  New Zn1.5Co1.5B7O13Br boracite crystals were grown by chemical transport
reactions in quartz ampoules, at a temperature of 1173 K. The crystal structure
was characterized by X-ray diffraction. The crystals present an orthorhombic
structure with space group Pca21, (No. 29). The determined cell parameters
were: a = 8.5705(3){\AA}, b = 8.5629(3) {\AA}, and c = 12.1198(4){\AA}, and
cell volume, V = 889.45(5) {\AA}3 with Z = 4. Magnetic properties in single
crystals of the new boracite, were determined. The Susceptibility-Temperature
(X -T) behavior at different magnetic intensities was studied. The inverse of
the magnetic susceptibility X-1(T) shows a Curie-Weiss characteristic with spin
s = 3/2 and a small orbital contribution, l. At low temperatures, below 10 K,
X(T) shows irreversibility that is strongly dependent on the applied magnetic
field. This boracite is ferrimagnetic up to a maximum temperature of about 16
K, as shows the coercive field. The reduction of the irreversibility by the
influence of the magnetic field, may be related to a metamagnetic phase
transition.
