In this paper, we review some of the key concepts in ultrathin film magnetism which underpin nanomagnetism. We survey the results of recent experimental and theoretical studies of well characterized epitaxial structures based on Fe, Co and Ni to illustrate how intrinsic fundamental properties such as the magnetic exchange interactions, magnetic moment and magnetic anisotropies change markedly in ultrathin films as compared with their bulk counterparts, and to emphasize the role of atomic scale structure, strain and crystallinity in determining the magnetic properties. After introducing the key length scales in magnetism, we describe the 2D magnetic phase transition and survey studies of the thickness dependent Curie temperature and the critical exponents which characterize the paramagnetic-ferromagnetic phase transition. We next discuss recent experimental and theoretical results on the determination of the exchange constant, followed by an overview of measurements of the magnetic moment in the elemental 3d transition metal thin films in the various crystal phases that have been successfully stabilized, thereby illustrating the sensitivity of the magnetic moment to the local symmetry and to the atomic environment. Finally, we discuss briefly the magnetic anisotropies of Fe, Co and Ni in the fcc crystalline phase, to emphasize the role of structure and the details of the interface in influencing the magnetic properties. The dramatic effect that adsorbates can have on the magnetic anisotropies of thin magnetic films is also discussed. Our survey demonstrates that the fundamental properties, namely, the magnetic moment and magnetic anisotropies of ultrathin films have dramatically different behaviour compared with those of the bulk while the comparable size of the structural and magnetic contributions to the total energy of ultrathin structures results in an exquisitely sensitive dependence of the magnetic properties on the film structure.

A study of magnetic and structural properties of (CoxFe100−x)50 (0≦x≦100) alloy thin films as functions of composition and substrate deposition-temperature Ts is carried out. The intrinsic perpendicular magnetic anisotropy Ku starts to increase with deposition temperature Ts for all the films (0≦x≦100) at about TS=250–300 °C, and then becomes nearly constant. The maximum values of Ku at room temperature thus obtained are 6×107, 4×107, and 2×107 erg/cc for Fe50Pt50, (Co43Fe57)50Pt50 and Co50Pt50, respectively. Also, the Ku of Fe50Pt50 films increases with the order parameter (S), being closely related with the tetragonality c/a. These results indicate that the evolution of Ku is due to the occurrence of the ordered fct phase.

Understanding of the magnetocrystalline anisotropy in magnetic materials (the influence of different elemental components on the direction of easy magnetization) can be greatly enhanced by measuring the orbital moment anisotropy of the elemental constituents. A circular x-ray dichroism technique is presented that allows the determination of the microscopic origin of the spin reorientation transition in ultrathin single-crystalline cobalt/nickel films. The stronger anisotropy contribution of a much thinner cobalt layer redirects the easy magnetization direction of the entire film.

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