Proximity‐induced tuning of spin–orbit coupling (SOC) is of paramount importance in emerging magnetic materials and in spintronics. Probing the above SOC via light–matter interaction assisted methods provides a novel route to investigate interesting material phenomena. Here, the proximity studies in a heterostructure of monolayer molybdenum disulfide (MS) and iron (Fe) to enhance and tune the interfacial SOC are reported. The augmented SOC of the MSFe heterostructure arises due to interfacial charge transfer, and is probed using magneto‐optic Kerr effect and a novel optical technique utilizing the spin Hall effect of light. Measuring the changes in the state of polarization of light reflected from the sample via weak measurement provides direct access to the real and imaginary parts of the complex weak value and, hence, the underlying SOC and induced magnetic effects from a single experiment. The results obtained are confirmed using other experimental and simulation tools.
Imaging atomically resolved surfaces and performing spectroscopy of exotic surfaces at cryogenic temperature in the presence of the magnetic field is an engineering challenge. Additionally, performing these measurements in an all-cryogen-free environment compounds the above complexity due to the associated vibration and acoustic noise generated by the running of cryogenic cold heads. We here report successful integration of a cryogen-free scanning tunneling microscope (STM) with a cryogen-free superconducting vector-magnet, connected to an ultra-high vacuum cluster assembly for in situ sample transfer. We present details of the integration involving vibration and electrical noise isolation procedures allowing for operation of the STM at extremely low noise levels below 30 fA/Hz during normal operations of the complete vacuum-line assembly with multiple turbomolecular pumps. We demonstrate the above STM capability at cryogenic temperature and in the presence of the magnetic field through atomic resolution imaging of graphite and thin films of gold on the mica substrate transferred in situ to the STM chamber. We also demonstrate spectroscopy signatures of the superconducting gap in MgB2 thin films. The design of our in-house customized cluster-vacuum-line assembly provides unsought opportunities in continuous uninterrupted imaging of ultra-clean in-vacuum grown surfaces without the need for cryogenic refills in either the STM or the magnet.
Exchange-bias as an interfacial phenomenon is extensively investigated in bilayer films of a ferromagnet (FM) and an antiferromagnet (AFM) with large internal magnetic anisotropy. This mechanism is also observable by replacing the AFM layer with a hard-FM of sufficiently strong magnetic anisotropy; a response that was recently demonstrated in the transport study of Fe/metal-phthalocyanine (MPc) bilayers [Mundlia et al., Phys. Rev. Appl. 14, 024095 (2020)]. In this bilayer system, hybridization with the molecule causes the surface-Fe to become magnetically hard and couple to the bottom soft-Fe layer via magnetic exchange-bias. In this letter, the planar-Hall study in such exchange-biased Fe/MPc devices is performed using cobalt- and vanadyl- phthalocyanine (CoPc and VOPc) molecules with their responses being sensitive to the choice of molecule and to the field-cooling conditions. For the case of zero-field or in-plane field cooling, the planar-Hall signal in Fe/VOPc devices is larger than in the Fe/CoPc devices arising due to the difference in the magnetization rotation pathway during magnetization reversal, with a possible transition through non-co-planar spin-configuration in the Fe/VOPc devices. In the case of the Fe/CoPc device, this rotation pathway could be activated by out-of-plane field-cooling resulting in more than double the increase in the planar Hall signal. We also investigate the variation in interfacial spin-disorder by field-cooling procedures and its effect on exchange-bias and planar Hall signal. The work support the spin-freezing response at the Fe/MPc interface, making this study exciting for further investigations.
Simultaneous extraction of the magnetic and spin‐orbit coupling (SOC) information of an interface using the weak measurement assisted spin‐Hall effect of light (SHEL) is demonstrated as a novel probe to characterize materials' magnetic properties, see article number 2000042 by Karthik V. Raman, Tharangattu N. Narayanan, Nirmal K. Viswanathan, and co‐workers. A heterostructure of Fe and MoS2 monolayers is shown for enhanced SOC due to the proximity effect, which is proven via SHEL method and then confirmed using magneto‐optic Kerr effect (MOKE) studies.
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