Reduction of Ordered Spin Moments in Antiferromagnets of <i>S</i> = 5/2 Ions (Fe ³⁺ , Mn ²⁺ ) Driven by Local Magnetic Excitation

For antiferromagnets composed of <i>S</i> = 5/2 ions such as Fe³⁺ and Mn²⁺, the moments of these ions in the ordered antiferromagnetic state can be significantly smaller than 5 μ_B (i.e., 1.56-4.48 μ_B) if these ions form quantum fluctuating entities (QFEs), e.g., quasi-one-dimensional uniform antiferromagnetic chains or quasi-zero-spin antiferromagnetic spin dimers. It is reasonable to suppose that the stronger the quantum fluctuation in such an antiferromagnet, the greater the reduction in its ordered moment, but this supposition has not yet been confirmed because quantifying the strength of quantum fluctuation is not a straightforward matter. Here we show that the local magnetic excitations involving the QFEs can be used to quantify the strength of quantum fluctuation by analyzing six antiferromagnets showing significant reduction in their ordered spin moments.