Single crystal growth and study of the magnetic properties of the mixed spin-dimer system Ba$_{3-x}$Sr$_{x}$Cr$_{2}$O$_{8}$ (1707.03721v2)

Abstract: The compounds Sr${3}$Cr${2}$O${8}$ and Ba${3}$Cr${2}$O${8}$ are insulating dimerized antiferromagnets with Cr$^{5+}$ magnetic ions. These spin-$\frac{1}{2}$ ions form hexagonal bilayers with a strong intradimer antiferromagnetic interaction, that leads to a singlet ground state and gapped triplet states. We report on the effect on the magnetic properties of Sr${3}$Cr${2}$O${8}$ by introducing chemical disorder upon replacing Sr by Ba. Two single crystals of Ba${3-x}$Sr${x}$Cr${2}$O${8}$ with $x=2.9$ (3.33\% of $mixing$) and $x=2.8$ (6.66\%) were grown in a four-mirror type optical floating-zone furnace. The magnetic properties on these compounds were studied by magnetization measurements. Inelastic neutron scattering measurements on Ba${0.1}$Sr${2.9}$Cr${2}$O${8}$ were performed in order to determine the interaction constants and the spin gap for $x=2.9$. The intradimer interaction constant is found to be $J_0$=5.332(2) meV, about 4\% smaller than that of pure Sr${3}$Cr${2}$O${8}$, while the interdimer exchange interaction $J_e$ is smaller by 6.9\%. These results indicate a noticeable change in the magnetic properties by a random substitution effect.