Low-temperature magnetic properties of the S = 1/2 kagomé antiferromagnet YCo3(OH)6.55Br2.45.

We report the synthesis, crystal structure, magnetization and specific heat measurements of YCo3(OH)6.55Br2.45 single crystal, in which Co2+ ions occupy a kagomé lattice. YCo3(OH)6.55Br2.45 crystallizes in trigonal structure with the formation of perfect kagomé lattice. The magnetic susceptibility reveals successive magnetic transitions at 6.5 and 7.8 K and the Curie-Weiss fitting demonstrates that YCo3(OH)6.55Br2.45 has strong antiferromagnetic coupling and pronounced magnetic frustration effect. Specific heat data suggest that low-T magnetic transitions are attributed to antiferromagnetic ordering of Co2+ ions and the magnetic entropy points to effective 1/2 spin in the system. These results indicate that an unusual magnetic ordering state with effective spin-1/2 is realized in kagomé lattice system YCo3(OH)6.55Br2.45.