We report investigations of the structural, magnetic, electrical transport and thermal properties of five compositions of the metallic perovskite GdRh$_3$C$_{1-x}$B$_x$ ($0.00 \le x \le 1.00$). Our results show that all the five compositions undergo magnetic ordering at low temperatures, but the nature of the ordered state is significantly different in the carbon- and the boron-rich compositions, where the former shows signatures of an amplitude-modulated magnetic structure and the latter exhibits evidences of an equal-moment incommensurate antiferromagnetic ordering. We also observe a remarkable field-dependent evolution of conduction carrier polarization in the compositionally disordered compounds. The outcomes indicate that this system is energetically situated in proximity to a magnetic instability where small variations in the control parameter(s), such as lattice constant and/or electron density, lead to considerably different ground states.
Femtosecond reflection spectroscopy was performed on a perovskite-type manganite, Gd0.55Sr0.45MnO3, with the short-range charge and orbital order (CO/OO). Immediately after the photoirradiation, a large increase of the reflectivity was detected in the mid-infrared region. The optical conductivity spectrum under photoirradiation obtained from the Kramers-Kronig analyses of the reflectivity changes demonstrates a formation of a metallic state. This suggests that ferromagnetic spin arrangements occur within the time resolution (ca. 200 fs) through the double exchange interaction, resulting in an …
We have investigated the structure and electronic properties of ferrimagnetic double perovskites, A2FeReO6 (A= Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m) and metallic, while the A=Ca phase is monoclinic (P21/n) and nonmetallic. 57Fe Mossbauer spectroscopy shows that iron is present mainly in the high-spin (S=5/2) Fe3+ state in the Ca compound, while it occurs in an intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. It is argued that a direct Re t2g - Re t2g interaction is the main cause for the metallic character of the Ba compound; the high covalency of Ca-O bonds and the…
A remarkable hardening (~ 30 cm-1) of the normal mode of vibration associated with the symmetric stretching of the oxygen octahedra for the Ba2FeReO6 and Sr2CrReO6 double perovskites is observed below the corresponding magnetic ordering temperatures. The very large magnitude of this effect and its absence for the anti-symmetric stretching mode provide evidence against a conventional spin-phonon coupling mechanism. Our observations are consistent with a collective excitation formed by the combination of the vibrational mode with oscillations of local Fe or Cr 3d and Re 5d occupations and spin m…
We report a study of the magnetoresistance (MR) of the metallic perovskite oxide LaNiO$_{3-δ}$ as a function of the oxygen stoichiometry $δ$ ($δ\leq$ 0.14), magnetic field (H $\leq 6T$) and temperature (1.5K $\leq $ T $\leq $ 25K). We find a strong dependence of the nature of MR on the oxygen stoichiometry. The MR at low temperatures change from positive to negative as the sample becomes more oxygen deficient (i.e, $δ$ increases). Some of the samples which are more resistive, show a resistivity minima at $T_{min}$ $\approx$ 20K. We find that in these samples the MR is positive at T > $T_{min}$…
We present the self-interaction corrected local spin density (SIC-LSD) electronic structure and total energy calculations, leading also to valencies of the ground state configurations, for the half-metallic double perovskites such as Sr$_{2}$FeMoO$_{6}$, Ba$_{2}$FeMoO$_{6}$, Ca$_{2}$FeMoO$_{6}$, and Ca$_{2}$FeReO$_{6}$. We conclude that the Fe and Mo (or Re) spin magnetic moments are anti-parallel aligned, and the magnitude of the hybridization induced moment on Mo does not vary much between the different compounds. The hybridization spin magnetic moment on Re is of the order of -1.1 $μ_{B}$, …
We study the effect of Coulomb interactions in transition metal oxides junctions. In this paper we analyze charge transfer at the interface of a three layer ferromagnetic-paramagnetic-ferromagnetic metallic oxide system. We choose a charge model considering a few atomic planes within each layer and obtain results for the magnetic coupling between the ferromagnetic layers. For large number of planes in the paramagnetic spacer we find that the coupling oscillates with the same period as in RKKY but the amplitude is sensitive to the Coulomb energy. At small spacer thickness however, large differe…
We consider a model of the double perovskite Ba2FeReO6, a room temperature ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in the background of Fe moments stabilized by Hund's coupling. We show that for such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are essential in driving a half-metallic ground state. Incorporating both strong spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure consistent with ab initio calculations. Using our model, we find a large spin polarization at the Fermi level, and obtain a semi-quantita…
We discuss Mott insulating and metallic phases of a model with $e_g$ orbital degeneracy to understand physics of Mn perovskite compounds. Quantum Monte Carlo and Lanczos diagonalization results are discussed in this model. To reproduce experimental results on charge gap and Jahn-Teller distortions, we show that a synergy between the strong correlation effects and the Jahn-Teller coupling is important. The incoherent charge dynamics and strong charge fluctuations are characteristic of the metallic phase accompanied with critical enhancement of short-ranged orbital correlation near the insulator…
We have measured the photoemission spectra of Nd$_{1-x}$Sm$_{x}$NiO$_{3}$, where the metal-insulator transition and the Néel ordering occur at the same temperature for $x \lesssim 0.4$ and the metal-insulator transition temperature ($T_{MI}$) is higher than the Néel temperature for $x \gtrsim 0.4$. For $x \le 0.4$, the spectral intensity at the Fermi level is high in the metallic phase above $T_{MI}$ and gradually decreases with cooling in the insulating phase below $T_{MI}$ while for $x > 0.4$ it shows a pseudogap-like behavior above $T_{MI}$ and further diminishes below $T_{MI}$. The results…
The double perovskite material \SFMO has the rare and desirable combination of a half-metallic ground state with 100% spin polarization and ferrimagnetic \Tc$\simeq 420$K, well above room temperature. In this two-part paper, we present a comprehensive theoretical study of the magnetic and electronic properties of half metallic double perovskites. In this paper we present exact diagonalization calculations of the "fast" Mo electronic degrees coupled to "slow" Fe core spin fluctuations treated by classical Monte Carlo techniques. From the temperature dependence of the spin-resolved density of st…
Double perovskites like Sr$_2$FeMoO$_6$ are materials with half-metallic ground states and ferrimagnetic T$_{\rm{c}}$'s well above room temperature. This paper is the second of our comprehensive theory for half metallic double perovskites. Here we derive an effective Hamiltonian for the Fe core spins by "integrating out" the itinerant Mo electrons and obtain an unusual double square-root form of the spin-spin interaction. We validate the classical spin Hamiltonian by comparing its results with those of the full quantum treatment presented in the companion paper "Theory of Half-Metallic Double …
We present a comprehensive theory of the temperature- and disorder-dependence of half-metallic ferrimagnetism in the double perovskite Sr$_2$FeMoO$_6$ (SFMO) with $T_c$ above room temperature. We show that the magnetization $M(T)$ and conduction electron polarization $P(T)$ are both proportional to the magnetization $M_S(T)$ of localized Fe spins. We derive and validate an effective spin Hamiltonian, amenable to large-scale three-dimensional simulations. We show how $M(T)$ and $T_c$ are affected by disorder, ubiquitous in these materials. We suggest a way to enhance $T_c$ in SFMO without sacri…
We present a powder inelastic neutron scattering study of magnetic excitations in Ba$_2$FeReO$_6$, a member of the double perovskite family of materials which exhibit half-metallic behavior and high Curie temperatures. We find clear evidence of two well-defined dispersing magnetic modes in its low temperature ferrimagnetic state. We develop a local moment model, which incorporates the interaction of Fe spins with spin-orbit locked magnetic moments on Re, and show that this captures our experimental observations. Our study further opens up double perovskites as model systems to explore the inte…
Based on the theoretical exploration of electronic structures, we propose that the ordered double perovskites LaAVRuO$_6$ and LaVO$_3$/ARuO$_3$ (001) superlattice (A = Ca, Sr and Ba) are strong candidates for half-metallic (HM) antiferromagnets (AFMs). %LaAVRuO$_6$ and LaVO$_3$/ARuO$_3$ have the %100% spin polarizations at the Fermi level but with zero %total magnetic moments. We have shown that the HM-AFM nature in LaAVRuO$_6$ is very robust regardless of (i) divalent ion replacement at A-sites, (ii) oxygen site relaxation, (iii) the inclusion of the Coulomb correlation, and (iv) cation disor…
We present a microscopic theory of carrier-induced ferrimagnetism in metallic double perovskite compounds such as ${\rm Sr}_{2}{\rm FeMoO}_{6}$ and ${\rm Sr}_{2}{\rm FeReO}_{6}$ which have recently attracted intense interest for their possible applications to magnetotransport devices. The theory is based on an effective "Kondo-like" Hamiltonian treated here within the large-$S$ expansion. We find that depending on the value of the carrier density the ground state is either a ferrimagnet or a layered antiferromagnet. The ferrimagnetic state has a robust half-metallic electronic structure. The t…
A previously unreported Pb-based perovskite PbMoO$_3$ is obtained by high-pressure and high-temperature synthesis. This material crystallizes in the $Pm\bar{3}m$ cubic structure at room temperature, making it distinct from typical Pb-based perovskite oxides with a structural distortion. PbMoO$_3$ exhibits a metallic behavior down to 0.1 K with an unusual $T$-sub linear dependence of the electrical resistivity. Moreover, a large specific heat is observed at low temperatures accompanied by a peak in $C_P/T^3$ around 10 K, in marked contrast to the isostructural metallic system SrMoO$_3$. These t…
We report an interesting reentrant metallic resistivity pattern beyond a characteristic temperature T* which is higher than other such characteristic transition temperatures like T(c)(Curie point), T(N) (Neel point), T(CO) (charge order onset point) or T(OO) (orbital order onset point) in a range of rare-erath perovskite manganites (RE(1-x)A(x)MnO(3); RE = La, Nd, Y; A = Sr, Ca; x = 0.0-0.5). Such a behavior is normally observed in doped manganites with doping level (x) higher than the critical doping level x(c) (= 0.17-0.22) required for the metallic ground state to emerge and hence in a syst…
The new perovskite cuprate material Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$, which behaves ferrimagnetically and shows an unusually high Curie temperature ($T_c \sim$ 440 K), is found from density-functional theory calculation to display several surprising properties after hole doping or chemical substitution: (1) Half metal (HM) is realized by replacing Re with W or Mo while $T_c$ remains high; (2) hole-doped Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$ is also HM with high $T_c$. Moreover, we find that the O atoms will carry a large magnetic moment after hole doping, which is in sharp contrast with the gen…
The zero-field conductivities ($σ$) of the polycrystaline title materials, are governed by inter-grain transport. In the majority of cases their $σ$(T) can be described by the "fluctuation induced tunneling" model. Analysis of the results in terms of this model reveals two remarkable features: 1. For \emph{all} Sr$_2$FeMoO$_6$ samples of various microstructures, the tunneling constant (barrier width $\times$ inverse decay-length of the wave-function) is $\sim$ 2, indicating the existence of an intrinsic insulating boundary layer with a well defined electronic (and magnetic) structure. 2. The t…
Using ab initio calculations, we have investigated a cubic perovskite BaOsO3 and a few related compounds that have been synthesized recently and formally have a metallic d^4 configuration. In BaOsO3, which shows obvious 3-dimensional fermiology, a nonmagnetism is induced by a large spin-orbit coupling (SOC), which is precisely equal to an exchange splitting ~0.4 eV of the $t_{2g}$ manifold. However, the inclusion of on-site Coulomb repulsion as small as $U^c$~1.2 eV, only 1/3 of the $t_{2g}$ bandwidth, leads to the emergence of a spin-ordered moment, indicating that this system is on the verge…
We report here on the electronic structure of electron-doped half-metallic ferromagnetic perovskites such Sr$_{2-x}$La$_x$FeMoO$_6$ ($x$=0-0.6) as obtained from high-resolved valence-band photoemission spectroscopy (PES). By comparing the PES spectra with band structure calculations, a distinctive peak at the Fermi level (E$_F$) with predominantly (Fe+Mo) t$_{2g}^\downarrow$ character has been evidenced for all samples, irrespectively of the $x$ values investigated. Moreover, we show that the electron doping due to the La substitution provides selectively delocalized carriers to the t$_{2g}^\d…
We investigate the unusual phase transitions in SrRuO$_{3}$ and Sr$_{0.5}$Ca$_{0.5}$Ru$_{1-x}$Cr$_{x}$O$_{3}$ (x=0,0.05 and 0.1) employing x-ray diffraction, resistivity, magnetic studies and x-ray photoemission spectroscopy. Our results show the compounds undergo crossover from $itinerant$ ferromagnetism to $localised$ ferromagnetism. The combined studies suggests Ru and Cr to be in 4+ valence state. A Griffith phase and an enhancement in Curie temperature (Tc) from 38 K to 107 K is observed with Cr doping. A shift in the chemical potential towards the valence band is observed with Cr doping.…
The gigantic decrease of resistance by an applied magnetic field, which is often referred to as colossal magnetoresistance (CMR), has been an attracting phenomenon in strongly correlated electron systems. The discovery of CMR in manganese oxide compounds has developed the science of strong coupling among charge, orbital, and spin degrees of freedom. CMR is also attracting scientists from the viewpoint of possible applications to sensors, memories, and so on. However, no application using CMR effect has been achieved so far, partly because the CMR materials which satisfy all of the required con…
he structural, transport, magnetic and optical properties of the double perovskite $A_2$CrWO$_6$ with $A=\text{Sr, Ba, Ca}$ have been studied. By varying the alkaline earth ion on the $A$ site, the influence of steric effects on the Curie temperature $T_C$ and the saturation magnetization has been determined. A maximum $T_C=458$ K was found for Sr$_2$CrWO$_6$ having an almost undistorted perovskite structure with a tolerance factor $f\simeq 1$. For Ca$_2$CrWO$_6$ and Ba$_2$CrWO$_6$ structural changes result in a strong reduction of $T_C$. Our study strongly suggests that for the double perovsk…
The two-dimensional layered perovskite Sr2IrO4 was proposed to be a spin-orbit Mott insulator, where the effect of Hubbard interaction is amplified on a narrow J_{eff} = 1/2 band due to strong spin-orbit coupling. On the other hand, the three-dimensional orthorhombic perovskite (Pbnm) SrIrO3 remains metallic. To understand the physical origin of the metallic state and possible transitions to insulating phases, we construct a tight-binding model for SrIrO3. The band structure possesses a line node made of J_{eff} = 1/2 bands below the Fermi level. As a consequence, instability towards magnetic …
Single crystalline (Bi,Ca)MnO3 (74< %Ca <82) were studied with neutron scattering, electron diffraction and bulk magnetic measurement. We discovered dynamic ferromagnetic spin correlations at high temperatures, which are replaced by antiferromagnetic spin fluctuations at a concomitant charge ordering and structural transition. Our results indicate that thermal-activated hopping of the Jahn-Teller active e_g electrons in these insulating materials, nevertheless, induce ferromagnetic interaction through double-exchange mechanism. It is the ordering of these charges competing with the double-exch…
We analyzed the possible magnetic and orbital orderings of double perovskites, using a simple extension of the double exchange model well suited for these compounds. Orbital ordering is favored by the on site repulsion at the Fe ions. We obtain a rich phase diagram, including ferri- and antiferromagnetic phases, which can, in turn, be metallic or insulating, depending on the existence of orbital order.
Structural study on the photo-switching system Pr{0.55}(Ca{1-y}Sr y){0.45}MnO3 thin films on perovskite (011) substrate has been made with synchrotron radiation diffraction experiment. The insulating phase of y=0.20 sample was found to be an antiferro-orbital ordered phase with large lattice distortion and the ferromagnetic metallic phase of y=0.40 film show no distinct lattice distortion from the paramagnetic phase, which are very similar with (Nd,Pr)0.5Sr0.5MnO3 films. A striking contrast of the orbital ordered phase of y=0.20 film to (Nd,Pr)0.5Sr0.5MnO3 films was its untwinned structure.
Recently, in the seemingly narrow gap insulating NiCrO$_3$ with the trigonally distorted (R-3c) perovskite-like structure, a compensated half-metal (CHM) is predicted, as applying a modest pressure. Using ab initio calculations including both Coulomb correlations and spin-orbit coupling (SOC), we investigate the as-yet-unsynthesized PdCrO$_3$, isostructural and isovalent to NiCrO$_3$. Upon applying the on-site Coulomb repulsion $U$ to both Pd and Cr ions, the Cr spin moment is precisely compensated with the antialigned spin moments of Pd and oxygens. Coincidentally only one spin channel remain…
We report angle-resolved photoemission spectroscopy (ARPES) results of A-site ordered perovskite CaCu$_3$Ti$_4$O$_{12}$. We have observed the clear band dispersions, which are shifted to the higher energy by 1.7 eV and show the band narrowing around 2 eV in comparison with the local density approximation calculations. In addition, the high energy multiplet structures of Cu 3$d^8$ final-states have been found around 8 - 13 eV. These results reveal that CaCu$_3$Ti$_4$O$_{12}$ is a Mott-type insulator caused by the strong correlation effects of the Cu 3$d$ electrons well hybridized with O 2$p$ st…
We have investigated the electronic and magnetic properties of perovskite SrRu1-xIrxO3 thin films grown by pulsed laser deposition on atomically-flat (001) SrTiO3 substrates. SrRuO3 has the properties of a ferromagnetic metal with Curie temperature 150 K. Substituting Ir for Ru in SrRuO3, films showed fully-metallic behavior and ferromagnetic ordering, although resistivity increased and the ferromagnetic TC decreased. Films with x = 0.25 underwent the metal-to-insulator transition at 75 K, and spin-glass-like ordering at 45 K with the elimination of ferromagnetic long-range ordering caused by …
In their ideal structure, double perovskites like Sr_2FeMoO_6 have alternating Fe and Mo along each cubic axes, and a homogeneous ferromagnetic metallic ground state. Imperfect annealing leads to the formation of structural domains. The moments on mislocated Fe atoms that adjoin each other across the domain boundary have an antiferromagnetic coupling between them. This leads to a peculiar magnetic state, with ferromagnetic domains coupled antiferromagnetically. At short distance the system exhibits ferromagnetic correlation while at large lengthscales the net moment is strongly suppressed due …
A microscopic characterisation of the phase transitions associated with colossal magnetoresistance (CMR) in manganese perovskite oxides is a very important ingredient in the quest of understanding its underlying mechanism. Scanning tunneling microscopy (STM) is most suitable to investigate some of their reported hallmarks, including charge ordering, lattice distortions, and electronic phase separation. Here we investigate Bi1-XCaXMnO3 (BCMO) with x=0.76. At this composition, BCMO develops an insulating charge-ordered phase upon cooling, whose study as a function of temperature will allow ident…
In the family of double perovskites, colossal magnetoresistance (CMR) has been so far observed only in half-metallic ferrimagnets such as the known case Sr$_2$FeMoO$_6$ where it has been assigned to the tunneling MR at grain boundaries due to the half-metallic nature. Here we report a new material-Tl$_2$NiMnO$_6$, a relatively ordered double perovskite stablized by the high pressure and high temperature synthesis-showing CMR in the vicinity of its Curie temperature. We explain the origin of such effect with neutron diffraction experiment and electronic structure calculations that reveal the ma…
We investigate the metal-insulator transition in the layered Ruddelsden Popper series of strontium iridates Srn+1IrnO3n+1. Tight-binding models of t2g orbitals for n = 1, 2, and infinity are constructed, and changes in band dispersion due to dimensionality and spin-orbit coupling are presented. Identifying the states near the Fermi level to be predominantly Jeff = 1/2, we use an effective Hubbard model to study the effect of correlations. Transitions from a metallic state to various magnetically ordered states at different critical interactions are obtained. A canted antiferromagnetic insulato…
Magnetic materials hosting topological spin textures like magnetic skyrmion exhibit nontrivial Hall effect, namely, topological Hall effect (THE). In this study, we demonstrate the emergence of THE in thin films of half-metallic perovskite manganites. To stabilize magnetic skyrmions, we control the perpendicular magnetic anisotropy by imposing a compressive epitaxial strain as well as by introducing a small Ru doping. When the perpendicular magnetic anisotropy is tuned so that it is balanced with the magnetic dipolar interaction, the film exhibits a sizable THE in a magnetization reversal proc…
Correlated oxides, such as BiMnO$_3$ and LaMnO$_3$, show complex interplay of electronic correlations and crystal structure exhibiting multiple first order phase transitions, some without a clear order parameter. The quantitative theoretical description of this temperature dependent electronic-structural interplay in the vicinity of a Mott transition is still a challenge. Here we address this issue by simultaneously considering both structural and electronic degrees of freedom, within a self-consistent density functional theory with embedded dynamical mean field theory. Our results show the ex…
We have studied the electronic and magnetic properties of double perovskites Gd2MgIrO6 by first-principles density functional theory (DFT). Based on the DFT calculations, Gd2MgIrO6 is found to have a ferromagnetic (FM) ground state. The material undergo half-metallic ferromagnets to Mott-Hubbard insulator transition which happens due to strong correlation in Gd-4f and Ir-5d states. Our results shows that the 5d electrons of Ir hybridize strongly with O-2p states near the Fermi level giving rise to the insulating state of Gd2MgIrO6. Our study suggests that the enhanced magnetic moment is a resu…
Single crystals of the perovskite-type $3d^{1}$ metallic alloy system Ca$_{1-x}$Sr$_x$VO$_3$ were synthesized in order to investigate metallic properties near the Mott transition. The substitution of a Ca$^{2+}$ ion for a Sr$^{2+}$ ion reduces the band width $W$ due to a buckling of the V-O-V bond angle from $\sim180^\circ$ for SrVO$_3$ to $\sim160^\circ$ for CaVO$_3$. Thus, the value of $W$ can be systematically controlled without changing the number of electrons making Ca$_{1-x}$Sr$_x$VO$_3$: one of the most ideal systems for studying band-width effects. The Sommerfeld-Wilson's ratio ($\sime…
The novel 4d perovskite compound SrRhO3 was investigated by isovalent doping studies. The solubility limits of Ca and Ba onto Sr-site were below 80% and 20%, respectively. Although SrRhO3 was chemically compressed, approximately 5.7% by the Ca doping, no significant influence was observed on the magnetic and electrical properties.
We discuss the effects of local structure on the electrical transport and magnetic properties of La(0.67)Ca(0.33)Mn(1-x)Ti(x)O(3) system.Based on the intercomparison of the structure, transport and magnetic properties of the Mn site substituted La(0.67)Ca(0.33)MnO(3) with isovalent diamagnetic and paramagnetic ions, we argue that local structural effects have a decisive role to play, compared to the local spin coupling effects, in the ferromagnetic-metallic ground state of the CMR manganites
A systematic study of (A,A')2FeMoO6 (A,A'=Ca, Sr, Ba) ferromagnetic oxides with double perovskite structure has been performed using 95,97Mo and 57Fe NMR spectroscopy. These oxides are isoelectronic but have substantially different Curie temperatures. The NMR analysis provides clear evidence that the magnetic moment at Mo sites is not constant but varies sensitively with the ionic size of the alkaline ions. The 95,97Mo frequency, and thus the electronic charge at Mo ions, is found to be smaller in Ba and Ca than in Sr-based oxides. The charge release from Mo sites is accompanied by an uptake a…
The short-range organization around Ni atoms in orthorhombic $R$NiO$_{3}$ ($R$=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni K-edge x-ray absorption spectroscopy. Our results demonstrate that two different Ni sites, with different average Ni-O bond lengths, coexist in those orthorhombic compounds and that important modifications in the Ni nearest neighbors environment take place across the metal-insulator transition. We report evidences for the existence of short-range charge-order in the insulating state, as found in the monoclinic compounds. Moreover, our results…
The layered compound La2-2xSr1+2xMn2O7 (x=0.3) consists of bilayers of metallic MnO2 sheets separated by insulating material. The compound exhibits markedly anisotropic magnetoresistance at temperatures well below the three-dimensional magnetic ordering temperature TC=90 K in addition to colossal magnetoresistance around TC. We present neutron diffraction data which show that the magnetic structure of this material switches from antiferromagnetic stacking of the (ferromagnetically ordered) sheets in zero field to ferromagnetic stacking in a field of 1.5 Tesla. The data are the first to be coll…
We systematically synthesized perovskite-type oxides Sr1-xCaxCoO3 containing unusually high valence Co4+ ions by a high pressure technique, and investigated the effect of systematic lattice change on the magnetic and electronic properties. As the Ca content x exceeds about 0.6, the structure changes from cubic to orthorhombic, which is supported by the first-principles calculations of enthalpy. Upon the orthorhombic distortion, the ground state remains to be apparently ferromagnetic with a slight drop of the Curie temperature. Importantly, the compounds with x larger than 0.8 show antiferromag…
A model of localized classical electrons coupled to lattice degrees of freedom and, via the Coulomb interaction, to each other, has been studied to gain insight into the charge and orbital ordering observed in lightly doped manganese perovskites. Expressions are obtained for the minimum energy and ionic displacements caused by given hole and electron orbital configurations. The expressions are analyzed for several hole configurations, including that experimentally observed by Yamada et al. in La_{7/8}Sr_{1/8}MnO_3. We find that, although the preferred charge and orbital ordering depend sensiti…
Interplay of Fermi surface topology and electron correlation is the quintessential ingredient underlying spontaneous symmetry breaking in itinerant electronic systems. In one-dimensional (1D) systems at half-filling, the inherent Fermi surface nesting makes the translationally invariant metallic state unstable, which is known as Peierls instability. Extending the scope of Peierls instability to two (2D) or three dimensions (3D), however, is not straightforward, since the Fermi surface in higher dimensions is generally not nested. In this work, we show that a perfectly nested Fermi surface can …
Proximity to an orbital order with charge disorder state in optimally-doped \textit{RE}\textsubscript{5/8}Ca\textsubscript{3/8}MnO\textsubscript{3} perovskites
