Fabrication and characterisation of high moment thin films for inductive write heads

This thesis describes results from an investigation of a variety of thin films with particular emphasis on their suitability for use as magnetic pole materials in inductive recording heads. Initially, the magnetic and structural properties of FeTaN and FeTiN were studied, and it was found that the transition metal elements were incorporated substitutionally into the bcc #alpha#-Fe crystal structure leading to an expanded lattice constant. Nitrogen was incorporated interstitially into the crystal structure in such a way that the average grain size was reduced to a value less than the ferromagnetic exchange length, thus making the alloy magnetically soft. Other previously unreported alloys were fabricated in a similar way, namely FeWN, FeCoN and FeCoTaN and it was noted that the addition of Co increased the saturation magnetisation of the alloy to around 20kG but also increased the coercivity. In addition to these nano-crystalline alloys it was found that adding Ta to FeCo beyond around 17 at.% effected a crystalline to amorphous phase change but the alloy retained a saturation magnetisation that was directly related to the Co content. This new alloy, FeCoTa, has not been reported previously. It was found that by depositing these alloys in a magnetic field, anisotropy could be induced in all of them. The nitrided alloys had an anisotropy due to their interstitial nitrogen and the anisotropy of FeCoTa was directly linked to the Co content. After annealing it was found that several of the alloys were thermally unstable. FeTiN and FeCoN were both severely damaged by annealing at 150 deg. C for short periods of time. FeTaN, FeWN and FeCoTaN improved with magnetic annealing up to around 200 deg. C and FeCoTa was thermally stable up to around 250 deg. C. It was found that FeCoTa was twice as resistant to cross-annealing than the nitrided alloys. The best magnetic properties (4#pi#M_s #approx# 20kG, H_c#approx#3Oe, #rho##approx#130#mu##OMEGA#-cm, H_k#approx#15-20 Oe were seen in the amorphous FeCoTa alloy and the author recommends that this alloy be further investigated for use as pole material in the next generation high data rate inductive writer. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN035231 / BLDSC - British Library Document Supply CentreGBUnited Kingdo