  The spin valve effect is a quantum phenomenon so far only realized in
multilayer thin films or heterostructures. Here we report a strong spin valve
effect existing in bulk single crystals of Ca3(Ru1-xCrx)2O7 having an
anisotropic, bilayered crystal structure. This discovery opens new avenues to
understand the underlying physics of spin valves, and fully realize its
potential in practical devices.
