Perpendicular Anisotropy in Heusler Alloy Thin Films for CPP-GMR Devices

Heusler alloys are a class of materials with some of the greatest potential for the advancement of magnetic recording and memory. Their combination of high
magnetisations, Curie temperatures and spin polarisations make them ideal for device applications. However perpendicular anisotropy is difficult to achieve in GMR devices as an interface with an oxide is required. To
develop these materials for GMR application the perpendicular anisotropy must be induced in other ways.
In this work polycrystalline Co2FeSi and Co2FeAl0.5Si0.5 Heusler alloys have been deposited on body-centred cubic seed layers of vanadium and tungsten. Their magnetic and crystallographic properties have been measured and quantified using a range of techniques, significantly mangnetometry and X-ray diffractometry. With the use of vanadium seed layers Co2FeSi was deposited with a strong {110} texture out-of-plane, ideal for the crystallisation
of the material. In Co2FeSi layers <5 nm thick perpendicular anisotropy
is induced by strain at the interface with vanadium. This is further enhanced by the addition of a top layer of vanadium, doubling the interface area and increasing the anisotropy.
When tungsten seed layers are used instead there is a significant increase in the perpendicular anisotropy of Co2FeSi. This anisotropy is maintained in films with thicknesses up to and beyond 12.5 nm. When incorporated into GMR stacks both Co2FeSi and Co2FeAl0.5Si0.5 are found to exhibit layer thickness dependent switching, ideal for device application. The heating of the film pre-deposition is found to heavily influence the structure and anisotropy of the samples, even at modest temperatures <70 ±C for less than two minutes. GMR devices were fabricated and a proof of principle for a perpendicular CPP-GMR device based on Heusler alloys presented.