10 research outputs found
Magnetic ordering and spin wave dynamics in transition metal arsenides
Ever since spin orbit torque based switching was proposed in antiferromagnets, there is a growing interest in using a metallic antiferromagnet as an active component of a spintronic device. Arsenic forms a large pool of magnetic metals in combination with transition metal atoms. In this report, we explore compounds in Cu-Mn-As phase space by identifying the transition temperatures using calorimetry and magnetometry measurements, understanding the magnetic structure at different temperatures using neutron powder diffraction techniques, and using inelastic neutron scattering techniques to characterize exchange interactions in these materials. We discover a new ternary metallic arsenide Cu0.82Mn1.18As which crystallizes in the hexagonal crystal system and contains a frustrated in-plane triangular arrangement of Mn spins. We also identify the two-step transition in Mn3As2 from a paramagnet to a collinear ferrimagnet and then, into a canted spin state. Using high resolution synchrotron x-ray diffraction and neutron powder diffraction measurements, we identify magnetically coupled structural transitions in tetragonal CuMnAs which result from exchange frustration between the Mn moments and finite Cu moments. Finally, using single crystal inelastic neutron scattering measurements, we determine exchange interactions in Fe2As (same structure as CuMnAs) and show that it has a highly two dimensional magnon character although the phonon interactions are three dimensional in nature
High-resolution diffraction reveals magnetoelastic coupling and coherent phase separation in tetragonal CuMnAs
Tetragonal CuMnAs was the first antiferromagnet where reorientation of the
N\'eel vector was reported to occur by an inverse spin galvanic effect. A
complicating factor in the formation of phase-pure tetragonal CuMnAs is the
formation of an orthorhombic phase with nearly the same stoichiometry.
Pure-phase tetragonal CuMnAs has been reported to require an excess of Cu to
maintain a single phase in traditional solid state synthesis reactions. Here we
show that subtle differences in diffraction patterns signal pervasive
inhomogeneity and phase separation, even in Cu-rich CuMnAs.
From calorimetry and magnetometry measurements, we identify two transitions
corresponding to the N\'eel temperature (T) and an antiferromagnet to weak
ferromagnet transition in CuMnAs and
CuMnAs. These transitions have clear crystallographic
signatures, directly observable in the lattice parameters upon in-situ heating
and cooling. The immiscibility and phase separation could arise from a
spinoidal decomposition that occurs at high temperatures, and the presence of a
ferromagnetic transition near room temperature warrants further investigation
of its effect on the electrical switching behavior.Comment: 10 pages, 9 figures, added author middle initia
Synthesis of Eu(HCOO) and Eu(HCOO)(HCONH) crystals and observation of their DF transition for quantum information systems
Two stoichiometric metal-organic frameworks containing Eu cations are
probed as candidates for photon-based quantum information storage. Synthesis
procedures for growing 0.2 mm, rod-shaped Eu(HCOO) and 1-3 mm, rhombohedral
Eu(HCOO)(HCONH) single crystals are presented with visible
precipitation as soon as 1 h into heating for Eu(HCOO) and 24 h for
Eu(HCOO)(HCONH). Room temperature and 1.4 K
photoluminescence measurements of the DF
transitions of Eu are analyzed for both compounds. Comparisons of peak
width and intensity are discussed along with the notable first report for both
of the DF transition, the hyperfine structure of
which has potential use in quantum memory applications. The air instability of
Eu(HCOO)(HCONH) and the transformation of its
photoluminescence properties are discussed.Comment: 15 pages, 16 figure
Electrodeposition of Atmosphere-Sensitive Ternary Sodium Transition Metal Oxide Films for Sodium-Based Electrochemical Energy Storage
Layered sodium transition metal oxides constitute an important class of materials with applications including electrochemical energy storage, high temperature superconductivity and electrocatalysis. However, electrodeposition of these compounds, an approach commonly used to grow other oxides, has been elusive due to their atmosphere instability and intrinsic incompatibility with aqueous electrolytes. Through use of a dry molten sodium hydroxide electrolyte, we demonstrate the high throughput electrodeposition of O3 (O’3) and P2 type layered sodium transition metal oxides across multiple transition metal chemistries, and apply these electrodeposits as high areal capacity cathodes in sodium-ion batteries. The electrodeposits are microns thick, polycrystalline, and structurally similar to materials synthesized classically at high temperature. This work enables fabrication of a wide group of previously inaccessible alkali and alkaline earth ion intercalated, higher valent transition group oxides in important thick film form factors.</p