  Antiferromagnetic (AFM) spintronics, where magneto-transport is governed by
an antiferromagnet instead of a ferromagnet, opens fascinating new perspectives
for both fundamental research and device technology, owing to their intrinsic
appealing properties like rigidness to magnetic field, absence of stray field,
and ultrafast spin dynamics. One of the urgent challenges, hindering the
realization of the full potential of AFM spintronics, has been the performance
gap between AFM metals and insulators. Here, we demonstrate the insulator-metal
transition and persistently large anisotropic magnetoresistance (AMR) in single
crystals Sr2(Ir1-xGax)O4 (0<x<0.09) which host the same basal-plane AFM lattice
with strong spin-orbit coupling. The non-doped Sr2IrO4 shows the insulating
transport with the AMR as big as ~16.8% at 50 K. The Ga substitution of Ir
allows a gradual reduction of electrical resistivity, and a clear
insulator-to-metal transition is identified in doped samples with x above 0.05,
while the AMR can still have ~1%, sizable in comparison with those in AFM
metals reported so far. Our experiments reveal that all the samples have the
similar fourfold AMR symmetry, which can be well understood in the scenario of
magnetocrystalline anisotropy. It is suggested that the spin-orbit coupled
antiferromagnets Sr2(Ir1-xGax)O4 are promising candidate materials for AFM
spintronics, providing a rare opportunity to integrate the superior spintronic
functionalities of AFM metals and insulators.
