IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 23 (2012) 035501 (6pp) doi:10.1088/0957-4484/23/3/035501 The advantages of the magnetic structure in ferromagnetic-film-coated carbon nanotube probes T Manago 1 , H Asada 2 , T Uzumaki 3 , F Takano 4 , H Akinaga 4 and H Kuramochi 5 1 Department of Applied Physics, Faculty of Science, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan 2 Graduate School of Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611, Japan 3 Fujitsu Laboratories, Ltd, 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan 4 Nanodevice Innovation Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan 5 International Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMC), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan E-mail: manago@fukuoka-u.ac.jp Received 5 October 2011 Published 16 December 2011 Online at stacks.iop.org/Nano/23/035501 Abstract The magnetic structures of ferromagnetic-film-coated carbon nanotube (CNT) probes and conventional pyramidal probes for a magnetic force microscope (MFM) were simulated using three-dimensional micromagnetic simulation. The CNT-MFM probes with a total probe diameter less than 60 nm are almost uniformly magnetized along the longitudinal direction of the CNT, which is the ideal magnetic structure for MFM observations. On the other hand, the pyramidal probes had a vortex structure around the point tip, which suggests that they require a greater thickness of the ferromagnetic film because only part of the magnetic moment participates in the detection of the z-component of the stray field from samples. The advantages of the CNT-MFM probe are uniform magnetization along the longitudinal direction and magnetic imaging ability using a smaller coating thickness. (Some figures may appear in colour only in the online journal) 1. Introduction A magnetic force microscope (MFM) is a powerful tool for observing the magnetic domains of magnetic thin films and magnetic nanodevices. It has been widely used for research on and evaluation of magnetic storage media due to various advantages including ease of operation, no tricky sample treatment, and relatively high resolutions. With the current progress in magnetic storage devices, the recording density continues to increase, and consequently the bit length continues to become smaller. A lateral resolution of less than 15 nm is required to observe recording media with densities in the range of Tbit in -2 . However, the resolution of a current commercial MFM system is generally 50–100 nm. Various efforts to improve the lateral resolution of MFMs have been made, including acumination of the tip [1–4], thinner coating of magnetic materials [1], and utilizing carbon nanotube (CNT) based probes [5, 6]. We have developed CoFe coated CNT-MFM probes [7] and have succeeded in observations of the magnetic domain structure of ultra-high-density perpendicular magnetic storage media with 1100 kilo flux changes per inch (FCI) [8]. The spatial resolution reached about 10 nm. It is clear that thin CNT tips with magnetic coatings are effective in improving the resolution, since similar resolutions were obtained using Ti/Co/Ti coated CNT probes [9]. However, the origin of these 1 0957-4484/12/035501+06$33.00 c  2012 IOP Publishing Ltd Printed in the UK & the USA