Induced anisotropy and small particle magnetism effects in nanocrystalline Fe-based materials

The proposed research project is focused on the better understanding of the composition-structure-property relationships in the nanocrystalline Fe-based magnetic materials. Of particular interest is the study of the magnetic behavior in the system of nanocrystalline particles embedded in matrix whose magnetic properties can be controlled. The nanocrystalline alloys of Fe-M-B-(Cu) type (where M=Zr,Nb,Hf,Mo,Ti,...) offer an excellent opportunity for such studies. Changing the composition of the starting material as well as the heat treatment conditions, the effects of the variations of grain sizes and the intergranular distances as well as the matrix being in ferro- or paramagnetic state on the magnetic behavior of prepared specimens will be investigated. It is expected that the investigations proposed could throw more light on the interparticle magnetic interaction effects as well as contribute to the better understanding of the influence of the magnetic properties of the matrix and the role of the nanocrystal-amorphous material interfaces in the affecting the magnetic properties of the nanocrystalline alloys. In this project we also propose to perform the comprehensive study of the influence of field/stress annealing on the development of induced anisotropy in the Fe-M-B-(Cu) type and Fe-Cu-Nb-Si-B type alloy systems. Here, we plan to prepare the modified composition alloys where the various amount of Fe atoms will be replaced by Ni (or other magnetic element) atoms in order to study the role of directional ordering by atom pairs mechanism in these alloys. Samples in different microstructural state will be prepared by varying the heat treatment parameters such as intensity and orientation of an applied field/stress as well as the temperature and duration of thermal treatment. The parameters of processing procedure will be varied in order to achieve the maximum response of investigated material to magnetic/stress annealing. For the alloy compositions, which will exhibit the best response to field/stress annealing, we plan to study in more details the domain wall pinning effects caused by stabilization of domain structure after "self magnetic annealing" in demagnetized or non saturated state. Various effects of magnetic anisotropy, which can be induced in nanocrystalline alloys are of considerable interest both to physicists, for the extending of their knowledge of magnetic phenomena in these systems, and to the technologists, who may wish to exploit them in the design of magnetic material for specific application. If the operative mechanisms for induced anisotropy can be better understood in these alloys, it may be possible to modify the alloy composition or to vary the field/stress annealing treatments to allow for stronger and/or better controlled induced anisotropy.