Phase Diagram of the Dzyaloshinskii-Moriya Helimagnet Ba2CuGe2O7 in Canted Magnetic Fields

TL;DR

This study maps the magnetic phase diagram of Ba2CuGe2O7 under various magnetic field orientations, confirming the existence of complex incommensurate phases and transitions, using neutron diffraction, magnetization, and specific heat measurements.

Contribution

It provides a systematic analysis of magnetic structures and phase transitions in Ba2CuGe2O7 for different field orientations, confirming the incommensurate double-k AF-cone phase and identifying a distorted cycloidal structure.

Findings

Confirmation of the incommensurate double-k AF-cone phase near the c-axis.

Observation of a complex distorted non-sinusoidal magnetic structure at large angles.

Identification of an incommensurate/commensurate transition around 9 T in the basal plane.

Abstract

The evolution of different magnetic structures of non-centrosymmetric Ba2CuGe2O7 is systematically studied as function of the orientation of the magnetic field H. Neutron diffraction in combination with measurements of magnetization and specific heat show a virtually identical behaviour of the phase diagram of Ba2CuGe2O7 for H confined in both the (1,0,0) and (1,1,0) plane. The existence of a recently proposed incommensurate double-k AF-cone phase is confirmed in a narrow range for H close to the tetragonal c-axis. For large angles enclosed by H and the c-axis a complexely distorted non-sinusoidal magnetic structure has recently been observed. We show that its critical field Hc systematically increases for larger canting. Measurements of magnetic susceptibility and specific heat finally indicate the existence of an incommensurate/commensurate transition for H /sim 9 T applied in the basal (a,b)-plane and agree with a non-planar, distorted cycloidal magnetic structure.