Crystal Phase Transition Induced by Magnetic Field.

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Magnetic field induced phase transitions of heavy rare earth metals Dy, Ho and Er have been investigated by means of x-ray diffraction technique and following results have been obtained :(1) The magnetic field dependence of the c-lattice parameter in Dy has been observed in the helix phase and the phase transition has been found to be the first order at low temperatures while it exhibits the second order transition near the Neel temperature. In the helix phase under magnetic field, the lattice modulation has been observed, which increases the modulation amplitude with increasing magnetic field.(2) The change of the c-lattice parameter of Ho accomanying to the helix-helifan-fan-ferro transtition has been studied. The lattice modulation is also found in helix and helifan phase and the range of the temperature and magnetic field for appearance of the helifan structure has been studied in detail.(3) The magnetic phase diagram of temperature and magnetic field has been determined for Er. The lattice modulation exhibits rather complicated behavior which is affected by the complicated magnetic structures. The magnetic structure at high field region which was unsure in neutron diffraction has been determined from the experimental results of the lattice modulation.