  Energy-efficient control of magnetization without the help of a magnetic
field is a key goal of spintronics. Purely heat-induced single-pulse
all-optical toggle switching has been demonstrated, but so far only in Gd based
amorphous ferrimagnet films. In this work, we demonstrate toggle switching in
the half-metallic compensated ferrimagnetic Heusler alloys Mn2RuxGa, which have
two crystallographically-inequivalent Mn sublattices. Moreover, we observe the
switching at room temperature in samples that are immune to external magnetic
fields in excess of 1 T, provided they exhibit compensation above room
temperature. Observations of the effect in compensated ferrimagnets without Gd
challenges our understanding of all-optical switching. The dynamic behavior
indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis
for fast optical switching of magnetization and break new ground for engineered
materials that can be used for nonvolatile ultrafast switches using ultrashort
pulses of light.
