The First Observation of Macroscopic Hysteresis Effect of LiDyF4 Crystal Powders at T>TN

• Micron-sized LiDyF 4 crystal powder is prepared by sintering LiF and DyF 3 powders. • Magnetization measurements of a powder LiDyF 4 sample reveal butterfly hysteresis loops in the paramagnetic state in the temperature range of 2-7 K. This observation is confirmed by single-crystal measurements. • The time-resolved magnetization study indicates slow magnetic relaxation in the same temperature range (2-7 K) with relaxation times up to 50 s. • The first observation of butterfly hysteresis loops for concentrated paramagnetic systems. A lithium – dysprosium double fluoride (LiDyF 4 ) powder is prepared by sintering LiF and DyF 3 powders. Magnetization of the sample is studied in the temperature range of 2-300 K and applied field range of 0-9 T. Butterfly hysteresis loops are observed for the first time in the paramagnetic phase at T < 7 K and are observable down to 2 K (experimental setup limit; T N = 0.6 K). The same hysteresis is revealed for a LiDyF 4 single crystal. Time-resolved magnetization measurements in increasing and decreasing magnetic field at different temperatures demonstrate slow magnetic relaxation with magnetic relaxation times up to 50 s. A diluted tetrafluoride LiYF 4 :Dy 1% single crystal does not display such phenomena.