Fermi surface studies near magnetic quantum critical points under high pressure

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1.We have developed piston-cylinder high-pressure cells suitable for de Haas-van Alphen (dHvA) effect measurements at pressures up to 3 GPa, using non-magnetic high-strength alloy NiCrAl.2.We have measured the dHvA effect in the ferromagnetic superconductor UGe_2 up to 〜2 GPa, exceeding the critical pressure, for the magnetic field parallel to the magnetic easy a-axis. We have found that the enhancement of quasiparticle mass at high pressures is not directly related to the ferromagnetic-paramagnetic transition at the critical pressure but is ascribed to the so-called T_x transition.3.We have measured the dHvA effect in ZrZn_2, which was reported to be a ferromagnetic superconductor, at pressures up to -2 GPa. We have found from detailed analyzes of exchange splitting of the Fermi surface a crossover between two magnetic states induced by the magnetic field and have proposed that UGe_2 and ZrZn_2 may have a common temperature-pressure-magnetic-field phase diagram.4.We have measured the dHvA effect in CeIn_3, which exhibits superconductivity near the antiferromagnetic-paramagnetic transition, at pressures up to 〜3 GPa. We have found the appearance of new Fermi surfaces at the critical pressure of the antifermmagnetism and have also found pronounced changes of the Fermi surface at other pressures. Those observations indicate that the change of the electronic structure accompanying the antiferromagnetic-paramagnet is transition occurs successively.