Intertwined Magnetic Sub-Lattices in the Double Perovskite Compound LaSrNiReO6
Ola Kenji Forslund, Konstantinos Papadopoulos, Elisabetta Noccerino, Gerald Morris, Bassam Hitti, Donald Arseneau, Vladimir Pomjakushin, Nami Matsubara, Jean Ch… 展开作者
Ola Kenji Forslund, Konstantinos Papadopoulos, Elisabetta Noccerino, Gerald Morris, Bassam Hitti, Donald Arseneau, Vladimir Pomjakushin, Nami Matsubara, Jean Christophe Orain, P. Anil Kumar, Peter Svedlindh, Daniel Andreica, Somnath Jana, Jun Sugiyama, Martin Månsson, Yasmine Sassa
We report a muon spin rotation ($μ^{+}$SR) study of the magnetic properties of the double perovskite compound LaSrNiReO$_{6}$. Using the unique length and time scales of the $μ^{+}$SR technique, we successfully clarify the magnetic ground state of LaSrNiReO$_{6}$, which was previously deemed as a spin glass state. Instead, our $μ^{+}$SR results point towards a long-range dynamically ordered ground state below $T_{\rm C}= 23$ K, for which a static limit is foreseen at $T=0$. Furthermore, between 23 K$<T\leq$300 K, three different magnetic phases are identified: a dense ($23$ K$<T\leq75$ K), a dilute ($75$ K$<T\leq250$ K), and a paramagnetic ($T>250$ K) state. Our results reveal how two separate, yet intertwined magnetic lattices interact within the unique double perovskite structure and the importance of using complementary experimental techniques to obtain a complete understanding of the microscopic magnetic properties of complex materials.
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…
Selenium and tellurium are among the few elements that form $AB$O$_3$ perovskite structures with a four valent ion in the $A$ site. This leads to highly distorted structures and unusual magnetic behavior. Here we investigate the Co and Ni selenite and tellurite compounds, CoSeO$_3$, CoTeO$_3$, NiSeO$_3$ and NiTeO$_3$ using first principles calculations. We find an interplay of crystal field and Jahn-Teller distortions that underpin the electronic and magnetic properties. While all compounds are predicted to show an insulating G-type antiferromagnetic ground state, there is a considerable diffe…
Compounds with distorted perovskite structure of the 4-f and 3-d transition metals with the common formula LnTO3 (where Ln is rare-earth element, T is an element from the Fe group) are the most multifold binary oxides of these two groups elements. Wide range of stability for this structure allows the realization of combinations of the Lanthanides with all the transition metals except the Nickel. Quite interesting physical phenomena take place in these oxides like charge and orbital ordering; relatively independent magnetic lattices of the both metals; particular magnetic structures; high optic…
Double perovskites extend the design space for new materials, and they often host phenomena that don't exist in their parent perovskite compounds. Here, we present a detailed first principles study of the correlated double perovskite Sr$_2$VNbO$_6$, where inter-cationic charge transfer and strength of electronic correlations depend strongly on the cation order. By using Density Functional Theory + Embedded Dynamical Mean Field Theory, we show that this compound has a completely different electronic structure than either of its parent compounds despite V and Nb being from the same group in the …
The extraction of exchange parameters from measured spin-wave dispersion relations has severe limitations particularly for magnetic compounds such as the transition-metal perovskites, where the nearest-neighbor exchange parameter usually dominates the couplings between the further-distant-neighbor spins. Very precise exchange parameters beyond the nearest-neighbor spins can be obtained by neutron spectroscopic investigations of the magnetic excitation spectra of isolated multimers in magnetically diluted compounds. This is exemplified for manganese trimers in the mixed three- and two-dimension…
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…
Using results of the band structure calculations in the local-spin-density approximation we demonstrate how the crystal distortions affect the magnetic structure of orthorhombically distorted perovskites leading to a non-collinear spin arrangement. Our results suggest that the non-collinearity of the spin magnetic moments, being generally small in La$M$O$_3$ series with $M$=Cr-Fe, is large in SrRuO$_3$.
The magnetism of double perovskites is a complex phenomenon, determined from intra- or interatomic magnetic moment interactions, and strongly influenced by geometry. We take advantage of the complementary length and time scales of the muon spin rotation, relaxation and resonance ($μ^+$SR) microscopic technique and bulk AC/DC magnetic susceptibility measurements to study the magnetic phases of the LaCaNiReO$_6$ double perovskite. As a result we are able to discern and report a newly found dynamic phase transition and the formation of magnetic domains below and above the known magnetic transitio…
We present an analysis of the electronic structure of perovskite-related iridates, 5d electron compounds where a subtle interplay between spin-orbit coupling, tetragonal distortions and electron correlations determines the electronic structure properties. We suggest via electronic structure calculations that a non-collinear calculation is required to obtain solutions close to the usually quoted $j_{eff}$ = 1/2 state to describe the $t_{2g}$ hole in the $Ir^{4+} :d^5$ cation, while a collinear calculation yields a different solution, the hole is in a simpler xz/yz complex combination with a sma…
We report structural, magnetic and dielectric properties of layered perovskite materials LnBaCuFeO5 (Ln = La and Lu). LaBaCuFeO5 shows magnetic cluster glass behavior below 60 K owing to the competing ferromagnetic and antiferromagnetic exchange interactions. Glassy dynamics of electric dipoles has also been observed in the vicinity of the magnetic glass transition temperature. The presence of significant coupling between spin and polar degrees of freedom results in the multiglass feature in LaBaCuFeO5. The LuBaCuFeO5 compound undergoes YBaCuFeO5 like commensurate to incommensurate antiferroma…
Superconductivity in the iron pnictides emerges from metallic parent compounds exhibiting intertwined stripe-type magnetic order and nematic order, with itinerant electrons suggested to be essential for both. Here we use X-ray and neutron scattering to show that a similar intertwined state is realized in semiconducting KFe$_{0.8}$Ag$_{1.2}$Te$_2$ (K$_5$Fe$_4$Ag$_6$Te$_{10}$) without itinerant electrons. We find Fe atoms in KFe$_{0.8}$Ag$_{1.2}$Te$_2$ form isolated $2\times2$ blocks, separated by nonmagnetic Ag atoms. Long-range magnetic order sets in below $T_{\rm N}\approx35$ K, with magnetic…
We measured the electrical resistivity, AC magnetic susceptibility, and specific heat of the cubic double perovskite Ba$_2$MgReO$_6$ under pressure. The application of pressure leads to a gradual increase in the transition temperature to the canted antiferromagnetic order, while the quadrupolar order is suppressed above 5 GPa, at which a collinear antiferromagnetic state appears. The obtained unit cell volume-temperature phase diagram for the compound as well as the related compounds suggests that Ba$_2$MgReO$_6$ exists near the phase boundary between the noncollinear and the collinear antifer…
Detailed magnetic properties of the compound Sr2YbRuO6 are presented here. The compound belongs to the family of double perovskites forming a monoclinic structure. Magnetization meas-urements reveal clear evidence for two components of magnetic ordering aligned opposite to each other, leading to a magnetization reversal, compensation temperature (T* = 34 K) and neg-ative magnetization at low temperatures and low magnetic fields. Heat capacity measurements corroborate the presence of two components in the magnetic ordering and a noticeable third anomaly at low temperatures (~15 K) which cannot …
Using first-principles density functional theory, we have investigated the electronic and magnetic properties of recently synthesized and characterized 5d double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure calculations show that in all compounds, the Os5+ (5d3) site is the only magnetically active one, while Y3+, In3+ and Sc3+ remain in nonmagnetic states, with Sc/Y and In featuring d0 and d10 electronic configurations, respectively. Our studies reveal the important role of closed-shell (d10) versus open-shell (d0) electronic configurations of the nonmagnetic sites in determin…
Here we report the magnetic and heat capacity studies of the double perovskite com-pounds Ba2SmRuO6 and Ba2DyRuO6. Antiferromagnetic transitions are inferred at 54 K and 47 K in Ba2SmRuO6 and Ba2DyRuO6, respectively in the magnetization measure-ments. Heat capacity measurements show large jumps at the corresponding temperatures and confirm the bulk magnetic ordering. Both the measurements provide clear indication of the ordering of the rare earth moments also along with the Ruthenium moments. How-ever, the heat capacity results suggest that the ordering of rare earth magnetic moments is spread…
The synthesis and physical properties of the double perovskite (DP) compound Ba2CdReO6 with the 5d1 electronic configuration are reported. Three successive phases originating from a spin-orbit-entangled Jeff = 3/2 state, confirmed by the reduced effective magnetic moment of 0.72 μB, were observed upon cooling. X-ray diffraction measurements revealed a structural transition from a high-temperature cubic structure to a low-temperature tetragonal structure at Ts = 170 K, below which the Jeff = 3/2 state was preserved. Magnetization, heat capacity, and thermal expansion measurements showed two mor…
The perovskite nickelates RNiO$_3$ (R: rare-earth) have been studied as potential multiferroic compounds. A certain degree of charge disproportionation in the Ni ions has been confirmed by high resolution synchrotron power diffraction: instead of the nominal Ni$^{3+}$ valence, they can have the mixed-valence state Ni$^{(3-δ)+}$ and Ni$^{(3+δ)+}$, though agreement has not been reached on the precise value of $δ$ (e.g. for NdNiO$_3$, $δ=0.0$ and $δ=0.29$ were reported). Also, the magnetic ground state is not yet clear: collinear and non-collinear Ni-O magnetic structures have been proposed to ex…
We have synthesized and characterized laser-deposited film samples of perovskite BaCrO_{3}, a missing member of the perovskite-chromate family. The BaCrO_{3} films have a substantially larger lattice constant than other chromates, are insulating, and exhibit weak ferromagnetism likely associated with canted antiferromagnetism. Comparison with the other sister compounds CaCrO_{3} and SrCrO_{3} suggest an anomalous Mott transition where magnetism is independent of whether the compound is metallic or insulating
We discuss here a comparative study of the role of local structure and/or nature of local magnetic coupling on the electrical transport properties of Mn site substituted La-Ca-Mn-O perovskites. Particular emphasis is being paid to explore the strong correlation between the insulator-metal transition (TIM) and the residual resistivity (rhoo) upon substitution. There exists an inverse relationship between ro and TIM in the compounds under present discussion. Best fit for TIM Vs ro could be obtained for the compounds understudy to a first order exponential decay with a functional form TIM = TIMO …
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 $μ_{B}$, …
A fully ab initio scheme based on quantum chemical wavefunction methods is used to investigate the correlated multiorbital electronic structure of a 3d-metal compound, LaCoO3. The strong short-range electron correlations, involving both Co and O orbitals, are treated by multireference techniques. The use of effective parameters like the Hubbard U and interorbital U', J terms and the problems associated with their explicit calculation are avoided with this approach. We provide new insight into the spin-state transition at about 90 K and the nature of charge carriers in the doped material. Our r…
We have studied the magnetic properties of Ba_2FeNbO_6 and Ba_2MnNbO_6. it is seen that Ba_2FeNbO_6 is an antiferromagnet with a weak ferromagnetic behaviour at 5K while Ba_2MnNbO_6 shows two magnetic transitions one at 45 K and the other at 12K. Electron spin resonance (ESR) measurements at room temperature show that the Mn compound does not show any Jahn-Teller distortion. It is also seen that the Neel temperature of the A_2FeNbO_6 (A=Ba,Sr, BaSr) compounds do not vary significantly. However variations in the average A-site ionic radius influence the formation of short range correlations tha…
In the perovskite Ti oxide RTiO3 (R=rare-earth ions), the Ti t2g orbitals and spins in the 3d^1 state couple each other through the strong electron correlations, resulting in a rich variety of orbital-spin phases. The origin and nature of orbital-spin states of these Mott insulators have been intensively studied. In this article, we review the studies on orbital physics in the perovskite titanates. We focus on the following three topics: (1) the origin and nature of the ferromagnetism as well as the orbital ordering in the compounds with relatively small R ions such as GdTiO3 and YTiO3, (2) th…
We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the well-known pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture…
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…
Perovskite iridates of 6H hexagonal structure present a plethora of possibilities in terms of the variety of ground states resulting from a competition between spin-orbit coupling (SOC), hopping, noncubic crystal field ($Δ_{CFE}^{NC}$) and superexchange energy scales within the Ir$_2$O$_9$ dimers. Here we have investigated one such compound Ba$_3$CdIr$_2$O$_9$ by x-ray diffraction, dc magnetic susceptibility($χ$), heat capacity($C_p$) and also ${}^{113}$Cd nuclear magnetic resonance (NMR) spectroscopy. We have established that the magnetic ground state has a small but finite magnetic moment on…
We report angle-resolved photoemission (ARPES) measurements, density functional and model tight-binding calculations on Ba$_2$IrO$_4$ (Ba-214), an antiferromagnetic ($T_N=230$ K) insulator. Ba-214 does not exhibit the rotational distortion of the IrO$_6$ octahedra that is present in its sister compound Sr$_2$IrO$_4$ (Sr-214), and is therefore an attractive reference material to study the electronic structure of layered iridates. We find that the band structures of Ba-214 and Sr-214 are qualitatively similar, hinting at the predominant role of the spin-orbit interaction in these materials. Temp…
Spin wave excitations were measured in the ferromagnetic phase of Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$ by neutron scattering. This compound is located in proximity to the A-type antiferromagnetic state, and it shows a clear anisotropy and anomalous softening of the spin wave excitations. The softening in the ferromagnetic phase is induced by the orbital ordering.
YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits magnetic ordering and dielectric anomaly above 200 K. Partial substitution of Fe with other magnetic and non-magnetic ion affects the magnetic and the structural properties of the system. We report detailed investigation of structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M=Co, Ni and Ga). We observed that the partial replacement of Ni and Co in place of Fe, results in magnetic dilution and broadening of the magnetic transition and shifting towards lower temperature. The replacement of Fe with non-m…
First-principles electronic structure calculations have been performed for the double perovskite Bi$_2$CoMnO$_6$ in its non-centrosymmetric polar state using generalized gradient approximation plus Hubbard U approach. We find that while Co is in a high spin state, Mn is in an intermediate spin state. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. Magnetic structure dependent phonon frequencies indicate the presence of spin-phonon coupling. Using Berry phase method, we obtain a spontaneous electronic polarization of 5.88 $μC/cm^2$ wh…
A large spin-orbit coupling is a way to control strong magnetodielectric (MD) coupling in a higher d-orbital materials. However reports are rare on such compounds due to often leaky conductive behavior. Here, we demonstrate MD coupling in a Ru-based 6H-perovskite system, Ba3NdRu2O9. The rare-earth ion in a 6H-perovskite makes the system insulating enough to carry out MD investigation. The compound is ferromagnetically ordered below 24 K (TC), followed by another magnetic feature at T~ 17 K (T2). The dielectric constant clearly traces the magnetic ordering, manifesting a peak at the onset of TC…
Four anti-perovskite-type compounds, ZnNNi3, ZnCNi3, SnNCo3, and SnCCo3, are synthesised through reactions between ingredient metal oxides and organic compound melamine (C3H6N6). ZnNNi3 and ZnCNi3 are selectively synthesised by choosing different reaction temperatures and nominal oxide-to-melamine ratios. SnNCo3 is synthesised for the first time by this melamine method. Resistivity, magnetisation, and heat capacity measurements reveal that SnNCo3 is a correlated metal with a high density of states at the Fermi level. Our results demonstrate that this feasible synthetic route using melamine is …
Fifteen parameters characterizing the crystal field of rare-earth ions in the RMO$_3$ perovskites (R = Pr, Nd, M = Ga, Co) are calculated by expanding the local Hamiltonian expressed in the basis of Wannier functions into a series of spherical tensor operators. The method contains a single adjustable parameter that characterizes the hybridization of R($4f$) states with the states of oxygen ligands. Subsequently the energy levels and magnetic moments of trivalent R ion are determined by diagonalization of an effective Hamiltonian which, besides the crystal field, contains the $4f$ electron-elec…
We have investigated the structural and magnetic properties of antiferroelectric $A_2$CoTeO$_6$ perovskites with $A$ = Cd, Ca, Sr, Pb, and Ba. All compounds are antiferromagnetic at low temperatures, with the antiferromagnetic transition temperature slightly decreasing with decreasing ionic size of the $A$ cation. Such a decrease in antiferromagnetic interaction is not observed in $A^{2+}_2$Co$M^{6+}$O$_6$ materials with other $M^{6+}$ cations of similar ionic sizes, suggesting that Te$^{6+}$ cations affect the electronic and in turn the magnetic structure of the system.
Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic properties of 5$d$ iridates. In this paper we have experimentally investigated the structural and physical properties of a series of Ir-based double perovskite compounds Pr$_{2-x}$Sr$_x$MgIrO$_6$ ($x$ = 0, 0.5, 1; hereafter abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have recently been proposed to undergo a transition from the spin-orbit-coupled Mott insulating phase at $x$ = 0 to the elusive half-metallic antiferromagnetic (HMAFM) state with Sr doping at $x$ = 1. However, our detailed magn…
We report on our investigation on the magnetism of the iridate double perovskite Sr$_2$CoIrO$_6$, a nominally Ir$^{5+}$ Van Vleck $J_{eff}=0$ system. Using x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy at the Ir-$L_{2,3}$ edges, we found a nearly zero orbital contribution to the magnetic moment and thus an apparent breakdown of the $J_{eff}=0$ ground state. By carrying out also XAS and XMCD experiments at the Co-$L_{2,3}$ edges and by performing detailed full atomic multiplet calculations to simulate all spectra, we discovered that the compound consists of ab…
The electronic structure and magnetism of Sr$_2$CeIrO$_6$, an Ir-based double perovskite system has been investigated using first-principles calculations. We found that a strong spin-orbit coupling dictate the electronic and magnetic properties of this system. A small value of $U$ along with SOC could open up a gap at the Fermi level, offering the possibility of novel J$_{eff}$ = 1/2 Mott quantum state. Our calculations reveal that the magnetic ground state is antiferromagnetic in agreement with the magnetization data and provide the value of spin and orbital moment for this system which is in…
The Jahn-Teller (JT) distortion that can remove electronic degeneracies in partially occupied states and results in systematic atomic displacements is a common underlying feature to many of the intriguing phenomena observed in 3d perovskites, encompassing magnetism, superconductivity, orbital ordering and colossal magnetoresistance. Although the seminal Jahn and Teller theorem has been postulated almost a century ago, the origins of this effect in perovskite materials are still debated, including propositions such as super exchange, spin-phonon coupling, sterically induced lattice distortions,…
Unveiling the magnetic ground states in the iridate double perovskite Pr(2-x)SrxMgIrO6 (x = 0 and 0.5) series
ISIS Neutron and Muon Source, STFC, Rutherford Appleton Laboratory（STFC 卢瑟福·阿普尔顿实验室 ISIS 中子与μ子源）；School of Materials Science, Indian Association for the Cultivation of Science（印度科学促进协会材料科学学院）；Institut Laue-Langevin（朗之万研究所）；University of Johannesburg（约翰内斯堡大学）
Ferromagnetism in Cr-based double perovskites is analyzed using effective model as well as simulation approach. Starting from a microscopic model proposed recently for this class of double perovskites, an effective spin-only model is derived in the limit of large exchange coupling at the B-site. Analytic expressions for the resultant exchange coupling is derived in certain limiting cases. The behaviour of this exchange is used to provide a plausible explanation for the enhanced ferromagnetic tendency as also the enigmatic increase in Curie temperature observed in Cr-based DP-s, in the series S…
Ceramics of A_{2}FeReO_{6} double-perovskite have been prepared and studied for A=Ba and Ca. Ba_{2}FeReO_{6} has a cubic structure (Fm3m) with $a\approx $8.0854(1) Åwhereas Ca_{2}FeReO_{6} has a distorted monoclinic symmetry with $a\approx 5.396(1) Å, b\approx 5.522(1) Å, c\approx 7.688(2) Å$ and $β=90.4^{\circ} (P21/n)$. The barium compound is metallic from 5 K to 385 K, i.e. no metal-insulator transition has been seen up to 385 K, and the calcium compound is semiconducting from 5 K to 385 K. Magnetization measurements show a ferrimagnetic behavior for both materials, with T_{c}=315 K for Ba_…
Spin and orbital magnetic moments of Re in AA'FeReO6 double perovskites (A,A' = Ba, Sr, Ca) have been directly probed employing XMCD spectroscopy at the Re L2,3-edges. A considerable orbital magnetic moment is observed in all the studied compounds despite octahedral coordination. Relative orbital to spin contribution per Re atom rises with lattice distortion from mL/mS = -0.28 to -0.34 for AA'=Ba2FeReO6 and Ca2FeReO6, respectively. A preliminary XMCD measurements at the Fe L2,3-edges reveals also a significant orbital moment of iron in Ca2FeReO6. The relation of the results to the magnetic pro…
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.
Synthesis, crystal structure and magnetic properties of a new 2:1 ordered triple perovskite Sr3CaOs2O9 are reported. The compound crystallizes in P21/c space group and features a unique buckled honeycomb lattice of osmium. It exhibits long-range antiferromagnetic ordering with a high Neel temperature of 385 K as confirmed by susceptibility, heat capacity and neutron diffraction measurements and is electrically insulating. This compound is also the first example of a 2:1 ordered osmate perovskite. Theoretical investigations indicate that Sr3CaOs2O9 features a sizeable antiferromagnetic exchange…
A detailed study of the low-temperature magnetic state and the relaxation in the phase-separated colossal magnetoresistance Nd2/3Ca1/3MnO3 perovskite has been carried out. Clear experimental evidence of the cluster-glass magnetic behavior of this compound has been revealed. Well defined maxima in the in-phase linear ac susceptibility $χ^{/}(T)$ were observed, indicative of the magnetic glass transition at $T_{g}$ = 60 K. Strongly divergent zero-field-cooled and field-cooled static magnetizations and frequency dependent ac susceptibility are evident of the glassy-like magnetic state of the comp…
AMX$_3$ compounds are structurally diverse, a notable example being the post-perovskite structure which adopts a two-dimensional framework with corner- and edge-sharing octahedra. Few molecular post-perovskites are known and of these, none have reported magnetic structures. Here we report the synthesis, structure and magnetic properties of molecular post-perovskites: CsNi(NCS)$_3$, a thiocyanate framework, and two new isostructural analogues CsCo(NCS)$_3$ and CsMn(NCS)$_3$. Magnetisation measurements show that all three compounds undergo magnetic order. CsNi(NCS)$_3$ (Curie temperature, $T_\ma…
The structures of the new compound La1.2Sr2.7IrO7+d and the recently discovered La1.2Sr2.7RuO7+d have been solved using a combination of X-ray and neutron diffraction. Both compounds crystallize in the trigonal space group R-3m and contain isolated MO6 (M=Ru,Ir) octahedra, which are arranged in well-defined layers. Results of the magnetic susceptibility and XANES measurements show that the transition metal cations are in a pentavalent state. While in La1.2Sr2.7RuO7+d an antiferromagnetic interaction between the Ru5+ ions is found, La1.2Sr2.7IrO7+d shows a very small temperature-independent par…
Taking into account Goodenough's superexchange rules, including both full structural relaxation and spin-orbit coupling, and checking strong correlation effects, we look for compensated half metals within the class of oxide double perovskites materials. Identifying likely half metallic (or half semimetallic) antiferromagnets, the full complications including orbital magnetism are included in order to arrive at realistic predictions of designed magnetic compounds with (near) vanishing net moment. After sorting through several candidates that have not been considered previously, two materials, K…
We have investigated low energy nuclear spin excitations in double perovskite compounds R$_2$CoMnO$_6$ (R = Y,Tb) by inelastic neutron scattering with a high-resolution back-scattering spectrometer. We observed inelastic signals at about 2.1 $μ$eV for Y$_2$CoMnO$_6$ and also for Tb$_2$CoMnO$_6$ at T = 2 K in both energy loss and energy gain sides. We interpret these inelastic peaks to be due to the transitions between the hyperfine split nuclear levels of $^{59}$Co nucleus. The inelastic peaks move towards the central elastic peak and finally merge with it at the magnetic ordering temperature …
We report the understanding of the electronic band structure of $Cs_4CuSb_2Cl_{12}$ perovskite through first-principles density-functional theory calculations. We find that the most stable state has the antiferromagnetic configuration where each $[CuCl_6]$ octahedral chain along the [010] direction is antiferromagnetic. The reasonable band structure of the compound can be obtained only if both the correct magnetic order and the improved exchange interaction of the Cu $\it{d}$ electrons are taken into account.
We show that the symmetry of the spin zigzag chain E phase of the orthorhombic perovskite manganites and nickelates allows for the existence of a finite ferroelectric polarization. The proposed microscopic mechanism is independent of spin-orbit coupling. We predict that the polarization induced by the E-type magnetic order can potentially be enhanced by up to two orders of magnitude with respect to that in the spiral magnetic phases of TbMnO3 and similar multiferroic compounds.
Using density-functional theory calculations, we investigated the electronic structure and magnetic exchange interactions of the ordered 3d-5d double perovskite Sr2FeOsO6, which has recently drawn attention for interesting antiferromagnetic transitions. Our study reveals the vital role played by long-range magnetic exchange interactions in this compound. The competition between the ferromagnetic nearest neighbor Os-O-Fe interaction and antiferromagnetic next nearest neighbor Os-O-Fe-O-Os interaction induces strong frustration in this system, which explains the lattice distortion and magnetic p…
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…
In this work multiferroic thin films of Bi containing perovskite oxides are discussed, where the driving force for ferroelectricity are the Bi3+ lone-pair electrons. First, a brief introduction of Bi containing multiferroic perovskite oxides will be presented to describe the mechanisms for establishing magnetic and ferroelectric order in these compounds and some recent developments in this field of research are reported. The second section addresses experimental aspects of epitaxial thin film growth of BiMnO3, (Bi0.9La0.1)2NiMnO6 (BLNMO) and BiFeO3 thin films by pulsed laser deposition. The th…
Polycrystalline rhodium(IV) oxide perovskite SrRhO3 was obtained by high-pressure synthesis techniques, followed by measurements of the magnetic susceptibility, electrical resistivity, and specific heat. The title compound has five 4d-electrons per perovskite unit and shows Fermi-liquid behavior in its electrical resistivity. The magnetic susceptibility is large [chi(300K) \~1.1*10^{-3} emu/mol-Rh] and proportional to 1/T^2 (< 380 K), while there is no magnetic long-range order above 1.8 K. The specific heat measurements indicate a probable magnetic contribution below ~ 15 K, which is not pred…
We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A2FeReO6 (A = Ba, Sr, Ca) by X-ray magnetic circular dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr2ScReO6 proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected …
