Nanomagnetism and Advanced Scattering Techniques (NaM-AST)

Research Interests

Material Characterization, Thin Films and Nanotechnology, Condensed Matter Physics, Magnetic Materials and Magnetism, Spintronics, Nanomagnetism, Thin Film Magnetism, Neutron Scattering, Magnetometry, Polarized Neutron Small Angle Scattering, X-Ray Reflectometry, X-Ray Absorption Spectroscopy.

All-spin-based technology with topologically stable helices

The magnetization process of two-dimensional randomly anisotropical system in the form of 2π-DWs is directly correlated with topologically stable helices. Using magnetization and susceptibility as function of temperature along with thermo-remanent magnetization measurements we have recently confirmed superspin-glass type of behavior within a RE/RE system. Additionally, an exchange bias field was also revealed for such rare-earth based multilayers. Interestingly, using detailed analysis of the polarized neutron reflectometry profiles, we find evidences of superimposed helical magnetic configurations within both materials associated with spin-frustrated interfaces. We believe that coexistence of helical ground states with superspin-glass-like ordering are fundamentally instrumental for topologically stability in RE/RE systems, which in principle, can be exploited in all-spin-based technology.

Engineering nanocrystalline magnetic phase diagram 

We reported on synthesis and investigation of nanocrystalline (NC) cobalt-iron-pyrites with an emphasis on nanocrystal structure, morphology and magnetic behavior. Temperature dependence of the DC magnetization and AC susceptibility versus frequency recently rvealed a number of magnetic phases in CoxFe1−xS2 like, superspin glass (SSG), superparamagnetic (SPM) behavior with antiferromagnetic clusters suppressing magnetic dipolar interactions. A phase diagram, thus obtained, was understood in terms of competition between the various dipolar, exchange, inter- and intracluster interactions. Our results suggest that NC size and shape can be tuned to engineer spin-polarized ferromagnetism of n-doped iron pyrite.

Self-diffusion in multilayers by in situ neutron reflectometry 

For the stability of nanostructured materials, grain boundaries (GBs) can be controlled by the grain size. We studied self-diffusion active at the GBs at from the change of the 57Fe isotopic fraction was monitored recently in situ by neutron reflectometry on the sub-nanometer length scale on Pt(4 nm)[56Fe(x nm)/57Fe(x nm)]4/Si with (x=4 and 8), in a dedicated furnace at REFSANS of HZG at FRM II in time-of-flight mode. In situ experiment is expected to follow the dynamics more efficiently and therefore the mixed interface width has been mapped with time at short intervals. We find an increase in the intensity of the first Bragg peak at lower temperatures which is probably related to exotic triple-junction grain boundaries. 

Proximity effects across superconductor-insulator-ferromagnet hybrid heterostructures 

A case study of electron tunneling or charge-transfer-driven orbital ordering in superconductor (SC)-ferromagnet (FM) interfaces has been conducted recently in heteroepitaxial YBa2Cu3O7(YBCO)/ La0.67Sr0.33MnO3(LSMO) multilayers interleaved with and without an insulating SrTiO3(STO) layer between YBCO and LSMO. X-ray magnetic circular dichroism (XMCD) experiments revealed anti-parallel alignment of Mn magnetic moments and induced Cu magnetic moments in a YBCO/LSMO multilayer. Electron energy loss spectroscopy (EELS) experiment showed the evidence of Ti magnetic polarization at the interfaces of the YBCO/STO/LSMO multilayer. This work provides an effective pathway in understanding the aspect of long range proximity effect and consequent orbital degeneracy parameter in magnetic coupling. 

Self-assembly of Nanolayers and Nanostructures 

Physical properties of nanoclusters, nanostructures and self-assembled nanodots, which in turn are concomitantly dependent upon the morphological properties, can be modulated for functional purposes. Magnetic nanodots of Fe on semiconductor TiO2 nanotubes (TNTs) were recently investigated with time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS) as a function of wavelength. As we probe the inside and the near-surface region of the Fe-dotted TNTs with respect to their homogeneity, surface distortion and long-range order using TOF-GISANS, gradual aberrations at the top of the near-surface region are identified.