Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userComplete melting of charge order in hydrothermally grown Pr_0.57 Ca_0.41 Ba_0.02 MnO_3 nanowires
211
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Nanowires of Pr_0.57 Ca_0.41 Ba_0.02 MnO_3 (PCBM) (diameter ~ 80-90 nm and length ~ 3.5 mm) were synthesized by a low reaction temperature hydrothermal method. Single-phase nature of the sample was confirmed by XRD experiments. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and microstructures of the nanowires. While the bulk PCBM is known to exhibit charge order (CO) below 230 K along with a ferromagnetic transition at 110 K, SQUID measurements on the nanowires of PCBM show that the charge order is completely absent and a ferromagnetic transition occurs at 115 K. However, the magnetization in the nanowires is observed to be less compared to that in the bulk. This observation of the complete melting of the charge order in the PCBM nanowires is particularly significant in view of the observation of only a weakening of the CO in the nanowires of Pr_0.5 Ca_0.5 MnO_3. Electron paramagnetic resonance experiments were also carried out on the PCBM nanowires using an X-band EPR spectrometer. Characteristic differences were observed in the line width of nanowires when compared with that of the bulk.
rate research
Read More
Nd_0.5 Ca_0.5 MnO_3 (NCMO) nanoparticles (average diameter ~ 20 and 40 nm) are synthesized by polymeric precursor sol-gel method and characterized by X- ray diffraction, transmission electron microscopy (TEM), selective area electron diffraction (SAED), superconducting quantum interference device (SQUID) magnetometery and resistivity measurements. Both single crystalline and polycrystalline particles are present in the samples and they are found to retain the orthorhombic structure of the bulk NCMO. However, most strikingly, in the 20 nm particles, the charge ordered (CO) and the antiferromagnetic phases observed in the bulk at 250 K and 160 K respectively are completely absent. Instead, a ferromagnetic (FM) transition is observed at 95 K followed by an insulator to metal transition at 75 K. In the 40 nm particles, though a weak, residual CO phase is observed, transition to FM state also occurs, but at a slightly higher temperature of 110 K. The magnetization is found to increase with the decrease of particle size.
We study the electronic structure, magnetic state, and phase stability of paramagnetic BiNiO$_3$ near a pressure-induced Mott insulator-to-metal transition (MIT) by employing a combination of density functional and dynamical mean-field theory. We obtain that BiNiO$_3$ exhibits an anomalous negative-charge-transfer insulating state, characterized by charge disproportionation of the Bi $6s$ states, with Ni$^{2+}$ ions. Upon a compression of the lattice volume by $sim$4.8%, BiNiO$_3$ is found to make a Mott MIT, accompanied by the change of crystal structure from triclinic $Pbar{1}$ to orthorhombic $Pbnm$. The pressure-induced MIT is associated with the melting of charge disproportionation of the Bi ions, caused by a charge transfer between the Bi $6s$ and O $2p$ states. The Ni sites remain to be Ni$^{2+}$ across the MIT, which is incompatible with the valence-skipping Ni$^{2+}$/Ni$^{3+}$ model. Our results suggest that the pressure-induced change of the crystal structure drives the MIT in BiNiO$_3$.
We report temperature-dependent surface x-ray scattering studies of the orbital ordered surface in La$_{0.5}$Sr$_{1.5}$MnO$_4$. We find that the interfacial width of the electronic order grows as the bulk ordering temperature is approached from below, though the bulk correlation length remains unchanged. Close to the transition, the surface is so rough that there is no well-defined electronic surface, despite the presence of bulk electronic order, that is the electronic surface has melted. Above the bulk transition, finite-sized isotropic fluctuations of orbital order are observed, with a correlation length equal to that of the electronic surfaces in-plane correlation length at the transition temperature.
We have studied the effect of electric field on transport properties of the prototypical phase separated manganite La5/8-yPryCa3/8MnO3 with y=0.34. Our results show that the suggested image in which the charge ordered state is melted by the appliance of an electric current and/or voltage has to be revised. We were able to explain the observed resistivity drop in terms of an artifact related to Joule heating and the particular hysteresis that the system under study display, common to many other phase separated manganites.
Charge density waves (CDWs) underpin the electronic properties of many complex materials. Near-equilibrium CDW order is linearly coupled to a periodic, atomic-structural distortion, and the dynamics is understood in terms of amplitude and phase modes. However, at the shortest timescales lattice and charge order may become de-coupled, highlighting the electronic nature of this many-body broken symmetry ground state. Using time and angle resolved photoemission spectroscopy with sub-30-fs XUV pulses, we have mapped the time- and momentum-dependent electronic structure in photo-stimulated 1T-TaS2, a prototypical two-dimensional charge density wave compound. We find that CDW order, observed as a splitting of the uppermost electronic bands at the Brillouin zone boundary, melts well before relaxation of the underlying structural distortion. Decoupled charge and lattice modulations challenge the view of Fermi Surface nesting as a driving force for charge density wave formation in 1T-TaS2.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
