MFM imaging of a Skyrmion lattice
In collaboration with Jan Seidel from UNSW Sydney, A. Bauer & C. Pfleiderer, TU Munich we have successfully imaged the elusive Skyrmions and their magnetic field evolution in the attoDRY1000 cryostats using the attoAFM/MFM I. See what’s possible nowadays with our sophisticated commercial instruments!
Imaging Fractional Incompressible Stripes in Quantum Hall Systems
In newer measurements, the group performed SGM measurements at the temperature and magnetic field conditions required to observe the fractional quantum Hall effect. The goal is to image for the first time the presence of fractional incompressible stripes, i.e. the existence of an inner structure within the integer edge channel. The measurements were performed at bulk filling factor n = 1 (B = 8.23 T, T = 300 mK). The corresponding SGM map in the region close to the QPC center is depicted in the lower Figure (a). Analogously to the n = 4 case, one expects to find plateaus when the local electron phase is gapped, i.e. when the local filling factor n* equals a robust fraction. The scan profile depicted in the right figure reveals a clear shoulder for Gsd = e2
(Data and images were generously provided by N. Paradiso, S. Heun et al., NEST, CNR-INFM and Scuola Normale Superiore, Pisa, Italy.)
This measurement was realized with the attoLIQUID3000.
N. Paradiso, et al., Phys. Rev. Lett. 108, 246801 (2012)
attoAFM III Mounted on Mixing Chamber
This AFM-topography test-measurement of an 20 nm high calibration grating was performed in a pulse-tube based dilution fridge from Leiden Cryogenics. Even though the sample was scanned with 3 µm/s, the temperature did not rise above 80 mK, while the base temperature of the (here not optimized) braid cooled sample was at around 62 mK. Geophone measurements verified the low vibrations of the platform and showed that it is a suitable approach for high resolution, ultra-low temperature AFM-type experiments.
(attocube applications in collaboration with Leiden Cryogenics, 2011)
Helimagnetic Phase of FeCo0.5Si0.5
Real space imaging of exotic magnetic phases provides a level of understanding that cannot be achieved with indirect techniques. The figure on the left shows one of the first observations of a helimagnetic phase using the attoMFM I. The periodicity of the stripes is around 100 nm. This phase is of particular interest because of its proximity to a skyrmion phase. Skyrmions are exotic magnetic excitations, studied extensively because of their potential use in spintronic applications. The measurement was performed on a FeCo0.5Si0.5 sample at cryogenic temperature (4K) using an attoMFM I inside a liquid helium cryostat (attoLIQUID).
(attocube application labs, 2013; sample courtesy of A. Bauer and C. Pfleiderer, Technical University of Munich, Garching, Germany)
High Resolution MFM on Bit Patterned Media Co-Pd at 10K
MFM measurement on Co-Pd dots with 50 nm diameter at 10 K using the attoMFM I. The image demonstrates the high magnetic resolution achievable with the attoMFM at cryogenics. Variations in magnetic field perpendicular to the surface allows switching domains from one magnetic state to the other (here recorded at 6250 Oe). For this measurement, the attoMFM was operated at constant height with the frequency shift measured using a phase-locked loop.
(attocube application labs, 2010; sample courtesy of Hitachi Global Storage Solutions, San Jose, USA)
Conductive-Tip AFM Measurements on Ruthenium
In this application, atomic steps on Ruthenium were investigated using conductive-tip AFM. Atomic steps as well as spiral dislocations can be identified on the molecular beam epitaxy-grown sample. The contrast in this measurement is highly enhanced due to a difference in conductance between edges and flat plateaus. Such high contrast was not observed in the accompanying topographic image. A voltage of +10 mV was applied to the standard Pt-coated AFM tip, while the sample was grounded via a current amplifier with gain 106 V/A. The measurement was performed at room temperature in a 20 mbar He atmosphere.
(Sample and measurement courtesy of V. Da Costa, J.-F. Dayen, B. Doudin, IPCMS-DMONS,CNRS/University of Strasbourg, France)
Switching the Magnetic Vortex Core in a Single Nanoparticle
Manipulating magnetic nanostructures is not only scientifically interesting but also offers great potential in nonvolatile data storage devices and spintronic applications.
Elena Pinilla-Cienfuegos and co-workers used a low temperature variable field attoAFM/MFM I to observe and manipulate the magnetic vortex states in 25nm diameter molecular-based magnetic nanoparticles. They found that the vortex core can be switched by the application of a very small magnetic field.
E. Pinilla-Cienfuegos, et al., ACS Nano 10 (2), 1764–1770 (2016)
Link between bulk electric and microscopic magnetic properties of LaPryCaMnO
A research team around Prof. Jian Shen from the low-dimensional material physics group at Fudan University (China) has studied extensively thin films of manganites (LaPrCaMnO on SrTiO). This family of materials has very unique electronic and magnetic properties, which can be tailored for all sorts of spintronic and electronic applications.
Their findings have been published in a series of 5 papers, in which they have been using an attoAFM/MFM Ixs in an attoDRY1000 & PPMS to characterize the microscopic origins of a magnetic and electronic phase separation at low temperatures and in high magnetic fields controlled by nanopatterning as well as shedding light on the connection between bulk electric and microscopic magnetic properties of such films.
attoAFM III in Toploading Insert
The depicted data was taken with a tuning fork attoAFM III specifically designed for mK operation. The extremely sensitive microscope was mounted on a toploading insert (see images and project description on the left page), which ensures a much higher usability in terms of turnaround times upon tip and sample exchange than if it were mounted directly on the mixing chamber. The sample temperature in the toploading DR was 55 mK during the scan at 100 nm/s. The images nicely demonstrates that the delicate microscope works reasonably well even under these extreme conditions.
MFM on Co Doped Mn2Sb Single Crystal
Magnetic domain structure in the ferrimagnetic state of Co doped Mn2Sb single crystal imaged using an attoAFM Ixs Magnetic Force Microscopy (here at 290 K). The image was taken in constant distance mode with the height above the sample surface set to 50 nm. The area shown in the figure corresponds to 15 µm x 15 µm with a size of 800 x 800 pixel.
(Image courtesy of Rajeev Rawat, UGC-DAE Consortium for Scientific Research, Indore, India)
attoAFM I Mounted on Mixing Chamber
This scan above nicely demonstrates the stability of a complete system, an attoAFM I together with a LD400 cryo-cooler from BluFors Cryogenics. For this 25 x 25 µm2 (800 x 800 pixel) scan, the pulse-tube cooler was enabled the whole time. The temperature was stable at ≈40 mK measured at the mixing chamber - it was slightly higher due to the higher scan speed of close to 1 µm/s.
(attocube applications in collaboration with BluFors Cryogenics, 2014)
Angle Dependent Magnetoresistance Measurement at Cryogenics
Due to the arbitrary orientation inherent to self-assembled materials on the substrate, typical characterization techniques such as magnetoresistance measurements conducted at cryogenic temperatures greatly benefit from the possibility to freely change the mutual orientation of external magnetic field and sample. Although this is easily possible e.g. by using a 3D vector magnet setup, the associated costs (>> 100 k$) are often prohibitive. Single axis sample rotator setups on the other hand not only require choosing either an out-of-plane or in-plane configuration prior to cooldown, but also put firm restrictions on certain measurements which rely on a precise orientation of the field e.g. perpendicular or parallel to an initially unknown direction along a sample structure. The perfect solution to such applications is attocube’s 3-dimensional rotator atto3DR.
Similar to a recent publication by C. H. Butschkow and co-workers from the group of Prof. Dieter Weiss (Univ. of Regensburg), magnetotransport measurements on individual GaAs/(Ga,Mn)As core-shell nanowires (top figure) have been conducted.
The center figure shows magnetoresistance at 5 T as a function of the angle between externally applied magnetic field and the nanowire axis for different rotation planes: (orange) in-plane rotation, referring to the SiO2 substrate plane, (green) out of plane (perpendicular) rotation with the long nanowire axis (typically 4 µm long and 100 nm in diameter) entirely in the rotation plane, and (blue) out of plane (transversal) rotation with the rotation plane transversal to the nanowire axis.
The bottom figure shows the normalized magnetoresistance as a function of the angle between externally applied magnetic field and the nanowire axis for various magnitudes of the external magnetic field.
(measured by C. Butschkow in collaboration with attocube application labs 2012; sample courtesy of C. Butschkow, University of Regensburg).
This measurement was realized with the atto3DR.
C. Butschkow et al., Phys. Rev. B 87, 245303 (2013)
Vortex Imaging on Iron Pnictides using the attoMFM Ixs
In their latest publication, H. Yang and co-workers from the group of Prof. Hai-Hu Wen, from Nanjing University, present results on vortex studies on Ba1-xKxFe2As2 - a potassium-doped superconductor of the pnictide family. Since their discovery in 2008, the iron-pnictides have drawn intensive attention, not only because they have broken the monopoly of the cuprates but also because of strong pinning effects observed in certain pnictide-compounds. A vortex consists of a circular supercurrent, which allows for exactly one flux quantum each to penetrate the superconductor.
Visualization of Edge State in LPCMO Manganite Strip
Edge states that are induced by broken symmetry effects in two-dimensional electronic systems are in the focus of research. However, the question about the existence of edge states in strong correlated oxides was not fully answered until the group of Prof J. Shen (State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China) demonstrated edge states in exactly these type of materials.
They used La0.325Pr0.3Ca0.275MnO3 (LPCMO) manganite strips and characterised these with an attoAFM Ixs with the upgrade for magnetic force measurements in a PPMS system at low temperatures. Experimental results including MFM images help to understand the edge states which are associated with the broken symmetry effect in manganites. The Figure shows MFM images under 9T and at temperatures of 10 K and 120 K. The scanned areas are 20?µm × 20?µm in the figures of the first row and 15?µm × 15?µm below.
Their findings prove the existence of novel edge state in strongly correlated oxides beyond the current two-dimensional electronic systems and opens a new understanding of broken symmetry effects in complex oxides.
(Image courtesy of K. Du, K. Zhang, and J.Shen, Fudan University, Shanghai, China)
Scanning probe microscopy in an ultra-low vibration closed-cycle cryostat
The attoDRY1000 is a cryogen-free cooling system setting new performance benchmarks. The attoDRY1000 was specifically designed to provide an ultra-low vibration measurement platform for cryogenic scanning probe experiments without the need for liquid helium.
The standard closed-cycle system enables vibration-sensitive experiments in a temperature range from 4 K to 300 K. The optionally available microscope inserts are cooled by a controlled exchange gas atmosphere. Superconducting magnets up to 9 T are available as an option. Due to a proprietary design, mechanical vibrations created by the pulse-tube coldhead are decoupled from the measurement platform.
When measured with the attoAFM I, vibration amplitudes of less than 0.15 nm RMS are routinely achieved (bandwidth of 200 Hz, vertical direction). Despite the mechanical decoupling between coldhead and sample platform, the cooling performance ot the attoDRY1000 is simply outstanding. Temperatures as low as 3 K and probe cooldown times as fast as 1 hour make cryogenic scanning probe experiments a delight.
For the attoDRY1000, a wide variety of scanning probe microscopy inserts is available, ranging from confocal (CFM) to magnetic force microscopy (MFM).
F.P. Quacquarelli et al., arXiv:1404.2046v1
Magnetic Resonance Imaging of Nanoscale Virus at 300 mK
attocube’s ANPx51 positioners were used in an MRFM setup with the task to precisely and reliably position a magnetic tip and a copper nanowire to close proximity of an ultra-sensitive cantilever. The MRFM setup was applied to investigate and reconstruct the 1H spin distribution of Tobacco Mosaic Virus particles, representing a 100-million fold improvement in volume resolution over conventional MRI.
This measurement was realized with the ANPx51/LT - linear x-nanopositioner.
Scanning Microwave Impedance Microscopy at 4 K and 9 T
A set of linear positioners and scanners made for cryogenic application was implemented into a microwave impedance microscope located inside a liquid Helium flow cryostat equipped with a 9 T superconducting magnet. The 1 GHz microwave signal was guided to the cantilever probe, which detected the dielectric constant and conductivity contrast of the sample during scanning. The system is a versatile tool for fundamental research on complex materials and phase transitions under various conditions.
Transition from slow Abrikosov to fast moving Josephson vortices
attocube proudly presents his cutting edge application using the ANR31 rotator: They observed the formation of fast moving Josephson vortices, which depends critically on the angular alignment. Using the ANR31, they were able to rotate the sample below 2 K with better than 0.1° precision and could observe no drifts while sweeping temperature and magnetic field.
This measurement was realized with the ANR31/LT rotator made from Titanium and CuBe.
Stress-strain behavior of fibrous biological material measured using an AFM/SEM hybrid
In this application, attocube‘s cantilever-based attoAFM I was used inside a FEI Quanta 3D Scanning Electron Microscope (SEM) to perform nanometer-scale tensile measurements of individual collagen fibrils. The fibrils were extracted from the fractured surface of antler and were attached to the cantilever using a high vacuum compatible glue. After the collagen fibril was attached and the glue had hardened, the cantilever was slowly retracted while the force imposed on the collagen fibril was recorded. The measurement was achieved by interferometrically tracking the deflection of the cantilever. With a typical cantilever spring constant of only 0.2 N/m, a force resolution better than 100 pN was readily achieved in a 1 kHz measurement bandwidth. The actual stress-strain measurement of a single collagen fibril indicates an ultimate strength of 0.18 GPa, which is nearly half as strong as structural steel (0.4 GPa).
(Images courtesy of A. Barber, Queen Mary University of London, UK)
F. Hang et al., Nanotechnology 22, 365708 (2011)
Piezo-Response Force Measurements on Ferroic Oxide Films
In the measurements presented here PFM data have been taken on a layered heterostructure (150 nm BiFeO3-Mn on top of 35 nm of SrRuO3 on a SrTiO3 (001) substrate) recorded at 82 K with a standard attoAFM I. Two squares have been written, a 1 x 1 µm2 and a smaller, rotated one with ±15 V tip voltage. It can be noted that the amplitude goes to zero in the domain walls and that the outside area shows natural domains.
(Images and data courtesy of K. Bouzehouane and S. Fusil, Unité Mixte de Physique CNRS/Thales, Paris, France)
This measurement was realized with the attoLIQUID1000.
Low Temperature MFM on Artifical Spin Ice
Frustrated systems are intriguing for physicists since they possess highly degenerate ground states with non-zero entropy at 0 K, which can give rise to interesting new phenomena. A prominent example which has been widely studied in condensed matter physics is artificial spin ice. Using Magnetic Force Microscopy (MFM), the group of W. Branford (Imperial College, UK) have studied the magnetic reversal of a nanostructured permalloy honeycomb lattice, demonstrating the breakdown of the artifical spin ice regime at cryogenic temperatures and in high magnetic fields.
(Data courtesy of W.R. Branford, Imperial College, UK)
K. Zeissler et al., Scientific Reports 6, 30218 (2016)
Vortex Barriers in Iron Pnictides
Iron-pnictide high-temperature superconductors are widely studied, but many open questions still remain. Using an attoAFM I for magnetic force microscopy, the group of O. Auslaender has studied twin boundaries and their interaction with vortices over a range of magnetic fields and temperatures. They find that stripes parallel to the twin boundaries repel vortices, effectively hindering vortex motion, and hence potentially affecting the critical current in such materials.
(Data courtesy of O. Auslaender, Technion, Israel)
A. Yagil et al., Phys. Rev. B 94, 064510 (2016)
MFM for Optimization of Sintered Magnets
MFM image of a NdFeB sintered magnet with the nominal c-axis orientation perpendicular to the surface. The sample is in the remanent state but some surface grains show already magnetization reversal. High resolution imaging allows deeper insights into the magnetic reversal mechanism and the optimization of magnetic properties. Image size is 30x30µm2.
(Image courtesy of T. Helbig and O. Gutfleisch, Functional Materials Group, TU Darmstadt, Germany and Fraunhofer IWKS Hanau, Germany.)
Angle-dependent characterizations of materials
Attocube's rotators offer a way to use the full magnetic field of a 1D magnet for field-angle dependent transport measurements at the sample. This benefit is used by the group of Anne de Visser at the Van der Waals - Zeeman Institute (University of Amsterdam, NL) in two setups with an ANR51 and an ANRv220 both in a closed loop configuration.
Magnetotransport measurements as a function of the angle θ in the trigonal basal plane of the topological superconductor SrxBi2Se3 revealed a large two-fold anisotropy of the upper critical field Bc2. Such a rotational symmetry breaking of Bc2(θ) cannot be explained with standard models, and indicates unconventional superconductivity with an exotic order parameter. More about this work can be found at .
In the second setup a home-built compact dilatometer was mounted on the ANRv220 in a dilution refrigerator. This was used to measure the anisotropy in the ferromagnetic and superconducting phase diagram of a single crystal of UCoGe by applying magnetic fields up to 14 T along the different crystallographic axes .
Quantized Conduction on Domain Walls of a Magnetic Topological Insulator
In a paper published in Science, researchers from the University of Tokyo and RIKEN (Japan) have studied “Quantized conduction on domain walls of a magnetic topological insulator” using an attoAFM/MFM in a 3He-cryostat down to 500 mK. In their paper, Yasuda et al. designed and fabricated magnetic domains in the quantum anomalous Hall state, and proved the existence of the chiral one-dimensional edge conduction along the domain walls through transport measurements.
This discovery would permit fully electrical control of the mobile domain walls and chiral edge states, which may lead to the realization of low-power-consumption spintronic, memory and quantum information processing devices in the future.
Yasuda et al., Science 358, 1311–1314 (2017)
Measurements of field-driven transformation of a domain pattern
The group of Erik Folven at the Norwegian University of Science and Technology (Trondheim, Norway) used an attoAFM I for MFM measurements with a closed cycle attoDRY1000 to demonstrate how topological defects may be invoked to understand magnetic domain state transitions. The atomically sharp and magnetized tip of the microscope is scanned across the thin film surface to pick up the out-of plane stray fields from the sample and thus is sensitive primarily to spin textures such as domain walls and defects. The MFM measurements taken at 5K help to understand and describe micromagnetic domain state transitions and to assess their stability in remanence. This insight may open for new approaches to control the switching properties of micro- and nanomagnets.
S. D. Sloetjes, et al., Appl. Phys. Lett. 112, 042401 (2018)
Terahertz near-field microscopy below 30nm spatial resolution
neaspec GmbH and Fraunhofer IPM have developed a ready-to-use terahertz system that is capable of achieving a spatial resolution of 30 nanometers in combination with neaspec’s near-field microscope – neaSNOM
nano-FTIR beats the diffraction limit in infrared bio-spectroscopy and probes secondary structure in individual protein complexes
nano-FTIR beats the diffraction limit in infrared bio-spectroscopy and probes secondary structure in individual protein complexes
Characterization of optical surface waves
Infrared near-field microscopy allows to study the propagation of surface waves in the infrared spectral regime. Amplitude and phase resolved near-field images reveal local interference effects or enable the determination of the complex wave vector of surface waves. Surface waves can be excited in the mid-infrared spectral regime by e.g. metal structures on Silicon Carbide…
Nanoscale phase transitions
The high spatial resolution of infrared near-field microscopy allows for detailed studies of phase transitions in materials like the insulator-to-metal transition of vanadium dioxide (VO2) thin films.
Rotating transport measurement setup at 25mK
When designing a setup for mK applications material choice and thermalization is crucial. Titanium becomes superconducting at temperatures below 400 mK consequently, the thermal contact to the sample is not ensure anymore. At Peking University (Beijing, China), Dr. Pengjie Wang from Xi Lin group has chosen the beryllium-copper version of the ANR101 positioner with resistive readout to realize their low-electron-temperature sample rotation system for transport measurements inside a dilution cryostat. The rotator allows to orient the sample in-situ with respect to a high magnetic field of up to 10 T.
The dilution cryostat with a diameter of 81 mm offers the required space for the rotator setup, see picture. The sample holder is designed for the use of up to four sample, each 5 mm x 5 mm large, a red LED is installed to illuminate the samples at 4 K for an easier orientation. The measured electron temperature in the setup is 25 mK, the same as the environmental temperature.The setup is designed for transport measurements and material characterization at ultra-low electron temperatures. A first application shows the tilt-induced localization and delocalization of the second landing level of the two-dimensional electron gas - an experiment for which a pressurized liquid ³He cell had been necessary elsewise.
(Figure reproduced from Rev. Sci. Instrum. 90, 023905 (2019); doi: 10.1063/1.5083994, with the permission of AIP Publishing)
This measurement was realized with the ANR101/RES/LT - rotator (360° endless).
A nanoscale quantum sensor at high pressures
Pressure affects phenomena ranging from the properties of planetary interiors to transitions between quantum mechanical phases. However, the enormous stress gradients generated in high pressure experimental apparatuses, such as the diamond anvil cell, limit the utility of most conventional spectroscopy techniques. To address this challenge, a novel nanoscale sensing platform was independently developed by three groups (given in alphabetic order): the Jean-Francois Roch group (Université Paris-Sud, FR), the Sen Yang group (Chinese University of Hong Kong, CN), and the Norman Yao group (University of California, Berkeley, USA). The researchers used quantum spin defects integrated into an anvil cell to detect minuscule signals under extreme pressures and temperatures with diffraction-limited spatial resolution.
For this purpose, Norman Yao and colleagues utilized the table-integrated closed cycle attoDRY800 cryostat - the ideal platform for precise and rapid temperature control of a diamond anvil cell while offering a large sample chamber and free-beam optical access. The convenience of the closed-cycle cryostat allowed the researchers to publish their results to arXiv just nine months after installation.
This measurement was realized with the attoDRY800.
S. Hsieh et al., Imaging stress and magnetism at high pressures using a nanoscale quantum sensor, arXiv:1812.08796 (2018)
M. Lesik, et al., Magnetic measurements on micron-size samples under high pressure using designed NV centers, arXiv:1812.09894 (2018)
K. Yau Yip et al., Quantum sensing of local magnetic field texture in strongly correlated electron systems under extreme conditions, arXiv:1812.10116 (2018)
Fine-scale Stripey Morphology of an Iron Pnictide - New Findings in Material Science
Iron-based superconducting pnictides feature relatively high transition temperature and a co-existence of the superconducting state with antiferromagnetic ordering. This remarkable combination brings these materials into the focus of research. The group of Prof. Susannah Speller at the Materials Department of the University of Oxford (Oxford, UK) used an attoAFM I cooled by a closed cycle attoDRY1000 for magnetic force measurements at about 4.6 K to investigate the local electronic structure and chemistry of RbxFe2-ySe2 crystals.
The group showed a fine-scale stripey morphology of the superconducting phase which - combined with previous findings - paves the way to understand the intriguing electronic and magnetic properties of these compounds.
P Dudin et al.; Supercond. Sci. Technol. 32, 044005 (2019)
Uncompensated Bound Charges at Improper Ferroelectric Domain Walls
The research focus of an international team led by researchers from NTNU Trondheim, ETH Zurich, and Institut Néel, CNRS, lies on domain walls in improper ferroelectrics, a promising type of functional interface for nanoscale electronics. The team demonstrated the stability of improper ferroelectric domain walls in hexagonal manganites against electrically uncompensated bound charges.
Using the attoAFM I, the authors investigated the electronic domain-wall transport, carrier distribution, and electrostatics at temperatures down to 4.2 K. attocube's atomic force microscope, the attoAFM I, enables atomic force microscopy at cryogenic temperatures, down to mK. The findings provide new insight into the fundamental domain-wall properties, bringing us yet another step closer towards next-generation's durable and ultra-small electronic components.
Peggy Schoenherr, et al.; Nano Lett.19, 3, 1659-1664 (2019)
Single Spin Magnetometry at the Nansocale
Since the discovery of ferromagnetism in 2D van der Waals crystals, the community aims to study the feature quantitatively at the nanoscale. This feat was now approached by the group of Patrick Maletinsky at the University of Basel (Basel, CH).
Using their single-spin magnetometer based on electronic spins in diamond with the attoAFM/CFM, they detected the magnetization distribution of atomically thin crystals of CrI3. attocube's attoAFM/CFM offers the possibility to combine atomic force with confocal microscopy for optically detected magnetic resonance. With their technique they found the magnetization of one monolayer to be ≈ 16 µB/nm2 and addressed an open question regarding the thickness-dependence of magnetisation in CrI3.
Next to the outstanding physical result it is the technique that will add new ways of detecting and manipulating of magnetic properties at the nanoscale. According to P. Maletinsky the "single-spin magnetometry" is a "close-to ideal tool to study the physics of atomically thin 2D magnets."
This measurement was realized with the attoAFM/CFM.