.fe / Ni Multilayer Structure And Magnetic Properties

As the demand for information storage continuously increases, magnetic recording has been widely studied and developed as the chief data-storage technique, gaining intense interest both from academe and industry. The areal recording density has increased from2 Kbit/in2 in 1957 to 329 Gbit/in2 recently. When the grain size of recording media is reduced to several nanometers, the magneto-crystalline anisotropy needs to be large enough to avoid superparamagnetic effect, in other words, to stabilize the recorded bit. However, high coercivity due to large anisotropy gives rise to the difficulty of magnetic writing, for the writing field has to be approximately twice the coercivity of the recording media for effective writing. Therefore, further increase of magnetic recording density is largely confined by the writing ability of the magnetic head.The material for magnetic writing head needs to be reasonably soft, its permeability must be sufficiently high and its coercivity sufficiently small so that the field intensity within the head pole and yoke becomes negligible. In early research, Fe-based material has high saturation magnetization, but also a high magneto-crystalline anisotropy, its coercivity then can hardly be lowered by traditional methods. However, the development of nanocrystallite materials ushered a new era for the study of soft magnetic materials. By reducing the grain size, the effective anisotropy can be decreased to extremely low value, usually several orders less than the local anisotropy. Multilayers preparation by sputtering is an effective way to fabricate nanocrystalline soft materials; IBM and Hitachi both have adopted Fe-based multilayers in the production of magnetic heads. In general, two kinds of multilayers are classified based on different spacer materials in between:one is nonmagnetic and the other ferromagnetic. The latter kind is more favorable, for ferromagnetic spacers can help to increase the saturation magnetization of multilayers.In our research, we prepare Fe/Ni multilayers to study their structural and magnetic properties. As the Fe (or Ni) layer thickness is far less than the domain wall width, due to exchange coupling, the magnetization of Fe and Ni layers cannot follow each easy axis, and then the anisotropies are averaged out, the coercivity of multilayers is largely decreased. In the first part of this paper, the structure and orientation of Fe/Ni multilayers is analyzed, and the influence of layer thickness on the coercivity is discussed in detail. Cu insertion confirms the dominant role of exchange coupling in the multilayer system. In the second part, the effects of interface roughness on the structural and magnetic properties of Fe/Ni multilayers are investigated. Interface roughness is introduced in two ways, one is to tune the growth temperature, and the other is to prefabricate Ag on MgO substrate as underlayer. The mechanism of Fe/Ni multilayers'magnetization is discussed, smoother interfaces are more advantageous to optimize the exchange coupling, and the coercivity can be decreased more effectively.