  Using first-principles density functional theory, we have investigated the
electronic and magnetic properties of recently synthesized and characterized 5d
double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure
calculations show that in all compounds, the Os5+ (5d3) site is the only
magnetically active one, while Y3+, In3+ and Sc3+ remain in nonmagnetic states,
with Sc/Y and In featuring d0 and d10 electronic configurations, respectively.
Our studies reveal the important role of closed-shell (d10) versus open-shell
(d0) electronic configurations of the nonmagnetic sites in determining the
overall magnetic exchange interactions. Although the magnetic Os5+ (5d3) site
is the same in all compounds, the magnetic super-exchange interactions mediated
by non-magnetic Y/In/Sc species are strongest for Sr2ScOsO6, weakest for
Sr2InOsO6, and intermediate in case of the Y (d0), due to different energy
overlaps between Os-5d and Y/In/Sc-d states. This explains the experimentally
observed substantial differences in the magnetic transition temperatures of
these materials, despite of an identical magnetic site and underlying magnetic
ground state. Furthermore, short range Os-Os exchange-interactions are more
prominent than long range Os-Os interactions in these compounds, which
contrasts with the behavior of other 3d-5d double-perovskites.
