Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D55: Low Dimensional Magnetism (Including Molecules and Surfaces)Focus
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Sponsoring Units: GMAG Chair: Masaaki Matsuda, Oak Ridge National Lab Room: Room 305 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D55.00001: High-Field EPR Spectroscopy of a Mn3+ Spin-Crossover Complex Brittany L Grimm, Irina Kühne, Conor Kelly, Grace Morgan, Stephen Hill When stimulated by changes in temperature, pressure, electric field, magnetic field, or optical irradiation, spin-crossover (SCO) complexes change their spin states and exhibit large atomic displacements, making them appealing for use in magnetoelectric applications. Coupling between the molecular magnetic properties and the charge/elastic degrees of freedom of the lattice drives cooperativity via local lattice strains, resulting in large changes in magnetic susceptibility with relatively small perturbations. To investigate the potential of molecular metal-organics as magnetoelectric candidates, a study utilizing continuous-wave high-field powder EPR spectroscopy was conducted on a Mn3+ complex that undergoes a sharp thermal transition (T1/2 = 51 K; with < 10 K hysteresis) from a pure high-spin (HS) S = 2 state to a pure low-spin (LS) S = 1 state. Spin-orbit coupling dominates the magnetic anisotropy in d-block transition metals, which admixes crystal field states. Indeed, significant zero-field splitting (D and E) parameters were obtained for both the LS (D = +21.23 cm-1, E = +2.275 cm-1) and HS states (D = + 5.66 cm-1, E = + 1.31 cm-1) in this study. Although positive D parameters are unusual for octahedral Mn3+ complexes, these observations are rationalized based upon the coordination environment of the compound and the associated spin state changes. |
Monday, March 6, 2023 3:12PM - 3:48PM |
D55.00002: New Paradigms in Heavy Transition Metal Molecular Magnetism Invited Speaker: Qiang Chen The spatially more extended d orbitals in heavy transition metals (i.e. 4d and 5d) usually lead to stronger inter-site hopping effects, which could dominate in 4d/5d transition metal cluster magnets. In that case, heavy transition metal molecular magnets can host a variety of intracluster interactions due to the delicate competition between Hund's coupling and orbital hopping that is enhanced by the larger spatial extent of the d-orbitals as compared to their 3d transition metal counterparts. Therefore, the electronic ground states of the molecules can be governed by local moment physics, molecular double exchange, metal-metal bonding, or even orbital selectivity. The variation in electronic ground states has been shown to generate new spin liquid candidates, low-lying spin state transitions, and large zero field splitting that may give rise to single molecule magnets with incredibly high blocking temperatures. This talk will present my recent work in this novel area of heavy transition metal molecular magnets. Topics covered will include experimental and theoretical criteria for establishing their electronic ground states, orbital selectivity at the molecular level, and the exotic collective magnetic properties that can be realized in these materials. We have carried out neutron spectroscopic and diffraction studies, dc and ac magnetic susceptibility, specific heat, and μSR measurements. We synthesized and systematically studied the magnetic properties of the 6H-perovskite ruthenates Ba3MRu2O9 (M = Ca, Y, In, Lu, La, Ce) featuring ruthenium dimers, and a few molybdenum trimer based molecular magnets with [Mo3]11+ building blocks. These two systems are among the most common structures of heavy transition metal molecular magnets. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D55.00003: A generalized model of magnon kinetics for two-dimensional spin transport Haocheng Fang, Shu Zhang, Yaroslav Tserkovnyak Long-distance spin transport is highly desirable for spintronic applications. In magnetic insulators, spin transport is dominated by the kinetics of magnon excitations. Here, we present a generalized model of magnon kinetics applicable across a wide range of length scales [1]. Based on a Boltzmann theory considering both spin-conserving magnon collisions and magnon-decay processes hence spin relaxation, our result reproduces the phenomenological spin diffusion equation in the long-distance diffusive limit and the Lindhard formalism in the short-distance ballistic limit, while providing a prediction for the intermediate regime, which can be explored with magnetic noise measurement using, e.g. nitrogen-vacancy centers [2]. The transport properties extracted from our theory also provides some insights to the recent experimental report of enhanced spin conductivity in magnetic thin films approaching two dimensions [3]. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D55.00004: Search for toroidal ground state and magneto-electric effect in single-moleculemagnets Hai-Ping Cheng Using spin Hamiltonians parameterized first-principles calculations, we investigate the magnetic properties of high-symmetry transition-metal trimers, Cr3 and Cu3. We derive exchange coupling and magnetic anisotropy tensor for each trimer, showing these parameters give an accurate modeling of ground state properties. Results for Cr3 indicate uniaxial magnetic anisotropy with an easy-axis aligned along the c-axis with a mostly isotropic exchange interaction due to its high rotational symmetry. The Cu3 molecule lacks rotational symmetry and results show strong antisymmetric interactions for three distinct exchange couplings within the molecule. Diagonalizing multi-spin Hamiltonians, we obtain the ground state for these systems and show that susceptibility and magnetization simulations reproduce experimental findings. The presence of a non-collinear spin structure is investigate using the same multi-spin model and results show negligible presence of a toroidal ordering of spins for Cr3 and a finite toroidal moment for Cu3. We then scan the parameter space of the Hamiltonian to understand and to give insights into which interaction would lead to a measurable toroidal moment. We apply an external electric field and measure the corresponding change in the isotropic and full exchange coupling interaction for Cr3 and Cu3, respectively, with results indicating the presence of a magneto-electric effect. Combining the parameter sampling search for toroidal moments and the application of an electric field, results hint at the possibility of controlling the magnetic state of these system through electronic means. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D55.00005: Effects of dimensionality on the magnetic behavior of cobalt-intercalated 2H-TaS2 Oscar Gonzalez, Kwabena Bediako, Samra Husremovic, Swathy Natarajan Transition metal dichalcogenides (TMDs) intercalated with first-row transition metals are potential candidates for integration into future spintronic devices due to their rich magnetic behavior. These systems exhibit a myriad of magnetic properties, governed by the intercalant identity and stoichiometry, and the choice of the host lattice. Though these degrees of freedom afford exceptional tunability, it is challenging to examine dimensionality effects in these systems. Namely, it is difficult to obtain two-dimensional (2D) analogs of these crystals with mechanical exfoliation due to the strong bonds between the layers and the intercalants. In this work, we successfully prepare atomically thin samples of CoxTaS2 by intercalating cobalt into ultrathin 2H-TaS2 with a soft chemistry approach. To examine the synthesized materials, we employ variable-temperature transport, transmission electron microscopy, and confocal Raman spectroscopy to understand the effects of dimensionality, degree of intercalation, and intercalant (dis)order on the magnetic behavior of CoxTaS2. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D55.00006: Quantum sensing of lanthanide atoms on MgO/Ag(100) Yujeong Bae, Stefano Reale, Jiyoon Hwang, Taehong Ahn, Jeongmin Oh, Harald Brune, Andreas Heinrich, Fabio Donati In this work, we propose a single erbium (Er) atom on MgO surface as a potential atomic spin qubit. To characterize the magnetic moments of Er, we employ a hydrogenated titanium (Ti) atom as a quantum sensor. We build Ti-Er dimers with different separations and orientations and investigate their magnetic interactions using electron spin resonance in a scanning tunneling microscope (ESR-STM). From the ESR spectra measured from Ti in the dimers, we determine the magnetic interactions between Ti and Er and, thus, the magnetic moments of Er at different magnetic field directions. The magnetic interaction varies significantly depending on the magnetic field directions due to the large magnetic anisotropy of Er on MgO. We further discuss the potential structures for the coherent control and detection of erbium spins. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D55.00007: Investigation of critical behavior of layered ferromagnetic Cr2Te3 anirban goswami, Emmanuel Yakubu, Nicholas Ng, Samaresh Guchhait High quality single crystal Cr2Te3 was synthesized by Chemical Vapor Transport (CVT) method.Single crystal XRD shows trigonal symmetry (P-31c). Critical behavior of ferromagnetic Cr2Te3was investigated by bulk isothermal magnetization around the ferromagnetic phase transition.From this data, we estimate modified Arrot plot, the Kouvel-Fisher plot, critical isotherm, Widom scaling and determine critical exponents β, γ, δ values & Curie temperature Tc=211.3K. After the scaling, the isothermal magnetization curves below and above the critical temperatures collapse into two independent universal branches which signifies the reliability of the critical exponent values estimation. The determined exponents match well with those calculated from the results of the renormalization group approach for a two-dimensional Ising system. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D55.00008: Synthesis and physical properties of a new layered ferromagnet, Cr1.21Te2 Zhixue Shu, Weiwei Xie, Nahyun Jo, Haozhe Wang, Tai Kong The Cr-Te binary hosts many unexplored magnetic materials. In this talk, we report the single crystal synthesis and physical properties of a new layered Cr-Te binary ferromagnet, Cr1.21Te2. Based on single crystal x-ray diffraction measurement, Cr1.21Te2 crystalizes in a trigonal structure with a space group P-3. Ferromagnetic transition occurs at ~174 K. Detailed physical property characterization data via temperature- and field-dependent magnetization, zero-field heat capacity and angle-resolved photoemission spectroscopy will be presented. By fitting low temperature magnetization according to the Bloch’s law, Cr1.21Te2 exhibits a finite spin excitation gap, which suggest its possible application as a low dimensional ferromagnet. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D55.00009: Layer and symmetry dependent magnetism in self-intercalated ferromagnet Cr1+xTe2 Mahesh R Neupane, Yuhang Liu, Sohee Kwon, Hang Chi, Gen Yin, Roger K Lake The self-intercalated Cr1+xTe2 is a ferromagnetic layered material composed of alternating CrTe2 and intercalated Cr layers. In this work, we investigate the symmetry and thickness dependent structural and magnetic properties of Cr1+xTe2. Exchange coupling constants, parameters required for the analysis of magnetic properties, are extracted by calculating the energies of different magnetic configurations. Investigation of different surface terminations shows that thin films terminated with CrTe2 layers are the most stable. The direction of magnetic anisotropy depends on the thickness and termination of the thin film. When strain is applied, the exchange coupling constant between the intercalated Cr atom and its nearest neighbor Cr atoms responds in different ways with different symmetries. Our results indicate that the unique symmetry dependent magnetic properties in Cr1+xTe2 are mainly contributed by the intercalated Cr atoms. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D55.00010: Noncollinear phases in twisted double bilayer magnets Mohammad Mushfiqur Rahman, Guanghui Cheng, Avinash Rustagi, Yong P. Chen, Pramey Upadhyaya Moiré superlattices formed by twisting atomically thin materials have traditionally provided a playground to study correlated electrons, and have shown remarkable properties such as superconductivity, Mott insulating states, and moiré excitons. Very recently, by combining moiré potentials with the spin degrees of freedom in twisted bilayer antiferromagnetic (AFM) systems (monolayer plus monolayer), noncollinear magnetic states have been reported [Proc. Natl. Acad. Sci. 117, 10721 (2020), Science 374, 1140 (2021), Nature Nanotechnol. 17, 143 (2022)]. In this work, we harness a new class of magnetic system, namely, the twisted double bilayer AFM (bilayer plus bilayer) to theoretically demonstrate a rich collection of magnetic ground states beyond those observed in the previous platforms. The results predicted from our theory show good qualitative agreement with our experiments [arXiv:2204.03837] and pave the way toward understanding the role of moiré potentials on spin degrees of freedom. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D55.00011: Lanthanide atoms on MgO(100)/Ag(100) as Candidate for Single-Atom-Qubits Stefano Reale, Aparajita Singha, Safa L Ahmed, Denis Krylov, Luciano Colazzo, Christoph Wolf, Carlo S Casari, Alessandro Barla, Edgar Fernandes, Francois Patthey, Marina Pivetta, Stefano Rusponi, Harald Brune, Fabio Donati Lanthanide atoms on surfaces are an exceptional platform for atomic-scale magnetic information storage [Science 352, 318 (2016)]. However, their potential as qubits is yet unexplored due to the limited number of experimental set-ups that can coherently drive the spins of single adatoms. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D55.00012: Defect Engineering and Magnetic Doping of 2D Materials Akash Singh, Chris Price, Vivek b Shenoy Low dimensional dilute magnetic semiconductors (DMSs) are attractive material platforms for applications in multifunctional nano-spintronics due to the prospect of embedding controllable magnetic order within nanoscale semiconductors. Identifying candidate host material and dopant systems requires consideration of doping formation energies, magnetic ordering, and the tendency for dopants to form clustered domains. In this work, we consider the defect thermodynamics and the dilute magnetic properties across charge states of 2D-MoS2 and 2D-WS2 with Mn magnetic dopants as candidate systems for 2D-DMSs. Using hybrid density functional calculations, we study the magnetic and electronic properties of these systems across configurations with thermodynamically favorable defects: 2D-MoS2 doped with Mn atoms at sulfur site (MnS), at two Mo sites (2MnMo), on top of a Mo atom (Mn-top), and at a Mo site (MnMo). While the majority of the Mn-defect complexes provide trap states, MnMo and MnW are amphoteric, although previously predicted to be donor defects. The impact of cluster formation of these amphoteric defects on magnetic ordering is also considered; both MnMo-MnMo (2Mn2Mo) and MnW-MnW (2Mn2W) clusters are found to be stable in ferromagnetic (FM) ordering. Interestingly, we observed the defect charge state dependent magnetic behavior of 2Mn2Mo and 2Mn2W clusters in 2D-TMDs. We investigate that the FM coupling of 2Mn2Mo and 2Mn2W clusters is stable in only a neutral charge state; however, the antiferromagnetic (AFM) coupling is stable in the +1 charge state. 2Mn2Mo clusters provide shallow donor levels in AFM coupling and deep donor levels in FM coupling. 2Mn2W clusters lead to trap states in the FM and AFM coupling. We demonstrate the AFM to FM phase transition at a critical electron density nce = 3.5 × 1013 cm-2 in 2D-MoS2 and 2D-WS2. At a 1.85% concentration of Mn, we calculate the Curie temperature of 580 K in the mean-field approximation. |
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