Nanoscale Magnetic Materials:  Synthesis, Advanced Characterization and Technique Development

Charles S. Fadley, Program Leader

     In this multi-investigator program, novel magnetic nanoscale structures are synthesized and studied with a powerful range of techniques.  The systems studied include vapor-phase deposited thin films and multilayers, structured or self-assembled nanoscale systems, nanoparticles, amorphous materials, metastable alloys, complex oxides, ferroelectric and multiferroic films, and nanocrystalline and single-crystal materials relevant to applications in spintronics and magnetics.  Properties of interest include exchange bias; giant-, tunnel- and colossal- magnetoresistance; half-metallic ferromagnetism; and current-induced phenomena.  Calorimetric measurements yield electron, phonon, and magnon densities of states, as well as magnetic ordering temperatures.  Advanced synchrotron-radiation techniques yield element-specific electronic and magnetic structures, including spatial resolution from micron to sub-nanometer scale, as well as time resolution to the picosecond scale.  These techniques include resonant soft x-ray scattering, soft x-ray microscopy, and high resolution spectroscopies (core- and valence- photoelectron, x-ray absorption, x-ray emission and inelastic scattering), and depth-resolved measurements using standing waves.

There are two complementary aspects to the program:

Synthesis & Advanced Characterization of Nanoscale Magnetic Materials    (C. Fadley, P. Fischer, F. Hellman, J. Kortright)  The goal of this aspect of the program is an in-depth exploration of the properties and behavior of novel magnetic materials that emerge from nanoscale heterogeneity, including surface and interface properties, as well as spin dynamics upon field and current excitations. The main areas of interest are:
Synthesis of novel magnetic materials and nanostructures that are of both fundamental and practical importance in spintronics and other magnetic applications.  Synthesis is done within our group, as well as by other groups in Berkeley and around the world.
Characterization of these materials and nanostructures with a powerful array of experimental and theoretical methods, including nanocalorimetry and third-generation synchrotron-radiation based soft x-ray scattering and microscopy with high spatio-temporal resolution; core and valence photoemission; x-ray absorption, x-ray emission and x-ray elastic and inelastic scattering. This involves a variety of forefront problems in surface, interface, and nanoscale magnetism.
Development of new instrumentation and characterization methods based on nanocalorimetry and x-ray optics/ spectroscopy/microscopy for the study of surfaces, buried interfaces, nanostructures, and complex materials exhibiting nanoscale heterogeneity. These methods will also be broadly useful to other scientific communities (e.g. energy science and technology, environmental science, semiconductor technology, and geophysics.
Part of this program is oriented towards extending soft x-ray microscopy of magnetic materials with X-ray optics to spatial resolutions below 10 nm, and to explore extensions of the present 70 psec temporal resolution towards the fsec region by exploring opportunities with emerging compact high-harmonic generation (HHG) and large scale free-electron laser (FEL) facilities.

Techniques for Nanoscale Imaging of Magnetic Materials   (P. Naullau, P. Fischer, et al.—the LBNL MSD Center for X-Ray Optics)
     The world’s only full-field transmission soft x-ray microscope, XM-1, at LBL’s Advanced Light Source (ALS) was fabricated by MSD’s Center for X-ray Optics (CXRO).  This system has achieved the world’s best spatial resolution (13 nm) and is used extensively for the study of nanomagnetic materials, as discussed above.   CXRO’s goal is to extend soft x-ray microscopy of magnetic materials to spatial resolutions of 10 nm and below, to explore extension of the present 70 psec temporal resolution towards the fsec region, and to develop a reflection, rather than transmission, soft x-ray microscope so as to extend the range of applications greatly and permit standing wave excitation.  Resolution improvement will be achieved by extending zone plate fabrication to outer zone widths of 10 nm using overlay techniques, and eventually to 5 nm resolution; improving Fresnel lens efficiency by stacking and shaping zones; and enhancing imaging capabilities based on magnetic phase contrast.