Using poloarised neutrons to study magnetic exchange bias.
The phenomenon known as magnetic exchange bias was discovered in the late 1950’s and is an essential property of many devices which are now ubiquitous in modern life – for example it is used in the read heads of computer hard disks. The exchange bias effect occurs in structures consisting of layers of different magnetic materials. Its effect is to pin the magnetism of one layer in a particular direction, thereby allowing a ‘free’ layer to sense the data passing by the head. In spite of its huge technological importance it still remains a very active area of experimental and theoretical research.
An antiferromagnetic layer is used to pin an adjacent ferromagnetic layer, and much effort is focused on studying the interface between these two layers. A possible mechanism to explain the exchange bias is that there exists a magnetic moment in the antiferromagnetic layer which is frozen at the interface and cannot rotate. To investigate this we have used polarised neutron techniques and innovative sample design to quantify the size and orientation of this moment and to relate this to the observed exchange bias.
M Ali, CH Marrows, BJ Hickey (University of Leeds), TR Charlton, S Langridge (ISIS)