Magnetic domain imaging with a scanning near-field optical microscope using a modified Sagnac interferometer (original) (raw)
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Observation of magnetic domains using a reflection-mode scanning near-field optical microscope
Applied physics letters, 1997
It is demonstrated that it is possible to image magnetic domains with a resolution of better than 60 nm with the Kerr effect in a reflection-mode scanning near-field optical microscope. Images taken of tracks of thermomagnetically prewritten bits in a Co/Pt multilayer structure magnetized out-of plane showed optical features in a track pattern whose appearance was determined by the position of an analyzer in front of the photomultiplier tube. These features were not apparent in the topography, showing this to be a purely magneto-optic effect.
Near-field magneto-optical microscopy
Microscopy Microanalysis Microstructures, 1994
2014 A scanning tunneling optical microscope (STOM) operating in total reflexion condition with variable incident angle and polarization sensitive detection of the evanescent mode has been developed to study near-field magneto-optical properties of thin magnetic films. The sample is deposited on the external face of a prism and illuminated in total reflexion conditions with linearly polarized laser light. The evanescent mode close to the surface is detected with a tip-ending monomode optical fiber connected at its other end to a photomultiplier tube equipped with a light-polarization analyzer. The polarization sensitivity of the whole system, which was found to depend on the tip condition, was characterized on the bare prism with sand p-polarized excitations. The magneto-optical effect in the evanescent mode is measured through a lock-in amplifier by modulating the external magnetic field produced by a coil surrounding the tip. With this setup we have mainly studied a dielectric garnet film exhibiting perpendicular magnetization. The images, obtained on this sample by measuring the magneto-optical effect under very low amplitude of the external magnetic field modulation, show up submicronic details due to magnetic domain wall motion.
AIP Advances, 2017
We describe a zero loop-area Sagnac interferometer at oblique incidence for detecting magneto-optic Kerr effect arising from in-plane magnetization in a sample. By exploiting properties of polarization states under relevant crystal symmetry transformation, we show that contributions from longitudinal and transverse Kerr effects can be separated. In addition we can select one optical arrangement out of four that detects the longitudinal effect with the highest signal-to-noise ratio. Compared to finite loop-area Sagnac interferometers operating at oblique incidence, the zero loop-area interferometer involves significantly fewer optical elements and is thus more stable against drifts in the optical system. For demonstration, we measured the in-plane magneto-optic Kerr effect from a 42-nm Ni film.
Cavity-enhanced near-field optical magnetometry
Nanoengineering: Fabrication, Properties, Optics, and Devices, 2004
We present the first near-field scanning optical magneto-optic Kerr effect (MOKE) of sub-micron magnetic structures, where a Kerr rotation of 0.11º from a 0.25µm nickel magnet was observed. This is enabled by a cavity based technique to enhance the Kerr rotation of light reflected from a magnetized surface. Spatially resolved magneto-optic measurements are performed involving both conventional microscopy and near-field scanning optical microscopy (NSOM). Cavity enhancement is achieved with either a single dielectric coating or a dielectric-metal bilayer coating applied to the ferromagnetic structure of interest. We present a scattering matrix approach to calculating the enhancement resulting from a multilayer dielectric coating and show good agreement with experiment. This demonstrates a non-invasive optical technique for magnetometry with ultrahigh spatial resolution.
Near-field optical magnetometry and magnetic imaging of nanomagnets
Eighth International Symposium on Laser Metrology, 2005
We present an all-optical approach to detecting magnetization reversal events in submicron ferromagnetic structures that is non-perturbative and compatible with ultrafast optical techniques. We demonstrate experimentally that structures much smaller than the wavelength of light can be probed using both near-field and far-field laser techniques combined with a cavity Kerr enhancement technique and two different polarimetry methods. Controlled magnetization reversal events are detected in nickel magnets approaching the 100nm scale. This leads to a promising way to measure subpicosecond dynamics of nanomagnets for fast device applications.
Apertureless scanning near‐field magneto‐optical microscopy of magnetic multilayers
Journal of Microscopy, 1999
We imaged magnetic domains in Pt/Co/Pt multilayers using an apertureless scanning near‐field optical microscope operating in reflection mode. As the magneto‐optical effects are weak for this kind of structure, a polarization modulation technique with a photoelastic modulator was used to reveal the contrast between magnetic domains. In the case of a Pt/Co/Pt trilayer structure, a strong improvement in lateral resolution is observed compared with far‐field magneto‐optical images and good sensitivity is achieved. In the case of a Pt/[Co/Pt]Pt multilayer structure, stripe domains of 200 nm width could be resolved, in good agreement with images obtained by magnetic force microscopy on the same structure.
A scanning laser microscope system to observe static and dynamic magnetic domain behavior
IEEE Transactions on Instrumentation and Measurement, 2002
Scanning laser microscopes (SLMs) have been used to characterize the magnetic properties of materials for some time. The first SLM built [1] was a purely static system capable of imaging magnetic domains. Dynamic capability was introduced with the development of the R-Theta microscope [2]. However, this microscope utilizes a rotating drive. A scanning laser microscope has been designed to observe the dynamic behavior of domain switching during the thermo-magnetic write process and the subsequent magnetization state (domain orientation) in stationary media, without the requirement for a rotating drive. It will also be used to write to the magneto-optic (MO) disk material thermo-magnetically prior to imaging. Images are derived from the longitudinal and polar magneto-optic Kerr effects. In this paper, the different configurations for imaging are described and some initial images are presented.
Theory of a magnetic microscope with nanometer resolution
Physical Review B, 2001
We propose a theory for a type of apertureless scanning near field microscopy that is intended to allow the measurement of magnetism on a nanometer length scale. A scanning probe, for example a scanning tunneling microscope (STM) tip, is used to scan a magnetic substrate while a laser is focused on it. The electric field between the tip and substrate is enhanced in such a way that the circular polarization due to the Kerr effect, which is normally of order 0.1% is increased by up to two orders of magnitude for the case of a Ag or W tip and an Fe sample. Apart from this there is a large background of circular polarization which is non-magnetic in origin. This circular polarization is produced by light scattered from the STM tip and substrate. A detailed retarded calculation for this light-in-light-out experiment is presented.