Ultimately high magnetic properties of low-temperature ferromagnets-dysprosium and holmium-produced by hydrostatic extrusion

Nonstationary hydrostatic extrusion was used to produce homogeneous grain-oriented samples of bulk Dy (d ≥ 30 mm and l = 2000 mm) with the basal plane and easy magnetization axis ([101 0] direction) oriented along the longer axis of samples. The magnetic properties of Dy were studied in magnetic fields of up to 150 kOe at temperatures of 4.2, 20.4, and 77 K. The field dependence of magnetization, the saturation magnetization (4πM s = 37.6 ± 0.1 kG), and the saturation field (H s = 135-136 kOe) correlate with those for a Dy single crystal. Thus, a low-temperature ferromagnet was obtained with the saturation magnetization higher than that for iron by a factor of 1.72. This material may be successfully used for fabricating both bulk magnetic field concentrators, which permit increasing the magnetic field of superconducting solenoids to 200 kOe, and miniature ones for operation at low temperatures. Unusual results obtained for grain-oriented Ho indicate the possibility of changing its ferromagnetic structure by hydrostatic extrusion.