Magnetism in ultrathin film structures

Abstract

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.

Influence of surface anisotropy on domain wall dynamics in magnetic nanotube

“…For samples of soft magnetic type, К < M s 2 , no noticeable dependence of the l z and K s * quantities on the bulk anisotropy constant K is obtained. The critical values of the surface anisotropy constant obtained numerically, K * s ≈ -1 erg/cm 2 , are close to that ones observed experimentally in thin magnetic films 2,4 . The calculations presented in Fig.…”

“…Surface magnetic anisotropy 1 , which can exist at a boundary of a ferromagnet with vacuum or a nonmagnetic material may have a significant influence on magnetic properties of thin magnetic films [2][3][4][5] and nanoparticles 6,7 . In this paper we study the effect of surface anisotropy on the properties of magnetic nanowires and nanotubes [8][9][10] , which are promising for various applications, in particular for the development of the racetrack memory 11 .…”

Interfacial magnetic coupling in ultrathin all-manganite La0.7Sr0.3MnO3-TbMnO3 superlattices

“…The long-range collective behaviors of spins in magnetic materials are well known to evolve with the film thickness, and the ground states in ultrathin films are results of energetic competition between surface, interface and dipolar anisotropies. [1][2][3] Transition metal oxides offer rich phase diagrams with fascinating magnetic orders as a result of the coupling between multiple degrees of freedom. 4 Particularly, mixed-valence manganites have attracted lots of interest after the discovery of colossal magnetoresistance (CMR) effect.…”

Perpendicular magnetic anisotropy in Co2Fe0.4Mn0.6Si

“…10,[12][13][14] The decreasing K U with increasing film thickness and the transition to in-plane magnetic anisotropy (negative duced PMA and the volume anisotropy, which tends to favor an in-plane easy axis. 15 The uniaxial anisotropy is given by K U = K V − 2πM 2 s + K S /t, where K V and K S are the bulk and interface anisotropy terms respectively, and the term 2πM 2 s is the shape anisotropy. K U .t CFMS is plotted against t CFMS in Fig.…”