MAGNETIC PHASE-DIAGRAM OF CONB2O6 - A NEUTRON-DIFFRACTION STUDY

Elastic neutron diffraction experiments were performed using both a powder sample and a single crystal of CoNb2O6. An intermediate and in the b-direction incommensurate magnetic structure between 2.95 and 1.97 K was found by a least-squares refinement to be sinusoidally modulated with moments lying in the a-c plane, including an angle of gamma = 29.6 degrees with the c-axis. The temperature-dependent propagation vector is k = (0 k(y) 0) with 0.37 less than or equal to k(y) less than or equal to 0.5 for 2.95 K greater than or equal to T greater than or equal to 1.97 K. The magnetic phase diagram for an external field applied in the c-axis direction was determined. With increasing field, two spin-flip phases could be found. Their propagation vectors are k = (0 1/3 0) at lower fields and k = (0 1/2 0) at higher fields.