Effect of reversible adsorption on the magnetic properties of iron garnet films
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Effect of Reversible Adsorption on the Magnetic Properties of Iron Garnet Films V. E. Zubov*, A. D. Kudakov, N. L. Levshin, and M. A. Vlasov Moscow State University, Moscow, 119991 Russia *email: [email protected] Received April 28, 2012
Abstract—The reversible change in the domain structure and the magnetic domain width in bismuthcon taining iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption–desorption processes occurring between methyl alcohol mol ecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects. DOI: 10.1134/S1063776113040171
1. INTRODUCTION Transition elements, in particular, 3d elements, are characterized by a partly filled 3d shell, which deter mines their magnetic properties. On the other hand, the adsorption properties of transition elements are known also to be related to the partial filling of 3d orbitals, which causes a relation between their adsorp tion and magnetic properties. In the energy of binding of adsorption molecules with a surface, adsorption is divided into the following two main types: chemical and physical adsorption. Ionic, covalent, or coordina tion bond is possible for chemical adsorption (chemi sorption). Physical adsorption is caused by the van der Waals interaction. An intermediate type of adsorption, namely, hydrogen bonds with an energy of 0.1–0.3 eV, is also distinguished. This type of adsorption is often reversible at room temperature. Water, ammonia, and alcohol molecules adsorb according to the mechanism of hydrogen bond formation. Most studies deal with the effect of irreversible chemical adsorption on mag netic materials. Physical (van der Waals) adsorption does not change their properties. We studied the effect of weak adsorption according to the hydrogen bond formation mechanism on the magnetic properties of ferromagnetic metals and insu lators. The investigations were carried out on a real sample surface. The real surface of solids is the surface in contact with an atmosphere that was not specially prepared. Under these conditions, all active surface centers are occupied by chemisorbed molecules and no new strong chemical bonds with atmosphere mole cules form. A real metal surface usually has a native oxide film. This film is then subjected to hydration: coordinationrelated water molecules (H2O)c and hydroxyl groups (OH) adsorb on it [1]. OH groups are bound to 3d atoms by covalent bonds. During coordi
nation bonding, the electron cloud of the electron lone pairs of oxygen in a coordinatively bound water molecule is pulled into the 3d core orbitals of an acceptor atom. The ability to form coordination bonds is inherent in not only water molecules. In
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