Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLone octupole and bulk magnetism in osmate 5d2 double perovskites
61
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Cubic double perovskites that host heavy ions with total angular momentum J = 2 can exhibit a singular magnetic state epitomized by a lone octupole and bulk ferro-type magnetism. It exists in the Chen - Balents Hamiltonian with a quadrupole interaction and competing exchange forces between the ions. Our symmetry inspired analysis mirrors the Dzyaloshinskii - Manko theory of latent antiferromagnetic ordering, and a 3-k collinear structure. Experimental tests of the singular state include neutron and x-ray Bragg diffraction.
rate research
Read More
We combine several numerical and semi-analytical methods to study the $5d$ double perovskites Sr2YIRO6 and Ba2YIRO6 which were recently proposed to exhibit excitonic magnetism. Starting from the density functional theory and constrained random phase approximation we construct effective multi-band Hubbard models. These are analyzed by means of static and dynamical mean-field theories and strong coupling expansion. We find both materials to be insulators, but, contrary to the experimental claims, with a large spin gap of several hundreds meV preventing formation of an ordered state at low temperature
We present a comprehensive experimental study of magnetization and magnetocaloric effect (MCE) in double perovskite (DP) materials $R_2$NiMnO$_6$ with $R =$ Pr, Nd, Sm, Gd, Tb, and Dy. While a paramagnetic to ferromagnetic transition, with T$_{rm C}$ in the range $sim 100 - 200~$K, is a common feature that can be attributed to the ordering of Mn$^{4+}$ and Ni$^{2+}$ magnetic moments, qualitatively distinct behavior depending on the choice of $R$ is observed at low temperatures. These low-temperature anomalies in magnetization are also manifest in the change in magnetic entropy, $-Delta S_{M}$, whose sign depends on the choice of $R$. In order to understand these results, we present theoretical analysis based on mean-field approximation and Monte Carlo simulations on a minimal spin model. The model correctly captures the key features of the experimental observations.
A recent polarized neutron diffraction experiment on the 5d2 rhenium double perovskite Ba2YReO6 held at a low temperature uncovered weak magnetic diffraction peaks. Data analysis inferred a significantly reduced Re dipole moment, and long-range order compatible with an antiferromagnet, non-collinear motif. To interpret the experimental findings, we present a model wavefunction for Re ions derived from the crystal field potential, Coulomb interaction, and spin-orbit coupling that fully respects the symmetry of the low-temperature ordered state. It is used to calculate in analytic form all multipole moments visible in neutron and resonance enhanced x-ray diffraction. A minimal model consistent with available neutron diffraction data predicts significant multipolar moments up to the hexadecapole, and, in particular, a dominant charge-like quadrupole moment. Calculated diffraction patterns embrace single crystal x-ray diffraction at the Re L-edge, and renewed neutron diffraction, to probe the presumed underlying multipolar order.
We use the LDA+U method to study the possibility of exciton condensation in perovskites of transition metals with $d^6$ electronic configuration such as LaCoO$_3$. For realistic interaction parameters we find several distinct solutions exhibiting spin-triplet exciton condensate, which gives rise to a local spin density distribution while the ordered moments are vanishingly small. Rhombohedral distortion from the ideal cubic structure suppresses the ordered state, contrary to the spin-orbit coupling which enhances the excitonic condensation energy. We explain the trends observed in the numerical simulations with the help of a simplified strong-coupling model. Our results indicate that LaCoO$_3$ is close to the excitonic instability and suggest ways to make it order.
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 alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
