Exchange Anisotropy of L1$_2$-Mn$_3$X (X$=$Ir, Rh, Ru)/Co-Fe Bilayers

The L1
$_2$
-phase formation and resultant exchange anisotropy were examined in Mn-Rh/Co-Fe and Mn-Ru/Co-Fe bilayers, varying the substrate temperature,
$T_ sub$
, during the deposition of Mn-Rh or Mn-Ru layer. The superlattice diffractions from the Mn
$_3$
Rh were detected. The unidirectional anisotropy constant,
$J_ K$
, was enhanced more than double with increasing
$T_ sub$
from room temperature to 130
$^circ$
C
$sim$
170
$^circ$
C, similarly to Mn-Ir/Co-Fe bilayers. The maximum
$J_ K$
value obtained was 0.77 erg/cm
$^2$
for the Mn-Rh/Co-Fe bilayer and 0.56 erg/cm
$^2$
for the Mn-Ru/Co-Fe bilayer. The blocking temperature,
$T_ B$
, was increased about 80
$^circ$
C to 100
$^circ$
C, in accordance with enhancing
$J_ K$
. Variations of
$J_ K$
and
$T_ B$
as a function of antiferromagnetic layer thickness,
$d_ AF$
, were also studied. The critical thickness of
$d_ AF$
was less than 5 nm for both the bilayers.