treger, D.M., (2001) Science, 204, p. 5546; Ohno, Y., Young, D.K., Beschoten, B., Matsukura, F., Ohno, H., Awschalom, D.D., (2000) Nature, 402, p. 790; Edmonds, K.W., Wang, K.Y., Campion, R.P., Neumann, A.C., Farley, N.R.S., Gallagher, B.L., Foxon, C.T., (2002) Appl. Phys. Lett, 81, p. 4991; Nazmul, A.M., Amemiya, T., Shuto, Y., Sugahara, S., Tanaka, M., (2005) Phys. Rev. Lett, 95, p. 017201; Sawicki, M., Wang, K.-Y., Edmonds, K.W., Campion, R.P., Staddon, C.R., Farley, N.R.S., Foxon, C.T., Gallagher, B.L., (2005) Phys. Rev. B, 71, p. 121302; Liu, X., Sasaki, Y., Furdyna, J.K., (2003) Phys. Rev. B, 67, p. 205204; Sawicki, M., Matsukura, F., Idziaszek, A., Dietl, T., chott, G.M., Ruester, C., Gould, C., Molenkamp, L.W., (2004) Phys. Rev. B, 70, p. 245325; Kim, Y.S., Jeong, I.T., Woo, J.C., Khim, Z.G., Lee, J.S., Choi, H.K., Oh, Y.S., Chun, S.H., (2005) J. Korean Phys. Soc, 47, p. 306; Ohno, H., Chiba, D., Matsukura, F., Omiya, T., Abe, E., Dietl, T., Ohno, Y., Ohtani, K., (2000) Nature, 408, p. 944; Oiwa, A., Mitsumori, Y., Moriya, R., Slupinski, T., Munekata, H., (2002) Phys. Rev. Lett, 88, p. 137202; Lee, S., Chung, S.J., Choi, I.S., Yuldashev, S.U., Im, H., Kang, T.W., Lim, W.-L., Furdyna, J.K., (2003) J. Appl. Phys, 93, p. 8307; Wojtowicz, T., Lim, W.L., Liu, X., Dobrowolska, M., Furdyna, J.K., Yu, K.M., Walukiewicz, W., Meyer, J.R., (2003) Appl. Phys. Lett, 83, p. 4220; Furdyna, J.K., Lee, S., Wojtowicz, T., Liu, X., Lim, W.L., Kuryliszyn, I., Sasaki, Y., Walukiewicz, W., (2003) J. Korean Phys. Soc, 42, p. 579. , S; Konig, J., Schliemann, J., Jungwirth, T., MacDonald, A.H., Ferromagnetism in (III, Mn) V Semiconductors (2002) Electronic Structure and Magnetism of Complex Materials, , edited by D. J. Singh and D. A. Papaconstantopoulos Springer Verlag; Ohno, H., Shen, A., Matsukura, F., Oiwa, A., Endo, A., Katsumoto, S., Iye, Y., (1996) App

The authors show that staggered asymmetric planar Hall resistance (PHR) loops observed in GaMnAs ferromagnetic semiconductor films with biaxial in-plane magnetic anisotropy result in four stable resistance states at zero magnetic field owing to the formation of a stable multidomain structure during magnetization reversal. The values of PHR can be systematically controlled by changing the direction and the scanning range of the applied magnetic field. The possibility of a quaternary memory device based on the observed four PHR states is demonstrated by obtaining consistent results in the writing process using appropriate sequences of magnetic field pulses. © 2007 American Institute of Physics., References: Daughton, J.M., (1992) Thin Solid Films, 216, p. 162; Gallagher, W.J., Parkin, S.S.P., Lu, Y., Bian, X.P., Marley, A., Roche, K.P., Altman, R.A., Xiao, G., (1997) J. Appl. Phys, 81, p. 3741; Tehrani, S., Chen, E., Durlam, M., DeHerrera, M., Slaughter, J.M., Shi, J., Kerszykowski, G., (1999) J. Appl. Phys, 85, p. 5822; Parkin, S.S., Roche, K.P., Samant, M.G., Rice, P.M., Beyers, R.B., Scheuerlein, R.E., O'Sullivan, E.J., Gallagher, W.J., (1999) J. Appl. Phys, 85, p. 5828; Zhu, J.G., Zheng, Y., Prinz, G., (2000) J. Appl. Phys, 87, p. 6668; Wang, Z., Nakamura, Y., (1996) J. Appl. Phys, 79, p. 6639; Zhang, R., Hassoun, M.M., Black Jr., W.C., Das, B., Wong, K.A., (1999) IEEE Trans. Magn, 35, p. 2829; Tang, H.X., Kawakami, R.K., Awschalom, D.D., Roukes, M.L., (2003) Phys. Rev. Lett, 90, p. 107201; Okamoto, K., (1983) J. Magn. Magn. Mater, 35, p. 353; Moore, G.P., Ferre, J., Mougin, A., Moreno, M., Daweritz, L., (2003) J. Appl. Phys, 94, p. 4530; Liu, X., Lim, W.L., Dobrowolska, M., Furdyna, J.K., Wojtowicz, T., (2005) Phys. Rev. B, 71, p. 035307; Sawicki, M., Matsukura, F., Idziaszek, A., Dietl, T., Schott, G.M., Ruester, C., Gould, C., Molenkamp, L.W., (2004) Phys. Rev. B, 70, p. 245325; Wang, K.Y., Edmonds, K.W., Campion, R.P., Zhao, L.X., Foxon, C.T., Gallagher, B.L., (2005) Phys. Rev. B, 72, p. 085201; Rüster, C., Borzenko, T., Gould, C., Schmidt, G., Molenkamp, L.W., Liu, X., Wojtowicz, T.J., Flatté, M.E., (2003) Phys. Rev. Lett, 91, p. 216602; Lim, W.L., Liu, X., Dziatkowski, K., Ge, Z., Shen, S., Furdyna, J.K., Dobrowolska, M., (2006) Phys. Rev. B, 74, p. 045303; Shin, D.Y., Chung, S.J., Lee, S., Liu, X., Furdyna, J.K., (2007) Phys. Rev. Lett, 98, p. 047201; Rüster, C., Borzenko, T., Gould, C., Schmidt, G., Molenkamp, L.W., Liu, X., Wojtowicz, T.J., Flatté, M.E., (2003) Phys. Rev. Lett, 91, p. 216602QC 20130513

The magnetization reversal process of ferromagnetic GaMnAs epilayers has been systematically investigated using the planar Hall effect (PHE) and magnetoresistance (MR). We have observed non-abrupt transitions between two orientations of magnetization in PHE and striking resistance dips at the second switching in MR. The observed behaviors indicate that multi-domain structures are formed as magnetization undergoes a reorientation. An asymmetric PHE hysteresis loop was obtained when the range of the field scan was restricted to fields below the final magnetization transition. This indicates that the domain structure formed at the moment of magnetization reorientation remains stable even after the magnetic field is removed. The time stability of the multi-domain structure was further tested by monitoring the change in the planar Hall resistance value for more than 24 h., References: Wolf, S.A., Awschalom, D.D., Buhrman, R.A., Daughton, J.M., von Molnár, S., Roukes, M.L., Chtchelkanova, A.Y., Treger, D.M., (2001) Science, 294, p. 1488; Ohno, H., Chiba, D., Matsukura, F., Omlya, T., Abe, E., Dietl, T., Ohno, Y., Ohtanl, K., (2000) Nature (London), 408, p. 944; Koshihara, S., Oiwa, A., Hirasawa, M., Katsumoto, S., Iye, Y., Urano, C., Takagi, H., Munekata, H., (1997) Phys. Rev. Lett., 78, p. 4617; Lee, S., Chung, S.J., Choi, I.S., Yuldashev, Sh.U., Im, H., Kang, T.W., Lim, W.L., Furdyna, J.K., (2003) J. Appl. Phys., 93, p. 8307; Wojtowicz, T., Lim, W.L., Liu, X., Dobrowolska, M., Furdyna, J.K., Yu, K.M., Walukiewicz, W., Meyer, J.R., (2003) Appl. Phys. Lett., 83, p. 4220; Wang, K.Y., Campion, R.P., Edmonds, K.W., Sawicki, M., Dietl, T., Foxon, C.T., Gallagher, B.L., (2004), cond-mat/0411475Shin, D.Y., Chung, S.J., Lee, S., Liu, X., Furdyna, J.K., (2007) Phys. Rev. Lett., 98, p. 047201; Lee, S., Shin, D.Y., Chung, S.J., Liu, X., Furdyna, J.K., (2007) Appl. Phys. Lett., 90, p. 152113; Tang, H.X., (2003) Phys. Rev. Lett., 90, p. 107201; Holleitner, A.W., (2004) Appl. Phys. Lett., 85, p. 5622; Wang, K.Y., (2005) Phys. Rev. B, 72, p. 085201; Tang, H.X., (2004) Nature, 431, p. 52; Welp, U., (2003) Phys. Rev. Lett., 90, p. 167206; Titova, L.V., (2005) Phys. Rev. B, 72, p. 165205; Tang, H., Roukes, M.L., (2004) Phys. Rev. B, 70, p. 205213; Okamoto, K., (1983) J. Magn. Magn. Mater., 35, p. 353QC 20130513

We carried out systematic planar Hall effect (PHE) measurements of GaMnAs ferromagnetic semiconductor film as a function of temperature. The two-step switching of the PHE occurring in the magnetization-reversal process was observed to change significantly as the temperature was increased. To investigate the mechanism responsible for such behavior, the temperature dependence of the PHE was continuously measured (with and without an external magnetic field) after the sample was first magnetized along one of the easy axes to produce an initial single-domain state at 3 K. A detailed temperature dependence of the magnetization direction was then obtained by taking the ratio of the planar Hall resistance measured with and without a magnetic field. As the temperature was increased, the direction of the easy axis of magnetization was observed to change from the [010] crystallographic direction to [110]. This reorientation of the easy axis direction can be understood in terms of the temperature dependence of the relative strengths of the magnetic anisotropy constants (i.e., of the ratio of uniaxial-to-cubic anisotropy) of the GaMnAs film. © 2007 The American Physical Society., References: Ohno, H., (1998) Science, 281, p. 951. , SCIEAS 0036-8075 10.1126/science.281.5379.951; Dietl, T., (2000) Science, 287, p. 1019. , SCIEAS 0036-8075 10.1126/science.287.5455.1019; Ohno, H., (2000) Nature (London), 408, p. 944. , NATUAS 0028-0836 10.1038/35050040; Tang, H.X., Kawakami, R.K., Awschalom, D.D., Roukes, M.L., (2003) Phys. Rev. Lett., 90, p. 107201. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.107201; Ohno, Y., (2001) Physica e (Amsterdam), 10, p. 489. , PELNFM 1386-9477 10.1016/S1386-9477(01)00143-6; Lim, W.L., Liu, X., Dziatkowski, K., Ge, Z., Shen, S., Furdyna, J.K., Dobrowolska, M., (2006) Phys. Rev. B, 74, p. 045303. , PRBMDO 0163-1829 10.1103/PhysRevB.74.045303; Bason, Y., (2004) Appl. Phys. Lett., 84, p. 2593. , APPLAB 0003-6951 10.1063/1.1695197; Dietl, T., (2001) Physica e (Amsterdam), 10, p. 120. , PELNFM 1386-9477 10.1016/S1386-9477(01)00066-2; Sawicki, M., (2003) J. Supercond., 16, p. 7. , JOUSEH 0896-1107 10.1023/A:1023251710725; Liu, X., Sasaki, Y., Furdyna, J.K., (2003) Phys. Rev. B, 67, p. 205204. , PRBMDO 0163-1829 10.1103/PhysRevB.67.205204; Sawicki, M., Matsukura, F., Idziaszek, A., Dietl, T., Schott, G.M., Ruester, C., Gould, C., Molenkamp, L.W., (2004) Phys. Rev. B, 70, p. 245325. , PRBMDO 0163-1829 10.1103/PhysRevB.70.245325; Dietl, T., Ohno, H., Matsukura, F., (2001) Phys. Rev. B, 63, p. 195205. , PRBMDO 0163-1829 10.1103/PhysRevB.63.195205; Wang, K.-Y., Sawicki, M., Edmonds, K.W., Campion, R.P., Maat, S., Foxon, C.T., Gallagher, B.L., Dietl, T., (2005) Phys. Rev. Lett., 95, p. 217204. , PRLTAO 0031-9007 10.1103/PhysRevLett.95.217204; Welp, U., Vlasko-Vlasov, V.K., Liu, X., Furdyna, J.K., Wojtowicz, T., (2003) Phys. Rev. Lett., 90, p. 167206. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.167206; Shin, D.Y., Chung, S.J., Lee, S., Liu, X., Furdyna, J.K., (2007) Phys. Rev. Lett., 98, p. 047201. , PRLTAO 0031-9007 10.1103/PhysRevLett.98.047201; McGuire, T.R., Potter, R.I., (1975) IEEE Trans. Magn., 11, p. 1018. , IEMGAQ 0018-9464

The planar Hall effect (PHE) and magnetoresistance (MR) measurements have been carried out on a GaMnAs ferromagnetic semiconductor. The PHE and MR spectra exhibit interesting two-step magnetization switching behavior arising from the magnetic anisotropy properties of the system. By fitting the angle-dependent planar Hall resistance (PHR) data taken at 5 kG with the Stoner-Wohlfarth model, the cubic and uniaxial anisotropy constants were independently obtained. The anisotropy constants lead to the precise determination of easy axis direction, which turns out to be in good agreement with the easy axis determined from the angular plot of the switching field. The domain pinning energies were further obtained by fitting the angle dependence of the switching field, including the effect of uniaxial anisotropy. © 2007 IEEE., References: Ohno, H., Making nonmagnetic semiconductors ferromagnetic (1998) Science, 281, pp. 951-956; Baxter, D.V., Ruzmetov, D., Scherschligt, J., Sasaki, Y., Liu, X., Furdyna, J.K., Mielke, C.H., Anisotropic magnetoresistance in GalxMnxAs (2002) Phys. Rev. B, 65, p. 212407; Moore, G.P., Ferre, J., Mougin, A., Moreno, M., Daweritz, L., Magnetic anisotropy and switching process in diluted Gal-xMnxAs magnetic semiconductor films (2003) J. Appl. Phys, 94, pp. 4530-4534; Tang, H.X., Kawakami, R.K., Awschalom, D.D., Roukes, M.L., Giant planar Hall effect in epitaxial (Ga,Mn)As devices (2003) Phys, Rev. Lett, 90, p. 107201; Hamaya, K., Taniyama, T., Kitamoto, Y., Moriya, R., Munekata, H., Magnetotransport study of temperature dependent magnetic anisotropy in a (Ga,Mn)As epilayer (2003) J. Appl. Phys, 94, pp. 7657-7661; Cowburn, R.P., Gray, S.J., Ferre, J., Bland, J.A.C., Miltat, J., Magnetic switching and in-plane uniaxial anisotropy in ultrathin Ag/Fe/Ag(100) epitaxial films (1995) J. Appl. Phys, 78, pp. 7210-7219; Welp, U., Vlasko-Vlasov, V.K., Menzel, A., You, H.D., Liu, X., Furdyna, J.K., Wojtowicz, T., Uniaxial in-plane magnetic anisotropy of Gal-xMnxAs (2004) Appl. Phys. Lett, 85, pp. 260-262; Tang, H.X., Roukes, M.L., Electrical transport across an individual magnetic domain wall in (Ga,Mn)As microdevices (2004) Phys. Rev. B, 70, p. 205213; Welp, U., Vlasko-Vlasov, V.K., Liu, X., Furdyna, J.K., Wojtowicz, T., Magnetic domain structure and magnetic anisotropy in GalxMnxAs (2003) Phys. Rev. Lett, 90, p. 167206; Liu, X., Lim, W.L., Dobrowolska, M., Furdyna, J.K., Wojtowicz, T., Ferromagnetic resonance study of the free-hole contribution to magnetization and magnetic anisotropy in modulation-doped Gal-xMnxAs/Gal-yAlyAs: Be (2005) Phys. Rev. B, 71, p. 035307; Okamoto, K., A new method for analysis of magnetic-anisotropy in films using the spontaneous hall-effect (1983) J. Magn. Magn. Mater, 35, pp. 353-355QC 20130513

The authors report the carrier transport and electrical breakdown behaviors of micron-long-channel suspended carbon nanotube (CNT) of carbon-based one-dimensional junction with CNTs as drain and source electrodes. The structure consisted of bundle-type CNT electrode-a CNT channel-bundle-type CNT electrode, produced by one-step in situ direct growth via a unique diluted magnetic nanothick film catalyst at low temperature. The unique suspended all-one-dimensional CNT-based junction provides some insights into recent reports that an electrical breakdown of CNTs can be induced not by the contact problem but by the nonhomogeneously Joule heating along nanotube without release of heat into contacts by the observed breakdown at midlength of a 1-2 μm long channel. The high current carrying all-CNT junction with bridging yield of 90% and stable operation at fixed voltage level can contribute into realization of practical integrated nanoelectronics such as interconnecter and transistor via junction formation of one-step final process. © 2006 American Institute of Physics., References: Honlein, W., (2002) Jpn. J. Appl. Phys., Part 1, 41, p. 4370; Chen, Z., Appenzeller, J., Lin, Y.M., Oakley, J.S., Rinzler, A.G., Tang, J., Wind, S.J., Avouris, P., (2006) Science, 311, p. 1735; Bockrath, M., Codden, D.H., McEuen, P.L., Chopra, N.G., Zettl, A., Thess, A., Smally, R.E., (1997) Science, 275, p. 1922; Tans, S.J., Verschuenen, A.R.M., Dekker, C., (1998) Nature (London), 393, p. 49; Chen, Z., Appenzeller, J., Liu, Y.M., Oakley, J.S., Rinzler, A.G., Tang, J., Wind, S.J., Avouris, P., (2006) Science, 211, p. 1735; Sazonova, V., Yaish, Y., Üstünel, H., Roundy, D., Arias, T.A., McEuen, P.L., (2004) Nature (London), 431, p. 284; Huang, J.Y., Chen, S., Jo, S.H., Wang, Z., Han, D.X., Chen, G., Dresselhaus, M.S., Ren, Z.F., (2005) Phys. Rev. Lett., 94, p. 236802; Sapmaz, S., Herrero, P.J., Blanter, Y.M., Dekker, C., Van Der Zant, H.S.J., (2006) Phys. Rev. Lett., 96, p. 026801; Kuroda, M.A., Cangellaris, A., Leburton, J.P., (2005) Phys. Rev. Lett., 95, p. 266803; Bourlon, B., Glattli, D.C., Placais, B., Berroir, J.M., Miko, C., Forro, L., Bachtold, A., (2004) Phys. Rev. Lett., 92, p. 026804; Li, H.J., Lu, W.G., Li, J.J., Bai, X.D., Gu, C.Z., (2005) Phys. Rev. Lett., 95, p. 086601; Chiu, H.-Y., Deshpande, V.V., Postma, H.W.Ch., Lau, C.N., Miko, C., Forro, L., Bockrath, M., (2005) Phys. Rev. Lett., 95, p. 226101; Cao, J., Wang, Q., Dai, H.J., (2005) Nat. Mater., 4, p. 745; Guo, J., Hasan, S., Javey, A., Bosman, G., Lundstrom, M., (2005) IEEE Trans. Nanotechnol., 4, p. 715; Lee, Y.-H., Jang, Y.T., Choi, C.H., Kim, D.H., Lee, C.W., Lee, J.E., Han, Y.S., Ju, B.K., (2001) Adv. Mater. (Weinheim, Ger.), 13, p. 1371; Lee, Y.-H., Yoo, J.M., Lee, J.A., Ahn, S.Y., Joo, J., Lee, S., Kim, D.H., Ju, B.K., (2005) Appl. Phys. Lett., 87, p. 121915; Javey, A., Guo, J., Wang, Q., Lundstrom, M., Dai, H.J., (2003) Nature (London), 424, p. 654; Y.-H. Lee, J. M. Yoo, J. H. Lee, and B. K. Ju (submitted)Nemec, N., Tomanek, D., Cuniberti, G., (2006) Phys. Rev. Lett., 96, p. 0

We have studied the effect of low-temperature (LT) annealing on the properties of Ga 1-xMn xAs/GaAs superlattices (SLs). One SL contained GaAs layers doped by Be (which acts as a p-type dopant), while the GaAs layers of the other SL were undoped. The Be-doped SL exhibited a coercive field (H C) three times larger than the undoped SL, and showed a much more robust remanent magnetization (M r). While the effect of LT annealing on the undoped SL was relatively minor, magnetic properties of the Be-doped SL changed significantly after annealing. The coercive field of the Be-doped SL was reduced about three times, becoming comparable to that of the undoped SL. After annealing the temperature dependence of M r in the Be-doped SL also became similar to the undoped SL. We discuss the effect of LT annealing on the magnetic properties of the two SL systems in terms of inter-diffusion of carriers, and of the reduced sensitivity to annealing characteristic of capped structures. © 2005 Springer Science+Business Media, Inc., References: Ohno, H., Shen, A., Matsukura, F., Oiwa, A., Endo, A., Katsumoto, S., Iye, Y., (1996) Appl. Phys. Lett., 69, p. 363; Dietl, T., Ohno, H., Matsukura, F., Cibert, J., Ferrand, D., (2000) Science, 287, p. 1019; Lee, S., Chung, S.J., Choi, I.S., Yuldeshev, S.U., Im, H., Kang, T.W., Lim, W.-L., Furdyna, J.K., (2003) J. Appl. Phys., 93, p. 8307; Wojtowicz, T., Lim, W.L., Liu, X., Dobrowolska, M., Furdyna, J.K., Yu, K.M., Walukiewicz, W., Meyer, J.R., (2003) Appl. Phys. Lett., 83, p. 4220; Stone, M.B., Ku, K.C., Potashnik, S.J., Sheu, B.L., Samarth, N., Schiffer, P., (2003) Appl. Phys. Lett., 83, p. 4568; Edmonds, K.W., Bogusławski, P., Wang, K.Y., Campion, R.P., Novikov, S.N., Farley, N.R.S., Gallagher, B.L., Bernholc, J., (2004) Phys. Rev. Lett., 92, p. 037201; Potashnik, S.J., Ku, K.C., Chun, S.H., Berry, J.J., Samarth, N., Schiffer, P., (2001) Appl. Phys. Lett., 79, p. 1495; Yu, K.M., Walukiewicz, W., Wojtowicz, T., Kuryliszyn, I., Liu, X., Sasaki, Y., Furdyna, J.K., (2002) Phys. Rev. B, 65, p. 201303; Singley, E.J., Kawakami, R.K., Awschalom, D.D., Basov, D., (2002) Phys. Rev. Lett., 89, p. 097203; Edmonds, K.W., Wang, K.Y., Campion, R.P., Neumann, A.C., Farley, N.R.S., Gallagher, B.L., Foxon, C.T., (2002) Appl. Phys. Lett., 81, p. 4991QC 20130513

We present a systematic study on the properties of the ferromagnetic (FM) III-V-based semiconductor GaMnAs, including extrinsically doped GaMnAs: Be and its heterostructures in the form of superlattices. In an attempt to further improve the Curie temperature T c of GaMnAs, we have undertaken a systematic program of extrinsic p-doping of this material. In GaMnAs with low x (x = 0.03), T c is, indeed, seen to increase monotonically with increasing Be doping. We also studied the effect of p-doping of non-magnetic spacer layers on the magnetic properties of GaMnAs/GaAs superlattices (SLs). While Be-doped SLs exhibited relatively robust remanent magnetization and a larger coercivity over a broad temperature range, undoped SLs showed a fast decrease in the remanent magnetization with temperature, and a rather small coercivity. We propose that the observed hardness of the magnetization in SLs with Be-doped GaAs layers is related to the interlayer coupling introduced by the doping of the non-magnetic layers., References: Wolf, S.A., Awschalom, D.D., Buhrman, R.A., Daughton, J.M., Von Molar, S., Roukes, M.L., Chtchelkamova, A.Y., Treger, D.M., (2001) Science, 294, p. 1488; Furdyna, J.K., (1988) J. Appl. Phys., 64, pp. R29; Lee, S., Yang, G., Dobrowolska, M., Furdyna, J.K., (2001) J. Korean Phys. Soc., 39, p. 447; Ohno, Y., Young, D.K., Beschoten, B., Matsukura, F., Ohno, H., Awschalom, D.D., (1999) Nature, 402, p. 790; Fiederling, R., Keim, M., Reuscher, G., Ossau, W., Schmidt, G., Waag, A., Molenkamp, L.W., (1999) Nature, 402, p. 787; Hanbicki, A.T., Jonker, B.T., Itskos, G., Kioseoglou, G., Petrou, A., (2002) Appl. Phys. Lett., 80, p. 1240; Furdyna, J.K., Lee, S., Wojtowicz, T., Liu, X., Lim, W.L., Kuryliszyn, I., Sasaki, Y., Walukiewicz, W., (2003) J. Korean Phys. Soc., 42, pp. S579; Ohno, H., Chiba, D., Matsukura, F., Omiya, T., Abe, E., Dietl, T., Ohno, Y., Ohtani, K., (2000) Nature, 408, p. 944; Koshihara, S., Oiwa, A., Hirasawa, M., Katsumoto, S., Iye, Y., Urano, C., Takagi, H., Munekata, H., (1997) Phys. Rev. Lett., 78, p. 4617; Yuldashev, Sh.U., Im, H.S., Kang, T.W., Lee, S.H., Sasaki, Y., Liu, X., Furdyna, J.K., Woo, Y.D., (2004) J. Korean Phys. Soc., 45, p. 572; Yuldasheva, Sh.U., Imb, H., Sh Yalisheva, V., Park, C.S., Kang, T.W., Lee, S., Sasaki, Y., Furdyna, J.K., (2003) Appl. Phys. Lett., 82, p. 1206; Grunberg, P., Schreiber, R., Pang, Y., Brodsky, M.B., Sowers, H., (1986) Phys. Rev. Lett., 57, p. 2442; Mathieu, R., Svedlindh, P., Sadowski, J., Swiatek, K., Karlsteen, M., Kanski, J., Ilver, L., (2002) Appl. Phys. Lett., 81, p. 3013; Akiba, N., Matsukura, F., Shen, A., Ohno, Y., Ohno, H., Oiwa, A., Katsumoto, S., Iye, Y., (1998) Appl. Phys. Lett., 73, p. 2122; Ohno, H., (1998) Science, 281, p. 951; Ohno, H., (1999) J. Magn. Magn. Mater., 200, p. 110; Dietl, T., Ohno, H., Matsukura, F., Cibert, J., Ferrand, D., (2000) Science, 287, p. 1019; Van Bockstal, L., Van Esch, A., Bogaerts, R., Herlach, F., Van Steenbergen, A., De Boeck, J., Borghs, G., (1998) Physi

We have studied the magnetic and transport properties of Ga 1-xMn xAs epilayers grown either on undoped or on p-type doped GaAs buffer layer. The temperature dependence of the resistivity at zero magnetic field reveals that the Curie temperature (T C) in the Ga 1-xMn xAs layer grown on p-type doped GaAs buffer is slightly higher than that observed in the layer grown on undoped GaAs buffer. The magnetic and transport properties of the two samples show significant differences when they are placed in a magnetic field. In SQUID measurements, the Ga 1-xMn xAs layer grown on p-type buffer shows a larger coercive field and much slower decay of remanent magnetization than the layer grown on undoped buffer. This robust magnetic behavior observed in the doped sample is discussed in terms of the increase of free carrier concentration in the system arising from p-type doping in the buffer layer., References: Prinz, G.A., (1998) Science, 282, p. 1660; Wolf, S.A., Awschalom, D.D., Buhrman, R.A., Daughton, J.M., Von Molnar, S., Roukes, M.L., Chtchelkanova, A.Y., Treger, D.M., (1998) Science, 294, p. 1660; Lee, S., Titova, L.V., Kutrowski, M., Dobrowolska, M., Furdyna, J.K., (2003) J. Korean Phys. Soc., 42, pp. S531; Ohno, Y., Young, D.K., Beschten, B., Matsukura, F., Ohno, H., Awschalom, D.D., (1999) Nature, 402, p. 790; Fiederling, R., Keim, M., Reuscher, G., Ossau, W., Schmidt, G., Waag, A., Molenkemp, L.W., (1999) Nature, 402, p. 787; Dietl, T., Ohno, H., Matsukura, F., Cibert, J., Ferrand, D., (2000) Science, 287, p. 1019; Ohno, H., (1998) Science, 281, p. 951; Ohno, H., (1999) J. Magn. Magn. Master., 200, p. 110; Lee, S., Chung, S.J., Choi, I.S., Yuldashev, Sh.U., Im, H., Kang, T.W., Lim, W.L., Furdyna, J.K., (2003) J. Appl. Phys., 93, p. 8307; Furdyna, J.K., Liu, X., Lim, W.L., Sasaki, Y., Wojtowicz, T., Kuryliszyn, I., Lee, S., Walukiewicz, W., (2003) J. Korean Phys. Soc., 42, pp. S579; Yuldashev, Sh.U., Im, H., Yalishev, V.Sh., Park, C.S., Kang, T.W., Lee, S., Sasaki, Y., Furdyna, J.K., (2003) Appl. Phys. Lett., 82, p. 1206; Blundell, S., (2001) Magnetism in Condensed Matter, p. 161. , New York: Oxford University; Welp, U., Vlasko-Vlasov, V.K., Liu, X., Furdyna, J.K., Wojtowicz, T., (2003) Phys. Rev. Lett., 90, p. 167206; Chiba, D., Yamanouchi, M., Matsukura, F., Ohno, H., (2003) Science, 301, p. 943; Chung, S.J., Lee, S., Park, I.W., Liu, X., Furdyna, J.K., J. Appl. Phys., , To be published; Baxter, D.V., Ruzmetov, D., Scherschligt, J., Sasaki, Y., Liu, X., Furdyna, J.K., Mielke, C.H., (2002) Phys. Rev. B, 65, p. 212407QC 20130513

We use electron spin resonance in the far infrared to probe the Landau-level spin splitting in symmetric and asymmetric InSb quantum wells. The asymmetric wells exhibit a strong deviation in behavior from the symmetric wells at low magnetic fields with apparent g factors far in excess of the bulk g factor of InSb. These asymmetry-induced shifts in the spin resonance depend on Landau-level index as predicted by the Bychkov-Rashba model. We analyze the shifts to extract values for the Rashba parameter.

We use electron spin resonance in the far infrared to probe the Landau-level spin splitting in symmetric and asymmetric InSb quantum wells. The asymmetric wells exhibit a strong deviation in behavior from the symmetric wells at low magnetic fields with apparent g factors far in excess of the bulk g factor of InSb. These asymmetry-induced shifts in the spin resonance depend on Landau-level index as predicted by the Bychkov-Rashba model. We analyze the shifts to extract values for the Rashba parameter.

The room temperature extraordinary magnetoresistance (EMR) of a mesoscopic sensor structure prepared from an InSb quantum well of dimension 30 nm wide/spl times/100 nm high/spl times/3 /spl mu/m long is reported. The observed EMR is 4.75% at a relevant field of 0.05 T. The advantages and disadvantages of this nonmagnetic composite semiconductor/metal structure relative to that of conventional magnetic giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices for use as read-heads in high-density magnetic recording are discussed.

A mesoscopic nonmagnetic magnetoresistive read-head sensor based on the recently reported extraordinary magnetoresistance ~EMR! effect has been fabricated from a narrow-gap Si-doped InSb quantum well. The sensor has a conservatively estimated areal-density of 116 Gb/in.2 with a 300 K EMR of 6% and a current sensitivity of 147 V/T at a relevant field of 0.05 T and a bias of 0.27 T. Because this sensor is not subject to magnetic noise, which limits conventional sensors to areal densities of order 100 Gb/in.2, it opens a pathway to ultra-high-density recording at areal densities of order 1 Tb/in.2.