Signature of gate-tunable magnetism in graphene grafted with Pt-porphyrins

Abstract

Inducing magnetism in graphene holds great promises, such as controlling the exchange interaction with a gate electrode, and generating exotic magnetic phases. Coating graphene with magnetic molecules or atoms has so far mostly lead to decreased graphene mobility. In the present work, we show that Pt-porphyrin molecules adsorbed on graphene lead both to an enhanced mobility, and to gate-dependent magnetism. We report that porphyrins can act both as donor or acceptor molecules, depending on the initial doping of the graphene sheet. The porphyrins transfer charge and ionize around the charged impurities on graphene, and, consequently, the graphene doping is decreased and its mobility is enhanced.In addition, ionized porphyrin molecules carry a magnetic moment. Using the sensitivity of mesoscopic transport to magnetism, in particular the superconducting proximity effect and conductance fluctuations, we explore the magnetic order induced in graphene by the interacting magnetic moments of the ionized porphyrin molecules.Among the signatures of magnetism, we find two-terminal-magnetoresistance fluctuations with an odd component, a tell-tale sign of time reversal symmetry breaking at zero field, that does not exist in uncoated graphene samples. When graphene is connected to superconducting electrodes, the induced magnetism leads to a gate-voltage-dependent suppression of the supercurrent, modified magnetic interference patterns, and gate-voltage-dependent magnetic hysteresis. The magnetic signatures are greatest for long superconductor/graphene/superconductor junctions, and for samples with the highest initial doping, compatible with a greater number of ionized, and thus magnetic porphyrin molecules. Our findings suggest that long-range (of the order of the coherence length, or micrometers) magnetism is induced through graphene by the ionized porphyrins' magnetic moment. This magnetic interaction is controled by the density of carriers in graphene, a tunability that could be exploited in spintronic applications.

Tuning magnetoresistance in molybdenum disulphide and graphene using a molecular spin transition

“…5a ). Increment of carrier mobility in graphene after the deposition of QDTP molecule can be explained by compensation of charged impurities, as has been reported in the previous studies of nanoparticles coated graphene 21 , 22 . From the difference of V D , we get the concentration of holes introduced by molecule for the two devices as Δ p = 252 × 10 10 cm −2 and 105 × 10 10 cm −2 , respectively.…”

Sensing at the Surface of Graphene Field‐Effect Transistors

“…[12] The broad sensing potential of graphene can only be unlocked by the introduction of sensitizer (bio)molecules and structures, e.g. various inorganic groups, [23][24][25][81][82][83][84][85][86][87][88][89][90] organic or organometallic molecules, [37,[91][92][93][94][95][96] DNAs, [97][98][99][100][101] proteins, [102] peptides, [30,31,103,104] nanoparticles, [105,106,107] and 2D heterostructure. [51,52,61,108] These molecules are able to respond chemically or physically to their nearby environment, whose responses could then be transduced into an appreciable change in the conductivity of the carbon-based honeycomb scaffold.…”

Observation of critical magnetic behavior in 2D carbon based composites

“…It was seen in N-doped GO, a-RuCl 3 /graphene heterostructures, and graphene graed with Pt-porphyrins, revealing the existence of ferromagnetic phases with signicant magnetic moments for particular values of V g . [152][153][154] However, the low-temperature competition between the Kondo effect and the indirect exchange interaction has been observed in many magnetic material doped graphene-based devices, in which the Kondo effect tends to suppress the magnetic moment while the RKKY interaction tends to maintain the spin ordering between the magnetic impurity and the substrate. In this regard, V g helps to maintain the magnetic ordering in the system.…”