We have synthesized for the first time the metastable compound 1T-CrTe2. We have done its complete structural characterization and measured its magnetization, specific heat and electrical resistivity between 4 and 330 K. We have also performed detailed band structure calculations. We have found that it crystallizes in the CdI2 structure type and that its electrical resistance follows a metallic behaviour below room temperature. Its magnetization and specific heat curves show that the compound has a transition to a ferromagnetic state at TC = 310 K, with the magnetic moments ordered parallel to the basal plane. From the specific heat measurements and the ferromagnetic solutions obtained from our DFT calculations, we conclude that the ferromagnetism is of itinerant nature.

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We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (T c and T CDW ) as a function of pressure in the transition metal dichalchogenides 2H -TaSe 2 and 2H -TaS 2 . Resistance and susceptibility measurements show that T c increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H -TaS 2 and 8.2 K at 23 GPa in 2H -TaSe 2 . We observe a kink in the pressure dependence of T CDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate T CDW slowly decreases, coexisting with superconductivity within our full pressure range.

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There are two known ludwigites containing a single transition metal element, Fe 3 O 2 BO 3 and Co 3 O 2 BO 3 . The structure of these materials has low-dimensional units in the form of three-legged ladders (3LL) that confer to each of them unique magnetic and electronic properties. Fe 3 O 2 BO 3 presents a staggered charge density wave (CDW) transition in the ladders near room temperature and two magnetic transitions. It has remained a mystery why the other compound Co 3 O 2 BO 3 behaves so conventionally, with a single magnetic transition and no CDW in spite of similar structural and electronic configurations. Neutron diffraction results presented here in this system finally unravel these differences. Far from a trivial explanation, we uncover a coexistence of low and high spin Co ions in well-defined octahedral sites. Our results allow one to solve the contrasting behavior of the Fe and Co ludwigites in terms of a subtle and unique charge ordering mechanism occurring at the microscopic level of the rungs of the 3LL.

We have studied the effect of substitution of Cr in metastable 1T -CrSe 2 by Ti and V on its structural and magnetic properties. The structural transitions observed between 165-180 K in the pure material are stomped by the doping. The pure compound has a magnetization corresponding to an antiferromagnetic (AF) ground state. On Ti substitution, we observe an increase of the lattice constants and a gradual passage towards a ferromagnetic state, while V replacement maintains AF order up to our highest doping, x V = 0.5. With our experimental results and the help of first-principles calculations, we construct the phase diagram of the system.

We present an extensive study of the oxyborate material Co 5 Ti͑O 2 BO 3 ͒ 2 using x-ray, magnetic, and thermodynamic measurements. This material belongs to a family of oxyborates known as ludwigites which presents low-dimensional subunits in the form of three leg ladders in its structure. Differently from previously investigated ludwigites the present material does not show long-range magnetic order although it goes into a spin-glass state at low temperatures. The different techniques employed in this paper allow for a characterization of the structure, the nature of the low-energy excitations and the magnetic anisotropy of this system. Its unique magnetic behavior is discussed and compared with those of other magnetic ludwigites.