Magnetisation States: Spin Interactions and Recording Media

This lecture discusses the fundamental concepts of spin interactions and magnetisation states in magnetic materials. It begins with an overview of paramagnetic and ferromagnetic materials, explaining how thermal fluctuations affect the orientation of magnetic moments. The instructor introduces the concepts of Curie and Neel temperatures, which are critical for understanding the behavior of ferromagnets and antiferromagnets. The lecture then transitions to the concept of macrospins, describing how isolated atoms can be represented as a single macrospin in a grain or particle formation. The importance of exchange energy in maintaining ferromagnetic alignment is highlighted. The discussion further explores the exchange breaking layer in magnetic recording technology, emphasizing its role in decoupling the recording layer from the soft underlayer. Finally, the lecture contrasts longitudinal and perpendicular recording media, detailing how the latter has been adopted to reduce dipolar interactions and improve data storage efficiency.