Future 10 Gb/in.2 recording densities represent submicron trackwidths and sub-100 nm bit lengths. This requires extremely small magnetic switching units and very high coercivities of the media to satisfy the signal-to-noise ratio requirements. At the same time the question of magnetic thermal stability and the lack of transducers capable of performing at these densities makes it difficult to evaluate media. An uncoupled, highly uniform magnetic grain size of about 10 nm is a compromise toward maintaining an adequately low media noise and yet maintaining magnetic stability. Here we discuss current media construction, the detrimental role of substrate roughness, the role of new media structures and alloys on microstructure and magnetic properties as well as techniques for evaluating media performance prior to the availability of the required playback heads.

Magnetoresistance (MR) measurements have been performed on Fe/Au/Co and Fei V /Au/Co trilayers with perpendicular orientation of the magnetization of the thin ferromagnetic layers. While the MR is larger for an antiparallel arrangement of the magnetizations than for a parallel one in Fe/Au/Co (the usual spin-valve-type MR), an inverse spin-valve e6'ect is observed in Fe& V /Au/Co. This inverse MR is attributed to an increase of the density of states at the Fermi level for majority-spin electrons when Fe is alloyed with V.

We present magnetoresistance {MR) measurements performed on two Au/Co/Au sandwiches with ultrathin cobalt layers (0.32 and 0.76 nm) and on a bilayer Au/Co/Au/Co/Au (0.75 nm Co). The easy magnetization axis is shown to be perpendicular to the films, in agreement with previous magnetization and ferromagnetic resonance measurements.The hysteretic behavior is easily observed by measuring the MR, leading to a determination of the coercive Selds of a few 10~6 . The Co bilayer exhibits a drastic enhancement of the MR e6'ect with respect to the corresponding monolayer (8R/R 1.3% at 300 K and 3% at 4.2 K) and s square hysteresis loop.Different mechanisms for the enhancement of the MR are proposed.The magnetic properties and especially the surface and interface anisotropy of ultrathin magnetic Slms are of considerable interest, both from a fundamental point of view and for their potential applications. Perpendicular anisotropy in such systems is particularly attractive for future applications in high4ensity magnetic recording.Since the pioneering work of Gradmann, ' much effort has been devoted to understanding magnetism in thin metallic films. Many types of magnetic systems consisting of sandwiches, multilayers, and superlattices have been experimentally and theoretically investigated, as described in several review papers.However to date little experimental data are available concerning the interface anisotropy of ferromagnetic Slms. We will concentrate here on ultrathin films of cobalt sandwiched between gold layers. Recent experimental results [superconducting quantum interference device (SQUID) measurements of the parallel and perpendicular remanent magnetizations, and ferromagnetic resonance experiments) have shown that the magnetic interface anisotropy leads to a perpendicular magnetization of the ferromagnetic Slm for very thin Co deposits (one or two monolayers). When increasing the Co thickness, the magnetization becomes in plane, due to the competition between interface and shape anisotropy.In this RapidCommunication we report the first observation of magnetoresistance (MR) effects in the same Au/Co systems, both at low temperature and at room temperature, which confirms the preceeding studies.Despite the fact that the measurement of anisotropic MR in ferromagnetic metals is a very old techmque, 6rst discovered by Lord Kelvin in 1857, s and widely used for Slms of a few tens of nanometers, there are, to our knowledge, no examples of such measurements on ultrathin ferromagnetic films. We intend to show that the study of the MR yields the most important characteristics of magnetic films down to the monolayer, i.e. , coercive and saturation Selds, and magnetic anisotropy.The samples are Au/Co/Au (111) and Au/Co/Au/ Co/Au (111)grown by slow evaporation in ultrahigh vacuum (10 '0 Torr) onto a glass substrate with very small surface roughness (0.5 nm). The film thickness is monitored by a quartz oscillator during deposition. The first Au layer (thickness 25 nm) consists of large polycrystals (typical lateral dimension...