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Magnetic resonance force microscopy (MRFM) images the three-dimensional spatial distribution of resonant spins by mechanical force detection. Image reconstruction in MRFM is challenging because the resonance occurs in a strongly curved shell that extends beyond the scan range. In contrast with conventional magnetic resonance imaging, where Fourier techniques work well, the curved-shell resonant geometry inherent to MRFM requires novel reconstruction methods. Here, we show the application of iterative reconstruction in an electron spin resonance imaging experiment with 80 nm voxels. The reconstructed image has a total scan volume of 0.5 cubic micrometers, and was generated by a magnetic resonant shell with a curvature radius of 2.3 μm. The imaged object was a paramagnetically doped solid with an obliquely tilted surface. The reconstructed image correctly identified the location and orientation of the surface, and mapped the spin distribution within the solid. Applications of MRFM include three-dimensional nanometer-scale mapping of dopant distributions in semiconductors, studies of magnetism of thin films, and spin diffusion physics. An ultimate goal of MRFM is the direct observation of molecular structure at the atomic scale.

The continuous wave ferromagnetic resonance (FMR) spectrometer operating in multioctave (0.05–40 GHz) frequency range has been built to investigate the magnetic properties of thin ferromagnetic films in the temperature range of 4–420 K. The spectrometer has two probeheads: one is the X-band microwave reflection cavity used to perform express room temperature measurements and the other is an in-cryostat microstrip line probe to carry out FMR experiments covering the entire frequency range offered by the microwave source. Very uniform and stable magnetic field up to 2.4 T, temperature 4 K–420 K, and continuous frequency scan performed by an HP8722D vector network analyzer provide various modes of operation. Both probe heads are equipped with two-circle high precision goniometers to ensure accurate characterization of magnetic anisotropy and magnetostatic waves spectra recording. Use of the phase sensitive detection, utilized by magnetic field modulation at audio frequency and computer triggering of the netw...

We have fabricated a superconducting resonator capable of generating a strong microwave magnetic field in a small (100 μm) volume for low temperature magnetic resonance experiments. While the resonator was specifically developed for use at millikelvin temperatures in a dilution refrigerator, where the total cooling power is limited to a few hundred microwatts, it is also useful at temperatures up to 5 K. The resonator consists of a 220 μm diameter, 2-1/2 turn niobium coil resonating with a short section of niobium microstripline. At a resonance frequency of 3 GHz, the loaded Q of the resonator was 780. The field strength was characterized by performing electron spin nutations. Operating at 100 mK with 320 μW of dissipated power, the resonator generated a field of 4 G at a distance of 100 μm from the coil.

We report on experimental advances in scanning electron microscopy with polarization analysis that allow the observation of ferromagnetic domains in external magnetic fields of about 0.1 T. This is achieved by using a modified electron optics that produces a magnetic field at the sample surface that is spatially confined on the length scale of 0.1 mm. During imaging, primary and secondary electrons pass through the magnetic field without significant disturbance. We demonstrate that the primary electron beam may be used to keep track of the generated magnetic field. As an exemplary application, the switching processes of rectangular Permalloy elements are analyzed.

We present the design of a scanning force microscope, which is optimized for magnetic force microscopy experiments. It can be operated at temperatures down to 5.2 K, in ultrahigh vacuum, and in magnetic fields of up to 5 T. Cooling is provided by a liquid helium bath cryostat, and the magnetic field is generated by a superconducting split-coil magnet. The design allows easy access from the side through a shutter system for fast in situ tip and sample exchange, while the microscope stays at temperatures below 25 K. The microscope itself features an all-fiber interferometric detection system, a 7.5×7.5 μm2 scan area at 5.2 K, and an xy table. The topographic resolution is demonstrated by imaging monoatomic steps on a nickel oxide surface, while magnetic contrast is shown on cobalt platinum multilayers and on a manganite perovskite film.

In this article, we present the first fully integrated nuclear magnetic resonance probe ever realized. Planar spiral coils, a radio-frequency preamplifier, a mixer, and an audio-frequency amplifier are integrated using a standard complementary metal–oxide–semiconductor technology on a single silicon chip of 10 mm2. A 1 mm3 solid sample of cis-polyisoprene, placed over one of the integrated coils, is used as resonating material. The realized integrated probe allows measurements of static magnetic fields from 0.7 to 7 T with a magnetic-field resolution better than 1 ppm/Hz1/2, an absolute accuracy better than 3 ppm, and a spatial resolution of about 1 mm.

In atomic force microscopy cantilevers are used to detect forces caused by interactions between probing tip and sample. The minimum forces which can be detected with commercial sensors are typically in the range of 10−12 N. In the future, the aim will be to construct sensors with improved sensitivities to detect forces in the range of 10−18 N. These sensors could be used for mass spectroscopy or magnetic resonance force microscopy. Achieving this goal requires smaller sensors and increased quality factor Q. In this article we describe a model to characterize the dynamics of cantilevers of each eigenmode. In contrast to previous models, the damping is treated rigorously in the calculations.

We report on the design and performance of an atomic force microscope which operates at temperatures down to 20 mK and in magnetic fields up to 9 T. The scan range at low temperatures is 4 μm×4 μm. The instrument features a piezoelectric linear motor for vertical coarse approach, and a horizontal sample translation stage with a 2 mm×2 mm range. A fiber interferometer is used to detect the force-sensing cantilever displacement. The performance demonstrated includes the ability to detect single atomic steps on a graphite surface at 4.2 K and the ability to locate and image nanometer scale electronic devices at millikelvin temperatures.

Magnetic resonance experiments were conducted on optically pumped Cs to investigate the use of atomic magnetic resonance in Cs atoms for precision magnetometry. The resonance frequencies agreed within 4 ppm with the theoretically calculated ones. The different amplitudes of the separate signals were ascribed to differences in the population densities in the sublevels. The noise level for low-field measurements was 10 pT/Hz.

We present our new setup of longitudinal nuclear magnetic resonance detected by a superconducting quantum interference device. It was built specifically for the study of metallic single crystals at low frequency. We report the main difficulties encountered with such measurements, mainly thermal effects which are usually barely discussed in the literature although they put the true limit of such measurements. We also illustrate in detail the actual performances of our experiment on different test samples up to the first measurement of a metallic single crystal with such a technique.

A novel miniature superconducting quantum interference device magnetometer with direct readout electronics has been developed. A high flux-to-voltage transfer factor of up to 2500 μV/Φ0 is achieved without additional positive feedback (Φ0 is the flux quantum). A flux resolution of 8×10−7 Φ0/Hz1/2, corresponding to a magnetic moment sensitivity of approximately 2×10−20 A m2/Hz1/2, has been measured. This magnetometer can be used to study the dynamic magnetization properties (including nuclear magnetic resonance and magnetic resonance imaging) of micron and submicron size particles and for high-resolution surface magnetometry.

This article presents a new modulation technique for noise reduction in magnetic resonance force microscopy. Applied fields are modulated at frequencies that are not rational fractions of the cantilever resonant frequency, thus avoiding overtones that contribute to the noise level. An on‐resonance signal is obtained because the nonlinear sample magnetization acts as a frequency mixer of the two modulation frequencies, producing a net force modulation at the cantilever resonant frequency. These techniques are experimentally demonstrated using electron spin resonance in a

An advanced scanning magnetoresistive microscopy (SMRM) - a robust magnetic imaging and probing technique - will be presented, which utilizes state-of-the-art recording heads of a hard disk drive as sensors. The spatial resolution of modern tunneling magnetoresistive sensors is nowadays comparable to the more commonly used magnetic force microscopes. Important advantages of SMRM are the ability to detect pure magnetic signals directly proportional to the out-of-plane magnetic stray field, negligible sensor stray fields, and the ability to apply local bipolar magnetic field pulses up to 10 kOe with bandwidths from DC up to 1 GHz. Moreover, the SMRM can be further equipped with a heating stage and external magnetic field units. The performance of this method and corresponding best practices are demonstrated by presenting various examples, including a temperature dependent recording study on hard magnetic L1(0) FeCuPt thin films, imaging of magnetic vortex states in an in-plane magnetic field, and their controlled manipulation by applying local field pulses.

We have constructed a scanned stylus atomic force microscope (AFM) with direct force modulation and integrated microfluorescence optics. The instrument was designed to image the surface of massive samples under various ambient conditions. In force modulation microscopy the imaging force is modulated during the scanning process via an external magnetic field that acts directly on the magnetic AFM tip. Polymeric Langmuir–Blodgett films on silicon oxide were imaged to evaluate the application range of the instrument. We demonstrate that direct force modulation microscopy permits the quantitative recording of the local complex compliance both as a function of the location and as a function of the frequency. In a novel imaging mode referred to as sample resonance mode, the contrast of the image can be selectively enhanced based on local elasticity differences.

The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb25(Fe75Co25)75 layers system with thermomagnetically written bits of various sizes were obtained at the x-ray microscope XM-1 at the Advanced Light Source in Berkeley, CA. The results prove the thermal stability of the bits in the recording process. Furthermore the capability of soft x-ray microscopy with respect to the achievable lateral resolution, element specificity and sensitivity to thin magnetic layers is demonstrated. The potential of imaging in applied magnetic fields for both out-of-plane and in-plane magnetized thin magnetic films is outlined.

We describe a fiber-optic interferometer that employs wavelength changes to achieve maximum sensitivity. Wavelength changes are induced by adjusting the operating temperature of the laser, eliminating the need for an actuator to vary the spacing between the sensing fiber and the object to be monitored. The instrument and techniques described are suitable for cryogenic, high vacuum applications such as magnetic resonance force microscopy, where space is limited and micromanipulation can be challenging. The noise floor of 1.6×10−3 nm/Hz is adequate for monitoring subangstrom displacement of force microscope cantilevers.

Contact Resonance Force Microscopy (CR-FM) is a leading atomic force microscopy technique for measuring viscoelastic nano-mechanical properties. Conventional piezo-excited CR-FM measurements have been limited to imaging in air, since the "forest of peaks" frequency response associated with acoustic excitation methods effectively masks the true cantilever resonance. Using photothermal excitation results in clean contact, resonance spectra that closely match the ideal frequency response of the cantilever, allowing unambiguous and simple resonance frequency and quality factor measurements in air and liquids alike. This extends the capabilities of CR-FM to biologically relevant and other soft samples in liquid environments. We demonstrate CR-FM in air and water on both stiff silicon/titanium samples and softer polystyrene-polyethylene-polypropylene polymer samples with the quantitative moduli having very good agreement between expected and measured values.

We report a rf coil design based on the Alderman–Grant coil called the modified Alderman–Grant coil (MAGC), and demonstrate its efficacy in the magnetic resonance force microscope (MRFM). The rf field of the MAGC has a magnitude comparable to that of a solenoidal coil of similar size (for the same input power) but the coil has a much smaller inductance. This is advantageous in electron spin resonance MRFM experiments which would benefit from rf frequencies in excess of 1000 MHz. The open design of the MAGC is also advantageous because it provides superior access to the sample mounted on a mechanical cantilever by the optical fiber and permanent magnet and so allows the sample to be placed at the center of the coil.

Magnetic field maps can rapidly and accurately be acquired on the surface of a cylinder or sphere with an array of nuclear magnetic resonance (NMR) coils multiplexed to a single radiofrequency receiver. Using an array of NMR probes significantly decreases the time necessary to map B0 and improves field map accuracy because the probes do not move. The spatial variation of the Larmor frequency is used to determine the spherical harmonic components present in the field. A limitation of this approach is that NMR resonant circuits are inherently narrow band which limits the apparatus to a specific field strength and only points in space defined by the array layout. This apparatus can characterize the magnetic fields of high homogeneity dipole magnets, quadrupole magnets, gradient coils, and shims used in NMR imaging systems.

High-speed atomic force microscopy (HS-AFM) enables visualizing dynamic behaviors of biological molecules under physiological conditions at a temporal resolution of 1s or shorter. A small cantilever with a high resonance frequency is crucial in increasing the scan speed. However, detecting mechanical resonances of small cantilevers is technically challenging. In this study, we constructed an atomic force microscope using a digital versatile disc (DVD) pickup head to detect cantilever deflections. In addition, a flexure-guided scanner and a sinusoidal scan method were implemented. In this work, we imaged a grating sample in air by using a regular cantilever and a small cantilever with a resonance frequency of 5.5 MHz. Poor tracking was seen at the scan rate of 50 line/s when a cantilever for regular AFM imaging was used. Using a small cantilever at the scan rate of 100 line/s revealed no significant degradation in the topographic images. The results indicate that a smaller cantilever can achieve a higher scan rate and superior force sensitivity. This work shows the potential for using a DVD pickup head in future HS-AFM technology.

We describe the design of a wide temperature range (300 mK-300 K) atomic force microscope/magnetic force microscope with a self-aligned fibre-cantilever mechanism. An alignment chip with alignment groves and a special mechanical design are used to eliminate tedious and time consuming fibre-cantilever alignment procedure for the entire temperature range. A low noise, Michelson fibre interferometer was integrated into the system for measuring deflection of the cantilever. The spectral noise density of the system was measured to be similar to 12 fm/root Hz at 4.2 K at 3 mW incident optical power. Abrikosov vortices in BSCCO(2212) single crystal sample and a high density hard disk sample were imaged at 10 nm resolution to demonstrate the performance of the system. (C) 2014 AIP Publishing LLC.

Nuclear magnetic resonance (NMR) technique is a well-established powerful tool to study the physical and chemical properties of a wide range of materials. However, presently, NMR applications are essentially limited to materials in the condensed phase. Although magnetic resonance was originally demonstrated in gas phase molecular beam experiments, no application to gas phase molecular ions has yet been demonstrated. Here, we present a novel principle of NMR detection for gas phase ions based on a "magnetic resonance acceleration" technique and describe the design and construction of an apparatus which we are developing. We also present an experimental technique and some results on the formation and manipulation of cold ion packets in a strong magnetic field, which are the key innovations to detect NMR signal using the present method. We expect this novel method to lead new realm for the study of mass-selected gas-phase ions with interesting applications in both fundamental and applied sciences.

A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.

A standard X-band electron paramagnetic resonance cavity has been adapted to measurements under uniaxial stress parallel to the external magnetic field direction. The system is applied to study single crystals under stress up to 100 MPa in the temperature range 100–400 K.

We have developed the variable temperature scanning force microscope capable of performing both magnetic resonance force microscopy (MRFM) and magnetic force microscopy (MFM) measurements in the temperature range between 5 and 300 K. Modular design, large scanning area, and interferometric detection of the cantilever deflection make it a sensitive, easy to operate, and reliable instrument suitable for studies of the dynamic and static magnetization in various systems. We have verified the performance of the microscope by imaging vortices in a Nb thin film in the MFM mode of operation. MRFM spectra in a diphenyl-picryl-hydrazyl film were recorded to evaluate the MRFM mode of operation.

A novel technique of high-frequency electron spin resonance (ESR) in a pulsed magnetic field is presented. Our technique is based on the magnetic detection of a magnetization change associated with the ESR absorption using a microcantilever. We successfully observed ESR signals of a microcrystal (mass approximately 1 microg) in the millimeter-wave region up to 130 GHz in pulsed magnetic fields of up to 2.4 T. This result corresponds to the spin sensitivity of approximately 10(11) spins/G, which is four orders of magnitude better than that of conventional transmission-type ESR techniques.

Highly sensitive magnetic detection of electron spin resonance (ESR) using a microcantilever is presented. By combining a modulation technique with the use of a piezoresistive cantilever, we successfully observed ESR signals of a tiny single crystal (mass1 microg) of Co Tutton salt, Co(NH(4))(2)(SO(4))(2) x 6 H(2)O, in the frequency region of 80-240 GHz. The achieved spin sensitivity was approximately 10(9) spins/G at 4.5 K, providing promising applications to high-resolution and high-sensitivity terahertz ESR.

Force detected electron spin resonance (FDESR) detects the presence of unpaired electrons in a sample by measuring the change in force on a mechanical resonator as the magnetization of the sample is modulated under magnetic resonance conditions. The magnetization is coupled to the resonator via a magnetic field gradient. It has been used to both detect and image distributions of electron spins, and it offers both extremely high absolute sensitivity and high spatial imaging resolution. However, compared to conventional induction mode ESR the technique also has a comparatively poor concentration sensitivity and it introduces complications in interpreting and combining both spectroscopy and imaging. One method to improve both sensitivity and spectral resolution is to operate in high magnetic fields in order to increase the sample magnetization and g-factor resolution. In this article we present FDESR measurements on the organic conductor (fluoranthene)(2)PF(6) at 3.2 T, with a corresponding millimeter-wave frequency of 93.5 GHz, which we believe are the highest field results for FDESR reported in the literature to date. A magnet-on-cantilever approach was used, with a high-anisotropy microwave ferrite as the gradient source and employing cyclic saturation to modulate the magnetization at the cantilever fundamental frequency.

We describe the design and performance of a detection unit for magnetic resonance force microscopy (MRFM) based on commercially available piezoresistive cantilevers. The magnetic tip attached to the cantilever acts as a field gradient source. The adjustable microstrip-line radio-frequency (rf) circuit, which is placed above the cantilever, enables to use a wide range of frequencies between 2.3 and 4.3GHz, and to fully benefit from a frequency sweep of the rf magnetic field. The integration of the necessary field gradient source and broadband microstrip-line rf excitation circuit into the MRFM detector allows us to investigate samples of arbitrary size and shape. The integrated system can also be operated as a conventional magnetic force microscope (MFM) detection unit. Performance of our mechanical detector is demonstrated with ferromagnetic resonance and MFM data obtained on CoO∕Co exchange biased microstructures. Spatial variations of the MRFM signal, which are induced by a spatially modulated exchange ...

A pressure-resisting cell system has been developed for high-pressure high-resolution nuclear magnetic resonance (NMR) measurements up to a maximum pressure of 600 MPa. This cell system is capable of performing high-pressure experiments with any standard spectrometer, including modern high field NMR machines. A full description of the high-pressure NMR assembly mounted on a 750 MHz spectrometer is presented along with a detailed explanation of the procedure for preparing the pressure-resisting quartz and glass cells.

There is a great advantage in signal to noise ratio (S/N) that can be obtained in nuclear magnetic resonance (NMR) experiments on very small samples (having spatial dimensions ∼100 μm or less) if one employs NMR “micro” receiver coils, “microcoils,” which are of similarly small dimensions. The gains in S/N could enable magnetic resonance imaging (MRI) microscopy with spatial resolution of ∼1–2 μm, much better than currently available. Such MRI microscopy however requires very strong (>10 T/m), rapidly switchable triaxial magnetic field gradients. Here, we report the design and construction of such a triaxial gradient system, producing gradients substantially greater than 15 T/m in all three directions, x, y, and z (and as high as 50 T/m for the x direction). The gradients are switchable within time ∼10 μs and adequately uniform (within 5% over a volume of [600μm3] for microcoil MRI of small samples.

A combined electron spin resonance (ESR)/optically detected magnetic resonance (ODMR) spectrometer is described. The microwave portion of the spectrometer is of the homodyne type and uses amplitude modulation of the reflected signal from the sample cavity for frequency stabilization and resonance detection. For ODMR spectroscopy microwave power incident on the resonant cavity can be pulse (Δt ≳ 100 μsec) or square wave modulated by a second modulating waveform.

A single‐coil (solenoid), nuclear magnetic double resonance sample probe, suited for a wide variety of solid state studies, is described. It was designed to be used in double resonance experiments where it is necessary to generate intense rf magnetic fields (rotating components with amplitudes ∼50 G) at two widely spaced frequencies and simultaneously to detect microvolt‐level signals. Designs for operation over the 12–270 MHz frequency range are discussed.

We show that helices can be used as resonant systems. We describe resonant helices for electron paramagnetic resonance in X‐bands and develop a comparison between their sensitivity and the sensitivity of a normal resonant cavity. For cylindrical samples less than 3 mm diam, the helix is more sensitive and can produce more intense microwave magnetic fields.

A combined magnetic circular dichroism and electron paramagnetic resonance spectrometer is described. This two‐channel spectrometer enables the detection of an optical microwave double resonance, which gives a direct correlation of optical and paramagnetic resonance spectra.

A simple circuit for obtaining nuclear magnetic resonance absorption signals has been developed. Conventional modulation of the magnetic field is replaced by frequency modulation of the oscillator, a method which is technically convenient for the accurate measurement of magnetic fields in the range of 1000 to 18,000 gauss. The principles of operation and construction techniques are described in order that the user may readily duplicate results.

An NMR spectrometer system is described which incorporates the use of magnetic field modulation for the simultaneous purpose of baseline stabilization and stabilization of the resonance condition. Several other modulation techniques are briefly described.

The application of a new Fourier transform technique to magnetic resonance spectroscopy is explored. The method consists of applying a sequence of short rf pulses to the sample to be investigated and Fourier‐transforming the response of the system. The main advantages of this technique compared with the usual spectral sweep method are the much shorter time required to record a spectrum and the higher inherent sensitivity. It is shown theoretically and experimentally that it is possible to enhance the sensitivity of high resolution proton magnetic resonance spectroscopy in a restricted time up to a factor of ten or more. The time necessary to achieve the same sensitivity is a factor of 100 shorter than with conventional methods. The enhancement of the sensitivity is essentially given by the square root of the ratio of line width to total width of the spectrum. The method is of particular advantage for complicated high resolution spectra with much fine structure.

A homonuclear spin decoupler has been developed which, in conjunction with a Varian HR60 nuclear magnetic resonance spectrometer system, may be used for frequency sweep single or double resonance or for field sweep double resonance.

The distinctive features of the tuned spin‐echo spectrometer described here are high sensitivity, high resolution, simple operation, and a frequency variation throughout the range 170–1700 MHz. In addition to magnetic structure and hyperfine interaction studies this apparatus is capable of detecting very small concentration of impurities in ferromagnetic compounds.

An automatic compensation method is applied to ESR measurements, and the corresponding addition to a standard spectrometer permits the measurement of the resonant magnetic susceptibility independently of microwave power level, magnetic field modulation amplitude, amplifier gain, etc. A calibration of the instrument is described. Using this, one obtains an accuracy in the measurement of the susceptibility of approximately 0.1%.