Longitudinal spin attenuation behavior induced by magnetic disorder in the noncollinear magnetic structure of the Invar alloy

There exists evidence indicating that the noncollinear magnetic structure is closely associated with the low-thermal-expansion property of the Fe-Ni Invar alloy. Here, atomic spin dynamics and constrained density functional theory are employed to examine the effect of noncollinear magnetic structures, including the orientation disorder and the moment magnitude, on the equilibrium volume of Fe₆₅Ni₃₅ alloy. Results show that the emergence of noncollinear magnetic structures in small volume could be attributed to complex magnetic exchange interactions, especially competing negative exchange interactions from further neighbors. However, the noncollinear orientation disorder, with the moment magnitude remaining fixed, would instead enhance the equilibrium volume of Invar alloy. The longitudinal spin attenuation (i.e., the reduction of moment magnitude) induced by magnetic disorder is related to the magnetostriction of Invar alloy. This study highlights the interaction between longitudinal and transverse spin fluctuations in the noncollinear magnetic structure model.