Development of CoX/Pd multilayer perpendicular magnetic recording media with granular seed layers (original) (raw)
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Magnetic Characterization of Perpendicular Recording Media
Ultra-High-Density Magnetic Recording: Storage Materials and Media Designs, G. Varvaro and F. Casoli Eds, Pan Stanford Publishing
Developing a nanostructured material to fit the design criteria for perpendicular magnetic recording (PMR) media requires a multiple approach, which involves the investigation of structural, microstructural and magnetic properties, analytical and numerical simulations as well as recording tests to evaluate the material’s read/write performance. Studying the magnetic properties represents a challenging task as the magnetic behavior of materials for PMR media is governed by a complex interplay among intrinsic material properties, magnetic interactions and various sources of microscopic inhomogeneity, the overall properties being further complicated by thermal effects that lead to time-dependent magnetic phenomena. Moreover, the magnetic behavior of systems with perpendicular anisotropy is significantly affected by the presence of strong demagnetizing fields that, in principle, should be corrected in all magnetic measurements for a proper investigation. This chapter will provide an overview of both basic and advanced magnetic characterization methods, mainly based on magnetometry techniques, commonly used to investigate the magnetic behaviour of materials for PMR media in relation to the requirements for high-density recording. Section I will provide a selection of methodologies for the investigation of granular thin films with perpendicular anisotropy, which are used in currently available PMR media being also at the basis of future recording systems. All the methods discussed in this section are also suitable for the characterization of exchange coupled composite systems and next generation bit patterned magnetic recording media, the analysis of their most relevant magnetic properties being discussed in sections II and III, respectively. Section IV will focus on the energy assisted magnetic recording (EAMR) technology by reporting on some specific measurements needed to verify if a material is able to match the peculiar requirements for the application.
Magnetisation reversal mechanism in CoCr media for perpendicular magnetic recording
Journal of Magnetism and Magnetic Materials, 1997
In this study Co-Cr thin films with perpendicular anisotropy are investigated. Three films with values for/-/'~ of 11, 90 and 170 kA/m have been selected for this paper. Besides the coercivity several other parameters such as the Ho/l-lk, Cr-segregation, domain structure, column sizes, etc. were studied by VSM, SEM, NMR, MFM, AFM and selective etching. The anomalous Hall effect (AHE) has been used to record the hysteresis curves of submicron Hall crosses. This very sensitive technique in combination with e-beam lithography and ion-beam etching resulted in the recording of AHE hysteresis loops with dimensions of the Hall crosses as small as 0.3 x 0.3 ~tm 2. The AHE loops of three samples, with less than 60 columns, show different micromagnetic properties. Only the sample with H~± = 90 kA/m shows clear steps in the curves above the noise level. The largest steps correspond with the reversal of one column and the total number of steps was five times the number of columns for this sample. The different reversal mechanisms observed by the AHE are related to the differences in structure, coercivity and domain size.
Magnetic structures in CoCr media for perpendicular magnetic recording
Journal of Magnetism and Magnetic Materials, 1996
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/in 2 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.
Exchange coupled composite media for perpendicular magnetic recording
IEEE Transactions on Magnetics, 2005
A novel exchange coupled composite (ECC) media was demonstrated and investigated systematically in this work. The writing capability and thermal stability were proved to be engineered separately based on this new media. Proper exchange coupling between [Co-PdSiO]n hard layer and FeSiO soft layer was implemented through a PdSi interlayer. Transmission electron microscope plan-view and cross section view observations, macromagnetic, and micromagnetic testing proved vertically grown magnetic grains with soft and hard regions for ECC media. The switching of the soft region of magnetic grains with the external field rotated the magnetization of the hard region of magnetic grains to about 45° with perpendicular direction, which resulted in a similar behavior as a dynamic tilted media. A much lower angle dispersion of the remanent coercivity for the ECC media was found, which is another advantage for such media. ECC media showed better recording performance compared to perpendicular media. Strong exchange coupling between the hard and soft regions of magnetic grains (exchange spring media) was discussed based on the above proposed layer structure too.
IEEE Transactions on Magnetics, 2006
The microstructure, magnetic properties, and recording performance of CoCrPt-oxide perpendicular media were investigated at different magnetic layer film thicknesses (MAG) from 2 to 27 nm. Media coercivity () reached a maximum value of 6.8 kOe at MAG = 18 nm and then decreased to 5.3 kOe. Both crystallographic and magnetic c-axis orientations remained constant in the film thickness range of 12-27 nm. The change in the degree of grain isolation and grain size was observed as MAG increased. Higher exchange coupling at MAG = 4 nm was observed due to less grain isolation, but the in-plane magnetization was not detected. At MAG = 10-18 nm, excellent grain isolation was achieved. However, the formation of many subgrains and less grain isolation at MAG = 27 nm was related to the reduced. When MAG increased to above 12 nm, media signal-to-noise ratio rapidly decreased because of significant increase in dc-erase media noise, even though no degradation of media properties was observed up to MAG = 18 nm. The significant increase in the dc-erase noise is related to poor media writability, contributed by both the increase in and the reduction in head field magnitude, caused by increasing head-to-soft magnetic underlayer distance.
IEEE Transactions on Magnetics, 2005
We have fabricated a new layered structure, named "U-mag," for perpendicular magnetic recording media, in terms of stacked films including a very thin (2 nm) ferromagnetic (Co) intermediate layer and lattice spacing control layers. The formed medium having a 100-nm soft magnetic underlayer with high coercivity over 6 kOe and sufficient nucleation field (1 5 kOe) shows higher signal-to-noise ratio (SNR) than a medium with a conventional Ru underlayer. The detailed microstructures of the U-mag medium were also revealed by a transmission electron microscope with an energy dispersive spectrometer. A double Co intermediate layer gave a significant improvement in the SNR compared to a single Co layer.
Journal of Applied Physics, 2003
In this work, we investigate the postannealing effects on the magnetic and structural properties of CoCrPt perpendicular films. We observe a coercivity of 5000 Oe in the films with a 2 nm CrMn overlayer, which is about two times larger than the coercivity of similar films without a CrMn overlayer. This increment is attributed to the decoupling of grains by diffusion of CrMn from the top layer through the grain boundaries. An increase in the negative nucleation field and a decrease in intergranular exchange coupling with annealing temperatures was observed for the films with a CrMn overlayer. On the other hand, the films without a CrMn overlayer show the opposite trends except at high annealing temperature ͑450°C͒. We observe a coercivity of ϳ7600 Oe and a negative nucleation field of ϳ2400 Oe for a film with a CrMn overlayer annealed at 450°C for 5 min.