Spin Dynamics on Two-Dimensional Heisenberg Antiferromagnets ---High Energy Neutron Inelastic Scattering from La₂CuO₄ and La₂NiO₄---

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Inelastic neutron scattering experiments were performed using a chopper spectrometer, MARI, to elucidate the spin dynamics of two-dimensional quantum Heisenberg antiferromagnets of both La₂CuO₄ (S=1/2) and La₂NiO₄ (S=1) over a wide range of both momentum and energy transfers. The spin dynamics at low temperatures well below the Néel temperature was confirmed to essentially follow two-dimensional spin-wave theory. A quantitative analysis based on spin-wave theory showed that the magnetic form factor determined from the spin excitation is well described by the calculated free-ion magnetic form factor.