For the first time the magnetic phase transition in DyF₃ at low temperatures was observed by ³He NMR. The spin kinetics of liquid ³He in contact with a mixture of microsized powders LaF₃ (99.67%) and DyF₃ (0.33%) at temperatures 1.5-3 K was studied by pulse NMR technique. The DyF₃ is a dipole dielectric ferromagnet with a phase transition temperature T_c = 2.55 K, while as the diamagnetic fluoride LaF₃ used as a diluent for optimal conditions for observation of ³He NMR. The phase transition in DyF₃ is accompanied by a significant changes in the magnetic fluctuation spectrum of the dysprosium ions. The spin kinetics of ³He in contact with the substrate is sensitive to this fluctuations. An significant change in the rates of the longitudinal and transverse nuclear magnetization of ³He in the region of magnetic ordering of solid matrix was observed. A technique is proposed for studying the static and fluctuating magnetic fields of a solid matrix at the low temperatures using liquid ³He as a probe.

Е.М. Аlakshin, Е.I. Kondratyeva, V.V. Kuzmin, К.R. Safiullin, А.А. Stanislavovas, А.V. Savinkov, А.V. Klochkov,  М.S. Tagirov

JETP Letters 107 issue 2, 2018