Fig. 2: Anomalous Hall effect and anisotropic magnetoresistance of Co-BP.
From: Electric field-tunable ferromagnetism in a van der Waals semiconductor up to room temperature
a Planar-view atomic-resolution HAADF image of a Co-doped multilayer BP flake. The image intensity is directly related to the atomic weight of the imaged species. The brightest spots in the planar view HAADF image (marked with red circles) are isolated Co atoms on the BP surface while the dimmer spots (yellow circles) show isolated Co atoms intercalated in deeper interlayer spaces. b Intensity histogram of the mapped atomic columns in (a), indicating the adsorbed and intercalated individual Co atoms with P atomic columns. c Optical micrograph and measurement schematics of the lateral Hall bar device (Device A) of Co-BP on 285-nm SiO2/Si substrate. The ultra-thin BN acts as an encapsulation/diffusion barrier that protects BP and allows dilute Co intercalation. Pairs of Ti/Au (2/85 nm) contacts labelled by #1 and #2 and by #1 and 3 are used for probing the Hall resistance (\({R}_{{xy}}\)) and the channel resistance (\({R}_{{xx}}\)), respectively under a constant current from source (S) to drain (D). Scale bar: 4 μm. d Top panel: Transconductance of the lateral Hall bar device at \({V}_{{{{\rm{SD}}}}}=\) −1 V. Bottom panel: The magnetization field (\({B}_{{{{\rm{C}}}}}\)) as a function of back-gate voltages. The error bars are extracted by fitting with a confidence interval of 99.7%. e Two representative anomalous Hall effect curves at 1.6 K in the hole regime (red dots, fitted by the black line) and electron regime (blue dots). f Optical micrograph and schematics of Device B for in-plane MR measurement. The MR is probed by the voltage between the contacts labelled by #1 and #2. The injection electrode is made of Co/Ti (1.5 nm/35 nm), where Co was deliberately deposited as a discontinuous dust layer of 1.5-nm nominal thickness. Scale bar: 3 μm. g Temperature dependence of MR at \({V}_{{{{\rm{g}}}}}=\) − 50 V and Ibias = −40 μA. For comparison, the bottommost curve (black) refers to the metallic electrode (Co/Ti) itself at \(T=\) 2.5 K, confirming it has no magnetoresistance. The in-plane field (\({B}_{{||}}\)) is collinear with the current. The zoomed-in details of the MR at 300 K are shown in the top panel.
