No abstract

Sputtered CoNiCr thin film has been proposed as a good medlum for longitudinal recording'-*. In this paper we consider the effect of the Cr underlayer on both the magnetic and the microstructural properties of CoNiCr thin films. Changes in the Cr layer microstructure and the changes In the magnetic properties of CoNiCr/Cr with sputtering conditions will be analyzed. Changes in the magnetic properties of CoNiCr/Cr with annealing in air and in vacuum will also be analyzed.It was found that the magnetic and structural properties of the CoNiCr layer depend strongly on the Cr underlayer microstructure: 1) Single layer CoNiCr/glass films were characterized by low coercivity (H,<200 Oe) and random crystal orientation: the FMR linewidths were narrow and the magnetic domains had ripple-like structures. (see Fig.1). 2) In bilayer CoNiCr/Cr films a) the CoNiCr layers initially grew epitaxially on the Cr layers: the CoN_iCr layer grains replicated those of the Cr underlayers. { 1 lo} Cr layer texture induced { 101 0 ) but { 1 lo} Cr texture resulted in (1 03 1 } CoNiCr film texture. The coercivity of CoNiCr/Cr was found to be much larger than that of CoNiCr/glass and increased monotonically with Cr layer thickness tCr (Fig.2). The FMR linewidths were broad and increased with increasing tcr. In CoNiCr films vortex-like structures were observed in the magnetic domains. b) As the CoNiCr thickness increased, (0002) texture began to develop and gradually became dominant. The coercivity was found to decrease sharply with CoNiCr layer thickness. These results suggest that the presence of {loib} and {1071} texture in CoNiCr layer is associated with high coercivity and that the presence of random orientation and (0002) texture Is associated with low coercivity.It was found that the sputtering conditions affect significantly the magnetic properties of CoNiCr/Cr thin films. In one series of samples the Cr underlayer was deposited at a very low rate (0.5 nm/min). In these samples the CoNiCr/Cr films were characterized by low H (<200 Oe) and narrow FMR linewidths. The magnetic domain structures were like those obsgrved in CoNiCr/glass films: for example, ripple-like structure was observed in the domains. TEM observations showed that the Cr underlayer was characterized by small grain size (5-10 nm) and was crystallographically randomly oriented (see Fig.3a): the CoNiCr layer had (0002) texture. By contrast, In samples for which Cr underlayer was deposited at the higher rate at 5 nm/min the underlayer was predominantly { l l o } in texture, the grain sizes were 10-15 nm (see Flg.3b)and the Coercivity was higher (400-800 Oe). It was also found that by applying a negative bias voltage to the substrate during deposition the coercivity can be Increased significantly.The magnetic properties of CoNiCrICr films were found to be sensitive to annealing temperature T, annealing time t , , and tCr. For samples with large tCr, H , increased significantly wlth t , , and approached a saturation value. At small T and for samples with small tCr, H , did n...