Frances HELLOGO.GIFellman Group

Amorphous and nanostructured Silicon
Fe/Cr Multilayers
Magnetic Oxides
Magnetic semiconductors
Magnetic Molecules
Fe/Cr Multilayers

Giant magneto-resistance (GMR) was first discovered in iron-chromium magnetic multi-layers (Fe-Cr MMLs) twenty-plus years ago.  This unique structure coupling the spin and conduction of the electrons set in motion an avalanche of technological innovation such as the data storage revolution of the mid-nineties and the emergent field of spintronics, which is why the co-discoverers of the phenomena (Fert and Grunberg) were awarded the Nobel Prize in Physics in 2007.

The densities of state of the materials in the MML structure play a key role in the system’s coupling behavior.  Our group utilizes our novel heat capacity devices to directly probe the density of states of these materials [1]. The data shown below indicates a very large enhancement in the DOS at the Fermi energy in Fe-Cr MMLs.  Ongoing research is examining the relationship of this enhancement to effects at the Fe-Cr interface to further our understanding of the spin-dependent scattering that results in GMR.

A tangential project to the work on GMR materials is that of the complex AFM Cr used as the “non-magnetic” spacer.  Through our unique thin film growth capabilities, we have shown how the spin density wave in this interesting transitional metal can exhibit a number of characteristics not seen in the bulk [2].

Related publications:

[1] Enhancement of the electronic contribution to the low temperature specific heat of an Fe/Cr magnetic multilayer. B. Revaz, M.-C. Cyrille, B. Zink, I. K. Schuller and F. Hellman, Phys. Rev. B 65, 944171 (2002).  

Spin-density wave in polycrystalline Cr films from infrared reflectivity. Z. Boekelheide, E. Helgren, F. Hellman, Phys. Rev. B, 76, 224429 (2007).