1. ELECTRODEPOSITED GIANT MAGNETORESISTANCE IN FeCoNiCu/Cu AND CrFeCoNiCu/Cu MULTILAYERED NANOWIRES PRAJON RAJ SHAKYA, B.E. M.S. in ELECTRICAL ENGINEERING ADVISOR: Dr. DESPINA DAVIS 16th December, 2010

2. Overview Motivation of the Research Discovery and Historical perspective Introduction Related Research Experimental Details Results and Discussions Conclusion and Future Work References Acknowledgements

4. The increase of storage density of 0.132Gb/inch2 in 1991 to 500Gb/inch2 as of today.[1]

5. Small size with high storage capacity demands the fabrication in nanostructures.

6. Electrodeposition is an economical method and can fabricate the nanowires with high aspect ratio.

8. Ferromagnetism

9. Electrons spin are aligned parallel to each other.

10. Magnetization is intact even after removal of external magnetic field.

11. Anti ferromagnetism

12. Electrons are arranged in antiparallel to each other.

13. Magnetoresistance (MR) ratio is defined as the ratio of the change in resistivity (due to change in configuration of electrons from antiparallel to parallel) to the resistivity in parallel configuration of electrons.

14. MR is due to spin of electrons and was first observed in ferromagnetic materials as AMR (Anisotropic Magnetoresistance).

16. Fert et al. and Grunberg et al. were first to observe GMR in Fe/Cr multilayers with the method of MBE (Molecular Beam Epitaxy). [1, 3, 4 ]Figure 1: Giant Magnetoresistance in (a) Fe/Cr multilayers by Fert et al. (left) [1, 3] and (b) Fe/Cr/Fe tri layers by Grunberg et al. (right) [1, 4]

20. Characteristic length = mean free path of electrons (λ) (CIP GMR)

21. Characteristic length = spin diffusion length (L)(CPP GMR)

22. L>> λFigure 4: Schematic Diagram of CIP and CPP GMR (left) with measurement techniques(right) [1]

24. Piraux et al. was first to study GMR in electrodeposited multilayered nanowires. They observed around 15% GMR at room temperature in Co/Cu layers. [5]

25. Blondel et al. observed GMR of 14% for Co/Cu and 10% for FeNi/Cu multilayered nanowires. [6]

26. Liu et al. investigated Co/Cu multilayerand observed GMR of 11% at room temperature and 22% at 5K . [7]

27. CoFeCu/Cu multilayered nanowires were studied by Seyama et al. and observed CPPGMR was twice that of CIP GMR on thin film for the same elements.[8]

29. Blondel et al. studied CoNi/Cu multilayered nanowires by pulsed potential technique and observed 20% GMR at room temperature with same ferromagnetic and nonmagnetic layer thickness. [10]

30. Schwarzacher et al. and Heydon et al. investigated CoNiCu/Cu in polycarbonate membranes and observed 22% GMR at room temperature. The reduction in the dissolution of Co was observed in the deposition of Cu with the addition of Ni.[11]

31. Evans et al. reported 55% GMR at room temperature and 115% GMR at low temperature on AAO with CoNiCu/Cu multilayers. They also reported that better GMR was observed with AAO template than with PC membranes. [12]

32. FeCoNiCu/Cu multilayers

33. Huang and Podlaha investigated quaternary system of FeCoNiCu and observed 4% GMR at 300K and 18% at 4K with a Cu layer thickness of 1.8nm. Anodic dissolution during multilayer deposition at low potential pulse was observed and galvanostatic triple pulses with relaxation period were introduced to reduce it. [13]

35. Dolati et al. studied FeCrNiMo alloys using chloride electrolyte and reported increase in Cr content increased the current density. They also observed fine-grain, smooth and compact deposits of FeCrNiMo. [15]

36. Xin-Quai et al. investigated pulse electrodeposition of Cr from trivalent bath and reported that thicker coatings and finer grains were observed with lower temperature and current density. [16 ]

37. Lallemandet al. studied electrodeposition of soft CoFeCr films and reported that the addition of Cr increases the resistivity of the alloy. [17]

38. Ericksson et al. investigated the effect of addition of chromium in FeNi alloy. They observed the improvement in crystal anisotropy with improved texture and small grain size that resulted in the decrease of saturation magnetization. [18]

40. Cathode: Gold sputtered AAO membrane

41. Anode: Platinum Mesh

42. Reference: Saturated Calomel Electrode (SCE)M1-> M1n+ + ne- (oxidation) M2n+ + ne- -> M2 (reduction) Figure 6: Schematic view of electrodeposition setup (left) and SEM picture of AAO membrane (right)

44. Two distinct mechanism:

46. Anomalous codeposition in Fe group elements so Fe>Co>Ni.Figure 5: Schematic diagram showing electrodeposition mechanism (left) and deposition of Cu, Fe group elements and Cr (right)

48. Pulsed potential: multilayered nanowiresCu top Cu layer Alloy layer Cu bottom Figure 7: Schematic view of electrodeposition technique

49. Measurement Techniques Figure 8: Lakeshore 7700 Hall Effect Measurement System for GMR measurement (left) and Alternating Gradient Magnetometer (AGM) Micromag 2900 for magnetic measurements (right)

50. 6. Results and Discussions Electrolyte Characterization Table 1: Molar Concentration of baths used for electrodeposition 0

52. Cu deposition range is identified as -0.25V to -0.4V and alloy deposition range as -1.4V to -2.6V.

53. Current density is increased with the addition of Cr which is due to increase of number of ions and hence conductivity.Figure 9:Polarization resistance curve for bath A and bath B at sweep rate of 2mvps

55. Range of Cu potentials from -0.25V to -0.4V were investigated.

56. Optimal Cu deposition potential was identified at -0.3V.Table 2: Compositional Analysis for bath A at lower Cu potentials Figure 10: Compositional Analysis for bath A for identification of optimal Cu potential

58. 20nm AAO membrane was used for constant potential electrodeposition. Table 3: Compositional Analysis of bath A at different alloy potentials Figure 11: Compositional Analysis for bath A at different alloy potentials

60. Co composition was found highest at all potentials.

61. Ni composition was found increasing and Cu decreasing with the alloy potential.Table 4: Compositional Analysis of bath B at different alloy potentials Figure 12: Compositional Analysis for bath B at different alloy potentials

64. Beside alloy potential time all other parameters were kept constant.

65. Maximum GMR obtained was 10.64% for alloy potential time of 1sec. (alloy thickness) where saturation field was the lowest.Figure 14: Optimum GMR on varying alloy pulsing time (left) and relation with Saturation field (T) with the change of alloy potential time (right)

67. GMR increased with the increase of number of bilayers and maximum of 14.56% at 2500 layers . Low saturation field was observed at this GMR. .Figure 15: Optimum GMR with varying number of layers (left) and relation with Saturation field (T) with the change of number of layers (right)

69. Maximum GMR observed was 5.62% at an alloy potential of -2.2V where the lowest saturation field was observed.Figure 16: Optimum GMR on varying alloy potential (left) and relation with Saturation field (T) with the change of alloy potential (right)

71. Maximum GMR of 5.62% was observed at an alloy potential time of 1sec and lowest saturation field was observed at that point.Figure 17: Optimum GMR on varying alloy pulsing time (left) and relation with Saturation field (T) with the change of alloy potential time (right)

74. Cu pulsing time was kept for 100secs and alloy pulsing time for 20secs.

75. 20nm pore size AAO and 200nm pore size PC were used as substrate.

76. Dichloromethane was used for dissolving membrane and liberating nanowires in case of PC template.

78. Dark layer were identified as Cu with thickness ranging from 28-40nm and gray alloy layer had thickness range from 72-90nm in AAO and 90-105nm in PC.Figure 19: SEM images of CrFeCoNiCu/Cu nanowires on 20nm AAO (left) and 200nm PC (right)

80. Highest GMR was observed at -2.2V, 1sec and 2500 layers.

81. The presence of Cr in the alloy layer decreased GMR because Cr being non-magnetic hinders the anti-ferromagnetic interlayer exchange coupling that is responsible for GMR.Figure 20: Variation of GMR for bath A and B with (a) change of alloy potential (left) (b) change of Alloy potential time (right-top)(c) number of layers (right-bottom)

83. With the addition of Cr, coercivity is reduced because Cr is non-magnetic and smoother deposits with finer grain size deposition of Cr reduces coercivity.Figure 21: Variation of Coercivity for bath A and B with (a) change of alloy potential (left) (b) change of alloy potential time (right-top)(c) number of layers (right-bottom)

85. Increase in number of bilayers increased GMR percentage with highest GMR obtained as 14.56% for FeCoNiCu/Cu and 5.82% for CrFeCoNiCu/Cu nanowires at 2500 layers.

86. Highest GMR curves tended to saturate faster which is desirable for read sensors.

87. Addition of Cr on the alloy region tended to decrease the GMR because Cr being non magnetic and its presence in ferromagnetic region deteriorated interlayer exchange coupling phenomena.

90. [10] A. Blondel, J. Meier, B. Doudin, J. –Ph. Ansermet, K. Attenborough, P. Evans, R. Hart, G. Nabiyouni and W. Schwarzacher, “Wire-shaped Magnetic Multilayers for ‘Current Perpendicular to Plane’ Magnetoresistance Measurements,” Journal of Magnetism and Magnetic Materials, vol. 148, no.1-2, pp. 317-318, 1st July 1995. [11] G. P. Heydon, S. R. Hoon, A. N. Farley, S. L. Tomlinson, M. S. Valera, K. Attenborough and W. Schwarzacher, “Magnetic Properties of Electrodeposited Nanowires,” Journal of Physics D: Applied Physics, vol. 30, no. 7, pp. 1083-1093, 7th April 1997. [12] P. R. Evans, G. Yi and W. Schwarzacher, “Current Perpendicular to Plane Giant Magnetoresistance of Multilayered Nanowires Electrodeposited in Anodic Aluminum Oxide Membranes,” Applied Physics Letters, vol. 76, no. 4, pp. 481-483, 24th January 2000. [13] Q. Huang, D. P. Young and E. J. Podlaha, “Magnetoresistance of Electrodeposited Iron-Cobalt-Nickel-Copper Multilayers,” Journal of Applied Physics, vol. 94, no. 3, pp. 1-4, 1st August 2003. [14] J. Gong, W. H. Butler, G. Zangari, “Optimization of Magnetoresistive Sensitivity in Electrodeposited FeCoNi/Cu Multilayers,” IEEE Transactions on Magnetics, vol. 41, no. 10, pp. 3634-3636, October 2005. [15] A. G. Dolati, M. Ghorbani and A. Afshar, “The Electrodeposition of Quaternary Fe-Cr-Ni-Mo Alloys from the Chloride-Complexing Agents Electrolyte. Part I. Processing,” Surface and Coatings Technology, vol. 166, no. 2-3, pp. 105-110, 24th March 2003. [16] H. Xin-Kuai, Q. Guan-Zhou, C. Bai-zhen, Z. Ning-bo, W. Lu-ye and X. Li-jian, “Process of Pulse Electrodeposition Nanocrystalline Chromium From Trivalent Chromium Bath,” Transactions of Nonferrous Metals Society of China, vol. 17, pp. s685-s691, 2007. [17] F. Lallemand, D. Comte, L. Ricq, P. Renaux, J. Pagetti, C. Dieppedale and P. Gaud, Effects of organic additives on electroplated soft magnetic CoFeCr films,” Applied Surface Science, vol. 225, no. 1-4, pp. 59-71, 2004. [18] H. Eriksson and A. Salwen, “50 Permalloy alloyed with Cr for increasing corrosion resistance”, IEEE Transactions on Magnetics, vol. 13, no.5, 1977. [19] H. W. Choi, K. H. Kim, J. Kim, S. H. Han and H. J. Kim, “The Effect of Cr Addition on Structure and Corrosion Resistance in FeTiN Nanocrystalline Soft Magnetic Thin Films,” IEEE Transactions on Magnetics, vol. 37, no. 4, July 2001.

92. Dr. Despina Davis

93. Dr. Chestor Wilson

94. Dr. DentchoGenov

95. Group Members