Presented are slotted permanent magnets (PM) for electric machines, motor generator units using slotted PMs, methods for making/using slotted PMs, and motor vehicles equipped with an electric traction motor using slotted PMs. An electric machine includes an annular stator with a hollow core and one or more internal stator slots. One or more electrically conductive windings is/are disposed in the stator slot(s). A cylindrical rotor is rotatably disposed inside the hollow core of the stator. One or more permanent magnets is/are mounted to the rotor. Each permanent magnet includes a rigid, single-piece PM body with opposing first and second faces. A first set of elongated grooves is recessed into the first face. An optional second set of elongated grooves is recessed into the second face. Each of the grooves has a depth that is substantially parallel to a direction of a magnetic field generated by the permanent magnet.