Magneto-electronic Phase Separation in Pr$_{1-x}$Ca$_{x}$CoO$_{3-\delta }$: Intrinsic Exchange Spring Magnetism*

We present a neutron diffraction, small-angle scattering, and magnetometry study of the narrow bandwidth perovskite cobaltite Pr$_{1-x}$Ca$_{x}$CoO$_{3}$, demonstrating an unusual form of magneto-electronic phase separation where long-range ordered ferromagnetism coexists spatially with short-range ferromagnetism. The two phases have very different coercivities and, remarkably, are strongly exchange coupled. The electronic phase separation thus leads to spontaneous formation of a hard-soft nanocomposite, exhibiting prototypical exchange-spring behavior in the absence of chemical interfaces.