1894 IEEE TRANSACTIONS ON MAGNETICS, VOL. 46, NO. 6, JUNE 2010 Barium-Ferrite Particulate Media for High-Recording-Density Tape Storage Systems Takeshi Harasawa , Ryota Suzuki , Osamu Shimizu , Sedat Ölçer , Fellow, IEEE, and Evangelos Eleftheriou , Fellow, IEEE Recording Media Research Laboratories, FUJIFILM Corporation, Odawara, Kanagawa 250-0001, Japan IBM Research-Zurich, 8803 Rüschlikon, Switzerland The feasibility of data storage on magnetic tape at an areal recording density of 6.7 employing barium-ferrite (BaFe) par- ticulate media was demonstrated in 2006 in a stringent demo. Recently, progress in BaFe media design has been made in three areas as compared with the medium used for the 6.7 demo: i) by using ultrafine BaFe magnetic particles, achieving a reduction in particle volume from 2100 to 1800 ; ii) by increasing the perpendicular squareness ratio from 0.52 to 0.7; iii) by achieving a smoother tape surface, effectively reducing surface roughness from 1.7 to 0.8 nm. This paper describes the characteristics of the new BaFe particles and medium, and discusses their potential for achieving areal recording densities as high as 20 . Index Terms—Barium-ferrite, particle orientation, particulate media, squareness ratio, surface roughness. I. INTRODUCTION T APE storage systems employing particulate media are widely used for data-backup and archiving applica- tions because of their low-cost advantage, the stability of the recording media for long-term data retention, and the relia- bility of the information retrieval and reproduction processes. The sharp rise in the amount of information that is nowadays created drives the need for high storage capacity, hence high areal recording density, in tape storage systems. The growth in areal recording density of tape storage is also spurred by the need to match that of hard-disk drives (HDDs) as well as by the increasing adoption of virtual tape storage systems. A one-terabyte (TB) cartridge technical demonstration, cor- responding to an areal recording density of approximately 1 , was achieved with metal particle (MP) tape media in 2003 [1]. Nowadays, 1 TB cartridges are produced on a com- mercial basis. Metal magnetic particles are needle-shaped. Because coer- civity originates from the magnetic shape anisotropy, it is dif- ficult to maintain high coercivity in fine magnetic metal parti- cles. The barium-ferrite (BaFe) magnetic particle was proposed as the future-generation magnetic particle because it allows the use of fine particles as well as achieves coercivity values that are fairly close to those of MP media. A technical demonstra- tion of 6.7 areal recording density, corresponding to a cartridge capacity of 8 TB, was achieved in 2006 with a BaFe- particle-based tape medium [2], [3]. Furthermore, a technical demonstration of 17.5 areal recording density was made the same year with a floppy disk employing BaFe mag- netic particles [4], [5]. Clearly, to be able to replace the metal magnetic particle of particulate tape storage systems, BaFe par- ticulate tape must exhibit a potential for higher areal recording Manuscript received October 30, 2009; revised December 15, 2009; accepted January 14, 2010. Current version published May 19, 2010. Corresponding au- thor: T. Harasawa (e-mail: Takeshi_Harasawa@fujifilm.co.jp). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2010.2042286 density. The present study shows, by improving upon the areal density value of 6.7 , that such a potential exists for BaFe tape. The tape medium for the 6.7 demonstration had the following features: 1) BaFe magnetic particle volume of 2100 , 2) random orientation, and 3) a surface rough- ness (Ra) of 1.7 nm. The new test tape described in this paper achieves improvements in all three features. II. EXPERIMENT A. Particle Characteristics and Tape Properties Table I lists the parameters of the ultrafine BaFe particles and the corresponding media, and compares them with the parame- ters of the medium used for the 6.7 demo and the MP media employed in the latest Linear Tape Open Generation-4 (LTO-4) products. Ultrafine BaFe particles having a volume of 1800 were created, achieving a significant reduction in particle volume compared with the 2100 particle volume of the 6.7 demo tape. The volume of the BaFe particles, which are hexagonal platelets, was calculated from the average diameters and thicknesses of 500 particles measured by trans- mission electron microscopy (TEM). To enable comparison of the two types of magnetic particles, the new tape using the ultrafine BaFe described above was made using the same formulation and process conditions as for the 6.7 demo tape. The thermal stability factor of the 6.7 demo tape was measured to be 87 [6], which is equal to the value found for the new tape. Several studies, e.g. [7], indicate the necessity of a thermal stability factor of at least 60. Thus the thermal stability of the new ultrafine BaFe particles is adequate. The new test tape with the ultrafine BaFe particles is oriented in the perpendicular direction, and its squareness ratio for this direction could be increased from 0.52 to 0.7, without demagnetization compensation. With demagnetization compen- sation, the squareness ratio for the perpendicular direction is 0.86. The properties were obtained with a vibrating 0018-9464/$26.00 © 2010 IEEE