This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON MAGNETICS 1 Plasmonic Magnetic Sensor Based on Graphene Mounted on a Magneto-Optic Grating Alireza Dolatabady and Nosrat Granpayeh Center of Excellence in Electromagnetics, Faculty of Electrical Engineering, K.N. Toosi University of Technology, Tehran 1631714191, Iran In this paper, we propose a magnetic sensor utilizing the non-reciprocal propagation of surface plasmons (SPs) on a graphene layer mounted on a magneto-optic grating. An incident electromagnetic wave upon the graphene layer can be absorbed and, under certain conditions, coupled to the SPs along the layer. The sensor structure is assumed to be parallel to the applied magnetic field, the parameter which should be sensed and measured. Contrary to the case with no magnetic field bias and due to magneto-optic characteristics of the grating substrate, wave absorbance for each incident mode can be realized in two different frequencies with non-reciprocal behavior. The frequency difference between these distinct modes depends on the applied magnetic field. This idea can provide a proper approach to sense and measure the magnitude of the applied magnetic field. The performance of the proposed structure is studied analytically and confirmed by numerical simulations. The sensor can be utilized extensively in various systems employing the magnetic field capabilities such as medical diagnostic devices and physicists’ experimental setups. Index Terms— Graphene-based structure, grating substrate, magnetic sensor, magneto-optic grating, non-reciprocal substrate, surface plasmon (SP) propagation. I. I NTRODUCTION E MPLOYING the magnetic fields in various systems such as various industries [1], processors [2], telecommunica- tions [3], and diagnostic tools in surgery applications [4] seems inevitable. Detected and utilized magnetic flux densities in all the above-mentioned cases as well as astronomical [5] and geophysical [6] studies require precise measurement instru- ments. So far, various magnetic flux densities measurement schemes such as magnetoresistance physics of resonance spin filtering [7], magnetoimpedance effect of amorphous magnetic micro-wires [8], Hall-effect devices [9], and single mode– multimode–single mode arrangement of optical fibers with magnetic fluid [10] have been investigated and realized. Mag- netic field sensors based on giant magnetoresistance [11], tunneling magnetoresistance (TMR) [12], and superconducting quantum interference device [13] are considered as promis- ing magnetic sensors in various applications. To be com- patible with new and extensive developments of optical circuits, assembled as photonic integrated circuits (PICs), subwavelength components and sensors are required [14]. One approach to provide such components is utilization of plasmonic structures. So far, many plasmonic structures, more especially plasmonic sensors, have been proposed and inves- tigated [15]–[18]. Previously, plasmonic structures have been implemented based on noble metals in which some intrinsic restrictions have hampered their extensive utilization [19]. Graphene, a 2-D carbon layer, has played a promising role to replace metals in plasmonic components [20]. Based on its fantastic features, such as higher confinement and lower propagation loss, more compact, and so, more appropriate Manuscript received July 12, 2017; revised September 19, 2017; accepted October 31, 2017. Corresponding author: N. Granpayeh (e-mail: granpayeh@kntu.ac.ir). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2017.2775190 structures for utilization in PICs for detection and measure- ment of the magnetic flux densities can be designed [21]–[23]. Until now, various plasmonic magnetic sensors have been realized [24], [25]. Also, some graphene-based magnetic field sensors have been proposed [26], [27]. Most of them utilize the Hall effect for realizing the sensing approach. As it is known, the Hall effect is proportional to the carrier mobility. Graphene, possessing high carrier mobility feature, can be a qualified candidate for implementating the Hall magnetic sensors [28], [29]. In this paper, a magnetic sensor comprising of a magneto- optic grating substrate covered by a graphene layer is pro- posed. By applying a magnetic field, the magneto-optic substrate responds non-reciprocally to the specific normally incident wave to the substrate. The non-reciprocal behavior causes two distinct plasmon modes with different propagation constants, excited on the graphene layer. Therefore, a change in absorbance spectrum of the sensor output compared to the un-magnetized substrate can be detected. By measuring the change, the applied magnetic field can be sensed. We also explain the technique which can be experimentally employed to measure the transmission through and absorbance off the grating substrate, i.e., terahertz time-domain spectroscopy. In addition, the effect of chemical potential on graphene characteristics for calibration applications is mentioned. Fur- thermore, the effect of temperature, degrading the overall performance of the structure is considered. The remaining of the paper is organized as follows. In Section II, the proposed structure is introduced and its operation is analytically investigated. In Section III, the simu- lation results are presented. Some additional notes in practical points of view are explained in Section IV. Finally, the paper is concluded in Section V. II. PROPOSED SENSOR AND ANALYTICAL I NVESTIGATION Fig. 1 demonstrates schematic view of the proposed plas- monic sensor comprising of graphene layer deposited on a 0018-9464 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.