Two professors in the College of Physics at Sichuan University, Prof. Gang Xiang and Prof. Junfeng Wang, have collaborated on quantum measurement of stray field in the two-dimensional (2D) magnetic material Fe₃GaTe₂ using silicon carbide (SiC) color centers. The research paper entitled "Quantum Sensing of Room-Temperature Ferromagnetism in 2D Van der Waals Fe₃GaTe₂ Using Divacancy Spins in SiC" has just been published in the journal of Advanced Functional Materials, which is a breakthrough in the interdisciplinary fields of quantum precise measurement and condensed matter physics.

In recent years, various van der Waals (vdW) ferromagnetic materials have emerged as promising platforms for 2D high-density low-power spintronic devices due to their reduced dimensionality and remarkable spintronic properties. However, a common limitation faced by most of 2D vdW ferromagnets lies in their low Curie temperatures (Tc), which restricts their practical applications in spintronic devices. Very recently, the discovery of vdW ferromagnet Fe3GaTe2 has captured significant interest due to its robust intrinsic ferromagnetism above room temperature. The growing novel magnetic materials inspire scientists to develop new technologies to investigate the local magnetic fields in these materials. Traditional magnetic field detection technologies, such as nuclear magnetic resonance (NMR) and magnetic force microscopy (MFM), have played crucial roles in studying magnetic materials. However, the low spatial resolution of NMR and the invasive characteristic of MFM limit their applications. To address these challenges, spin qubits such as nitrogen-vacancy centers in diamond and boron vacancy defects in hexagonal boron nitride (hBN) have been exploited as magnetic quantum sensors with the advantages of noninvasive, high sensitivity and nanoscale spatial resolution. However, integrating these spin qubits with practical devices is still of great challenge, since the diamond and hBN crystals are not easy to grow and process and not compatible with current CMOS technology. Fortunately, recent accomplishments have highlighted SiC as a promising system for quantum technologies, which is a semiconductor characterized by well-established inch scale single-crystalline growth and subsequent doping and device fabrication protocols. SiC enjoys widespread adoption in high-power electronic devices, making it an ideal candidate for integration with 2D vdW ferromagnetic materials in spintronic and electronic applications.

In this work, the researchers have achieved the noninvasive in situ local stray field detection of the 2D vdW-layered Fe3GaTe2 using divacancy spins in SiC at room temperature, where a layer of shallow divacancies serves as the local magnetic probes of small pieces of Fe3GaTe2 flakes. The crystal structure, lattice vibration, magnetization and anomalous Hall resistance properties of the Fe3GaTe2 sample are firstly characterized. Then the temperature-dependent ODMR signals from divacancies located near and far from the Fe3GaTe2 sample are compared, which indicates that the Tc of Fe₃GaTe₂ is ~360 K. Additionally, the magnetic field-dependent ODMR signals are measured to study the evolution of magnetization with magnetic field. Finally, a peak in the spin relaxation rate around the Tc is discovered through the temperature-dependent spin relaxometry. These experiments lay the groundwork for the applications of mainstream semiconductor technology-friendly SiC-based quantum sensors to noninvasive in situ local stray field detection of 2D vdW ferromagnets.

Figure 1. (a) Temperature-dependent OP and IP magnetization curves of Fe3GaTe2 under ZFC and FC (1000 Oe) conditions, and the inset shows the obtained Tc using temperature-dependent dM/dT curve under OP-FC condition. (b) Schematic of an hBN/ Fe3GaTe2 heterostructure transferred onto SiC, where shallow divacancy defects are used for stray field detection. (c) The magnetic fields of Fe3GaTe2 BFGT as a function of temperature. From the experiments, we obtain the Tc is ~360 K. (d) Temperature-dependent relaxation rate of the Fe3GaTe2, which exhibits a peak around Tc.

Chen Xia, a PhD student, and Luo Qinyue, an undergraduate student (currently PhD  student at the Hong Kong University of Science and Technology), both from the College of Physics at Sichuan University, are co-first authors of this work. Prof. Wang Junfeng and Professor Xiang Gang are the co-corresponding authors. This work was supported by the Ministry of Science and Technology, the National Natural Science Foundation of China, the Science and Technology Department of Sichuan Province, and Sichuan University.

Paper Link: https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202413529