Doping dependence of the magnetic ground state in the frustrated magnets Ba$_2$$M$Te$_{1-x}$W$_{x}$O$_6$ ($M$ = Mn, Co)

Abstract

Theoretically, the relative change of the Heisenberg-type nearest-neighbor coupling $J_1$ and next-nearest-neighbor coupling $J_2$ in the face-centered-cubic lattice can give rise to three main antiferromagnetic orderings of type-I, type-II, and type-III. However, it is difficult to tune the $J_2/J_1$ ratio in real materials. Here, we report studies on the influence of Te$^{6+}$ and W$^{6+}$ ions replacement to the magnetic interactions and the magnetic ground states in the double-perovskite compounds Ba$_2$$M$Te$_{1-x}$W$_{x}$O$_6$ ($M$ = Mn, Co). For Ba$_2$MnTe$_{1-x}$W$_{x}$O$_6$, the W$^{6+}$ doping on Te$^{6+}$ site is successful in $0.02 \leq x \leq 0.9$ with short-range orders of the type-I ($0.02 \leq x \leq 0.08$) and type-II ($0.1 \leq x \leq 0.9$). In Ba$_2$CoTe$_{1-x}$W${_x}$O$_6$, x-ray diffraction measurements reveal two crystal structures, including the trigonal phase ($0 \leq x \leq 0.1$) and the cubic phase ($0.5 \leq x \leq 1$), between which is a miscibility gap. Two magnetic transitions are identified in the trigonal phase due to two magnetic subsystems, and the type-II magnetic order is observed in the cubic phase. Magnetic phase diagrams of Ba$_2M$Te$_{1-x}$W$_{x}$O$_6$ ($M$ = Mn, Co) are established. Our work shows that the magnetic interactions and ground states of Ba$_2$$M$Te$_{1-x}$W$_x$O$_6$ can be tuned effectively by the replacement of Te$^{6+}$ by W$^{6+}$ ions.