Magnetic Force Microscopy Tip Research Articles

High-Resolution Magnetic Force Microscope Tip Coated with Co Film Prepared by Ultra-High Vacuum Evaporation

High-Resolution Magnetic Force Microscope Tip Coated with Co Film Prepared by Ultra-High Vacuum Evaporation

Magnetic Force Microscope Tips Prepared by Coating Sharp Si-Base Tips with Thin Co Films

Magnetic Force Microscope Tips Prepared by Coating Sharp Si-Base Tips with Thin Co Films

振幅変調型MFMによるコプレーナウェーブガイドの高周波近傍磁気計測

This paper proposes our newly measurement method of the GHz range near field from a coplanar waveguide (CPW) using a Ni‐Fe coated magnetic force microscope tip and amplitude modulation of the line current. Cantilever resonance frequency modulation of approximately 25 kHz supplies the CPW with current and carrier frequencies up to 1.0 GHz. The CPW has a signal line width of 3 μm and a ground line width of 50 μm. The RF magnetic near field was evaluated from the difference in the oscillation amplitudes of the tip with and without Ni-Fe coating for a carrier frequency range up to 1.0 GHz, and became maximum near the center of gap on the CPW. This result also suggests that this method may be applicable to high resolution measurements of the magnetic near field distribution near RF power lines and ground lines, which have downsized for microscale radio frequency integrated circuit (RFIC) chips.

Optimization of perpendicular magnetic anisotropy tips for high resolution magnetic force microscopy by micromagnetic simulations

Magnetic Force Microscopy (MFM) tip coated with perpendicular magnetic anisotropy film (PMA tip) is one of the choices for high resolution imaging at low scan height (SH), since it has negligible tip–sample interaction related to its stable magnetic state, sharp, and small tip stray field. In this work, detailed micromagnetic studies are carried out to understand the effect of geometrical and magnetic parameters including the cone angle θ of the PMA tip, intergrain exchange constant \(A_{2}^{*}\), saturation magnetization M s and uniaxial crystalline anisotropy constant K 1 of the tip coating on the MFM tip resolution. To evaluate the resolution performance of the optimized PMA tip, MFM images of high-density granular recording media and patterned media are simulated. We find that, for the PMA tip and its coating, a cone angle in a range of 36.9∘ to 53.1∘, a saturation M s of 700 emu/cm3, a large uniaxial crystalline anisotropy constant K 1 (>4.9×106 erg/cm3) and a high intergrain exchange constant \(A_{2}^{*}\) of (0.3–1.0)×10−6 erg/cm are optimized conditions for high resolution imaging. The optimized PMA tip has an excellent performance on imaging of high-density thin film media (bit size of 8×16 nm2) at low SH of 2–8 nm and bit pattern media with a pitch of 50 nm, edge-edge spacing of 5–15 nm at SH of 8–15 nm.

Radio Frequency Magnetic Near Field Measurements of Coplanar Waveguide Simulated Power and Ground Lines in Radio Frequency Integrated Circuits Using a MFM Tip

This paper describes our study on high-resolution measurements of the distribution of the radio frequency (RF) magnetic near field from a coplanar waveguide (CPW) with a size similar to power and ground lines in radio frequency integrated circuit chips using a magnetic force microscope tip and amplitude modulation of the line current. Cantilever resonance frequency modulation of approximately 25 kHz supplies the CPW with current and carrier frequencies up to 0.1 GHz. The CPW has a signal line width of 3 μm and a ground line width of 50 μm. The oscillation amplitudes of the tip with and without a DC magnetic field indicates that the distribution of the RF magnetic near field in the proximity of the CPW can be observed for a carrier frequency up to 0.1 GHz. This result also suggests that this method has potential as a new technique for high-resolution RF field measurements.

Performing quantitative MFM measurements on soft magnetic nanostructures

We have extended our previous work (Rawlings et al 2010 Phys. Rev. B 82 085404) on simulating magnetic force microscopy (MFM) images for magnetically soft samples to include an accurate representation of coated MFM tips. We used an array of square 500 nm nanomagnets to evaluate our improved MFM model. A quantitative comparison between model and experiment was performed for lift heights ranging from 20 to 100 nm. No fitting parameters were used in our comparison. For all lift heights the qualitative agreement between model and experiment was significantly improved. At low lift heights, where the magnetic signal was strong, the difference between theory and experiment was less than 30%.

Micromagnetic study of effect of tip-coating microstructure on the resolution of magnetic force microscopy

The properties of a magnetic force microscopy (MFM) tip are very important for high-resolution magnetic imaging. In this work, micromagnetic models of tips are set up to study the effect of tip-coating microstructure, especially the randomness of anisotropy on tip edge and tip end, on the resolution of MFM. The effective coating height and the resolution potential of tips with various microstructures and magnetic properties have been characterized by investigating the obtained signals from high-density continuous granular thin film disk media with a bit size of 8×16 nm2 and bit-patterned media with a pattern period p of 50 nm. The magnetic moment distribution at the tip end should be perpendicular to the sample to realize a ‘magnetically sharp’ tip, which explains further the improved resolution in the recent experimental reports. Tips with well-controlled grain structure and magnetic anisotropy of coating materials can be applied to both high-density thin film disk media and bit-patterned media.

Rapid preparation of electron beam induced deposition Co magnetic force microscopy tips with 10 nm spatial resolution

Magnetic force microscope Co spike tips with lateral magnetic resolution of 10 nm have been prepared. The Co spikes are grown by electron beam induced deposition of Co from Co(2)(CO)(8) gas precursor. The high resolution Co spikes are fabricated at the spot of a tightly focused electron beam on the tip of commercial atomic force microscope cantilevers. Qualitative investigations indicate that a spike grown on a planar base of Co improves the signal to noise.

Clock field in arrayed magnetic logic gates with a magnetic force microscope tip

A magnetic logic gate (MLG), which is based on magnetic quantum dot cellular automata (MQCA), is capable of NAND/NOR logic operations. By arranging MLGs in a two-dimensional periodic array, a highly functional circuit can be created. However, NAND/NOR gates are difficult to form into a two-dimensional periodic arrangement. Here, we propose NOT/AND/ORs gate based on MLGs, which can be arranged in a two-dimensional periodic array. To demonstrate logic operations, we performed numerical simulations based on the macro-spin model. To execute logic operation in the arrayed structure, we used the stray field from a magnetic force microscope tip.

Advanced Magnetic Force Microscopy for High Resolution Magnetic Imaging

Magnetic force microscopy (MFM) is one of the primary imaging tools for studying magnetic nanostructures. The resolution of MFM has been considered as a main issue in characterizing magnetic nanostructures smaller than 30 nm; especially for high density recording media beyond 1 Tbit/in 2 . In this letter, we investigated three different kinds of MFM tips such as those with a perpendicular magnetic anisotropy (PMA) derived from a crystallographic texture, antiferromagnetic coupled perpendicular (AFC) tips and tips with no crystallographic textures, resulting in no PMA. Their resolution, as measured using a recording media with written information, was compared with that of commercial MFM tips. The tip in the PMA configuration was found to provide the best resolution among all of them.

Influence of magnetic material composition of Fe100−xBx coated tip on the spatial resolution of magnetic force microscopy

Magnetic force microscope (MFM) tips are prepared by coating Si tips of 3 nm radius with 20-nm-thick Fe100−xBx (x = 0, 8, 18, and 34 at. %) alloys. As the B composition increases, the wettability of Fe-B alloy material to Si surface increases and a sharper and smoother MFM tip is obtained. The remanent magnetization of Fe-B alloy material decreases with increasing the B composition, which degrades the MFM signal detection sensitivity. The MFM resolution is influenced by both the tip sharpness and the remanent magnetization of coated Fe-B alloy material. Resolutions of 10.2, 9.2, 7.3, and 9.3 nm are obtained with tips coated with Fe, Fe92B8, Fe82B18, and Fe66B34 materials, respectively. Magnetic bits of 14.9 nm in length of a perpendicular magnetic medium recorded at 1700 kfci are distinguishable in the MFM image observed by using an Fe82B18-alloy coated tip. Fe-B coated tips are suitable to observe the magnetization structures of future high-density recording media.

Micromagnetic studies on resolution limits of magnetic force microscopy tips with different magnetic anisotropy

In magnetic force microscopy (MFM), it is effective to control the magnetic properties of the coating materials on the MFM tip to achieve higher resolution. In this work, the effect of the magnetic anisotropy of the tip-coating, such as perpendicular magnetic anisotropy (PMA), in-plane magnetic anisotropy (IMA), and random magnetic anisotropy (RMA), on the MFM image resolution are studied by micromagnetics. An accurate 3 D micromagnetic model of the CoPt pyramid MFM tip, with a cone angle of 37°, tip height of 120 nm, coating thickness of 7.6 nm, and average grain size of about 8.8 nm, was setup to calculate the domain structure and the stray field of the tip. A CoPt disk medium, with a bit size of 24 × 32 nm2 and film thickness of 8 nm, was chosen for image simulation. The PMA tip is advantageous in low scan height (SH) measurement with little tip-sample interaction due to its sharp and small stray field, while the IMA tip will disturb the magnetic moments of the medium at a low SH due to its strong stray field, and the RMA tip cannot read the bits with clear image contrast due to its broader field distribution.

Characterization of high‐density bit‐patterned media using ultra‐high resolution magnetic force microscopy

AbstractBit‐patterned media at one terabit‐per‐square‐inch (Tb/in2) recording density require a feature size of about 12 nm. The fabrication and characterization of such magnetic nanostructures is still a challenge. In this Letter, we show that magnetic dots can be resolved at 10 nm spacing using magnetic force microscopy (MFM) tips coated with a magnetic film possessing a perpendicular magnetic anisotropy (PMA). Compared to MFM tips with no special magnetic anisotropy, MFM tips with PMA can resolve the bits clearly, because of a smaller magnetic interaction volume, enabling a simple technique for characterizing fine magnetic nanostructures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic Force Microscopy of High-Density Magnetic Recording Media by Using High-Resolution Tips

Magnetic force microscope (MFM) tips were prepared by coating Si tips of 5 nm radius with 3d ferromagnetic transition metals (Ni, NiFe, Fe, and Co). The effects of coated-film thickness and coating material on the MFM signal sensitivity and resolution were investigated. As the film thickness increases, the sensitivity increases due to the increase of magnetic volume of tip. Higher sensitivity is observed for the same film thickness in the order of tip coated with material with higher remanent magnetization, Ni < NiFe < Fe < Co. Resolutions of 14.0, 13.4, 10.6, and 9.1 nm are obtained with tips coated with 40-nm-thick Ni, 40-nm-thick NiFe, 20-nm-thick Fe, and 20-nm-thick Co films, respectively. As the film thickness further increases, the resolution decreases due to the increase of tip radius. The MFM resolution is influenced by both the remanent magnetization of coating material and the tip radius. Bit lengths of around 28 nm of an HDD medium with 528 Gb/in2 area density are clearly observed by employing the tips coated with 20-nm-thick Fe and 20-nm-thick Co films. A positioning technique of MFM observation of a same area for high-density magnetic recording media is also proposed.

Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy–magnetic force microscopy combination

The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable technique to detect weak magnetic fields arising from low dimensional complex systems such as organic nanomagnets, superparamagnetic nanoparticles, carbon-based materials, etc. In all these cases, the magnetic nanocomponents and the substrate supporting them present quite different electronic behavior, i.e., they exhibit large surface potential differences causing heterogeneous electrostatic interaction between the tip and the sample that could be interpreted as a magnetic interaction. To distinguish clearly the origin of the tip–sample forces we propose to use a combination of Kelvin probe force microscopy (KPFM) and MFM. The KPFM technique allows us to compensate in real time the electrostatic forces between the tip and the sample by minimizing the electrostatic contribution to the frequency shift signal. This is a great challenge in samples with low magnetic moment. In this work we studied an array of Co nanostructures that exhibit high electrostatic interaction with the MFM tip. Thanks to the use of the KPFM/MFM system we were able to separate the electric and magnetic interactions between the tip and the sample.

Effect of Magnetic Film Thickness on the Spatial Resolution of Magnetic Force Microscope Tips

Magnetic force microscope (MFM) tips were prepared by coating commercial atomic force microscope (AFM) tips of 5 nm radius with Co and CoCrPt magnetic thin films varying the thickness in a range of 10–80 nm. The structural and the magnetic properties of coated magnetic thin films were investigated by scanning electron microscopy, AFM, X-ray diffraction, and vibrating sample magnetometry. The tip radius and the film surface roughness increase with increasing the film thickness. With increasing the film thickness, the MFM signal sensitivity increases, whereas the resolution decreases due to increase of tip radius. The MFM observation resolutions of 10 nm and 23 nm are obtained with the tips coated with 20-nm-thick Co and 40-nm-thick CoCrPt films, respectively. The MFM resolution is influenced by both the tip radius and the magnetic moment of coated material.

Quantitative assessment of pinning forces and magnetic penetration depth in NbN thin films from complementary magnetic force microscopy and transport measurements

Epitaxial niobium nitride thin films with a critical temperature of ${T}_{\mathrm{c}}=16$ K and a thickness of 100 nm were fabricated on MgO (100) substrates by pulsed laser deposition. Low-temperature magnetic-force-microscopy (MFM) images of the supercurrent vortices were measured after field cooling in a magnetic field of 3 mT at various temperatures. The temperature dependence of the penetration depth has been evaluated by a two-dimensional fitting of the vortex profiles in the monopole-monopole model. Its subsequent fit to a single $s$-wave-gap function results in the superconducting gap amplitude, $\ensuremath{\Delta}(0)=(2.9\ifmmode\pm\else\textpm\fi{}0.4)$ meV $=(2.1\ifmmode\pm\else\textpm\fi{}0.3){k}_{\mathrm{B}}{T}_{\mathrm{c}}$, which perfectly agrees with the previous reports. The pinning force has been independently estimated from the local depinning of individual vortices by the lateral forces exerted by the MFM tip and from transport measurements. A good quantitative agreement between the two techniques shows that for low fields, $B\ensuremath{\ll}{\ensuremath{\mu}}_{0}{H}_{\text{c2}}$, MFM is a powerful and reliable technique to probe the local variations of the pinning landscape. We also demonstrate that the monopole model can be successfully applied even for thin films with a thickness comparable to the penetration depth.

Enhanced resolution in magnetic force microscropy using tips with perpendicular magnetic anisotropy

Magnetic force microscopy (MFM) is commonly used for the characterization of magnetic nanostructures, which gets challenging for sub-20 nm features. The typical resolution of commercial MFM tips stands at about 30 nm, whereas sub-15 nm resolution has been reported by extensive modifications of the tip. In this paper, we show that a tip coated with a magnetic film possessing a perpendicular magnetic anisotropy (PMA) offers superior resolution compared to tips without PMA. The advantages of a tip with PMA have been demonstrated based on writing magnetic transitions in a commercial perpendicular media. MFM images and line scans at different scan heights are presented along with an explanation for the observed improvement in performance.

Switching Magnetization Magnetic Force Microscopy — An Alternative to Conventional Lift-Mode MFM

Switching Magnetization Magnetic Force Microscopy — An Alternative to Conventional Lift-Mode MFM In the paper we present an overview of the latest progress in the conventional lift-mode magnetic force microscopy (MFM) technique, achieved by advanced MFM tips and by lowering the lift height. Although smaller lift height offers improved spatial resolution, we show that lowered tip-sample distance mixes magnetic, atomic and electric forces. We describe an alternative to the lift-mode procedure - Switching Magnetization Magnetic Force Microscopy [SM-MFM], which is based on two-pass scanning in tapping mode AFM with reversed tip magnetization between the scans. We propose design and calculate the magnetic properties of such SM-MFM tips. For best performance the tips must exhibit low magnetic moment, low switching field, and single-domain state at remanence. The switching field of such tips is calculated for Permalloy hexagons.

Correlation between shape and stray field in indented square nanomagnets: Experimental and theoretical study

We have used the scanning probe technique, magnetic force microscopy (MFM), to study the magnetization distribution in a system of indented rectangles made from permalloy. An accurate linear approximation to the micromagnetic equations was implemented in commercial finite element software. This model was used to study the important effect of tip-sample interaction on our MFM measurements. Comparison between experiment and our model confirmed that even for large indents the nanomagnets adopted vortex ground states. A qualitative relationship between the sample's magnetization, in the absence of the MFM tip's magnetic field, and the induced contrast was identified. The optimum ratio of charge contrast to induced contrast when observing vortex states was found to be proportional to the tip moment raised to the power of 0.4. This was subject to the limitations imposed by resolution and thermal noise. It occurred for large separation between tip and sample.