Superparamagnetic-like behavior and spin–orbit coupling in (Co,Zn)RE4W3O16 tungstates (RE=Nd, Sm, Eu, Gd, Dy and Ho)

Magnetic susceptibility measurements carried out on (Co,Zn)RE4W3O16 compounds revealed a disordered state of magnetic moments above 4.2 K for all compounds under study, and a weak response to magnetic field and temperature for ZnSm4W3O16 and ZnEu4W3O16 samples. The temperature independent component of magnetic susceptibility has a negative value for ZnGd4W3O16 and a positive one for the rest of the tungstates, indicating a domination of van Vleck contribution. The magnetization isotherms of majority of the tungstates under study revealed both spontaneous magnetic moments and hysteresis characteristic for the superparamagnetic-like behavior with blocking temperature TB∼30 K, except for ZnEu4W3O16. Fitting procedure of the Landé factor revealed that the stronger the orbital contribution, the weaker the superparamagnetic effect, namely for ZnRE4W3O16. In case of CoRE4W3O16 a significant participation of the Co2+ moment in the spontaneous magnetization was observed.

► (Co,Zn)RE4W3O16 are promising materials to use in white light emitting diodes.
► Majority tungstates under study revealed superparamagnetic-like behavior.
► The stronger the orbital contribution, the weaker the superparamagnetic effect.