ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Among all the known magnetic materials with vanishingly small magnetostriction, alloys with the composition Co90Fe10 have the highest magnetization at 300 K. Despite this combination of useful properties, thin films of these alloys have been little studied. This study investigated the magnetic characteristics of Co90Fe10 alloy thin films deposited by rf diode sputtering. The hysteresis loops of nominal 1000-A(ring)-thick Co90Fe10 films deposited in ≈150 Oe planar field exhibited complex biaxiality. Two, orthogonal easy axis loops with different coercivities were observed. The direction corresponding to the hysteresis loops with the smallest (largest) coercivity are referred to as the soft (easy) axis. Dual hard axes were found at ±68° on either side of the easy axis. Similar biaxial hysteresis loops were observed in Co90Fe10 films deposited by sequential sputtering from pure Co and Fe targets on static or rotating substrates, and in films deposited from a Co90Fe10 alloy target on stationary substrates. The magnetization and resistivity of the sequentially sputtered films were 19.66 kG and 18.4 μΩ cm, while those deposited from the alloy target were 19.00 kG and 14.5 μΩ cm. The biaxiality was sensitive to a number of parameters which appeared to destabilize the soft axis state compared to the hard axis states. With increasing film thickness (to 3400 A(ring)), the biaxiality disappeared, and films deposited under similar conditions exhibited rotatable anisotropy. The biaxiality could also be reduced, and the coercivity increased, by increasing the magnetic bias applied during deposition. Films annealed at 370 °C became uniaxial when a 1.3 kOe field was applied parallel to the easy axis, and became isotropic when the field was parallel to the hard axis.The biaxiality was enhanced, and Hc reduced, by depositing 1000-A(ring)-thick Co90Fe10 films onto a 500 A(ring) 80Ni20Fe underlayer. In all cases, whenever the biaxiality was eliminated, the films exhibited a rotatable uniaxial anisotropy. The biaxiality of these films likely has its origin in the coupling of two uniaxial anisotropies as previously analyzed. The deposited films are highly polycrystalline. In addition, the symmetries of the planar magnetic state obtained were the same for crystalline and amorphous substrates. Thus, it is unlikely that either uniaxial anisotropy is due to magnetocrystallinity, but are probably induced. The experimental trends observed in the study can in principle be understood in terms of a two layer model in which a rotatable, stress induced uniaxial anisotropy in an underlayer, is exchange coupled to the field induced uniaxial anisotropy of an overlayer. In this model the complex biaxiality is modified by experimental parameters which modify the relative strength and coupling strength of these anisotropies. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.361598
Permalink