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1. Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van der Waals Semiconductor CrSBr

   https://doi.org/10.1002/adma.202003240  

   Telford, Evan J. ; Dismukes, Avalon H. ; Lee, Kihong ; Cheng, Minghao ; Wieteska, Andrew ; Bartholomew, Amymarie K. ; Chen, Yu‐Sheng ; Xu, Xiaodong ; Pasupathy, Abhay N. ; Zhu, Xiaoyang ; et al ( August 2020 , Advanced Materials)

   The recent discovery of magnetism within the family of exfoliatable van der Waals (vdW) compounds has attracted considerable interest in these materials for both fundamental research and technological applications. However, current vdW magnets are limited by their extreme sensitivity to air, low ordering temperatures, and poor charge transport properties. Here the magnetic and electronic properties of CrSBr are reported, an air‐stable vdW antiferromagnetic semiconductor that readily cleaves perpendicular to the stacking axis. Below its Néel temperature,T_N= 132 ± 1 K, CrSBr adopts an A‐type antiferromagnetic structure with each individual layer ferromagnetically ordered internally and the layers coupled antiferromagnetically along the stacking direction. Scanning tunneling spectroscopy and photoluminescence (PL) reveal that the electronic gap is Δ_E= 1.5 ± 0.2 eV with a corresponding PL peak centered at 1.25 ± 0.07 eV. Using magnetotransport measurements, strong coupling between magnetic order and transport properties in CrSBr is demonstrated, leading to a large negative magnetoresistance response that is unique among vdW materials. These findings establish CrSBr as a promising material platform for increasing the applicability of vdW magnets to the field of spin‐based electronics.

    

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2. Emergent Multifunctional Magnetic Proximity in van der Waals Layered Heterostructures

   https://doi.org/10.1002/advs.202200186  

   Choi, Eun‐Mi ; Sim, Kyung Ik ; Burch, Kenneth S. ; Lee, Young Hee ( July 2022 , Advanced Science)

   Proximity effect, which is the coupling between distinct order parameters across interfaces of heterostructures, has attracted immense interest owing to the customizable multifunctionalities of diverse 3D materials. This facilitates various physical phenomena, such as spin order, charge transfer, spin torque, spin density wave, spin current, skyrmions, and Majorana fermions. These exotic physics play important roles for future spintronic applications. Nevertheless, several fundamental challenges remain for effective applications: unavoidable disorder and lattice mismatch limits in the growth process, short characteristic length of proximity, magnetic fluctuation in ultrathin films, and relatively weak spin–orbit coupling (SOC). Meanwhile, the extensive library of atomically thin, 2D van der Waals (vdW) layered materials, with unique characteristics such as strong SOC, magnetic anisotropy, and ultraclean surfaces, offers many opportunities to tailor versatile and more effective functionalities through proximity effects. Here, this paper focuses on magnetic proximity, i.e., proximitized magnetism and reviews the engineering of magnetism‐related functionalities in 2D vdW layered heterostructures for next‐generation electronic and spintronic devices. The essential factors of magnetism and interfacial engineering induced by magnetic layers are studied. The current limitations and future challenges associated with magnetic proximity‐related physics phenomena in 2D heterostructures are further discussed.

    

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3. Tunable layered-magnetism–assisted magneto-Raman effect in a two-dimensional magnet CrI 3

   https://doi.org/10.1073/pnas.2012980117  

   Jin, Wencan ; Ye, Zhipeng ; Luo, Xiangpeng ; Yang, Bowen ; Ye, Gaihua ; Yin, Fangzhou ; Kim, Hyun Ho ; Rojas, Laura ; Tian, Shangjie ; Fu, Yang ; et al ( October 2020 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   We used a combination of polarized Raman spectroscopy experiment and model magnetism–phonon coupling calculations to study the rich magneto-Raman effect in the two-dimensional (2D) magnet CrI 3 . We reveal a layered-magnetism–assisted phonon scattering mechanism below the magnetic onset temperature, whose Raman excitation breaks time-reversal symmetry, has an antisymmetric Raman tensor, and follows the magnetic phase transitions across critical magnetic fields, on top of the presence of the conventional phonon scattering with symmetric Raman tensors in N -layer CrI 3 . We resolve in data and by calculations that the first-order A g phonon of the monolayer splits into an N -fold multiplet in N -layer CrI 3 due to the interlayer coupling ( N ≥ 2 ) and that the phonons within the multiplet show distinct magnetic field dependence because of their different layered-magnetism–phonon coupling. We further find that such a layered-magnetism–phonon coupled Raman scattering mechanism extends beyond first-order to higher-order multiphonon scattering processes. Our results on the magneto-Raman effect of the first-order phonons in the multiplet and the higher-order multiphonons in N -layer CrI 3 demonstrate the rich and strong behavior of emergent magneto-optical effects in 2D magnets and underline the unique opportunities of spin–phonon physics in van der Waals layered magnets. 

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4. Coherent helicity-dependent spin-phonon oscillations in the ferromagnetic van der Waals crystal CrI3

   https://doi.org/10.1038/s41467-022-31786-3  

   Padmanabhan, P. ; Buessen, F. L. ; Tutchton, R. ; Kwock, K. W. C. ; Gilinsky, S. ; Lee, M. C. ; McGuire, M. A. ; Singamaneni, S. R. ; Yarotski, D. A. ; Paramekanti, A. ; et al ( August 2022 , Nature Communications)

   The discovery of two-dimensional systems hosting intrinsic magnetic order represents a seminal addition to the rich landscape of van der Waals materials. CrI₃is an archetypal example, where the interdependence of structure and magnetism, along with strong light-matter interactions, provides a new platform to explore the optical control of magnetic and vibrational degrees of freedom at the nanoscale. However, the nature of magneto-structural coupling on its intrinsic ultrafast timescale remains a crucial open question. Here, we probe magnetic and vibrational dynamics in bulk CrI₃using ultrafast optical spectroscopy, revealing spin-flip scattering-driven demagnetization and strong transient exchange-mediated interactions between lattice vibrations and spin oscillations. The latter yields a coherent spin-coupled phonon mode that is highly sensitive to the driving pulse’s helicity in the magnetically ordered phase. Our results elucidate the nature of ultrafast spin-lattice coupling in CrI₃and highlight its potential for applications requiring high-speed control of magnetism at the nanoscale.

    

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5. Interlayer magnetophononic coupling in MnBi2Te4

   https://doi.org/10.1038/s41467-022-29545-5  

   Padmanabhan, Hari ; Poore, Maxwell ; Kim, Peter K. ; Koocher, Nathan Z. ; Stoica, Vladimir A. ; Puggioni, Danilo ; Hugo) Wang, Huaiyu ; Shen, Xiaozhe ; Reid, Alexander H. ; Gu, Mingqiang ; et al ( December 2022 , Nature Communications)

   Abstract The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for interlayer magnetophononic coupling in the layered magnetic topological insulator MnBi 2 Te 4 . Employing magneto-Raman spectroscopy, we observe anomalies in phonon scattering intensities across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise ‘forbidden’ by momentum conservation. Our microscopic model based on density functional theory calculations reveals that this phenomenon can be attributed to phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi 2 Te 4 , the magnetophononic coupling represents an important step towards coherent on-demand manipulation of magnetic topological phases. 

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