Role of Double Exchange in the Magnetic Structure ofLixMn1−xSe

The details of the magnetic behavior of the ${\mathrm{Li}}_x{\mathrm{Mn}}_{1-x}\mathrm{Se}$ system are attributed to the double-exchange interaction. At low temperatures, the hole which is introduced by the ${\mathrm{Li}}^{+}$ is loosely bound to the ${\mathrm{Li}}^{+}$ itself. In the region of the Li ion, double exchange causes local distortions of the spin system which we refer to as clusters. As the Li concentration is increased ($x=0.07\mathrm{}$), the clusters overlap sufficiently so that a magnetic field will induce an appreciable magnetic moment ($0.5{\mu }_B$). At temperatures below 45°K a canted spin ordering is suggested as the magnetic model for the $x=0.07\mathrm{}$ composition. Finally, at $x=0.10\mathrm{}$ we find that spontaneous magnetization develops below 110°K. As the temperature is lowered through 70°K the spontaneous moment disappears and antiferromagnetism is found. It is not inconsistent with the data for $x=0.10\mathrm{}$ that this antiferromagnetic state is a canted-spin system with very small canting angle and therefore small magnetic moment. The theory of de Gennes is used in our discussion of the magnetic model.