Magnetic relaxation in La 0.250 Pr 0.375 Ca 0.375 MnO 3 with varying phase separation

We have studied the magnetic relaxation properties of the phase-separated manganite compound La 0 . 2 5 0 Pr 0 . 3 7 5 Ca 0 . 3 7 5 MnO 3 . A series of polycrystalline samples was prepared with different sintering temperatures, resulting in a continuous variation of phase fraction between metallic (ferromagnetic) and charge-ordered phases at low temperatures. Measurements of the magnetic viscosity show a temperature and field dependence which can be correlated to the static properties. Common to all the samples, there appears to be two types of relaxation processes: at low fields associated with the reorientation of ferromagnetic domains and at higher fields associated with the transformation between ferromagnetic and nonferromagnetic phases.