Magneto-optical effects have been investigated over the infrared visible spectral range in $A{\mathrm{Cr}}_2{\mathrm{O}}_4$ ($A=\text{Fe},\text{Co}$) spinel oxides with noncollinear spin orders in their ground states. We found large magneto-optical Kerr rotation and ellipticity at the on-site $d-d$ transitions of the $A^{2+}$ ions located within the charge gap. The magneto-optical Kerr rotation of ${\vartheta }_{\mathrm{Kerr}}\approx {12}^{\circ }$ observed in ${\mathrm{CoCr}}_2{\mathrm{O}}_4$ is unprecedentedly large among magnetic semiconductors and points toward the uniqueness of tetrahedrally coordinated ${\mathrm{Co}}^{2+}$ ions in generating strong magneto-optical response. Criteria of strong magneto-optical effects emerging at on-site $d-d$ transitions of transition metal ions are discussed.

中文翻译：

---

四面体配位过渡金属离子产生的ACr2O4（A = Fe，Co）尖晶石氧化物中的强磁光效应

已经在红外可见光谱范围内研究了磁光效应。 $\mathrm{一个}{铬}_{\mathrm{2个}}{\mathrm{Ø}}_4$ （$\mathrm{一个}=\text{铁}，\text{有限公司}$）在基态中具有非共线自旋顺序的尖晶石氧化物。我们在现场发现了较大的磁光Kerr旋转和椭圆率$d-d$ 的过渡 ${\mathrm{一个}}^{\mathrm{2个}+}$离子位于电荷隙之内。磁光克尔旋转${\vartheta }_{\mathrm{克尔}}\approx {12}^{\circ }$ 在观察 ${\mathrm{钴铬}}_{\mathrm{2个}}{\mathrm{Ø}}_4$ 在磁性半导体中是前所未有的大，并指出了四面体配位的唯一性 ${\mathrm{有限公司}}^{\mathrm{2个}+}$离子在产生强烈的磁光响应时。现场出现强磁光效应的标准$d-d$ 讨论了过渡金属离子的跃迁。