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An increase in the amount of nickel in LiMO2 (M = Ni, Co, Mn) layered system is actively pursued in lithium‐ion batteries to achieve higher capacity. Nevertheless, fundamental effects of Ni element in the three‐component layered system are not systematically studied. Therefore, to unravel the role of Ni as a major contributor to the structural and electrochemical properties of Ni‐rich materials, Co‐fixed LiNi0.5+xCo0.2Mn0.3–xO2 (x = 0, 0.1, and 0.2) layered materials are investigated. The results, on the basis of synchrotron‐based characterization techniques, present a decreasing trend of Ni2+ content in Li layer with increasing total Ni contents. Moreover, it is discovered that the chex.‐lattice parameter of layered system is not in close connection with the interslab thickness related to actual Li ion pathway. The interslab thickness increases with increasing Ni concentration even though the chex.‐lattice parameter decreases. Furthermore, the lithium ion pathway is preserved in spite of the fact that the c‐axis is collapsed at highly deintercalated states. Also, a higher Ni content material shows better structural properties such as larger interslab thickness, lower cation disorder, and smoother phase transition, resulting in better electrochemical properties including higher Li diffusivity and lower overpotential when comparing materials with lower Ni content.

We present comprehensive measurements of the structural, magnetic and electronic properties of layered van-der-Waals ferromagnet VI3 down to low temperatures. Despite belonging to a wellstudied family of transition metal trihalides, this material has received very little attention. We outline, from high-resolution powder x-ray diffraction measurements, a corrected room-temperature crystal structure to that previously proposed and uncover a structural transition at 79 K, also seen in the heat capacity. Magnetization measurements confirm VI3 to be a hard ferromagnet (9.1 kOe coercive field at 2 K) with a high degree of anisotropy, and the pressure dependence of the magnetic properties provide evidence for the two-dimensional nature of the magnetic order. Optical and electrical transport measurements show this material to be an insulator with an optical band gap of 0.67 eV -the previous theoretical predictions of d-band metallicity then lead us to believe VI3 to be a correlated Mott insulator. Our latest band structure calculations support this picture and show good agreement with the experimental data. We suggest VI3 to host great potential in the thriving field of low-dimensional magnetism and functional materials, together with opportunities to study and make use of low-dimensional Mott physics.Two-dimensional van-der-Waals (vdW) magnetic materials have in recent years become the subject of a wide range of intense research 1 . While a large portion of research into two-dimensional materials has centered on graphene, the addition of magnetism into such a system leads to many interesting fundamental questions and opportunities for device applications 2-6 . Particularly for future spintronics applications, semiconducting or metallic materials which exhibit ferromagnetism down to monolayer thickness are an essential ingredient. This has led to a large volume of recent publications on two-dimensional honeycomb ferromagnet CrI 3 7-12 . CrI 3 and VI 3 belong to a wider family of MX 3 transition metal trihalides, with X = Cl, Br, I, which were synthesized in the 60s 13,14 but have since seen little interest until recently 15 . VI 3 is an insulating two-dimensional ferromagnet with a Curie Temperature, T c , given as 55 K and reported to have the layered crystal structure of BiI 3 with space group R-3 [16][17][18] . As shown in a recent review 15 , there is very little available information on VI 3 other than the structure and the expected S = 1 from the 3d 2 configuration of the vanadium sites. Calculations using density functional theory, which additionally yield the exchange constants, have suggested VI 3 to not only remain ferromagnetic down to a single crystalline layer, but to also exhibit Dirac half-metallicity, of interest for spintronic applications 19 .In these vdW materials, hydrostatic pressure forms an extremely powerful tuning parameter. Given the weak mechanical forces between the crystal planes, the application of pressure will dominantly have the effect of pressing the ab planes together, and gradually an...

Magnetic ordering in the two-dimensional limit has been one of the most important issues in condensed matter physics for the past several decades. The recent discovery of new magnetic van der Waals materials heralds a much-needed easy route for the studies of two-dimensional magnetism: the thickness dependence of the magnetic ordering has been examined by using Isingand XXZ-type magnetic van der Waals materials. Here, we investigated the magnetic ordering of MnPS3, a two-dimensional antiferromagnetic material of Heisenberg-type, by Raman spectroscopy from bulk all the way down to bilayer. The phonon modes that involve the vibrations of Mn ions exhibit characteristic changes as temperature gets lowered through the Néel temperature. In bulk MnPS3, the Raman peak at ~155 cm -1 becomes considerably broadened near the Néel temperature and upon further cooling is subsequently red-shifted. The measured peak positions and polarization dependences of the Raman spectra are in excellent agreement with our first-principles calculations. In few-layer MnPS3, the peak at ~155 cm -1 exhibits the characteristic red-shift at low temperatures down to the bilayer, indicating that the magnetic ordering is surprisingly stable at such a thin limit. Our work sheds light on the hitherto unexplored magnetic ordering in the Heisenberg-type antiferromagnetic systems in the atomic-layer limit. ∑ ∑where XY J and I J are spin-exchange energies on the basal plane and along the c-axis, respectively; j S α is the α (α = x, y, or z) component of total spin; and j and δ run through all lattice sites and all nearest-neighbors, respectively. All three fundamental models can be realized with the generic Hamiltonian: 0 XY J = for the Ising model, 0 I J = for the XY model, and XY I J J = for the Heisenberg model. According to the Mermin-Wagner theorem [4], no magnetic ordering is possible at any nonzero temperature in one-or two-dimensional isotropic Heisenberg models. On the other hand, 2D Ising systems can have magnetic ordering at finite temperatures according to Onsager [5].Transition metal phosphorus trisulfides (TMPS3) belong to a class of 2D van der Waals magnetic materials that can be exfoliated to atomically thin layers [6,7]. For transition metal elements like Fe, Ni, and Mn, the materials share the same crystal structures but the magnetic phase at low temperatures vary depending on the magnetic elements: Ising (Fe), XXZ (Ni), and

The results of a single-crystal X-ray-diffraction study of the evolution of crystal structures of VI3 with temperature with emphasis on phase transitions are presented. Some related specific-heat and magnetization data are included. The existence of the room-temperature trigonal crystal structure R-3 (148) has been confirmed. Upon cooling, VI3 undergoes a structural phase transition to a monoclinic phase at Ts ~ 79 K. Ts is reduced in magnetic fields applied along the trigonal c-axis. When VI3 becomes ferromagnetic at TFM1 ~ 50 K, magnetostriction-induced changes of the monoclinic-structure parameters are observed. Upon further cooling, the monoclinic structure transforms into a triclinic variant at 32 K which is most likely occurring in conjunction with the previously reported transformation of the ferromagnetic structure. The observed phenomena are preliminarily attributed to strong magnetoelastic interactions.