Anisotropic Cooperative Jahn-Teller Effect and Metamagnetism in PrCu₂

Abstract

We have studied the origin of the cooperative Jahn-Teller effect and themetamagnetic transition in the orthorhombic compound PrCu_2.We have determined the anisotropic ferroquadrupole phase diagram bymeasuring the specific heat and thermal expansion under magnetic fields.With increasing the field, the Jahn-Teller transition temperature increasesslightly for the field along a- and c-axes, while it decreases intensively along the b-axis.The phase diagram can be explained quantitatively by including thequadrupolar interaction of-K_JT‹ O_xy › O_xyin the crystalline electric field and Zeeman Hamiltonian.The metamagnetic transition, which brings about the conversion between theeasy (a)- and hard (c)-axes magnetization, has beenalso studied through the magnetostriction.This phenomenon is also explained quantitatively on the basis of thequadrupolar interaction of-K_M‹ O₂² › O₂².The sign of ‹ O₂² › is found tobe negative in the state where the c-axis is thehard one, while it changes from negative to positive above themetamagnetic transition field.