TOWARDS CONTROL OF THE SWITCHING FIELD - MANGANITE PERMALLOY HETEROSTRUCTURES

It is well established that the resistance of manganites is a function of magnetization. In a conventional experiment, the magnetization is changed by the application of a magnetic field, and a resistance chang e is measured. The manganites show two different forms of colossal mag netoresistance: that which is associated with very narrow domain walls in polycrystalline samples with grain boundaries, and that associated with magnetic ordering near to the transition temperature. Although t he former only requires low fields, it is also only observed at low te mperatures. Hence there is a real need to reduce the magnetic field re quired to observe the effect near to the transition where, currently, fields of the order of 1 T are required. An alternative approach is to change the state of magnetization by injection of spin-polarized carr iers. We have recently taken out a patent which describes a general te chnique which may be used to inject carriers: a manganite permalloy he terostructure. This paper discusses the background to this approach in terms of the band structures of permalloy and manganite, and the way in which the switching field may be reduced. We present results from o ur experimental programme: which is attempting to realize a structure in current perpendicular to plane geometry to study spin injection.