Hostname: page-component-78c5997874-xbtfd Total loading time: 0 Render date: 2024-11-19T03:12:44.702Z Has data issue: false hasContentIssue false
  • English
  • Français

Interparticle Interaction Effects in Nonmiscible CoAg Thin Films With High Co Concentration

Published online by Cambridge University Press:  10 February 2011

A. Butera  and
J. A. Barnard
A. Butera
Affiliation:
Center for Materials for Information Technology and Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, Alabama 35487-0209
J. A. Barnard
Affiliation:
Center for Materials for Information Technology and Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, Alabama 35487-0209
Get access

Abstract

A series of Co-rich CoAg heterogeneous thin films, with Co concentrations greater than 65 % volume fraction and film thickness in the range 5 nm - 50 nm, was prepared by dc magnetron sputtering. Annealing in high vacuum (P < 3x10-7 Torr) above 400°C was necessary to promote phase separation between the two elements. Maximum room temperature coercivities, Hc ∼ 900 Oe, were obtained at a thickness of 20 nm for CoAg 70:30 vol % films. These coercivities are almost two orders of magnitude larger than the values observed in as-deposited films. The concentration of maximum coercivity, that is usually associated to the threshold for magnetic percolation, is much higher than the 40-50 vol % commonly observed in bulk granular materials. The shift in the magnetic percolation limit was related to the reduced dimensionality of the very thin films. Coercivity was found to vary both with film composition and with thickness. Delta M curves and time decay (magnetic viscosity) measurements were done to determine the interparticle interactions and the activation volumes. A maximum in the remanent coercivity (coincident with the maximum in Hc) was found for a film thickness φ ∼ 15-20 nm in all the alloys. At this same thickness a negative minimum in the interparticle interaction parameter α (indicating that the particle interactions favor the demagnetized state) was observed. The absolute value of a increases for larger Co concentrations. The irreversible susceptibility is an increasing function of film thickness and the magnetic viscosity has a minimum for φ ∼ 15-20 nm. The activation volume also increases with thickness, changing from (15 nm)3 to (40 nm)3 for the more diluted alloys, values similar to the average particle size determined by transmission electron microscopy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 517: Symposium F – Wide Bandgap Semiconductors for High Power, High Frequency , January 1998 , 349
Copyright
Copyright © Materials Research Society 1998

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1 Berkowitz, A. E., Mitchell, J. R., Carey, M. J., Young, A. P., Zhang, S., Spada, F. E., Parker, F. T., Hutten, A., and Thomas, G., Phys. Rev. Lett. 68 (1992).10.1103/PhysRevLett.68.3745Google Scholar
2 Xiao, J. Q., Jiang, J. S., and Chien, C. L., Phys. Rev. Lett. 68, 3749 (1992).10.1103/PhysRevLett.68.3749Google Scholar
3 Barnard, J. A., Waknis, A., Tan, M., Haftek, E., Parker, M. R., and Watson, M. L., J. Magn. Magn. Mater. 114, L230 (1992).10.1016/0304-8853(92)90257-OGoogle Scholar
4 Xiao, Q., Chien, C. L., and Gavrin, A., J. Appl. Phys. 79, 5309 (1996).10.1063/1.361361Google Scholar
5 Butera, A., Klemmer, T. J., and Barnard, J. A., J. Appl. Phys. (1998 in press).Google Scholar
6 Butera, A., Klemmer, T. J., Minor, K., Cho, H. S., and Barnard, J. A., IEEE Trans. Magn. (1998 in press).Google Scholar
7 Delaunay, J.-J., Hayashi, T., Tomita, M., Hirono, S., and Umemura, S., Appl. Phys. Lett. 71, 3427 (1997).10.1063/1.120356Google Scholar
8 Chien, C. L., J. Appl. Phys. 69, 5267 (1991).10.1063/1.348946Google Scholar
9 Liou, S. H., Malhotra, S., Shan, Z. S., Sellmyer, D. J., Nafis, S., Woollam, J. A., Reed, C. P., DeAngelis, R. J., and Chow, G. M., J. Appl. Phys. 70, 5582 (1991).Google Scholar
10 Childress, J. R. and Chien, C. L., J. Appl. Phys. 70, 5585 (1991).10.1063/1.350095Google Scholar
11 Kelly, P. E., O'Grady, K., Mayo, P. I., and Chantrell, R. W., IEEE Trans. Magn. 116, 3881 (1989).10.1109/20.42466Google Scholar
12 Che, X.-d. and Bertram, H. N., J. Magn. Magn. Mater. 116, 121 (1992).10.1016/0304-8853(92)90155-HGoogle Scholar
13 Harrell, J. W., Richards, D., and Parker, M. R., J. Appl. Phys. 73, 6722 (1993).10.1063/1.352514Google Scholar
14 O'Grady, K., Chantrell, R. W., and Sanders, I. L., IEEE Trans. Magn. 29, 286 (1993).10.1109/20.195584Google Scholar
15 In materials where the magnetization reversal is governed by a narrow energy barrier distribution the time dependence may not be linear with In(t). See for example Dova, P., O'Grady, K., Morales, M. P., and Doemer, M. F., J. Appl. Phys. 81, 3949 (1997).10.1063/1.365037Google Scholar
16 Street, R. and Wooley, J. C., Proc. Phys. Soc. London, Sec. A 62, 562 (1949).10.1088/0370-1298/62/9/303Google Scholar
17 Wohlfarth, E. P., J. Phys. F 14, L155 (1984).10.1088/0305-4608/14/8/005Google Scholar
18 Wan, H., Tsoukatos, A., Hadjipanayis, G. C., Li, Z. G., and Liu, J., Phys. Rev. B 49, 1524 (1994).10.1103/PhysRevB.49.1524Google Scholar
19 Yu, C., Yang, Y., Zhou, Y., Li, S., Lai, W., and Wang, Z., J. Appl. Phys. 76, 6487 (1994).10.1063/1.358234Google Scholar
20 Stinnett, S., Doyle, W. D., Flanders, P. J., and Dawson, C., IEEE Trans. Magn. (1998 in press).Google Scholar
21 Butera, A., Weston, J. L., and Barnard, J. A., J. Appl. Phys. 81, 7432 (1997).10.1063/1.365283Google Scholar
22 Wohlfarth, E. P., J. Electr. Contr. 10, 33 (1961).Google Scholar