Direct and Real-Time Observation of Sub-Micron Domain Dynamics in Magnetically Biased Strontium Ferrite Permanent Magnet
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Direct and Real-Time Observation of Sub-Micron Domain Dynamics in Magnetically Biased Strontium Ferrite Permanent Magnets by Room Temperature Scanning Micro-Hall Probe Microscopy Adarsh Sandhu, Naoji Iida, Hiroshi Masuda1, Ahmet Oral2, and Simon J. Bending3 Department of Electrical and Electronic Engineering, Tokai University, 1117 Kitakaname, Hiratsuka-shi, Kanagawa 239-1292, Japan. 1 Toei Kogyo Ltd, 8-13-1, Tadao, Machida, Tokyo, 194-0035, Japan. 2 Department of Physics, Bilkent University, 06533 Ankara, Turkey. 3 Department of Physics, University of Bath, Claverton Down, UK. ABSTRACT A room temperature scanning micro-Hall probe microscope (RT-SHPM) was used for imaging stray magnetic field fluctuations at the surfaces of strontium ferrite permanent magnets (SFM) in the presence of external bias fields. The RT-SHPM enables the extremely fast, non-invasive, and quantitative measurement of localized surface magnetic fields on the sub-micron-scale. A 0.8 x 0.8 µm2 GaAs/AlGaAs micro-Hall probe (300K Hall coefficient =0.3Ω/G; field sensitivity=0.04 G/√Hz ) with an integrated STM tip for precise vertical positioning was used as a magnetic field sensor. External bias fields (Hex) of up to 2700 Oe were applied parallel to the easy and hard axes of thermally demagnetized SFMs. Sample areas of up to 50x50 µm were imaged at a height of 0.3 µm above the SFM surface for each Hex, with scan speeds of approximately one frame/second (128x128 pixels) enabling quasi-real time imaging in synchronization with bias field changes. RT-SHPM images of surfaces normal to the easy axis of demagnetized samples at Hex=0, clearly showed the presence of 8-15 µm sized domains and stray magnetic field fluctuations of ±200G; images of surfaces normal to the hard axis showed 20 µm sized domains with magnetic field fluctuations of ±100G. Pronounced domain movement and rotation was observed for surfaces normal to the easy axis at bias fields above 700 Oe applied along the easy axis. A good correlation was found between domain movement and vibrating sample magnetometer hysteresis measurements. The RT-SHPM system was demonstrated to be a valuable tool for the direct and non-invasive study of micro-magnetic phenomena in ferromagnetic materials. INTRODUCTION The development of ferromagnetic materials for high performance permanent magnets requires a fundamental understanding of the behavior magnetic domains in external bias fields. U3.2.1
To-date, magnetic force microscopy (MFM) has been extensively used for imaging magnetic domains of a wide range of materials [1]. However, it has been found that the interpretation of MFM images can be complicated due to artifacts arising from the MFM tip field [2]. The situation is even more complex when the MFM imaging is carried out in the presence of external bias fields [3]. In this paper we describe the unique features of a new versatile room temperature scanning Hall probe microscope (RT-SHPM) system used for the direct, non-invasive, and quantitative imaging of domains at the surface of strontium ferrite perma
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