Ferromagnetic to antiferromagnetic transition in the Fe$_{1/3}$(Ta$_{1-x}$Nb$_{x}$)S$_{2}$ layered dichalcogenides

Fe$_{1/3}$TaS$_{2}$ is known to order ferromagnetically with $T_{C}$ = 40 K, while the isostructural Nb compound orders antiferromagnetically below $T_{N}$ = 40 K. The Ta-Nb solid solution provides an opportunity to search for a quantum phase transition (QPT) as we tune the magnetic order in Fe$_{1/3}$TaS$_{2}$ by doping between T = Ta and T = Nb. We will analyze magnetization, specific heat, and resistivity data to search for signatures of a $T$ = 0 transition (QPT). Additionally, we will explore the magnetoresistive effects in these Fe-intercalated TS$_{2}$ (T = Ta, Nb) and compare with our previous results on Fe$_{x}$TaS$_{2}$ ($x$ = 0.25, 0.28). Small departures from the superstructure Fe compositions ($x$ = 0.25, 0.33) in Fe$_{x}$TaS$_{2}$ resulted in two orders of magnitude increase in the magnetoresistance.