Spin Relaxation via Low-Lying Energy Level ofFe2+in MgO

Abstract

The spin-relaxation time ($T_1$) of ${\mathrm{Fe}}^{2+}$ in MgO was measured from 4.2 to 13°K. The excess relaxation above that attributed to the direct processes dominant at low temperature is described by $\frac{1}{T_1}=A{e}^{-\frac{\Delta }{T}}$, where $A=6.5\mathrm{}\times {10}^{10}$ ${\sec }^{-1\mathrm{}}$ and $\Delta =140\mathrm{}°$K. This result establishes, via a measurement of the Orbach process, that there is a sharp electronic energy level at 100±10 ${\mathrm{cm}}^{-1\mathrm{}}$ for the ${\mathrm{Fe}}^{2+}$ ion in MgO.