Magnetic structures in Co---Cr media for perpendicular magnetic recording

High bit densities have been demonstrated in longitudinal as well as in perpendicular magnetic recording. For the latter an area density of more than 12 Gbit/in2 has been obtained in a sputtered Co---Cr---Ta hard disk with a soft magnetic underlayer recorded with a special single pole head. In this paper the role of microstructure and morphology in relation to the compositional separation is discussed. Very sensitive anomalous Hall measurements have been performed from submicron Co---Cr samples to obtain more detail information about the reversal characteristics of the material. The results obtained have been used in our model for micromagnetic simulations. One of the conclusions is that most of the magnetic entities reversing their magnetisations are much smaller than the volume of one Co---Cr column

Patterned Nanomagnetic Films

Nano-fabrication technologies for realising patterned structures from thin films are reviewed. A classification is made to divide the patterning technologies in two groups namely with and without the use of masks. The more traditional methods as well as a few new methods are discussed al in relation with the application. As mask less methods we discussed direct patterning with ions including FIB, nanopaterning with electron beams, interferometric laser annealing and ion beam induced chemical vapour deposition. The methods using masks are ion irradiation and projection, interference lithography, the use of pre-etched substrates and templates from diblock copolymers and imprint technologies. First a few remarks are given about the magnetic properties of patterned films but the main part of this paper is focussed on the various patterning technologies. Finally two important applications are summarized such as media for ultra high-density recording and magnetic logic devices. Nanometer scale magnetic entities (nanoelements, nanodots, nanomagnets) form a fast growing new area of solid-state physics including the new fields of applications

Co-evaporation of Co-Cr at intermediate oblique incidence

The Co-evaPoration technique has been used for deposition of Co-Cr layers. Deposition has been done under intermediate angle of incidence of opposing vapour streams. The layers showed a single Phase hcP poly-crystalline structure. The (002) plane turned out to be tilted towards the direction of the CO source. The layers showed good perpendicular magnetic behaviour although the magnetic anisotropy axis was also inclined towards the Co-source. Because of the opposing angle of incidence for Co and Cr atoms, a process-induced segregation takes place which causes a relative high coercivity also at low Process temFeratures. A simple model for the segregation effect can explain the relation between the existance of a non-magnetic region and an increased coercivity of th Co-Cr film

Recording performances of perfectly aligned HSS heads

The recording characteristics of helical scan silicon (HSS) heads with perfect alignment of the magnetic poles were investigated. Their overall performances were found to be superior to those of ferrite MIG heads, especially the side writing. Erase bands of 0.25 /spl mu/m were measured using a HSS head and ME tape with 50 nm thick magnetic layer. Side writing and erasing were studied from the frequency response of microtracks, as well as from triple-track profiles

Influence of R.F. sputter parameters on the magnetic orientation of Co-Cr layers

Co-Cr layers for the perpendicular recording mode were deposited by means of RF-sputtering. The most important sputter parameters, i.e. the RF sputter high voltage VRF, the argon pressure Parand the substrate holder temperature Tsh, gave an optimum value for perpendicular orientation of the magnetization. The crystal structure is always hcp within the ranges of varied parameters and no other magnetic phases were observed. If the sputter parameters do not have optimum values an additional hcp compound with in-plane orientation of the c-axis is observed. This orientation causes an increase of the in-plane remanenceS//= (M_{r}/M_{s}). Measurements of the substrate temperature Tsas an function of the various sputter parameters lead to the conclusion that an exclusive perpendicular c-axis orientation is only obtained atT_{s} sim 15thetadegc. At other Tsestablished either directly by changing Tshor indirectly by changing the sputter conditions an additional hcp compound with in-plane c-axis orientation appears. We concluded that Tsis the dominant parameter for sputtering CoCr layers

Kondo effect and impurity band conduction in Co:TiO2 magnetic semiconductor

The nature of charge carriers and their interaction with local magnetic moments in an oxide magnetic semiconductor is established. For cobalt-doped anatase TiO2 films, we demonstrate conduction in a metallic donor-impurity band. Moreover, we observe a clear signature of the Kondo effect in electrical transport data with remarkably high Kondo temperatures of up to 120 K. This indicates a strong coupling between local Co moments and delocalized electrons in the impurity band

Internal field corrections in perpendicular columnar structured Alumite films

An investigation of the remanent and hysteretic properties of perpendicular media such as Alumite involves calculation of internal fields which requires the demagnetisation factor to be known. Demagnetisation effects have been calculated for Alumite, which is an ideal model material, by considering it as a hexagonal matrix of columns. This predicts that the demagnetising effects are less than that of a continuous film at saturation but increase as the magnetisation decreases

Sign of tunnel spin polarization of low-work-function Gd/Co nanolayers in a magnetic tunnel junction

Magnetic tunnel junctions having a low-work-function Gd/Co nanolayer at the interface with an Al2O3 tunnel barrier are shown to exhibit both positive and negative values of the tunnel magnetoresistance. The sign of the tunnel spin polarization of the Gd/Co nanolayer electrode depends on the thickness of the Gd and Co layers, temperature, and applied voltage. This reflects the nature of the interaction between the conduction electrons of the rare-earth and transition metals. \u