Magnetic films and nanostructures

We are using polarized neutron reflectivity and resonant magnetic x-ray scattering to study the details of the depth dependence of the magnetization and the lateral domain structure in the vicinity of the interfaces in compound magnetic structures.
 

These include ferromagnetic films deposited on antiferromagnets (so-called "exchange-bias" systems), multilayers exhibiting the giant magnetoresistance (GMR) effect or spin-valve systems, ferromagnet/semiconductor interfaces (so-called "spin injection systems"), magnetic nanodot arrays deposited on solid substrates, and hole arrays in magnetic films. We are also in the process of preparing antiferromagnetic nanoparticles with a view to studying their spin structures and/or superparamagnetic behavior.
 

Issues we are interested in include the correlation between interfacial roughness and magnetic domain structure and coercive field; the origin and location of the so-called "uncompensated spins" in an antiferromagnet in contact with a ferromagnet and their domain structure and its relation to the domain structure in the ferromagnet as a function of applied magnetic field; the magnetic domain structure in films with periodic microscopic arrays of holes; the so-called vortex structure in magnetic nanodots; how the spin structures of nanoparticles differ from those of the corresponding bulk structures; the dynamics of how superparamagnetic moments fluctuate in magnetic nanopartices as studied by coherent magnetic x-ray scattering; the depth profile of spins injected into a semiconductor from a ferromagnet, etc.
 

We have recently developed a theoretical formalism for efficiently calculating resonant magnetic scattering from magnetic interfaces with roughness and domain structures [see Publications below], which we use in analyzing our magnetic x-ray scattering data.
 

We are planning to use resonant magnetic x-ray scattering using coherent x-rays to observe magnetic "speckle" from spin systems, such as spin glasses or systems with frustrated magnetic order to observe how the dynamics of the spins freeze out as the freezing transition is approached.
 

We are also planning to study the profile of spins at a normal metal/ferromagnetic metal interface under applied current conditions to investigate the so-called "spin blockade" which builds up at the interface.

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Publications

Combined Magnetic X-Ray and Polarized Neutron Reflectivity Study of the Origins of Exchange Bias in the Co/FeF₂ System

M. R. Fitzsimmons, S. Roy, B. J. Kirby, S. Park, Igor V. Roshchin, Zhi-Pan Li, J. B. Kortright, Sunil Sinha, and Ivan K. Schuller
Superlattices and Microstructures 41, 109 (2007). DOI: 10.1016/j.spmi.2007.02.004

Evidence of modified ferromagnetism at a buried Permalloy/CoO interface at room temperature
S. Roy, C. Sanchez-Hanke, S. Park, M. R. Fitzsimmons, Y. J. Tang, J. I. Hong, David J. Smith, B. J. Taylor, X. Liu, M. B. Maple, A. E. Berkoitz, C.-C. Kao, and S. K. Sinha
Phys. Rev. B 75, 014442 (2007). DOI: 10.1103/PhysRevB.75.014442

Probing Dynamics at Surfaces with X-rays and Neutrons
S. K. Sinha
J. Neutron Res. 14, 205 (2006). DOI: 10.1080/10238160600974336

Combined neutron and synchrotron studies of magnetic films
S. K. Sinha, S. Roy, M. R. Fitzsimmons, S. Park, M. Dorn, O. Petracic, I. V. Roshchin, Z.-P. Lee, X. Batlle, R. Morales, A. Misra, X. Zhang, K. Chesnel, J. B. Kortright and I.K.Schuller
Pramana - J. Phys. 67, 47 (2006).

Future science at next generation neutron sources
S. K. Sinha
Physica B 356, 269 (2005). DOI: 10.1016/j.physb.2004.10.089

Depth profile of unpinned and pinned uncompensated spins in the antiferromagnetic layer of an exchange bias heterostructure
S. Roy, M. R. Fitzsimmons, S. Park, M. Dorn, O. Petracic, I.V. Roshchin, Zhi-Pan Li, X. Batlle, R. Morales, A. Misra, X. Zhang, K. Chesnel, J.B. Kortright, S.K. Sinha and Ivan K. Schuller
Phys. Rev. Lett. 95, 047201 (2005). DOI: 10.1103/PhysRevLett.95.047201

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