Magnetization steps in manganite films: Time delay of the metamagnetic transition

Abstract

We report the appearance of ultrasharp magnetization steps in PLD-grown films of ${\mathrm{Pr}}_{0.65}({\mathrm{Ca}}_{y}{\mathrm{Sr}}_{1\ensuremath{-}y}{)}_{0.35}{\mathrm{MnO}}_{3}$ (PCSMO) with $0.7<~y<~0.8,$ generalizing the phenomena recently observed in polycrystal and single-crystal specimens of this mixed-phase manganite. Our data show that the appearance of steps in these films depends strongly on the nature of the magnetization measurement. In a ``typical'' magnetic field sweep, the magnetization steps appear only in $y=0.8$ thick $(>0.5\ensuremath{\mu}\mathrm{m})$ films. Otherwise, only broad metamagnetic transistions are observed during magnetic field sweeps. However, for these other films, these ``typical'' magnetization curves with broad transitions can be converted to steplike curves upon waiting for a period of minutes to hours at fields close to a phenomenologically defined threshold field, ${H}_{c}.$ Despite the epitaxial film form, the appearance of this ``induction period'' does not appear to result as a consequence of substrate-induced strain. We thus present a picture where the ultrasharp steps are an intrinsic feature of the phase segregated manganites PCSMO independent of their polycrystalline, crystalline, or epitaxial film form. The observation of these step transitions, however, depends strongly on extrinsic effects (i.e., measurement protocol) that may indeed express differences based on the bulk or film geometry of the material.