Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S35: Low-Dimensional Van Der Waals MagnetsInvited Live
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Sponsoring Units: GMAG Chair: Travis Williams, Oak Ridge National Lab |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S35.00001: Stacking dependent magnetism in van der Waals magnets Invited Speaker: Di Xiao In recent years it has become increasingly clear that stacking engineering in van der Waals materials can be a powerful tool to realize novel properties and functionalities. In this talk, I will discuss stacking dependent magnetism in van der Waals magnets, using bilayer CrI3 as an example. I will first show that a relative shift between the two layers at the fraction of the lattice constant can lead to drastic change in the magnetic states. As a result, stacking domain walls can host one dimensional magnon channels, which have lower energies than bulk magnons. Interestingly, some magnon channels are hidden in magnetically homogeneous background. In a moire superlattice, these 1D magnon channels form an interconnected network, which will dominate low-energy spin and thermal transport. These results reveal the importance of stacking domain walls in understanding magnetic properties of van der Waals magnets, and extend the scope of stacking engineering to magnetic dynamics. |
Thursday, March 18, 2021 12:06PM - 12:42PM Live |
S35.00002: Rich behaviors of magnetic excitations in a two-dimensional honeycomb Ising magnet CrI3 Invited Speaker: Liuyan Zhao Two-dimensional (2D) magnetism has been long sought-after, and only very recently realized in atomic crystals of magnetic van der Waals materials. So far, a comprehensive understanding of the magnetic excitations in such 2D magnets remain to be fully explored and comprehensively understood. In this talk, we report polarized micro-Raman spectroscopy studies on a 2D honeycomb magnet CrI3. We will show the presence of two types of magnetic excitations in 2D CrI3, one being the spin waves (i.e., magnons) and the other being a static-magnetism-phonon coupled entity. By exploring their symmetry properties and temperature dependence, we confirm the magnetic nature of both types of excitations. By performing layer number and magnetic field dependent Raman measurements, we show the rich behaviors of both excitations across the phase transition from the layered antiferromagnetic to ferromagnetic order. These results of two types of magnetic excitations demonstrate the intriguing magnetic properties and intricate interplay between spin and lattice in 2D magnets, thus opening up opportunities for spintronics incorporating 2D magnets. |
Thursday, March 18, 2021 12:42PM - 1:18PM Live |
S35.00003: Ferromagnetism in van der Waals compound Mn(Sb, Bi)2Te4 Invited Speaker: Jun Zhu The prospect of realizing the quantum anomalous Hall effect at elevated temperatures has inspired many recent explorations of magnetic van der Waals compounds with the composition of MnBi2Te4, MnBi2nTe3n+1 and their Sb-substituted alloys such as Mn(Sb, Bi)2Te4. While most single crystals synthesized to date exhibit a type-A antiferromagnetic ground state, we show that under certain synthetic conditions, Sb-rich compound MnSb1.8Bi0.2 Te4 can form a net ferromagnetic state with a Curie temperature of 26 K. We report on the structural, magnetic, and electrical properties of MnSb1.8Bi0.2 Te4 combining magneto-transport, SQUID magnetometry, x-ray and neutron scattering techniques. We show that the low-field slope of the Hall signal serves as a good proxy for the magnetic susceptibility in microscopic samples. Mn-Sb site mixing may play a key role in mediating the observed ferro (ferri)magnetism. Excess anomalous Hall effect similar to topological Hall effect reported in other materials onsets at T ~ 10 K and together with other probes, suggests possible new magnetic ground states. |
Thursday, March 18, 2021 1:18PM - 1:54PM Live |
S35.00004: Manipulating the magnetism in Fe5GeTe2 by cobalt substitution Invited Speaker: Andrew May The van der Waals metal Fe5-xGeTe2 has one of the highest reported Curie temperatures (270-310K) for cleavable materials. The crystal structure contains three Fe sublattices, one of which possesses intrinsic disorder and greatly impacts the magnetism. Here, the impact of cobalt substitution on the lattice and magnetic properties will be discussed. Ferromagnetism persists with modest cobalt concentration and a change in the magnetic anisotropy occurs near 20% cobalt for iron. Near 50% cobalt, the layer stacking changes from rhombohedral to primitive and a decrease in stacking fault density occurs. A concomitant change to antiferromagnetic order is demonstrated through magnetization measurements that reveal a Néel temperature near 340K. These experimental findings are supported by first principles calculations that suggest site preference exists for cobalt substitution, and the calculations also demonstrate that both a relatively high cobalt content and the primitive layer stacking are required to produce the antiferromagnet ground state. These results demonstrate a strong coupling of atomic configurations and interlayer stacking to the magnetism in a metallic, cleavable system. |
Thursday, March 18, 2021 1:54PM - 2:30PM Live |
S35.00005: Van der Waals magnets based heterostructures Invited Speaker: Yong Chen Layered van der Waals (vdW) magnets have attracted significant recent interests due to their novel physical properties and potential applications in spintronics. These vdW magnets may be insulators or conductors, ferromagnets and/or antiferromagnets, and may even host other exotic magnetic states such as spin liquids. As transferrable layered 2D materials, they can be easily interfaced with other materials to form hybrids and heterostructures. This talk will present some recent efforts along these lines, where we have fabricated various hybrids and heterostructures interfacing vdW/2D magnets with other (both vdW and non-vdW) materials and characterized them with optical (such as MOKE and Raman) and transport measurements. For example, interfacing ferromagnetic (FM) CrGeTe3 (CGT) layers with NiO (a common antiferromagnetic oxide) leads to significantly enhanced FM Curie temperature (from ~60K to ~120K) and coercive field in CGT, suggesting enhanced magnetic anisotropy. Further studies suggest that wrinkle formation and strains play important roles in the enhanced magnetism. We also interfaced 2D magnets with strongly spin-orbit-coupled materials (including topological insulators and spin-Hall heavy metals) and studied various proximity induced transport phenomena to probe/engineer relevant spintronic order. Interfacing and heterostructuring open many possibilities to modify and probe the magnetism, as well as using the magnetism in these vdW magnets to influence and induce additional electronic/magnetic phenomena in other materials and in the hybrids. |
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