Europhys. Lett.
Volume 61, Number 4, February 2003
Page(s) 534 - 540
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 01 February 2003
DOI: 10.1209/epl/i2003-00162-1
Europhys. Lett., 61 (4) , pp. 534-540 (2003)

Quantum phase transition in $\chem{Pr_2CuO_4}$ to collinear non-spin-flop state in magnetic field: A neutron diffraction study

V. P. Plakhty1, S. V. Maleyev1, S. V. Gavrilov1, F. Bourdarot2, 3, S. Pouget2, 3 and S. N. Barilo4

1  Petersburg Nuclear Physics Institute RAS - Gatchina, 188300 St. Petersburg, Russia
2  CEA-Grenoble, DRFMC/SPSMS/MDN - 38042 Grenoble Cedex 9, France
3  Institut Laue-Langevin - BP 156, 38042 Grenoble Cedex 9, France
4  Institute for Solid State and Semiconductor Physics BYAS - 220072 Minsk, Belarus

(Received 17 July 2002; accepted in final form 4 December 2002)

In the external field applied to the tetragonal antiferromagnet $\chem{Pr_2CuO_4}$, a transition is discovered from the phase with orthogonal antiferromagnetic spin subsystems along [1,0,0] and [0,1,0] to the phase with collinear spins, which are inclined about $45^\circ$ to the field. This phase is shown to be due to the interplane pseudodipolar interaction, and transforms into the spin-flop phase $(\bm{S}\perp\bm{H})$ asymptotically at very high field. The discovered phase transition is of first order, if the field is along [1,0,0], or [0,1,0], and becomes of second order if the field is slightly inclined to these axes. It holds at T = 0 and is a quantum one, with the transition field being the critical point and the angle between two subsystems below the critical point being the order parameter.

75.25.+z - Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source X-ray scattering, etc.).
75.30.Kz - Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.).
75.50.Ee - Antiferromagnetics.

© EDP Sciences 2003