Electric Signatures of Structural and Chemical Ordering of Heusler Alloy Films

In this paper, we present the results of in situ temperature measurements of resistivity for some amorphous or partially crystalline Heusler alloy (HA) films: ${\hbox {Co}}_{2}{\hbox {CrAl}}$, ${\hbox {Co}}_{2}{\hbox {MnGa}}$ , and off-stoichiometric ${\hbox {Ni}}_{2}{\hbox {Mn}}_{1+{\rm x}}{\hbox {Sn}}_{1-{\rm x}}$, ${\hbox {Ni}}_{2}{\hbox {Mn}}_{1+{\rm x}}{\hbox {Ga}}_{1-{\rm x}}$ that are known to exhibit half-metallic properties and martensitic transformations, respectively. From resistivity $\rho$ versus $T$ characteristics we distinguish various stages of chemical and structural ordering in the films. They appear to be quite distinct in both systems investigated due to differences in their electronic structure. The resistivity results are compared with magnetic characteristics for ${\hbox {Co}}_{2}{\hbox {MnGa}}$ with a high Curie temperature. High-temperature resistivity measurement is a sensitive tool for tracing the chemical and structural ordering in HA films.