Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session Z61: Cooperative Phenomena II 
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Sponsoring Units: GMAG Chair: Clarina dela Cruz, Oak Ridge National Laboratory Room: 208AB 
Friday, March 8, 2024 11:30AM  11:42AM 
Z61.00001: Abstract Withdrawn

Friday, March 8, 2024 11:42AM  11:54AM 
Z61.00002: Protection of spin excitations in Yb quantum magnets Lazar L Kish, Lisuo Wu, Leonid Vasylechko, Andrey Podlesnyak, Robert M Konik, Daniel M Pajerowski, Andreas Weichselbaum, Igor A Zaliznyak Fractionalized excitations present evidence of entangled states in quantum magnets such as 1D Heisenberg S=1/2 systems (quantum spin chains). Conventionally, systems with larger angular momenta (S≥3/2) are closer to the classical limit and quantum entanglement is less important. Rare earth systems can break this rule by exhibiting quantum behaviors by acting as S_{eff}=½ systems due to the selection of groundstate Kramers doublets by crystal electric fields and by virtue of strong spinorbit coupling. Furthermore, the 4f electronic subshells responsible for magnetism in the rareearths experience protection from coherencedestroying fluctuations by the outer 5s shells and by spinpreserving angular momentum conservation laws. 
Friday, March 8, 2024 11:54AM  12:06PM 
Z61.00003: Firstprinciples calculations of the magnetic properties of a Co_{2} molecule Shuanglong Liu, Daphné LubertPerquel, Stephen Hill, George Christou, HaiPing Cheng We present density functional theory (DFT) and complete active space selfconsistent field (CASSCF) calculations of a Co_{2} magnetic molecule in order to understand results of electron paramagnetic resonance (EPR) measurements. In the Co_{2} molecule, one Co atom is sixcoordinated (octahedral Co), and the other is fourcoordinated (tetrahedral Co). Our CASSCF calculations yield easyplane magnetic anisotropy for both Co atoms in agreement with the measurements. The calculated ZFS parameter D for the octahedral Co is about eight times larger than the D parameter for the tetrahedral Co. DFT calculations falsely yield easyaxis anisotropy for the octahedral Co. The effective gfactors calculated by CASSCF and the pseudospin Hamiltonian approach are close to experimental results. We also calculated the EPR absorption spectrum using quasidegenerate perturbation theory (QDPT) on top of CASSCF. The QDPT calculations reproduced the polar angle dependence of the EPR signal. However, the azimuthal angle dependence of the EPR signal remains a puzzle. The results show that extra precautions should be taken when using DFT for magnetic molecules. 
Friday, March 8, 2024 12:06PM  12:18PM 
Z61.00004: Anisotropyinduced spin parity effect in an antiferromagnetic spin chain Shuntaro Sumita, Akihiro Tanaka, Yusuke Kato Spin parity effects — physics which alters between integer and halfodd integer spin cases — often manifest themselves in quantum spin systems, perhaps the most prominent example being the Haldane conjecture for onedimensional antiferromagnets. In this study we discuss a new and very general mechanism by which spin parity effects can emerge, through the detailed study of an antiferromagnetic spin chain that possesses a spinion anisotropy and is subjected to a transverse magnetic field. Using numerical exact diagonalization, we examine the manner in which the ground state undergoes a series of level crossings upon sweeping the magnetic field, between states with crystal momenta 0 and π. We find that such level crossings disappear in integerspin systems when the anisotropy becomes large, whereas they are robustly present in the case of halfodd integer spins. These results are attributed to the quantitative difference in the nature of the excitation gap in the thermodynamic limit for the two cases, which can be understood in terms of Tomonaga–Luttinger liquid notions, augmented with perturbation theory, as well as with field theory. We will point out how the anisotropyinduced spin parity effect we discovered can be extended to higherdimensional spin systems. 
Friday, March 8, 2024 12:18PM  12:30PM 
Z61.00005: Quantum geometry induced nonlinear transport in altermagnets Yuan Fang, Jennifer Cano, Sayed Ali Akbar Ghorashi Quantum geometry plays a pivotal role in the secondorder response of PTsymmetric antiferromagnets. Here we study the nonlinear response of 2D altermagnets protected by C_{n} T symmetry and show that their leading nonlinear response is thirdorder. Furthermore, we show that the contributions from the quantum metric and Berry curvature enter separately: the longitudinal response for all planar altermagnets only has a contribution from the quantum metric quadrupole (QMQ), while transverse responses in general have contributions from both the Berry curvature quadrupole (BCQ) and QMQ. We show that for the wellknown example of dwave altermagnets the Hall response is dominated by the BCQ. Both longitudinal and transverse responses are strongly dependent on the crystalline anisotropy. While altermagnets are strictly defined in the limit of vanishing SOC, real altermagnets exhibit weak SOC, which is essential to observe this response. Specifically, SOC gaps the spingroup protected nodal line, generating a response peak that is sharpest when SOC is weak. 
Friday, March 8, 2024 12:30PM  12:42PM 
Z61.00006: Electronic, magnetic, and structural properties of CoVMnSb: ab initio study Pavel V Lukashev, Adam Ramker, Brandon Schmidt, Paul M Shand, Parashu R Kharel, Vagharsh Mkhitaryan, Zhenhua Ning, Liqin Ke We present results of a computational study of electronic, magnetic, and structural properties of CoVMnSb, a quaternary Heusler alloy. Our calculations indicate that this compound may crystallize in two energetically close structural phases: inverted and regular cubic. The inverted cubic phase is the ground state, with ferromagnetic alignment, and around 80% spin polarization. Despite having a relatively large band gap in the minorityspin channel close to the Fermi level, this phase does not undergo a halfmetallic transition under pressure. At the same time, the regular cubic phase is halfmetallic, and retains its perfect spin polarization under a wide range of mechanical strain. Transition to regular cubic phase may be attained by applying uniform pressure (but not biaxial strain). In practice, this pressure may be realized by atomic substitution of nonmagnetic atom (Sb) with another nonmagnetic atom (Si) of smaller radius. Our calculations indicate that 25% substitution of Sb with Si results in halfmetallic regular cubic phase being the ground state. In addition, CoVMnSb_{0.5}Si_{0.5} retains its halfmetallic properties under a considerable range of mechanical pressure, thus making it attractive for potential spintronic applications. We hope that the presented results will stimulate experimental efforts to synthesize this material. 
Friday, March 8, 2024 12:42PM  12:54PM 
Z61.00007: Complex magnetic interactions and large inverse magnetocaloric effect in TbSi and TbSi_{0.6}Ge_{0.4} Ajay Kumar, Alex Schmidig, Deborah L. Schlagel, Yaroslav Mudryk We aim to investigate correlations between physical behaviors and crystal structure of TbSi and TbSi_{0.6}Ge_{0.4} compounds through comprehensive analysis of magnetization, specific heat, and temperaturedependent xray diffraction (XRD) measurements. Despite their distinct crystal structures (FeBtype Pnma for TbSi and CrBtype Cmcm for TbSi_{0.6}Ge_{0.4}), both samples exhibit similar temperature and magnetic fielddependent magnetization behaviors. Each sample displays two antiferromagnetic (AFM) transitions, consistent with previous studies [1, 2], as well as metamagnetic behavior. Moreover, both samples exhibit a significant inverse magnetocaloric effect, with magnetic entropy change (∆S_{M}) of 9.6 J/KgK for TbSi and 11.6 J/KgK for TbSi_{0.6}Ge_{0.4} at µ_{0}∆H=7T. Remarkably, the temperaturedependent ∆S_{M }for the TbSi_{0.6}Ge_{0.4} sample reveals the appearance of two additional minima at higher magnetic fields, indicating the emergence of fieldinduced ferromagnetic (FM) coupling, which is further supported by the evolution of the additional peaks in the specific heat curves at elevated magnetic fields. Additionally, our temperaturedependent XRD measurements unveil anisotropic thermal expansion of the unit cell in both samples, while combined XRD and magnetization data highlight the critical role of the 3^{rd} and 4^{th} nearest neighbor TbTb interactions in governing low and hightemperature AFM coupling in both samples. 
Friday, March 8, 2024 12:54PM  1:06PM 
Z61.00008: Spin Dynamics And Quadrupole Fluctuations In The RareEarth Vanadates YbVO4 And TmVO4 Yuntian Li, Linda Ye, Mark P Zic, Ian R Fisher Nematic fluctuations in a number of correlated quantum materials are intricately linked to their physical properties and quantum phase transitions. Here, we propose that a group of rareearth vanadates (RVO_{4}) can be used to capture multipolelattice dynamics associated with the localized nematic order of the 4f degree of freedom. As an illustrative example, we present an experimental study of the dynamical susceptibilities of YbVO_{4} and TmVO_{4}, with Kramers’ and nonKramers’ doublet crystal field ground states, respectively. We will discuss the thermal modeling of the dynamic susceptibility, as well as the implications of the observed slow dynamics in the context of a potential “nematic glass” phase. 
Friday, March 8, 2024 1:06PM  1:18PM 
Z61.00009: Site symmetry analysis and magnonic dispersion of Er_{2}O_{3} including the dipolar interaction Mehdi Maleki Sanukesh, Michael E Flatté Rareearth magnets may provide useful magnetic properties for quantum technologies, including quantum transduction and quantum memories. Erbium(III) oxide (Er2O3) may be able to host magnons because of the localized f shell electrons. Out of the 32 Erbiums in Er2O3 non primitive unit cells, 24 have C2 symmetry and 8 have C3i symmetry. At zero temperature, Er2O3 is in non collinear antiferromagnetic state and the site symmetry plays an important role in exchange interaction in this state. Here we analyze the site symmetry of the crystal and show how C3i sites do not provide exchange coupling that influences the magnon dispersion. Then the HolsteinPrimakoff representation and paraunitary diagonalization are employed to quantize the Hamiltonian. Er2O3. The effect of the dipolar interaction in the magnons is presented and the energy gap between the dipolar magnons and exchange magnons is calculated. 
Friday, March 8, 2024 1:18PM  1:30PM 
Z61.00010: Possible Devil’s Staircase magnetization in Manganese Bismuthides Md Rafique Un Nabi, Rabindra Basnet, Gokul Acharya, Dinesh Upreti, Santosh Karki Chhetri, Jin Hu Manganese bismuthides represent a class of intriguing intermetallic compounds with interesting magnetic and electronic properties. Here, we present the successful growth of single crystals of manganese bismuthides using the flux method and provide a comprehensive analysis of their magnetic and electronic transport properties. Our research has unveiled a remarkable magnetic phenomenon known as the "devil's staircase" within these compounds that is tunable by composition and hence provides a promising platform to study unusual magnetism in materials. 
Friday, March 8, 2024 1:30PM  1:42PM 
Z61.00011: Linear and nonlinear THz spectroscopy of CoNb_{2}O_{6} Hansen S Wu, Nisheeta Desai, Rimika Jaiswal, Ribhu K Kaul Understanding both the linear and nonlinear spectral responses of magnetic insulators to pulses of THz light is a powerful window into the nature of their lowenergy excitations. Here we theoretically study the response in the context of the domain wall bound states of the onedimensional Ising quantum magnet CoNb_{2}O_{6}, using density matrix renormalization group calculations. 
Friday, March 8, 2024 1:42PM  1:54PM 
Z61.00012: Spin Seebeck measurements in a frustrated magnetic system Tanner Legvold, Renjie Luo, Douglas Natelson Frustrated magnetic systems and quantum spin liquid candidates can have complex magnetic phase diagrams as a function of temperature and field, due to the competition between different ordered and disordered states. Phase boundaries are typically detected through detailed measurements of inelastic neutron scattering, magnetization or magnetic susceptibility, and thermodynamic quantities like specific heat. Local spin Seebeck effect measurements are an electrically driven, electrically detected method that is sensitive to the low energy spincarrying excitations in magnetic systems, and thus is another approach for transitions between different magnetic phases. We present initial measurements of the spin Seebeck effect in devices patterned on the surface of single crystals of BaCo2(AsO4)2 as a function of field and temperature. We discuss the signals observed in the context of the rich magnetic phase diagram for this system below 10 K. 
Friday, March 8, 2024 1:54PM  2:06PM 
Z61.00013: Unusual Magnetic Field and Temperature Dependence of the Metamagnetic Transition in UCu_{0.6}Bi_{2} Daniel T Duong, Hope A Long, John Singleton, Joanna Blawat, Vladislav Klepov, Rongying Jin Uraniumbased compounds are an active source of interest due to the wide variety of exotic states that they can host. UCu_{0.6}Bi_{2} orders antiferromagnetically below T_{N }≈ 54 K. For T < T_{N}, there is a firstorder metamagnetic transition under the application of magnetic field. The temperature and fieldorientation dependence of the transition have been mapped using magnetization and MHz susceptibility measurements in fields of up to 60 T and for temperatures down to 0.65 K. Unusually large hysteresis is observed at the transition under certain conditions; the possible origin of this and other features will be discussed. 
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