Neutron Scattering Studies of the Random Field Domain State in CsCo$_{0.83}$Mg$_{0.17}$Br$_3$

We have extended previous neutron scattering measurements on CsCo$_{0.83}$Mg$_{0.17}$Br$_3$[1], a dilute stacked triangular lattice Ising antiferromagnet. Pure CsCoBr$_3$ exhibits three magnetic phase transitions[2]. At $T_{n1}$=28.3 K a 3 sublattice Neel state forms, in which two sublattices are ordered up and down, while the third remains disordered. This disordered sublattice itself orders below $T_{n2} \sim 16 K$, forming ferrimagnetic sheets which stack antiferromagnetically. The non-magnetic dopants induce a random field domain state at $T_{n1}$ in CsCo$_{0.83}$Mg$_{0.17}$Br$_3$, as the magnetic vacancies couple to the disordered sublattice as a random field. We resent new high resolution results showing the evolution of this random field state in both zero magnetic field and for the case where a magnetic field is applied along the Ising moment direction, the c-axis. [1] J. van Duijn et al. Phys. Rev. Lett. 92, 077202 (2004) [2] M. Mao et al. Phys. Rev. B 66, 184432 (2002)