Showing 53 results for Author: Daniel M. Pajerowski
Nov, 2023
Journal
Trilayer nickelates, which exhibit a high degree of orbital polarization combined with an electron count (d8.67) corresponding to overdoped cuprates, have been identified as a promising candidate platform for achieving high-Tc superconductivity. One such material, La4Ni3O8, undergoes a semiconductor-insulator transition at ∼105  K, which was recently shown to arise from th…
Nov, 2023
Journal
Employing elastic and inelastic neutron scattering (INS) techniques, we report on the microscopic properties of the ferromagnetism in the dilute magnetic topological insulator (Bi0.95Mn0.05)2Te3. Neutron diffraction of polycrystalline samples shows the ferromagnetic (FM) ordering is long range within the basal plane, and mainly two dimensional (2D) in character with short-…
Nov, 2023
Journal
TbBaFe2O5+δ (TBFO) is a mixed valence compound with an antiferromagnetic order (TN=450K) that changes along with the crystal structure and conductivity upon cooling below a Verwey-like transition (TV=280K). This type of double-cell-layered perovskite is useful to study putative charge ordering in fractional valence systems because the crystal structure develops unique site…
Nov, 2023
Journal
Recently, a local-Ising-type magnetic order was inferred from neutron diffraction of the antiferromagnetic Er2Ge2O7 (pg-ErGO) with an applied magnetic field. Here, we use neutron spectroscopy to investigate the energetics of pg-ErGO and the isostructural Yb2Ge2O7 (pg-YbGO) to evaluate the adequacy of the local-Ising description. To begin, we generate a model of the magneti…
Nov, 2023
Journal
[Ni(HF2)(3−Clpyridine)4]BF4 (NBCT) is a one-dimensional, S=1 spin chain material that shows no magnetic neutron Bragg peaks down to temperatures of 0.1 K. Previous work identified NBCT as being in the Haldane phase and near a quantum phase transition as a function of D/J to the large-D quantum paramagnet phase (QPM), where D is the axial single-ion anisotropy and J is the…
Nov, 2023
Journal
The extended charge carrier lifetime in metal halide perovskites is responsible for their excellent optoelectronic properties. Recent studies indicate that the superb device performance in these materials is intimately related to the organic cation dynamics. Here, we focus on the investigation of the two-dimensional hybrid perovskite, (C8H17NH3)2PbI4 (henceforth, OA+ = C8H…
Nov, 2023
Journal
The lattice dynamics and high-temperature structural transition in SnS and SnSe are investigated via inelastic neutron scattering, high-resolution Raman spectroscopy and anharmonic first-principles simulations. We uncover a spectacular, extreme softening and reconstruction of an entire manifold of low-energy acoustic and optic branches across a structural transition, refle…
Nov, 2023
Journal
We present methods to quantify sample shapes and generate sample mounts as motivated by the needs of neutron scattering experiments. The 3D sample scanning was performed using photogrammetry and laser scanning, and a comparison is made between the two techniques. The aluminum alloy AlSi10Mg is shown to have favorable properties for many types of mounts used in neutron scat…
Jun, 2023
Journal
Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi2Se3-based dilute ferromagnetic (FM) TIs and MnBi2Te4 (MBT)-based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scat…
Jan, 2022
Journal
MnBi2Te4 (MBT) is a promising van der Waals layered antiferromagnetic (AFM) topological insulator that combines a topologically nontrivial inverted Bi-Te band gap with ferromagnetic (FM) layers of Mn ions. The inelastic neutron scattering on single crystals reported here describes rather complex magnetism in MBT. The magnetic anisotropy that controls the bulk and surface m…
Jun, 2020
Journal
The antiferromagnetic (AFM) compound MnBi2Te4 is suggested to be the first realization of an AFM topological insulator. We report on inelastic neutron scattering studies of the magnetic interactions in MnBi2Te4 that possess ferromagnetic triangular layers with AFM interlayer coupling. The spin waves display a large spin gap and pairwise exchange interactions within the tri…
Apr, 2019
Journal
We use inelastic neutron scattering to study energy and wave vector dependence of spin fluctuations in SrCo2As2, derived from SrFe2−xCoxAs2 iron pnictide superconductors. Our data reveal the coexistence of antiferromagnetic (AF) and ferromagnetic (FM) spin fluctuations at wave vectors QAF=(1,0) and QFM=(0,0)/(2,0), respectively. By comparing neutron scattering results with…