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 Cu$_{1.18}$Mn$_{0.82}$As. From calorimetry and magnetometry measurements, we identify two transitions corresponding to the N\'eel temperature (T$_N$) and an antiferromagnet to weak ferromagnet transition in Cu$_{1.18}$Mn$_{0.82}$As and CuMn$_{0.964}$As$_{1.036}$. 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)3_3 and Eu(HCOO)3⋅_{3}\cdot(HCONH2_2)2_2 crystals and observation of their 5^5D0→7_{0}\rightarrow ^{7}F0_0 transition for quantum information systems

Two stoichiometric metal-organic frameworks containing Eu$^{3+}$ cations are probed as candidates for photon-based quantum information storage. Synthesis procedures for growing 0.2 mm, rod-shaped Eu(HCOO)$_3$ and 1-3 mm, rhombohedral Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$ single crystals are presented with visible precipitation as soon as 1 h into heating for Eu(HCOO)$_3$ and 24 h for Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$. Room temperature and 1.4 K photoluminescence measurements of the $^5$D$_{0}\rightarrow {^7}$F$_J$ transitions of Eu$^{3+}$ are analyzed for both compounds. Comparisons of peak width and intensity are discussed along with the notable first report for both of the $^5$D$_{0}\rightarrow {^7}$F$_0$ transition, the hyperfine structure of which has potential use in quantum memory applications. The air instability of Eu(HCOO)$_{3}\cdot$(HCONH$_2$)$_2$ 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