Magnetic graphene for microwave absorbing application: Towards the lightest graphene-based absorber

Graphene, a single two-dimensional sheet of carbon atoms with an arrangement mimicking the honeycomb hexagonal architecture, has captured immense interest of the scientific community since its isolation in 2004. Besides its extraordinarily high electrical conductivity and surface area, graphene shows a long spin lifetime and limited hyperfine interactions, which favors its potential exploitation in spintronic and biomedical applications, provided it can be made magnetic. However, pristine graphene is diamagnetic in nature due to solely sp2 hybridization. Thus, various attempts have been proposed to imprint magnetic features into graphene. The present review focuses on a systematic classification and physicochemical description of approaches leading to equip graphene with magnetic properties. These include introduction of point and line defects into graphene lattices, spatial confinement and edge engineering, doping of graphene lattice with foreign atoms, and sp3 functionalization. Each magnetism-imprinting strategy is discussed in detail including identification of roles of various internal and external parameters in the induced magnetic regimes, with assessment of their robustness. Moreover, emergence of magnetism in graphene analogues and related 2D materials such as transition metal dichalcogenides, metal halides, metal dinitrides, MXenes, hexagonal boron nitride, and other organic compounds is also reviewed. Since the magnetic features of graphene can be readily masked by the presence of magnetic residues from synthesis itself or sample handling, the issue of magnetic impurities and correct data interpretations is also addressed. Finally, current problems and challenges in magnetism of graphene and related 2D materials and future potential applications are also highlighted.

Emerging chemical strategies for imprinting magnetism in graphene and related 2D materials for spintronic and biomedical applications

We examine the magnetic properties of two-dimensional graphene with topological line defect using first-principles calculations and predict a weak ferromagnetic ground state with spin-polarized electrons localized along the extended line defect. Our results show that tensile strain along the zigzag direction can greatly enhance local magnetic moments and ferromagnetic stability of the system. In sharp contrast, tensile strain applied along the armchair direction quickly diminishes these magnetic moments. A detailed analysis reveals that this intriguing magnetism modulation by strain stems from the redistribution of spin-polarized electrons induced by local lattice distortion. It suggests a sensitive and effective way to control magnetic properties of graphene which is critical for its applications in nanoscale devices.

Tunable magnetism in strained graphene with topological line defect

A system for magnetic detection includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, and a controller. The optical signal is based on hyperfine states of the NV diamond material. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

Dnv magnetic field detector

A device includes a propulsion unit configured to move the device and a steering unit configured to control the direction of the device. The device also includes a power unit configured to provide power to the propulsion unit and a charging unit configured to use an electric field to provide electrical power to the power unit. The device further includes a first magnetic sensor configured to determine a vector of one or more magnetic fields and a processor communicatively coupled to the propulsion unit, the steering unit, the power unit, and the magnetic sensor. The processor is configured to receive, from the magnetic sensor, a time-varying signal indicative of a magnetic field and determine, based on the time-varying signal, that the magnetic field is associated with an electrical power transmission line. The processor is further configured to cause the steering unit to direct the device toward the electrical power transmission line.

In-situ power charging

Graphite oxide (GO) and reduced graphene oxide (RGO) have been prepared using standard chemical methods. The formations of the oxides are characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies. Both the oxides exhibit weak superparamagnetism and hysteresis for the first time at room temperature. Magnetic moment for RGO is comparatively smaller than that of GO sample. The superparamagnetism in these oxides is attributed to the presence of single domains, each domain being cluster of defect induced magnetic moments coupled by ferromagnetic interaction. Apart from these single domain clusters there are other defect induced moments coupled by ferromagnetic interaction which show ferromagnetism and hysteresis.

S.K. Sarkar

Papers

Magnetic properties of graphite oxide and reduced graphene oxide