Magnetic resonance diffraction using the magnetic field from a ferromagnetic sphere

The theory of magnetic resonance diffraction is developed for the case of a crystal in close proximity of a ferromagnetic sphere. Distinct spectral peaks in the magnetic resonance signal are discovered for the specific ferromagnetic sphere and magnetic field configurations, and the appearance of the peaks is a direct signature of the presence of discrete atomic sites in the crystal lattice. The positions of the spectral peaks are sensitive to the crystal unit-cell size, thereby providing a method for determination of the basic parameters of the crystal at the atomic scale. The appearance of the spectral peaks is explained, and the dependence of the magnetic resonance spectra on the sphere size and the angle of the sphere magnetization with respect to the sample surface is analyzed. Applications to the studies of crystals, thin films, and crystallites are reviewed, and potential measurement methods for the confirmation of the diffraction theory are proposed. The analysis suggests that the long-desired goal of detecting atomic resolution magnetic resonance diffraction is well within reach of current experimental techniques

Recording processes in perpendicular patterned media using longitudinal magnetic recording heads

An experimental study of the recording processes in patterned magnetic media is presented. The reading of patterned media using spin-valve elements is compared to the signal levels from magneto-resistive sensors. Writing and reading of patterned columnar media at high areal densities is demonstrated. A new experimental technique has been developed that allows precise determination of the location of the write gap poles with respect to the patterned media column during the write process. Implications for patterned media write synchronization and the write head field requirements are discussed

Stray Field Magnetic Resonance Tomography using Ferromagnetic Spheres

The methodology for obtaining two- and three-dimensional magnetic resonance images by using azimuthally symmetric dipolar magnetic fields from ferromagnetic spheres is described. We utilize the symmetric property of a geometric sphere in the presence of a large externally applied magnetic field to demonstrate that a complete two- or three-dimensional structured rendering of a sample can be obtained without the motion of the sample relative to the sphere. Sequential positioning of the integrated sample-sphere system in an external magnetic field at various angular orientations provides all the required imaging slices for successful computerized tomographic image reconstruction. The elimination of the requirement to scan the sample relative to the ferromagnetic tip in this imaging protocol is a potentially valuable simplification compared to previous scanning probe magnetic resonance imaging proposals

Two-Dimensional Magnetic Resonance Tomographic Microscopy using Ferromagnetic Probes

We introduce the concept of computerized tomographic microscopy in magnetic resonance imaging using the magnetic fields and field gradients from a ferromagnetic probe. We investigate a configuration where a two-dimensional sample is under the influence of a large static polarizing field, a small perpendicular radio-frequency field, and a magnetic field from a ferromagnetic sphere. We demonstrate that, despite the non-uniform and non-linear nature of the fields from a microscopic magnetic sphere, the concepts of computerized tomography can be applied to obtain proper image reconstruction from the original spectral data by sequentially varying the relative sample-sphere angular orientation. The analysis shows that the recent proposal for atomic resolution magnetic resonance imaging of discrete periodic crystal lattice planes using ferromagnetic probes can also be extended to two-dimensional imaging of non-crystalline samples with resolution ranging from micrometer to Angstrom scales.Comment: 9 pages, 11 figure

Stripe sensor tomography

We introduce a general concept of tomographic imaging for the case of an imaging sensor that has a stripelike shape. We first show that there is no difference, in principle, between two-dimensional tomography using conventional electromagnetic or particle radiation and tomography where a stripe sensor is mechanically scanned over a sample at a sequence of different angles. For a single stripe detector imaging, linear motion and angular rotation are required. We experimentally demonstrate single stripe sensor imaging principle using an elongated inductive coil detector. By utilizing an array of parallel stripe sensors that can be individually addressed, two-dimensional imaging can be performed with rotation only, eliminating the requirement for linear motion, as we also experimentally demonstrate with parallel coil array. We conclude that imaging with a stripe-type sensor of particular width and thickness (where the width is much larger than the thickness) is resolution limited only by the thickness (smaller parameter) of the sensor. We give examples of multiple sensor families where this imaging technique may be beneficial such as magnetoresistive, inductive, superconducting quantum interference device, and Hall effect sensors, and, in particular, discuss the possibilities of the technique in the field of magnetic resonance imaging

Sample-detector coupling in atomic resolution magnetic resonance diffraction

A technique for potential realization of atomic resolution magnetic resonance diffraction was recently proposed for the case of a crystalline sample in proximity of a ferromagnetic sphere [M. Barbic, J. Appl. Phys. 91, 9987 (2002)]. This article predicted the detection of distinct peaks in the number of resonant spin sites at different magnetic field values for specific sphere and crystal configurations. Here, the focus is on the specific detection coupling mechanisms between the resonant spin population of the sample and the magnetic sphere probe. We investigate and compare the force, torque, and flux detection mechanisms in order to provide guidance to the experimental efforts towards the realization of the atomic resolution magnetic resonance diffraction. We also investigate the dependence of the magnetic resonance diffraction spectrum on the relative position of the magnetic sphere with respect to the crystal lattice

Perpendicular patterned media in an (Al0.9Ga0.1)2O3/GaAs substrate for magnetic storage

By using electron beam lithography, chemically assisted ion beam etching, and electroplating, we have fabricated high aspect ratio magnetic columns, 60–170 nm in diameter, embedded in an aluminum–gallium–oxide/gallium–arsenide [(Al0.9Ga0.1)2O3/GaAs] substrate. In our previous work, we demonstrated storage of data in individual columns spaced 2 µm apart. Here the electroplated Ni columns are in the form of tracks (0.5 and 0.25 µm in the down-track direction, and 1 µm in the cross-track direction), corresponding to areal densities of 1.3 and 2.6 Gbits/in.2, respectively. In this report we describe in more detail the issues in the fabrication of patterned media samples, such as dry etching and oxidation of AlGaAs, and electrodeposition of Ni into GaAs substrate. Initial characterization of the resulting magnets using magnetic force microscopy are also presented