High-Moment-Low-Moment Description of Magnetovolume Effects in Y(Mn x Al 1− x ) 2 and Y x Sc 1− x Mn 2
Based on the assumption of a high-moment-low-moment instability of the Mn atom, we construct a simple spin model with coupled magnetic and spatial degrees of freedom to describe the Laves phase systems Y(Mn x Al 1 m x ) 2 and Y x Sc 1 m x Mn 2 . Monte Carlo simulations of this model qualitatively reproduce anomalies observed in these materials like a discontinuous giant volume change and anomalous thermal expansion behavior.
First-principles calculations of the instability leading to the Invar effect.
An attempt is made to show the close connection between martensitic transformations, the Invar effect, magnetovolume instabilities, and associated low-moment-high-moment (LM-HM) transitions. For that purpose we study the volume dependence of electron occupation and magnetization of eg and μg states in ordered Fe 3 Ni. We show that in this compound the instability against small tetragonal distortions, the Invar behavior, and the LM⇄HM transitions are a consequence of the delicate balance of charge distribution and magnetic order from d orbitals having different bonding character
Moment-Induced Magnetic Scattering and Magnetovolume Effect in Fe 65 (Ni 1− x Mn x ) 35 Alloys
The temperature dependences of electrical resistivity and thermal expansion were measured for face-centered cubic Fe 65 (Ni 1- x Mn x ) 35 ternary alloys. The electrical resistivity of ferromagnetic alloys ( x 0.3) increases below the Neel temperature and shows a resistance minimum. These behaviors are explained in terms of the magnetic scattering by induced moments below the magnetic ordering temperature. The expansion of volume due to the magnetic ordering was observed in both ferro- and antiferromagnetic alloys. To explain the volume expansion by the magnetic ordering, a new mechanism of magnetovolume effect based on the change of cohesive energy due to the spin polarization in 3 d band is proposed.