Exchange coupled thin film magnets

The object of this work is the study of structural and magnetic properties of Sm-Co based thin films. One important aim is to obtain large energy-product values, the primary requirement in the permanent magnet industry.; The materials are prepared by sputter deposition and an anneal at elevated temperature is required to crystallize the film and form the hard magnetic phases. Nb is used as a buffer layer between the Si substrate and the Sm-Co film due to its mechanical hardness and lack of chemical reactivity.; The <<classical>> composition SmCo5 is prepared first in nanocrystalline form. High coercivities (up to 37 kOe) are obtained along with rather modest values for energy product (∼5 MG.Oe).; Multilayers of the form SmCo5/Co are prepared next. An anneal leads to the destruction of the multilayers and the crystallization of SmCo 5 and Co phases. The composition of these films is chosen to exploit the exchange-spring mechanism between the hard (SmCo5) and soft (Co) magnetic phases, in an attempt to obtain higher energy products. These films have crystallite size of the order 10 nm---a requirement if the soft and hard magnetic phases are to be strongly coupled. A large increase in energy product is observed (the best value ∼12 MG.Oe) compared to the SmCo5 films.; Nominally homogeneous Sm-Co films were then prepared and after an anneal crystallites of size about 15 nm are formed. The energy product here is larger than in our earlier films due primarily to a larger magnetic moment and a strong coupling between soft and hard phases. A value of 19 MG.Oe is reported, which is the highest value reported so far for a Sm-Co-based thin film permanent magnet.; Finally, Sm-Co films with Fe, Cu, and Zr additions are prepared. Their energy product is in between the SmCo5 magnets and SmCo5/Co magnets. The coercivity is 39 kOe, the best coercivity obtained in this project.; We use the micromagnetic theories Gaunt and Kronmuller to study the mechanism of coercivity in the films and find that pinning of domain walls is the primary coercivity mechanism.