The microstructure of a thermotropic liquid crystalline polymer orientated in a magnetic field is observed to consist of tessellated domains of high alignment bounded by inversion walls. The presence of these walls limits the degree of global orientation achievable with a given held strength, and leads to the rapid loss of orientation on removal of the field. A supra-molecular lattice model for simulating textures in liquid crystals is utilized to simulate the effect of an applied field on a nematic, and the role of disclinations in the formation and destruction of the network of walls is considered.