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Wright, J. G. (1964) The growth, structure and magnetic properties of thin ferromagnetic films with particular reference to cobalt. Doctoral thesis, Sir John Cass College.
This work has been concerned with the growth and properties of electrodeposited thin films of cobalt and nickel which in general have been prepared on single crystal substrates. In the first part of the work the structure of these films has been studied by electron diffraction.
Conditions have been established for the growth of good single crystal films of both a and β cobalt using f-c-c copper as the substrate. The phase exhibited by the Co deposit has been shown to be very dependent upon the pH of the solution. Furthermore, it has been shown that deposition in a magnetic field may influence the structure of the cobalt deposit provided that the other bath conditions are energetically favourable.
In the case of Ni deposits it has been shown that, provided the correct substrate is used, a h.c.p form of nickel may be deposited in a single crystal form. The lattice spacing of hexagonal Ni has been measured and found to be a = 2.50 + 0.01 Å and c/a = 1.59 +/- 0.02. The values are compared with the values for a-Co and h.c.p Cu and found to be reasonable.
Magnetic anisotropy has been studied in Co films using a torque magnetometer. In the case of single crystal films of β-Co the anisotropy constants have been evaluated, the values obtained being K1 = (-6.3 +/- 0.1) x 10⁵ ergs/cc and K2 = (-10.8 +/- 1.2) x 10⁵ ergs/cc. These results have been compared with the results on bulk material obtained at high temperatures and also the results obtained at room temperatures from precipitated particles. The empirical formula K1 = K110 exp(-aT2 ) which holds at high temperatures has been modified so that it fits the experimental data and the suggested formula K1 = Ko/{exp(aT2 ) + A} appears to fit all the anisotropy curves for all cubic materials reasonably well.
In the case of hexagonal nickel tentative measurements have been made and values of K1 = -2.1 × 10⁶ ergs/cc and K2 = -1.0 x 10⁶ ergs/cc have been evaluated.
The analysis of all the torque curves obtained from single crystal films showed a uniaxial component of anisotropy which was a function of film thickness. The thinner the film the larger this value of anisotropy. Experiments were performed to try and find the nature of this induced anisotropy. These consisted of experiments concerning the surface roughness and the effect of a strong magnetic field (up to 13.5 kilo-Oersteds). These did not lead to a full explanation of the uniaxial anisotropy.
Brief measurements on the coercive force of polycrystalline and single crystal films of cobalt have been made.
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