The Magnetic Phase of Lithium Transition Metal Phosphates LiMPO4 (M=Mn, Co, Ni) Detected by μ+SR

AbstractThe magnetic properties of the olivine-type compounds LiMPO4 (M = Mn, Co, Ni) are probed using muon spin rotation/relaxation (μSR). These materials pose an appealing magnetic structure and a high -potential technological interest as cathode materials for future rechargeable Li-ion batteries. The LiMPO4 family of compounds consists of a corner-sharing MO6 octahedra of high-spin M2+ ions manifesting an antiferromagnetic ground state below TN ≈ 30K. Additionally, these compounds belong to a class of materials exhibiting properties between two-and three dimensional systems. A comparative study between the family members is presented

Singlet state formation and its impact on magnetic structure in tetramer system SeCuO3_3

We present an experimental investigation of the magnetic structure in a tetramer system SeCuO$_3$ using neutron diffraction and nuclear resonance techniques. We establish a non-collinear, commensurate antiferromagnetic ordering with a propagation vector $\textbf{k} = \left(0,0,1 \right)$. The order parameter follows a critical behavior near $T_N = 8$ K, with a critical exponent $\beta = 0.32$ in agreement with a 3D universality class. Evidence is presented that a singlet state starts to form on tetramers at temperatures as high as 200 K, and its signature is preserved within the ordered state through a strong renormalization of the ordered magnetic moment on two non-equivalent copper sites, $m_{Cu1} \approx 0.4 \mu_B$ and $m_{Cu2} \approx 0.7 \mu_B$ at 1.5 K

Perspectives on Neutron Scattering in Lanthanide-Based Single-Molecule Magnets and a Case Study of the Tb2(μ-N2) System

Single-molecule magnets (SMMs) based on lanthanide ions display the largest known blocking temperatures and are the best candidates for molecular magnetic devices. Understanding their physical properties is a paramount task for the further development of the field. In particular, for the poly-nuclear variety of lanthanide SMMs, a proper understanding of the magnetic exchange interaction is crucial. We discuss the strengths and weaknesses of the neutron scattering technique in the study of these materials and particularly for the determination of exchange. We illustrate these points by presenting the results of a comprehensive inelastic neutron scattering study aimed at a radical-bridged diterbium(III) cluster, Tb2(μ-N23−), which exhibits the largest blocking temperature for a poly-nuclear SMM. Results on the YIII analogue Y2(μ-N23−) and the parent compound Tb2(μ-N22−) (showing no SMM features) are also reported. The results on the parent compound include the first direct determination of the lanthanide-lanthanide exchange interaction in a molecular cluster based on inelastic neutron scattering. In the SMM compound, the resulting physical picture remains incomplete due to the difficulties inherent to the problem

Ferromagnetic Cluster Spin Wave Theory: Concepts and Applications to Magnetic Molecules

Ferromagnetic cluster spin wave theory (FCSWT) provides an exact and concise description of the low-energy excitations from the ferromagnetic ground state in finite magnetic systems, such as bounded magnetic molecules. In particular, this theory is applicable to the description of experimental inelastic neutron scattering (INS) spectra at low temperatures. We provide a detailed conceptual overview of the FCSWT. Additionally, we introduce a pictorial representation of calculated wavefunctions, similar to the usual depiction of vibrational normal modes in molecules. We argue that this representation leads to a better intuitive understanding of the excitations, their symmetry properties, and has links to the energy and wavevector dependence of intensity in the neutron scattering experiments. We apply FCSWT and illustrate the results on a series of examples with available low-temperature INS data, ranging from the Mn10 supertetrahedron, the Mn7 disk to the Mn6 single molecule magnet

Interplay of long-range and short-range Coulomb interactions in an Anderson-Mott insulator

In this paper, we tackle the complexity of coexisting disorder and Coulomb electron-electron interactions (CEEIs) in solids by addressing a strongly disordered system with intricate CEEIs and a screening that changes both with charge carrier doping level Q and temperature T. We report on an experimental comparative study of the T dependencies of the electrical conductivity σ and magnetic susceptibility χ of polyaniline pellets doped with dodecylbenzenesulfonic acid over a wide range. This material is special within the class of doped polyaniline by exhibiting in the electronic transport a crossover between a low-T variable range hopping (VRH) and a high-T nearest-neighbor hopping (NNH) well below room temperature. Moreover, there is evidence of a soft Coulomb gap ΔC in the disorder band, which implies the existence of a long-range CEEI. Simultaneously, there is an onsite CEEI manifested as a Hubbard gap U and originating in the electronic structure of doped polyaniline, which consists of localized electron states with dynamically varying occupancy. Therefore, our samples represent an Anderson-Mott insulator in which long-range and short-range CEEIs coexist. The main result of the study is the presence of a crossover between low- and high-T regimes not only in σ(T) but also in χ(T), the crossover temperature T∗ being essentially the same for both observables over the entire doping range. The relatively large electron localization length along the polymer chains results in U being small, between 12 and 20 meV for the high and low Q, respectively. Therefore, the thermal energy at T∗ is sufficiently large to lead to an effective closing of the Hubbard gap and the consequent appearance of NNH in the electronic transport within the disorder band. ΔC is considerably larger than U, decreasing from 190 to 30 meV as Q increases, and plays the role of an activation energy in the NNH

Crystal Structure, Transport, and Magnetic Properties of an Ir⁶⁺ Compound Ba₈Al₂IrO₁₄

The novel iridate Ba8Al2IrO14 was prepared as single crystals by self-flux method, thereby providing a rare example of an all-Ir(VI) compound that can be synthesized under ambient pressure conditions. The preparation of all-Ir6+ iridate without using traditional high-pressure techniques has to our knowledge previously only been reported in Nd2K2IrO7 and Sm2K2IrO7. The monoclinic crystal structure (space group C2/m, No.12) is stable down to 90 K and contains layers of IrO6 octahedra separated by Ba and AlO4 tetrahedra. The material exhibits insulating behavior with a narrow band gap of ∼0.6 eV. The positive Seebeck coefficient indicates hole-like dominant charge carriers. Susceptibility measurement shows antiferromagnetic coupling with no order down to 2 K