Bandwidth-limited control of orbital and magnetic orders in half-doped manganites by epitaxial strain

Abstract

The magnetotransport phase diagram of half-doped manganites Ln0.5A0.5MnO3 (Ln=La3+, Nd3+, etc., and A=Sr2+, Ca2+, etc.) is primarily dictated by the bare conduction bandwith (W0), which itself is controlled by the Mn-O-Mn bond angle, and the carrier concentration. In thin films, epitaxial strain (ε) provides an additional tool to tune W0 by selecting orbital ordering at fixed carrier concentration. Here, we will show that compressive or tensile epitaxial strain on half-doped manganites can have a tremendous and distinct effect on La0.5Sr0.5MnO3 (LSMO5) and La0.5Ca0.5MnO3 (LCMO5), having broad or narrow W0, respectively. It is found that in LSMO5, large compressive strain triggers a change from a ferromagnetic and metallic ground state to an insulating and antiferromagnetic state whereas a tensile strain produces an antiferromagnetic but metallic state. In contrast, under strain, LCMO5 remains an antiferromagnetic insulator irrespectively of the strain state. These results illustrate that orbital ordering largely depends on the interplay between W0 and ε and provide a guideline towards responsive manganite layers

Observation of the Strain Induced Magnetic Phase Segregation in Manganite Thin Films

“…Fine-tuning the growth conditions, in this case the laser frequency, triggers the subtle change of tetragonality required to produce one state or another. Similar dependencies of the saturation magnetization have been observed as a function of the substrate used in half-doped LCMO and LSMO 13 . Interestingly, coercivity follows the same evolution, presenting very low values (< 150 Oe) for low tetragonality and much higher ones above τ C , ranging between 400-600 Oe, which is the indication of a radical change in the magnetic state of the highly strained thin films, as shown later.…”

Correlating melting and collapse of charge ordering with magnetic transitions in La 0.5-x Pr x Ca 0.5 MnO 3

“…2(b) shows variation of major peak, which is shifted to lower temperatures with magnetic field, although, the temperature of minor peak corresponding to T C is not changed. These results can be summarized for the successive magnetic phases with lowering of temperature, namely, PM from room temperature to charge ordered state which is in competition with FM phase and then finally converts into AFM insulator [27,28], as shown in Fig. 2(b).…”

Strain-Driven Orbital and Magnetic Orders and Phase Separation in Epitaxial Half-Doped Manganite Films for Tunneling Devices

“…By inducing a metal to insulator transition in the manganite, a modification in the tunnel barrier width could lead to a giant tunnel electroresistance [5], much larger than in conventional BaTiO 3 -based ferroelectric tunnel junctions [5,6,7] and even larger than in BaTiO 3 ferroelectric barriers with polarization dependent depletion layer in the semiconducting ferroelectric layer [8]. However, although such heterostructures have been fabricated yielding promising results [9], the actual properties and response of the ultrathin HD layer required for tunnel devices may differ from the known properties of nanometric layers [10].…”

“…However, the strain is not the only relevant factor, since the electronic bandwidth seems to play a key role. For instance, Gutiérrez et al [10] recently showed, by means of an exhaustive study of the transport and magnetic properties of La 0.5 Sr 0.5 MnO 3 (LSMO) and La 0.5 Ca 0.5 MnO 3 (LCMO) thin films, that the magnetization and metallic behaviour of LSMO films can be largely controlled by strain, while LCMO films remain in a non-FM insulating state independently of the applied strain. The narrower bandwidth of LCMO seems to play a relevant role, by promoting electron localization and favouring the appearance of electronic phase separation and charge localization as already observed in bulk HD manganites [15].…”