Magnetic and Structural Properties of L10 Mn–Ga–Al Epitaxially Grown Thin Films of Island Structure

The epitaxially grown L1
₀
Mn
_53-x
Ga
₄₇
Al
_x
(x = 0-6) thin films of island structure were fabricated onto MgO (100) substrates held at about 600 °C during deposition. Those islands possess the (001) axis perpendicular to the substrate surface; the order parameters S of which are found to be 0.9, 0.7, and 0.4 for x = 0, 3, and 6, respectively. It is emphasized that the highly ordered LL1
₀
phase (S = 0.7) is fabricated with even Mn 50 at%, much less than 55 at%, which is the boundary for LL1
₀
phase in the bulk phase diagram. The saturation magnetization Ms is about 380, 480, and 90 emu/cm
³
at 5 K for x = 0, 3, and 6, respectively. In order to estimate the Curie temperature T
_c
, the temperature dependence of M
_s
was fit to an empirical relation of M
_s
(T)/M
_s
(0) = (1- T/T
_c
)
^α
, where α is a fitting parameter. It is found that T
_c
is about 600 K for both x = 0 and 3, and 550 K for x = 6, respectively. The values of the uniaxial magnetic anisotropy constant K
_u
are 1.1 x 10
⁷
, 6 x 10
⁶
, and 2 x 10
⁵
erg/cm
³
at 5 K for x = 0, 3, and 6, respectively. The power law exponent n for the correlation between K
_u
(T) and M
_s
(T) for a temperature range from 5 to 400 K is found to be about 2.6 and 2.2 for x = 0 and 3, respectively. Therefore, one cannot conclusively assign which mechanism (the single-ion or two-ion mechanism) plays a role in the magnetic anisotropy mechanism. However, the overall correlation strongly suggests a deviation from the single-ion mechanism, consistent with theoretical predictions of the non-negligible site decomposed magnetic anisotropy of Ga in the magnetic anisotropy mechanism.