  The spin-orbit assisted Mott insulator $\alpha$-RuCl3 is proximate to the
coveted quantum spin liquid (QSL) predicted by the Kitaev model. In the search
for the pure Kitaev QSL, reducing the dimensionality of this frustrated magnet
by exfoliation has been proposed as a way to enhance magnetic fluctuations and
Kitaev interactions. Here, we perform angle-dependent tunneling
magnetoresistance (TMR) measurements on ultrathin $\alpha$-RuCl3 crystals with
various layer numbers to probe their magnetic, electronic and crystal
structure. We observe a giant change in resistance - as large as ~2500% - when
the magnetic field rotates either within or out of the $\alpha$-RuCl3 plane, a
manifestation of the strongly anisotropic spin interactions in this material.
In combination with scanning transmission electron microscopy, this tunneling
anisotropic magnetoresistance (TAMR) reveals that few-layer $\alpha$-RuCl3
crystals remain in the high-temperature monoclinic phase at low temperature. It
also shows the presence of a zigzag antiferromagnetic order below the critical
temperature TN ~ 14 K, which is twice the one typically observed in bulk
samples with rhombohedral stacking. Our work offers valuable insights into the
relation between the stacking order and magnetic properties of this material,
which helps lay the groundwork for creating and electrically probing exotic
magnetic phases like QSLs via van der Waals engineering.
