This is because the raw material consists of many magnetic crystallites whose magnetic moments cancel each other until they are aligned. The moments on the Mn atoms at the corners of the cube point in one direction, and at the centre of the cube they point in the opposite direction.
Many magnetic structures are much more complex.
Single crystal techniques using polarized neutrons and strong magnetic fields are needed however, to understand the most complex magnetic structures. Or consider the importance of magnets in communications and other electronic equipment. Already such materials are being used by IBM to make computer hard drives of much higher capacity. This GMR material has a familiar perovskite-type structure, which is subtly distorted with temperature. The complex magnetic structure is not shown, but this, together with the structural distortions, are important for understanding the unique properties of these materials.