Competing two-phase coexistence in doped manganites: Direct observations byin situLorentz electron microscopy

Abstract

We examined thin epitaxial films La 5/8−y Pr y Ca 3/8 MnO 3 ͑LPCMO: y = 0.275− 0.3͒ in situ by Lorentz transmission electron microscopy ͑TEM͒ and other microscopy methods. Clear evidence was obtained for the competing two-phase coexistence of antiferromagnetic charge-ordered ͑CO͒ and ferromagnetic ͑FM͒ phases that exhibit mesoscale phase separation below the metal-to-insulator transition ͑MIT͒ at ϳ164 K. In addition, we observed some regions of mixed CO-and FM-domain contrast attributed earlier to formation of the new CO-FM phase. Using in situ heating/cooling TEM experiments, we interpret this effect as the interfacial wetting phenomenon inherent to the first-order CO-FM phase transition, rather than to the formation of new CO-FM phase. It is evidenced by the partial magnetic melting of CO phase at interfaces with the FM phase, thereby creating charge-disordered spin-glass metastates. For coexisting CO-and FM-domain configurations, we directly refined the relationship between charge-orbital and spin-ordering vectors, consistent with FM moments pinned by ͑101͒-crystal twins in LPCMO films. We also discuss the striking linear dependence observed below MIT for the log-resistance behavior and the CO fraction in LPCMO directly measured by TEM. Such linear dependence does not follow typical percolation equations, suggesting that percolation model needs further revisions for transport description of manganites.

Direct Imaging of Dynamic Glassy Behavior in a Strained Manganite Film

“…Although the dynamics of PS state may be inferred from the transports through a manganite nanowire [13], but these measurements are limited to a narrow temperature range with sufficient conductivity. To date, the PS state with distinct physical properties has been visualized by various microscopy techniques such as scanning tunneling microscopy [14], electron microscopy [15], photoemission spectroscopy [16], magnetic force microscopy [17,18], and recently near-field microwave impedance microscopy (MIM) [19]. However, most of these studies focus on the static phase-separation.…”

Multiple magnetic transitions, dynamical magnetic liquid and magnetic glass in La1−−Pr Ca MnO3 (x≈0.42, y≈0.40) thin films: A thickness dependent study

“…These characteristics are representative of a first order phase transition and have been observed in La 1-x-y Pr y Ca x MnO 3 for wide range of x and y. [6][7][8][9][10][11]14,15 The magnetic liquid freezes at temperatures below the glass transition temperature (T g ) and is characterised by thermally reversible M-T and -T. Although the precise origin of the glass transition is still unclear, it is believed to be driven by the accommodation strain between the interfaces created by the distinct structural symmetries of FMM and AFM/COI phases and has been called as strain glass (SRG).…”

“…[1][2][3][4] Among the large number of compounds investigated for strong intrinsic phase separation, 1 La 1-x-y Pr y Ca x MnO 3 (x>0.3, y>0.4) have emerged as the representative of mesoscopic PS. [5][6][7][8][9][10][11][12][13] One of the unique feature of this family is the keen competition and delicate balance between the FM and AFM magnetic orders over a wide range of x and y values. The balance between FM and AFM phases gives rise to magnetic frustration, which in turn leads to non-equilibrium states below the FM transition temperature (T C ), e.g., the magnetically disordered liquid which is believed to transforms into a random strain glass (SRG) below the glass transition temperature (T g ).…”

“…In strongly phase separated systems like La 1-xy Pr y Ca x MnO 3 the variation in film thickness can also modify the multiple order coupling and associated phase transitions and affect the nature of the dynamical magnetic liquid state through the modulation of the interfacial strain between the coexisting FMM and AFM/COI sublattices via substrate induced strain and its relaxation, which in turn is expected to influence the nature of the frozen SRG. [8][9][10][11][12][13][14]19,[21][22][23][24] Although several studies have reported the impact of substrate induced strain in La 1-x-y Pr y Ca x MnO 3 , [8][9][10][11][12][13]19,[21][22][23][24] investigations embodying a wide range of film thickness sufficient to provide a high strain state and a fully relaxed state have not been carried out. A recent study by Jeon et al 13 has studied the impact of the film thickness in La 0.35 Pr 0.35 Ca 0.30 MnO 3 .…”

Publisher’s Note: Direct Imaging of Dynamic Glassy Behavior in a Strained Manganite Film [Phys. Rev. Lett.115, 265701 (2015)]

“…Although the dynamics of PS state may be inferred from the transports through a manganite nanowire [13], but these measurements are limited to a narrow temperature range with sufficient conductivity. To date, the PS state with distinct physical properties has been visualized by various microscopy techniques such as scanning tunneling microscopy [14], electron microscopy [15], photoemission spectroscopy [16], magnetic force microscopy [17,18], and recently near-field microwave impedance microscopy (MIM) [19]. However, most of these studies focus on the static phase-separation.…”