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Browsing by Author "Mazumdar, Dipanjan"

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    Magnetic field control of charge excitations in CoFe2O4
    (American Institute of Physics, 2018) Holinsworth, Brian S.; Harms, Nathan C.; Fan, Shiyu; Mazumdar, Dipanjan; Gupta, Arun; McGill, Stephen A.; Musfeldt, Janice L.; University of Tennessee Knoxville; University of Alabama Tuscaloosa; Florida State University; Southern Illinois University
    We combine magnetic circular dichroism and photoconductivity with prior optical absorption and first principles calculations to unravel spin-charge interactions in the high Curie temperature magnet CoFe2O4 . In addition to revising the bandgap hierarchy, we reveal a broad set of charge transfer excitations in the spin down channel which are sensitive to the metamagnetic transition involving the spin state on Co centers. We also show photoconductivity that depends on an applied magnetic field. These findings open the door for the creation and control of spin-polarized electronic excitations from the minority channel charge transfer in spinel ferrites and other earth-abundant materials. (C) 2018 Author(s).
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    Robust room-temperature magnetism of (110) CrO2 thin films
    (American Physical Society, 2009-12-14) Pathak, Manjit; Sims, Hunter; Chetry, Krishna B.; Mazumdar, Dipanjan; LeClair, Patrick R.; Mankey, Gary J.; Butler, William H.; Gupta, Arunava; University of Alabama Tuscaloosa
    We have used x-ray magnetic circular dichroism (XMCD) and ab initio electronic-structure calculation techniques to investigate the magnetic properties of high-quality epitaxial (110) and (100) CrO2 thin films. A relatively larger XMCD was observed on the Cr L-2,L-3 edge of (110)-oriented CrO2 films compared to (100)-oriented CrO2 films at room temperature. Analysis of our data with conventional sum rules for 3d elements shows a nearly 50% higher spin moment on (110) films compared to (100) orientation, consistent with bulk magnetometry measurements. The orbital moment is found to be similar for both orientations. Robust magnetism is attributed to increased collinearity of Cr spins in strain-free (110) films as compared to strained (100) films. Zero-temperature density-functional calculations show opposing trends in nearest-neighbor and next-nearest-neighbor exchange interactions between relaxed and strained CrO2.