Neutron Optical Study of Ferromagnetic Multilayers
Abstract
We present a theoretical neutron optical study of the surface-interface characteristics of thin films and multilayers, in particular Ferro-magnetic multilayers. The essence of neutron optics is that neutrons, like acoustic or light waves, can interfere constructively or destructively, thereby exhibiting phenomena like reflection, refraction, diffraction and dispersion. We study the temperature dependence of the magnetization depth profile for a EuS-EuO multi -bilayer film on a glass substrate, by neutron reflection. Other parameters including number of bilayers, and the bilayer thickness are also considered. The motivation for this study is the fact that due to the large disparity in the Curie temperatures of EuS and EuO, we expect the magnetic properties of the multi-bilayer to be very different from those of bulk EuS and EuO. Thereby a new magnetic material can be fabricated to tailor a specific application. The theoretical model used is based on the inhomogeneous Ginzburg -Landau free energy functional. The analysis includes studying the neutron reflectivity as a function of the perpendicular component of the wave vector transfer, q_ {rm z}. We observe that the reflectivity patterns truly represent the modulations in the magnetization in a direction orthogonal to the reflecting surface. In particular, the intensity reflects the decrease of magnetization as the temperature approaches the critical temperature, T_{rm c}, of the multilayer. T_{rm c} depends only on the thickness of the EuS and EuO layers, and lies between the bulk Curie temperatures of the two materials. We also note that it is advantageous to use a large number of bilayers, since the reflectivity signal is enhanced with increasing number of bilayers. We also study the surface micro-roughness of a non-magnetic mirror, by taking into account, both, the specular and the diffuse neutron beams, reflected by and transmitted into these materials. An important practical application of this study is in estimating the loss of neutrons in neutron guide tubes, due to the roughness of the inner walls of the tubes.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT.........9I
- Keywords:
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- EUROPIUM SULFIDE;
- Physics: Optics