ISSN 0253-2778

CN 34-1054/N

open

Magnetic characterizations. (a–c) The hysteresis loop of (a) Fe3O4, (b) NaGdF4:Yb,Er-Fe3O4 (t=18 h) and (c) NaGdF4:Yb,Er-Fe3O4 (N∶F=4∶1). (d) Photograph of the NaGdF4:Yb,Er-Fe3O4 (N∶F=4∶1) sample attracted by the magnet.