Commensurate-incommensurate magnetic phase transition induced in TbNi^sub 5^ by an external magnetic field

Neutron-diffraction studies of a single crystal of TbNi^sub 5^ have been performed. Temperature and field dependences of the intensities of the Bragg reflection (001) and magnetic satellites (001)^sup -^ and (001)^sup +^ have been determined. In the temperature range of 7-10 K, sharp changes in the intensities of both the Bragg reflection and its satellites have been revealed. A conclusion is made that these changes are due to the existence of a magnetic transition from an incommensurate into a lock-in structure. It has been found that at 11 K an external magnetic field μ^sub 0^ H = 0.1 T oriented along the [100] axis induces the same magnetic state of the crystal as its cooling to 7 K in the absence of a field. In an external magnetic field μ^sub 0^ H = 0.4 T, there occurs a magnetic transition from the incommensurate phase with a wave vector k = 2π/c (0, 0, 0.18) into a commensurate ferromagnetic phase with k = 0. In the ferromagnetic phase, an increase in the field from 0.4 to 0.6 T is accompanied by an increase in the intensity of the ferromagnetic reflection (001) by a factor of 1.6. This indicates the existence of strong fluctuations of the magnetization at 0.4 T.[PUBLICATION ABSTRACT]