On Line Widths of Paramagnetic Resonance Absorption

Paramagnetic resonance absorption of microwave (9970 MC) by thirteen salts containing manganese or copper ions was observed with special attention to obtain correct line shapes. The widths obtained were plotted against 1/ a ³ , a being the lattice constant when the arrangement of ions are considered as simple cubic lattice. For smaller values of 1/ a ³ , line shapes are near to gaussian type and the widths coincide with those by dipolar coupling calculated by Van Vleck. When 1/ a ³ is larger, that is, when ions come nearer, line shapes are near to resonance types and widths are in general smaller than those expected by dipolar coupling. This narrowing is caused by the existence of exchange coupling between magnetic ions. It is shown that the narrowing in salts of Mn ⁺⁺ , Fe ⁺⁺⁺ (S-state) and C ⁺⁺ can be related to the value of θ in the Curie-Weiss law of static susceptibility \(\chi_{s}{\backsim}C/(T+\theta)\).