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     COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
AND THE SCHOOL OF PHYSICS, ASTRONOMY, & COMPUTATIONAL SCIENCES
                            (CSI 898-Sec 001)
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Electronic origin of the spin-disorder resistivity enhancement in 
                    the heavy rare-earth metals

                             James K. Glasbrenner

              Center for Computational Materials Science, 
               Naval Research Laboratory, Washington DC

There are several scattering contributions to the resistivity of a magnetic
metal: scattering due to impurities, thermal vibrations of ions (phonons), and
thermal fluctuations of the local magnetic moments. Above the magnetic
ordering temperature the local moments are noncollinear and randomly
disordered (paramagnetic state) and the spin-disorder scattering contribution
saturates. This saturated magnetic resistivity is called the spin-disorder
resistivity (SDR). Here we calculate the SDR for the heavy rare-earth Gd-Tm
series using two complimentary first-principles approaches, which we find to
be in excellent agreement. The SDR in the series follows an almost universal
dependence on the exchange splitting and is underestimated when compared with
experiment. A simple quantum correction improves agreement with experiment but
does not fully account for the discrepancy.

In order to understand the origin of this discrepancy, we evaluated the mutual
effects of phonon- and spin-disorder scattering in Gd along with the
transition metal Fe for comparison. Calculations are performed using a
supercell approach with random noncollinear spin configurations combined with
displacements of the atomic positions according to the Gaussian distribution,
and the resistivity is evaluated as a function of the atomic mean-square
displacement u2. We find that the resistivity grows non-linearly as u2 is
increased and the growth is more rapid in Gd than in Fe. As u2 is increased
further the resistivity crosses over to a saturation regime where the slope
changes slowly and the resistivity is insensitive to the local moment. Fitting
to this region in Gd yields an intercept ~2.5 times larger than the “bare”
SDR, significantly improving the agreement with experiment. This behavior is
electronic in origin, and the rapid increase in the resistivity of Gd can be
traced to an interaction between its hole and electron Fermi surfaces
activated by disorder.
 
                          October 7, 2013
                               4:30 pm
              Exploratory Hall, room 3301, Fairfax Campus

Refreshments will be served at 4:15 PM.
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