EPR Investigation Of Local Lattice Structure Of Mn～(2+) In Diamagnetic Garnets

Diamagnetic gamets doped with transition metal ions (Nd³⁺, Cr⁴⁺, Fe³⁺, etc.) is one of the most important crystal materials. For example, Yttrium aluminum gamet (YA1G) doped with transition metal ions (Nd³⁺, Cr⁴⁺, etc.) is the most important crystal material for solid lasers that are widely used in medical, commercial, military and industrial applications. The EPR parameters D and(a-F) of Mn²⁺ ion in diamagnetic gamets had been measured by Hodges. Yu et al, have given an explanation for the observed axial term D of Mn²⁺ ions at the octahedral sites in diamagnetic garnets. However, it is known that for a d⁵ configuration ion in a trigonal ligand-field, the high-spin ground state is the ⁶A₁ state. In order to describe the ⁶A₁ ground state splitting, the spin Hamiltonian should include three different EPR parametersα, D and (α-F).The parameter a relates to a fourth-order spin operator and represents a cubic component of the crystalline electric field. Parameters D and (α-F) relate to the axial ligand-field. Generally speaking, D and (α-F) should be simultaneously considered in the determination of the distortion of the local crystal structure of Mn²⁺ in diamagnetic garnets. The local structure around the Mn²⁺ ion should be different from that of the Al³⁺ or Ga³⁺ ion due to the difference in the radius and ionic charges between the substituent Mn²⁺ and the host cation Al³⁺ or Ga³⁺ ion. Moreover, we also find that the impurity-ligand distance R≈R_H+1/2(r_i-r_h) is not suitable for Mn²⁺ in diamagnetic gamets which has been approximately takenin a previous work.