Strain-induced metal–insulator phase coexistence in perovskite manganites

Abstract

The coexistence of distinct metallic and insulating electronic phases within the same sample of a perovskite manganite, such as La(1-x-y)Pr(y)Ca(x)MnO3, presents researchers with a tool for tuning the electronic properties in materials. In particular, colossal magnetoresistance in these materials--the dramatic reduction of resistivity in a magnetic field--is closely related to the observed texture owing to nanometre- and micrometre-scale inhomogeneities. Despite accumulated data from various high-resolution probes, a theoretical understanding for the existence of such inhomogeneities has been lacking. Mechanisms invoked so far, usually based on electronic mechanisms and chemical disorder, have been inadequate to describe the multiscale, multiphase coexistence within a unified picture. Moreover, lattice distortions and long-range strains are known to be important in the manganites. Here we show that the texturing can be due to the intrinsic complexity of a system with strong coupling between the electronic and elastic degrees of freedom. This leads to local energetically favourable configurations and provides a natural mechanism for the self-organized inhomogeneities over both nanometre and micrometre scales. The framework provides a physical understanding of various experimental results and a basis for engineering nanoscale patterns of metallic and insulating phases.

Electronically soft phases in manganites

“…Nevertheless, closer inspection of phase diagrams in many manganites reveals complex phases where the two order parameters of magnetism and charge modulation unexpectedly coexist [6,7].Here we show that such experiments can be naturally explained within a phenomenological Ginzburg-Landau theory.In contrast to models where phase separation originates from disorder [8] or as a strain induced kinetic phenomenon [9], we argue that magnetic and charge modulation coexist in new thermodynamic phases. This leads to a rich diagram of equilibrium phases, qualitatively similar to those seen in experiment.…”

“…In contrast to models where phase separation originates from disorder [8] or as a strain induced kinetic phenomenon [9], we argue that magnetic and charge modulation coexist in new thermodynamic phases. This leads to a rich diagram of equilibrium phases, qualitatively similar to those seen in experiment.…”

“…Another consequence of assuming continuous phase transitions is that phase separation cannot be predicted. In real systems phase separation is possible since strain [3,9], or disorder [8], can make more or less localised phases dominate within a given region.Orbital ordering is described by a vector order parameter, thus our simple model cannot address the complexity of different orbitally ordered phases that have been proposed [12].The Ginzburg-Landau phenomenology we propose is capable of systematizing some puzzling data for manganites near x = 1/2, but of course the propensity for mixed and homogeneous phases is driven by the underlying physical parameters that make the energetic cost of spatial fluctuations low. This "electronic softness" means that as well as spatially disordered "phase separation", one finds new ordered phases which are long period arrangements of the two competing orders.…”

Electric field driven dynamic percolation in electronically phase separated (La0.4Pr0.6)Jeen1, Biswas2 2013Phys. Rev. B321310View full textAdd to dashboardCite

“…An alternate route for controlling the magnetism with an electric field is offered in materials with centrosymmetric structures such as perovskite-type manganese oxides (manganites), where the ferromagnetic metallic phase is in competition with a non-ferromagnetic insulating phase close to a first order phase transition [4][5][6]. In the prototypical manganite (La 1−y Pr y ) 1−x Ca x MnO 3 , the competition among the ferromagnetic metallic (FMM), charge-ordered insulating (COI), paramagnetic insulating (PMI) phases leads to multiphase coexistence over a broad range of temperatures [4,7] and makes it possible to tune their properties using external parameters such as magnetic field, electric field, and strain [8][9][10][11].…”

Impact of nanostructuring on the magnetic and magnetocaloric properties of microscale phase-separated La5/8−yPryCaBingham1, Lampen2, Phan3 et al. 2012Phys. Rev. B

“…[11][12][13] The sensitivity of such phase separated systems to a variety of parameters including electric and magnetic field, strain, doping, and particle size introduces the potential for a large degree of tunability in magnetic and structural properties. 5,14,15 Phase separation is most often observed between an insulating antiferromagnetic chargeordered (CO) phase and a metallic ferromagnetic (FM) phase. 1 Charge ordering refers to the periodic arrangement of cations of different oxidation states within a crystal lattice, a common phenomenon in narrow bandwidth manganites in which long-range Coulomb interactions overcome the kinetic energy of the charge carriers.…”