dHvA Effect Study of Metamagnetic Transition in CeRu₂Si₂ II - The State above the Metamagnetic Transition

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We have performed an extensive dHvA effect study of CeRu₂Si₂ to gain more insight into the nature of the metamagnetic transition. The angular dependence of the dHvA frequencies confirms the transition of the Fermi surfaces from those of the itinerant f electron below the metamagnetic transition field (H_m) to those of the localized f electron above H_m. The field dependence of the frequencies and effective masses are measured for all the frequencies observed with fields parallel to [001]. A waveform analysis suggests that the Fermi surfaces of the up and down spin electrons are similar in size, whereas the effective masses are significantly different. The amplitudes of the dHvA oscillations and their field dependence are anomalous above H_m, implying that the dHvA oscillations above H_m may possibly come from a state which is not well developed near H_m.