## 1 Introduction  
Following the groundbreaking discovery of graphene, many two-dimensional (2D) materials have entered people's vision for their unique electronic and magnetic properties and promising applications in nanoscale devices. Various types of 2D materials, such as transition metal dichalcogenides (TMDs), silicene, and phosphorene, have been synthesized so far [1; 2; 3]. These materials exhibit a wide range of physical properties that are being actively sought to fabricate high-performance electronic devices. While efforts in this area have been focused on the investigation of 2D semiconductors and optoelectronic or thermoelectric materials [4; 5], 2D magnetic materials remain largely unexplored. Theoretically, 2D magnetic materials are an ideal platform for investigating how the Hamiltonians of the fundamental magnetism models, such as the Ising, XY, and Heisenberg models, behave in the 2D limit [6]. In practice, robust and tunable magnetic properties in 2D materials can be valuable in quantum computation, logic and memory operations, spintronics, and other electronic devices where the spin degree of freedom of the carriers is manipulated [7; 8; 9; 10]. The magnetic ground states of these materials can be controlled via proximity effects and moire patterns, or by external perturbations, such as gating and strain [11; 12; 13; 14]. For successful implementation in real devices, it is of the utmost importance to understand and exploit the control of the ground state via strain and gating [15]. In addition to tuning the carrier spin degree of freedom in devices, the search for intrinsically magnetic 2D materials is also of fundamental interest in understanding the basic physics of spin processes. One class comprising 2D materials that are simultaneously robust, adjustable, and intrinsically magnetic, namely MXenes, is considered to be of research value in spin electronic devices. With the general formula of \(\mathrm{M}_{n+1}\mathrm{X}_{n}\mathrm{T}_{x}\) (where M represents transition metal, X represents C/N, and T is O/OH/F, \(n\) = 1-4), MXenes have rich tunability, including compositional tunability, elemental flexibility, and 2D crystallinity, allowing the fine tuning of desirable magnetic properties [16; 17; 18; 19]. In addition, some published works have suggested that MXenes' tunable electronic and magnetic properties can be tailored remarkably via surface functionalization. For example, [PERSON] et al. pointed out that metallic Nb\({}_{2}\)CO\({}_{2}\) can be transformed into a semiconductor by the substitution of carbon with nitrogen [20]. In some recent theoretical reports, the effects of different surface terminating species on work function and electronic, vibrational, and thermal properties have been explored; they commonly include O, OH, NH, N, S, F, Cl, Br, I, which are bonded to the outer layer M atoms [20; 21]. The experimental work also demonstrates that phosphorous (P) doping on the surface has proved effective in improving the electrochemical properties [22]. These studies provide a guide for researchers who are exploring relevant properties of MXenes. However, there are few reports on double-M 2D nitride MXenes (M'M'Xene) so far. [PERSON] et al. and [PERSON] et al. have envisioned in theory that the layering effect owing to different types of M atoms will be even more pronounced [23; 24]. Such layering is expected to play a crucial role in improving the properties of many promising 2D magnetic materials and devices. A good example in this category is the implementation of out-of-plane mirror symmetry breaking, i.e., 2D Janus MXenes, which would be an interesting issue due to atomic configuration of M layers in MXenes. Over the past few years, it has been found that the unique characteristics of 2D Janus MoSSe, the 2D Janus TMDC that was first prepared, can lead to its novel phenomena, such as Rashba spin splitting [25; 26; 27; 28], piezoelectric polarization [25; 27; 28], second-harmonic generation [25; 29], catalytic effects [25; 26; 30], and long carrier recombination [26; 29; 30; 31].