Exchange stiffness in Co$_{2}$-based Heusler compounds

TL;DR

This study measures the exceptionally high exchange stiffness in Co$_{2}$-based Heusler compounds using Brillouin light scattering, revealing its dependence on valence electron concentration and crystallographic order.

Contribution

The paper reports the first measurement of an extraordinarily high exchange stiffness in Co$_{2}$-based Heusler compounds and systematically analyzes its dependence on electronic and structural factors.

Findings

Exchange stiffness D=715 meV Å$^2$ in Co$_2$-based Heusler.

Exchange stiffness increases with valence electron concentration.

Exchange stiffness increases with L2$_1$ ordering.

Abstract

We determine the spin wave exchange stiffness $D$ and the exchange constant $A$ for the full Heusler compound \CFS using Brillouin light scattering spectroscopy. We find an extraordinarily large value of $D=715\pm20$ meV \AA$^2$ ($A=31.5\pm1.0$ pJ/m) which is, to the best of our knowledge, only surpassed by the intermetallic compound Fe$_{53}$Co$_{47}$ (J. Appl. Phys. \textbf{75}, 7021 (1994)). Furthermore, we provide a systematization of the exchange stiffnesses determined for a variety of Co$_2$-based Heusler compounds. We find that for the investigated compounds, the exchange stiffness is a function of the valence electron concentration and the crystallographic ordering. The exchange stiffness increases when the valence electron concentration and/or the amount of the L2$_1$ ordering increase. A qualitative explanation for the dependence on the valence electron concentration is provided.