Excited state resonance study of critical behavior in singlet-ground-state antiferromagnets

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Abstract
The EPR of the excited Γ5(2) level of Tb3+ in TbVA (VA=P, As, Sb) intermetallic compounds has been studied. The temperature dependence of the EPR intensity for TbP serves to confirm that the EPR is originating from the excited Γ5(2) state. For TbP and TbAs the g‐shift from the crystal‐field only value can be expressed as A/(T‐TN( n where A=300 (TbP), 350 (TbAs) and n=1.3±0.3 (for both TbP and TbAs). These results are interpreted by assuming that the g‐shift is proportional to the staggered magnetic field. The line widths of TbP and TbAs do not broaden when the temperature approaches T N , while that of TbSb increases. These results may be explained by the Kawasaki–Huber and Kruger theory for the line width in antiferromagnets in the vicinity of the Néel temperature. The temperature dependence of the line widths of TbP and TbAs can be accounted for under the assumption that the line width is proportional to the auto‐correlation function of the spin fluctuations. From these analyses the energies of the Γ4 and Γ5 (2) levels of Tb3+ in TbP and TbAs are about 16K and 35K respectively.

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