Visualization of magnetic domains by near-field scanning microwave microscope Kiejin Lee a,Ã , Harutyun Melikyan a , Arsen Babajanyan a , Tigran Sargsyan a , Jongchel Kim a , Seungwan Kim a , Barry Friedman b a Department of Physics and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Seoul 121-742, Republic of Korea b Department of Physics, Sam Houston State University, Huntsville, TX 77341, USA article info PACS: 68.37.d 68.37.Uv 07.79.Pk 06.30.Ka 07.10.Cm Keywords: Magnetic domains Hard disk Permeability Near-field Microwaves abstract A near-field scanning microwave microscope (NSMM) system was used for the investigation of magnetic properties of a hard disk (HD) under an external magnetic field. To demonstrate local microwave characterization of magnetic domains by NSMM, we scanned the HD surface by measuring the microwave reflection coefficient S 11 of the NSMM at an operating frequency near 4.4 GHz. The NSMM offers a reliable means for quantitative measurement of magnetic domains with high spatial resolution and sensitivity. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Recently, methods for monitoring magnetic domains have been investigated by semiconductor Hall bar sensors, magnetic force microscopy (MFM), and the magneto-optical microscope (MOM) [1–5]. However, as magnetic storage technology is extended to the micro-scale distance and operating frequencies of integrated circuit reach the microwave regime, there is a strong need to quantitatively measure local magnetic properties at microwave frequencies and to develop tools to characterize magnetic imaging for micro-scale magnetic devices. This requires local measure- ment of magnetic properties such as the magnetic permeability. Electromagnetic measurements using a near-field microwave scanning microscope (NSMM) has been emerging in the past few years to study electromagnetic properties with micro-scale resolution at microwave wavelengths [6–10]. To achieve such a goal, the probe tip of the NSMM has to be improved from the conventional metal tip and developed as a quantitative metrology tool with micro-scale resolution. For a conventional metal probe tip consisting of an apex and a taper, however, it is difficult to quantitatively calculate the relationship between the probe geometry and the sample properties. Thus, a new design of the probe tip with a distance regulation system is imperative for quantitative near-field microwave imaging. In general, high spatial resolution in near-field microscope images is determined primarily by aperture size and high sensitivity can be achieved by the quality factor of the resonator [11,12]. Thus, we used a high- quality dielectric resonator coupled to a tapered probe tip utilizing the distance control sensor provided by a tuning fork. In this work, we report a NSMM system with improved sensitivity and high spatial resolution for the magnetic domain investigation of a 1.2Gb magnetic hard disk (HD) platter under an external magnetic field at an operating frequency f ¼ 4.4 GHz. To demonstrate local microwave characterization of magnetic domains by NSMM we scanned the HD surface to visualize magnetic domains. The dependence of the magnetic domains on the external magnetic field could be imaged by measuring the microwave reflection coefficient S 11 and interpreted by the transmission line theory [13]. This high-resolution measurement of the magnetic domains has a great potential for investigating the magnetic profile with high sensitivity. 2. Experimental Fig. 1(a) shows the experimental setup of the NSMM [10]. In order to boost the sensitivity of the probe, we employed a ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ultramic Ultramicroscopy 0304-3991/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ultramic.2009.03.013 Ã Corresponding author. Tel.: +82 2705 8429; fax: +82 2 715 8429. E-mail address: klee@sogang.ac.kr (K. Lee). Ultramicroscopy 109 (2009) 889–893