Magneto-optical investigation of the field-induced spin-glass-insulator to ferromagnetic-metal transition in the bilayer manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7

We measured the magneto-optical response of (La0.4Pr0.6)(1.2)Sr1.8Mn2O7 in order to investigate the microscopic aspects of the magnetic-field-driven spin-glass-insulator to ferromagnetic-metal transition. Application of a magnetic field recovers the ferromagnetic state with an overall redshift of the electronic structure, growth of the bound carrier localization associated with ferromagnetic domains, development of a pseudogap, and softening of the Mn-O stretching and bending modes. We discuss field- and temperature-induced trends within the framework of the Tomioka-Tokura global electronic phase diagram picture and suggest that controlled disorder near a phase boundary can be used to tune the magnetodielectric response. Remnants of the spin-glass-insulator to ferromagnetic-metal transition can also drive 300 K color changes in (La0.4Pr0.6)(1.2)Sr1.8Mn2O7.