Coercivity, magnetic thin films

Rizzo, N.D., T.J. Silva, and A.B. Kos. 1999. Relaxation times for magnetization reversal in a high coercivity magnetic thin film. Physical Review Letters 83(23) 4876-4879. 

Coercivity of Thin-Film Media. The coercivity ia a magnetic material is an important parameter for appHcations but it is difficult to understand its physical background. It can be varied from nearly zero to more than 2000 kA/m ia a variety of materials. For thin-film recording media, values of more than 250 kA / m have been reported. First of all the coercivity is an extrinsic parameter and is strongly iafluenced by the microstmctural properties of the layer such as crystal size and shape, composition, and texture. These properties are directly related to the preparation conditions. Material choice and chemical inborn ogeneties are responsible for the Af of a material and this is also an influencing parameter of the final In crystalline material, the crystalline anisotropy field plays an important role. It is difficult to discriminate between all these parameters and to understand the coercivity origin ia the different thin-film materials ia detail. 

Concerns about the corrosion of thin films resulted in the evaluation of Co—Pt alloys. Sputtered Co—Pt magnetic thin films containing 25% Pt and 500 A thick have a coercivity of 1700 Oe [154]. A co-ercivity higher than 3000 Oe was obtained with Co—Cr—Pt—B sputtered media [155] on 3000 A thick Cr underlayer (no intermediate layer is required). Boron, the fourth element, is added at an amount of about 3 to 7 at%. A coercivity of 4200 Oe was obtained for sputtered Co—Cr—Pt alloys for a thickness range between 100 and 350 A. These films require a Cr underlayer and a special intermediate layer composed of Co or Co—Cr—Ta [156]. 

Interest is maintained ia these materials because of the combination of mechanical, corrosion, electric, and magnetic properties. However, it is their ferromagnetic properties that lead to the principal appHcation of glassy metals. The soft magnetic properties and remarkably low coercivity offer tremendous opportunities for this appHcation (see Magnetic materials, bulk Magnetic materials, thin film). 

Schmool, D.S., Keller, N., Guyot, M., Krishnan, R., and Tessier, M. (1999) Evidence of very high coercive fields in orthoferrite phases of PLD grown thin films. Journal of Magnetism and Magnetic Materials, 195, 291-298. 

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