NDRO thin-film memory device exhibiting triangular hysteresis loop

Abstract

Certain thin Permalloy films which have a basically uniaxial character show square hysteresis loops in both easy and hard direction. The hard-direction coercivity H_{c2} is about half that of the easy direction. If a saturating magnetic field is applied at an angle α, a few degrees from the hard direction, a loop typical of uniaxial films results. Application of a small bias field normal to the drive field results in a triangular loop. This has two stable remanent states, in the first of which the magnetization has been left in a hard-direction low-permeability zero state. The other remanent state has the magnetization in a high permeability, easy direction, the one state. Whether the interrogating pulses of magnitude less than H_{c2} will result in an output pulse or not depends on the state of the device. No destruction of the stored information occurs. It is possible to write into either state by using the coincident current techniques, as long as precautions are taken against creep from the hard direction.