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(a) Topography of a high-density HDD, recorded with a custom-made tip with 20 nm coating. The lateral resolution is below 10 nm. (b) Corresponding MFM image showing single domains with alternating OOP orientations. (c) Frequency shift profile along the line shown in (b) that gives an inter-domain distance of about 25 nm.
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Magnetic force microscopy (MFM) is a widely used technique for magnetic imaging. Besides its advantages such as the high spatial resolution and the easy use in the characterization of relevant applied materials, the main handicaps of the technique are the lack of control over the tip stray field and poor lateral resolution when working under standa...
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... could be achieved by reducing the thickness deposited onto the AFM tips at the expense of reducing their magnetic sensitivity. Figure 3 displays the topography and MFM image of a different region of the same hard disk obtained by a custom-made tip with a 20 nm thick coating. Figure 3a shows grains of the order of 10 nm in size, a remarkable resolution even for non-magnetic AFM probes. ...
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... 3 displays the topography and MFM image of a different region of the same hard disk obtained by a custom-made tip with a 20 nm thick coating. Figure 3a shows grains of the order of 10 nm in size, a remarkable resolution even for non-magnetic AFM probes. The corresponding MFM image shows series of bright and dark stains associated to domains with alternate OOP magnetization (Figure 3b). ...
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... 3a shows grains of the order of 10 nm in size, a remarkable resolution even for non-magnetic AFM probes. The corresponding MFM image shows series of bright and dark stains associated to domains with alternate OOP magnetization (Figure 3b). The frequency shift along the profile drawn is displayed in Figure 3c and confirms the inter-domain distance to be around 25 nm. ...
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... corresponding MFM image shows series of bright and dark stains associated to domains with alternate OOP magnetization (Figure 3b). The frequency shift along the profile drawn is displayed in Figure 3c and confirms the inter-domain distance to be around 25 nm. Note that no smoothing has been applied to the profile data. ...
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... Different solutions have been reported to simultaneously improve resolution and sensitivity. For instance, the deposition of non-magnetic material on the apex of the probe by electron beam lithography, subsequently coating one side of the tip with a ferromagnetic film by evaporation [22,23]; FIB milling to reduce the diameter of a previously coated AFM tip [24,25]; the growth of carbon nanotubes coated with ferromagnetic films [26,27], or the sputtering deposition only on one side of the tip pyramid [28]. These approaches have yielded good results in terms of resolution and sensitivity. ...
High-resolution micro- and nanostructures can be grown using Focused Electron Beam Induced Deposition (FEBID), a direct-write, resist-free nanolithography technology which allows additive patterning, typically with sub-100 nm lateral resolution, and down to 10 nm in optimal conditions. This technique has been used to grow magnetic tips for use in Magnetic Force Microscopy (MFM). Due to their high aspect ratio and good magnetic behavior, these FEBID magnetic tips provide several advantages over commercial magnetic tips when used for simultaneous topographical and magnetic measurements. Here, we report a study of the durability of these excellent candidates for high-resolution MFM measurements. A batch of FEBID-grown magnetic tips was subjected to a systematic analysis of MFM magnetic contrast for 30 weeks, using magnetic storage tape as a test specimen. Our results indicate that these FEBID magnetic tips operate effectively over a long period of time. The magnetic signal was well preserved, with a maximum reduction of 60% after 21 weeks of recurrent use. No significant contrast degradation was observed after 30 weeks in storage.
... Regarding the resolution and sensitivity of the MFM, different routes can be followed to enhance them. The first approach is the development of high-performance MFM probes by using different methods to control the tip stray field [25,26]. On the other hand, the dissipation maps obtained by using the MDFM mode, is an alternative way to improve the resolution of the magnetic imaging. ...
Magnetic Force Microscopy (MFM) is the principal characterization technique for the study of low-dimensional magnetic materials. Nonetheless, during years, the samples under study was limited to samples in the field of data storage, such as longitudinal hard disk, thin films, or patterned nanostructures. Nowadays, thanks to the advances and developments in the MFM modes and instrumentation, other fields are emerging like skyrmionic structures, 2D materials or biological samples. However, in these experiments artifacts in the magnetic images can have strong impact and need to be carefully verified for a correct interpretation of the results. For that reason, in this paper we will explore new ideas combining the multifrequency modes with the information obtained from the experimental dissipation of energy associated to tip-sample interactions.
... Intermediate moment tips were coated in a homemade built RF sputtering chamber. 49 For sputtering coated tips, Co was deposited on tips under 10 -2 mbar argon pressure, with a bias voltage of 295 V and 50 W of power. ...
Topologically non-trivial structures such as magnetic skyrmions are nanometric spin textures of outstanding potential for spintronic applications due to their unique features. It is well known that Néel skyrmions of definite chirality are stabilized by the Dzyaloshinskii-Moriya exchange interaction (DMI) in bulk non-centrosymmetric materials or ultrathin films with strong spin-orbit coupling at the interface. In this work, we show that soft magnetic (permalloy) hemispherical nanodots are able to host three-dimensional chiral structures (half-hedgehog spin textures) with non-zero tropological charge. They are observed at room temperature, in absence of DMI interaction and they can be further stabilized by the magnetic field arising from the Magnetic Force Microscopy probe. Micromagnetic simulations corroborate the experimental data. Our work implies the existence of a new degree of freedom to create and manipulate complex 3D spin-textures in soft magnetic nanodots and opens up future possibilities to explore their magnetization dynamics.
... Intermediate moment tips were coated in a homemade built RF sputtering chamber. 49 For sputtering coated tips, Co was deposited on tips under 10 −2 mbar argon pressure, with a bias voltage of 295 V and 50 W of power. ...
Topologically non-trivial structures such as magnetic skyrmions are nanometric spin textures of outstanding potential for spintronic applications due to their unique features. It is well known that Néel skyrmions of definite chirality are stabilized by the Dzyaloshinskii-Moriya exchange interaction (DMI) in bulk non-centrosymmetric materials or ultrathin films with strong spin-orbit coupling at the interface. In this work, we show that soft magnetic (permalloy) hemispherical nanodots are able to host three-dimensional chiral structures (half-hedgehog spin textures) with non-zero tropological charge. They are observed at room temperature, in absence of DMI interaction and they can be further stabilized by the magnetic field arising from the Magnetic Force Microscopy probe. Micromagnetic simulations corroborate the experimental data. Our work implies the existence of a new degree of freedom to create and manipulate complex 3D spin-textures in soft magnetic nanodots and opens up future possibilities to explore their magnetization dynamics.
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This thesis focuses on micromagnetic and analytical modeling of the magnetization processes in individual cylindrical nanowires with different geometries (modulations in diameter) and compositions. The objective is the design of nanowires to control the type of magnetic domains and domain walls as well as their pinning mechanisms which may serve as a basis for nanotechnological applications of these objects. The first part is dedicated to remanent states, hysteresis processes and pinning properties of Co-based and Permalloy nanowires with antinotches and diameter modulations. On the other hand, magnetic domains are studied in nanowires of CoxNi100-x, and we present the numerical modelling of signals of Transmision X-Ray Microscopy with X-Ray Magnetic Circular Dichroism for different magnetization configurations to interpret the magnetic state in nanowires of CoNi/Ni. We additionally evaluate the heat dissipation of Permalloy and Co nanowires under an alternating magnetic field and interpret it by a simple analytical model of the domain wall motion. The results of this thesis constitute a basis for nanowires design for different nanotechnological applications such as 3D magnetic memories, sensors, permanent magnets, bio-magnetic applications (magnetic hyperthermia) or water purification treatments.
... Examples for modified geometries are coatings on sharp needles with high aspect ratio grown by electron beam assisted deposition (EBID), 9 subsequent focussed ion beam (FIB) trimming 10,11 and the attachment of Fe-filled carbon nanotubes (Fe-CNT) 12 or even of single magnetic molecules 13 to non-magnetic cantilevers. Likewise, thin films can be optimized for specific applications, such as smooth and thin coatings for high lateral resolution, 14,15 high coercive CoPt tips, which should provide a stable tip moment configuration also at higher fields 16 or multilayer films with reduced 17 or even tunable magnetic moment. 18 Especially when MFM is sought to allow for quantitative measurements the most essential property of the tip is its rigidity with respect to magnetic fields, either stray fields of the sample or additional external fields. ...
Cantilever based scanning force sensors, which probe a specific tip-sample interaction through a functional tip coating, are limited by the material performance achievable in the coating process. In case of the wide spread magnetic force microscopy (MFM) technique, the magnetic performance of MFM tips, especially the response to magnetic fields and the coercivity, fall far behind the quality known from permanent magnet films prepared with optimized process conditions on appropriate substrates. We resolve this limitation by starting from an optimized thin film architecture - a highly anisotropic SmCo5 film grown epitaxially on MgO(110) substrates - from which a tip is separated by focused ion beam and is attached to a cantilever. Not compromising on resolution and sensitivity, we demonstrate an unrivaled rigidity in magnetic fields, which will largely advance quantitative microscopic investigation of magnetic materials with strong stray fields and allows MFM measurements in external magnetic fields of currently up to 0.7 T. The material optimization for a specific sample - cantilever interaction without restrictions in substrate, film architecture, film preparation conditions and tip shape, is not limited to MFM but offers new opportunities also for other scanning force microscopy modes.
... [16][17][18][19] Therefore, the improvement in MFM resolution would have to be compromised with the probe sensitivity. [19][20][21] Also, the commercially used probes are mainly composed of hard or soft magnetic materials with tip memory effect that results in a distorted MFM image. 10,20 To overcome these limitations, the superparamagnetic (SP) tip is a good candidate although the small magnetic moment gives low sensitivity. ...
... [19][20][21] Also, the commercially used probes are mainly composed of hard or soft magnetic materials with tip memory effect that results in a distorted MFM image. 10,20 To overcome these limitations, the superparamagnetic (SP) tip is a good candidate although the small magnetic moment gives low sensitivity. 10,20 Previously, we proposed magnetic energy imaging by using the SP tip with alternating magnetic force microscopy (A-MFM) method for detecting the AC magnetic fields energy from the recording head. ...
... 10,20 To overcome these limitations, the superparamagnetic (SP) tip is a good candidate although the small magnetic moment gives low sensitivity. 10,20 Previously, we proposed magnetic energy imaging by using the SP tip with alternating magnetic force microscopy (A-MFM) method for detecting the AC magnetic fields energy from the recording head. 10 The proposed SP tip showed high resolution and found independent of the a) ...
In this report, the magnetic energy flow of AC magnetic field is imaged from a perpendicular magnetic recording head by alternating magnetic force microscopy (A-MFM) with high magnetic moment Co0.43(GdOx)0.57 superparamagnetic (SP) tip. The present magnetic energy flow imaging phenomenon is able to detect the flow direction of AC magnetic field energy from the recording head. A simple model for the flow direction of the AC magnetic energy is given and revealed that when the AC magnetic field energy from the surface of main pole increases, the energy from the side cross section decreases due to the periodical change of magnetization direction at the main pole area. The A-MFM magnetic energy imaging performance by 100 nm Co0.43(GdOx)0.57 SP tip is compared with the magnetic field imaging with the 25 nm Co0.80Zr0.05Nb0.15 soft magnetic (SM) tip. The spatial resolution measured by Fourier analysis for Co0.43(GdOx)0.57 SP tip is enhanced dramatically to ∼10 nm with low thermal noise, as compared to ∼13 nm by Co0.80Zr0.05Nb0.15 SM tip as well as the previously reported MFM tip. Moreover, the sensitivity and resolution are investigated for a range of head current to confirm the suitability of the magnetic energy flow imaging by Co0.43(GdOx)0.57 SP tip to low as well as high magnetic field source. Further, the A-MFM measurements are performed with the 100 nm Au coated conducting tip to investigate the possibility of electrostatic contribution in magnetic energy imaging by Co0.43(GdOx)0.57 SP tip and revealed that the present A-MFM measurement is free from any electrostatic artifacts. The present magnetic energy flow imaging phenomena with the high magnetic moment Co0.43(GdOx)0.57 SP tip provides an avenue for the analysis of the magnetic field energy component from the head field profile.
... In terms of security, Flash and EEPROMs can be read out with special laborious chip reverse-engineering procedures at small scale [4]. The magnetic polarity of spin-based memory elements such as MTJs can be read with Magnetic Force Microscopy (MFM) with sub-micron resolution on a small scale [7]. RRAM cells are particularly difficult to read under scanning electron microscopy [26]. ...
Logic locking is an attractive defense against a series of hardware security threats. However, oracle guided attacks based on advanced Boolean reasoning engines such as SAT, ATPG and model-checking have made it difficult to securely lock chips with low overhead. While the majority of existing locking schemes focus on gate-level locking, in this paper we present a layout-inclusive interconnect locking scheme based on cross-bars of metal-to-metal programmable-via devices. We demonstrate how this enables configuring a large obfuscation key with a small number of physical key wires contributing to zero to little substrate area overhead. Dense interconnect locking based on these circuit level primitives shows orders of magnitude better SAT attack resiliency compared to an XOR/XNOR gate-insertion locking with the same key length which has a much higher overhead.
... In general, when using a uniform magnetic coating, its thickness is linked to the sharpness of the probe's apex, as well as the stray field and coercivity of the probe. This does not allow for much freedom in the variation/optimization of the probe 19 . Thereby, the most common scenario is to use a probe matching sample -probe properties in each particular case. ...
Domain wall probes (DW-probes) were custom-made by modifying standard commercial magnetic force microscopy (MFM) probes using focused ion beam lithography. Excess of magnetic coating from the probes was milled out, leaving a V-shaped nanostructure on one face of the probe apex. Owing to the nanostructure's shape anisotropy, such probe has four possible magnetic states depending on the direction of the magnetization along each arm of the V-shape. Two states of opposite polarity are characterised by the presence of a geometrically constrained DW, pinned at the corner of the V-shape nanostructure. In the other two states, the magnetization curls around the corner with opposite chirality. Electron holography studies, supported by numerical simulations, demonstrate that a strong stray field emanates from the pinned DW, whilst a much weaker stray field is generated by the curling configurations. Using in situ MFM, we show that the magnetization states of the DW-probe can be easily controlled by applying an external magnetic field, thereby demonstrating that this type of probe can be used as a switchable tool with a low or high stray field intensity. We demonstrate that DW-probes enable acquiring magnetic images with a negligible interference with the sample magnetization, similar to that of commercial low moment probes, but with a higher magnetic contrast. In addition, the DW-probe in the curl state provides complementary information about the in-plane component of the sample's magnetization, which is not achievable by standard methods and provides additional information about the stray fields, e.g. as when imaging DWs.
... Intermediate moment tips were coated in a homemade built RF sputtering chamber. 49 For sputtering coated tips, Co was deposited on tips under 10 −2 mbar argon pressure, with a bias voltage of 295 V and 50 W of power. ...
Magnetic skyrmions are nanometric spin textures of outstanding potential for spintronic applications due to unique features governed by their non-trivial topology. It is well known that skyrmions of definite chirality are stabilized by the Dzyaloshinskii-Moriya exchange interaction (DMI) in bulk non-centrosimmetric materials or ultrathin films with strong spin-orbit coupling in the interface. In this work, we report on the detection of magnetic hedgehog-skyrmions at room temperature in confined systems with neither DMI nor perpendicular magnetic anisotropy. We show that soft magnetic (permalloy) nanodots are able to host non- chiral hedgehog skyrmions that can be further stabilized by the magnetic field arising from the Magnetic Force Microscopy probe. Analytical calculations and micromagnetic simulations confirmed the existence of metastable N\'eel skyrmions in permalloy nanodots even without external stimuli in a certain size range. Our work implies the existence of a new degree of freedom to create and manipulate skyrmions in soft nanodots. The stabilization of skyrmions in soft magnetic materials opens a possibility to study the skymion magnetization dynamics otherwise limited due to the large damping constant coming from the high spin-orbit coupling in materials with high magnetic anisotropy.
