Title: Magnetism in Semiconducting Molybdenum Dichalcogenides,
Abstract: Transition metal dichalcogenides (TMDs) are interesting for understanding
fundamental physics of two-dimensional materials (2D) as well as for many
emerging technologies, including spin electronics. Here, we report the
discovery of long-range magnetic order below TM = 40 K and 100 K in bulk
semiconducting TMDs 2H-MoTe2 and 2H-MoSe2, respectively, by means of muon
spin-rotation (muSR), scanning tunneling microscopy (STM), as well as density
functional theory (DFT) calculations. The muon spin rotation measurements show
the presence of a large and homogeneous internal magnetic fields at low
temperatures in both compounds indicative of long-range magnetic order. DFT
calculations show that this magnetism is promoted by the presence of defects in
the crystal. The STM measurements show that the vast majority of defects in
these materials are metal vacancies and chalcogen-metal antisites which are
randomly distributed in the lattice at the sub-percent level. DFT indicates
that the antisite defects are magnetic with a magnetic moment in the range of
0.9-2.8 mu_B. Further, we find that the magnetic order stabilized in 2H-MoTe2
and 2H-MoSe2 is highly sensitive to hydrostatic pressure. These observations
establish 2H-MoTe2 and 2H-MoSe2 as a new class of magnetic semiconductors and
opens a path to studying the interplay of 2D physics and magnetism in these
interesting semiconductors.