The evolutions of the structure occurring into the lithium rich cobalt free layered cathode material Li 1.2 Mn 0.61 Ni 0.18 Mg 0.01 O 2 upon the first electrochemical cycle were investigated by the means of high angle annular dark field (HAADF) imaging in a scanning transmission electron microscope and electron diffraction in a transmission electron microscope. They are coupled with electron energy loss spectroscopy (EELS) experiments in order to probe the chemical evolutions occurring during the first charge/discharge cycle. In the pristine material, the analysis of the HAADF images and electron diffraction patterns confirmed the ordering between the cations (Li or Ni with Mn) and the existence of disoriented domains stacked along the c axis. Moreover, the partial solid solution of Ni into Li 2 MnO 3 leading to a composite material is evidenced. Upon the first charge, a loss of material is shown to have occurred, and the presence of a defect spinel phase due to the transfer of transition metal cations to the interslab is clearly established. It is localized at the edge of the particles. This defect spinel phase apparition is confirmed by EELS experiments and identified as (Li)Mn (2−x) Ni x O 4 . After the first discharge, the spinel phase is still present, and structural discrepancies from one crystal to another are observed. Also, it seems that all the domains would not have the same behavior upon discharge.

Magnetic spinel ferrite MFe2O4 (M = Mn, Co, Ni, Zn) nanoparticles have been prepared via simple, green and scalable hydrothermal synthesis pathways utilizing sub- and supercritical conditions to attain specific product characteristics. The crystal-, magnetic- and micro-structures of the prepared crystallites have been elucidated through meticulous characterization employing several complementary techniques. Analysis of energy dispersive X-ray spectroscopy (EDS) and X-ray absorption near edge structure (XANES) data verifies the desired stoichiometries with divalent M and trivalent Fe ions. Robust structural characterization is carried out by simultaneous Rietveld refinement of a constrained structural model to powder X-ray diffraction (PXRD) and high-resolution neutron powder diffraction (NPD) data. The structural modeling reveals different affinities of the 3d transition metal ions for the specific crystallographic sites in the nanocrystallites, characterized by the spinel inversion degree, x, [M2+1-xFe3+x]tet[M2+xFe3+2-x]octO4, compared to the well-established bulk structures. The MnFe2O4 and CoFe2O4 nanocrystallites exhibit random disordered spinel structures (x = 0.643(3) and 0.660(6)), while NiFe2O4 is a completely inverse spinel (x = 1.00) and ZnFe2O4 is close to a normal spinel (x = 0.166(10)). Furthermore, the size, size distribution and morphology of the nanoparticles have been assessed by peak profile analysis of the diffraction data, transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The differences in nanostructure, spinel inversion and distinct magnetic nature of the M2+ ions directly alter the magnetic structures of the crystallites at the atomic-scale and consequently the macroscopic magnetic properties of the materials. The present study serves as an important structural benchmark for the rapidly expanding field of spinel ferrite nanoparticle research.

We use nuclear magnetic resonance to map the complete low-temperature phase diagram of the antiferromagnetic Ising-like spin-chain system BaCo2V2O8 as a function of the magnetic field applied along the chains. In contrast to the predicted crossover from the longitudinal incommensurate phase to the transverse antiferromagnetic phase, we find a sequence of three magnetically ordered phases between the critical fields 3.8 T and 22.8 T. Their origin is traced to the giant magnetic-field dependence of the total effective coupling between spin chains, extracted to vary by a factor of 24. We explain this novel phenomenon as emerging from the combination of nontrivially coupled spin chains and incommensurate spin fluctuations in the chains treated as Tomonaga-Luttinger liquids.PACS numbers: 75.10. Pq, 75.30.Kz, 71.10.Pm, The study of emergent phenomena in interacting quantum systems is at the heart of condensed-matter physics. Interacting fermions confined to one dimension (1D) emerge in a quantum-critical state with non-particle-like excitations, whose low-energy description is known as the Tomonaga-Luttinger liquid (TLL) [1]. As any correlation function adopts a universal form, insensitive to the microscopic details, the TLL description applies to a wide range of systems, like 1D metals [2], edge states of quantum Hall effect [3], quantum wires [4], carbon nanotubes [5] and 1D arrays of atoms on surfaces [6] or in optical traps [7]. The simplest and experimentally most accessible TLLs are realized in 1D quantum antiferromagnets hosting spin chains or ladders, which can be mapped onto interacting spinless fermions [8]. In particular, two spin-ladder systems, (C 5 H 12 N) 2 CuBr 4 (BPCB) [9-13] and (C 7 H 10 N) 2 CuBr 4 (DIMPY) [14][15][16][17][18][19], allowed to confirm the predicted correlation functions not only in form, but also quantitatively as a function of the magnetic field, which controls the Fermi level [1].While isolated TLLs cannot order because of strong quantum fluctuations, a weak coupling between TLLs leads at low temperatures to the 3D ordered state, which inherits the properties of the dominant fluctuation mode.As the Fermi surface in a TLL is reduced to two points, k F and −k F , fermionic fluctuations can only occur at the wavevectors q = 0 and q = 2k F [1]. In antiferromagnetic spin chains or ladders in a magnetic field, the corresponding spin fluctuations are transverse (i.e., involving spin components perpendicular to the field) antiferromagnetic, at the antiferromagnetically shifted wavevector q = π, and longitudinal (i.e., involving spin components along the field) incommensurate at the incommensurate wavevector q = 2k F , respectively [1]. For the Heisenberg exchange between spins, the transverse fluctuations dominate and a weakly coupled system develops a transverse antiferromagnetic order at low temperatures [20,21], in the gapless region between the critical fields B c and B s , which correspond to the edges of the fermion band. Examples include BPCB [10,22] [24]. More interestingly, for t...

In the past years, magnetism-driven ferroelectricity and gigantic magnetoelectric effects have been reported for a number of frustrated magnets featuring ordered spiral magnetic phases. Such materials are of high-current interest due to their potential for spintronics and low-power magnetoelectric devices. However, their low-magnetic ordering temperatures (typically <100 K) greatly restrict their fields of application. Here we demonstrate that the onset temperature of the spiral phase in the perovskite YBaCuFeO5 can be increased by more than 150 K through a controlled manipulation of the Fe/Cu chemical disorder. Moreover, we show that this novel mechanism can stabilize the magnetic spiral state of YBaCuFeO5 above the symbolic value of 25 °C at zero magnetic field. Our findings demonstrate that the properties of magnetic spirals, including its wavelength and stability range, can be engineered through the control of chemical disorder, offering a great potential for the design of materials with magnetoelectric properties beyond room temperature.