http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

The chemical and structural analysis of graphene oxide with different degrees of oxidation

Future generations of electric vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium batteries is mandatory while also maintaining similar or improved rate capability, lifetime, cost, and safety. The vast majority of electric vehicles that will appear on the market in the next 10 years will employ nickel-rich cathode materials, LiNi1–x–yCoxAlyO2 and LiNi1–x–yCoxMnyO2 (x + y < 0.2), in particular. Here, the potential and limitations of these cathode materials are critically compared with reference to realistic target values from the automotive industry. Moreover, we show how future automotive targets can be achieved through fine control of the structural and microstructural properties.

Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives

Ni-rich layered oxides and Li-rich layered oxides are topics of much research interest as cathodes for Li-ion batteries due to their low cost and higher discharge capacities compared to those of LiCoO2 and LiMn2O4. However, Ni-rich layered oxides have several pitfalls, including difficulty in synthesizing a well-ordered material with all Ni3+ ions, poor cyclability, moisture sensitivity, a thermal runaway reaction, and formation of a harmful surface layer caused by side reactions with the electrolyte. Recent efforts towards Ni-rich layered oxides have centered on optimizing the composition and processing conditions to obtain controlled bulk and surface compositions to overcome the capacity fade. Li-rich layered oxides also have negative aspects, including oxygen loss from the lattice during first charge, a large first cycle irreversible capacity loss, poor rate capability, side reactions with the electrolyte, low tap density, and voltage decay during extended cycling. Recent work on Li-rich layered oxides has focused on understanding the surface and bulk structures and eliminating the undesirable properties. Followed by a brief introduction, an account of recent developments on the understanding and performance gains of Ni-rich and Li-rich layered oxide cathodes is provided, along with future research directions.

Nickel-Rich and Lithium-Rich Layered Oxide Cathodes: Progress and Perspectives

Monoclinic α- NaMnO2 is re-investigated electrochemically as a positive electrode material for sodium ion batteries. About 0.85 Na can be deintercalated from NaMnO2 and 0.8 Na be intercalated back during potentiostatical intermittent charge and discharge. Galvanostatical cycling between 2.0 V and 3.8 V gives 185 mAh/g discharge capacity for the first cycle at C/10 rate and 132 mAh/g remains after 20 cycles. Charge and discharge curves are significantly different indicating more hysteresis than is typical for lithium intercalation compounds. We also explain the remarkable difference between layered LiMnO2 and NaMnO2 upon alkali removal.

https://iopscience.iop.org/article/10.1149/2.035112jes/pdf

Electrochemical Properties of Monoclinic NaMnO2

In the manganite ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3},$ charge ordering occurs at a much higher temperature than the antiferromagnetic order ${(T}_{\mathrm{CO}}=250 \mathrm{K},$ ${T}_{N}=160 \mathrm{K}).$ The magnetic behavior of the phase ${T}_{N}lTl{T}_{\mathrm{CO}}$ is puzzling: its magnetization and susceptibility are typical of an antiferromagnet while no magnetic order is detected by neutron diffraction. We have undertaken an extensive study of the crystallographic, electric, and magnetic properties of ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ and established its phase diagram as a function of temperature and magnetic field. The charge disordered paramagnetic phase above ${T}_{\mathrm{CO}}$ presents ferromagnetic correlations. An antiferromagnetic charge exchange phase prevails below ${T}_{N},$ with complete charge and orbital ordering. In the intermediate temperature range, charge ordering occurs while orbital ordering sets in progressively, with no magnetic order. Strong magnetic fields destroy the charge ordered phases in a first-order transition towards a ferromagnetic state.

Charge, orbital, and magnetic order in Nd 0.5 Ca 0.5 MnO 3

A route toward enhancing the energy product $(\mathrm{BH}{)}_{\mathrm{max}}$ of permanent magnetic materials, at room temperature, based on ferromagnetic-(FM-) antiferromagnetic (AFM) exchange interactions has been developed. The exchange coupling, which is induced by ball milling hard magnetic ${\mathrm{SmCo}}_{5}$ with AFM NiO powders, results in an enhancement of coercivity ${H}_{C}$ and squareness ratio ${M}_{R}{/M}_{S}$ (remnant-saturation magnetizations), which depends on the FM:AFM ratio and the processing conditions. However, the presence of the AFM in the composite results also in a competing effect, i.e., reduction of the overall saturation magnetization, which decreases $(\mathrm{BH}{)}_{\mathrm{max}}.$ Nevertheless, it has been found that after an optimization of the FM:AFM ratio and the milling conditions it is possible to achieve an improvement of $(\mathrm{BH}{)}_{\mathrm{max}}.$

Improving the energy product of hard magnetic materials

The room-temperature coercivity, HC , and squareness, MR / MS ~remanence/saturation magnetizations!, of permanent magnet, SmCo 5 powders have been enhanced by ball milling with antiferromagnetic NiO ~with Neel temperature, T N 5590 K!. This enhancement is observed in the as-milled state. However, when the milling of SmCo 5 is carried out with an antiferromagnet with T N below room temperature ~e.g., for CoO, TN5290 K!, the coercivity enhancement is only observed at low temperatures after field cooling throughTN . The ferromagnetic-antiferromagnetic exchange coupling induced either by local heating during milling (SmCo51NiO) or field cooling (SmCo51CoO) is shown to be the origin of the HC increase. © 2001 American Institute of Physics. @DOI: 10.1063/1.1392308#

/pdf/coercivity-and-squareness-enhancement-in-ball-milled-hard-2yh69nw96n.pdf

Coercivity and squareness enhancement in ball-milled hard magnetic-antiferromagnetic composites

A large coercive field, HC=20kOe, is obtained at room temperature in e‐Fe2O3 nanoparticles embedded in a silica matrix, produced by sol-gel chemistry. The combination of a relatively high magnetic anisotropy together with the small saturation magnetization are responsible for this large HC. Upon cooling, a strong reduction of HC is observed at T∼100K, which is accompanied by a drastic reduction of the squareness ratio MR∕MS. Neutron-diffraction measurements reveal the existence of a low-temperature magnetic transition to which the softening of this material can be ascribed.

Large coercivity and low-temperature magnetic reorientation in ε‐Fe2O3 nanoparticles

The magnetic phase diagram of ${\mathrm{La}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{MnO}}_{3}$ powdered samples has been studied as a function of $\ensuremath{\delta}$ in the low doping range $(\ensuremath{\delta}l0.1).{\mathrm{La}}_{0.97}{\mathrm{MnO}}_{3}$ has a canted magnetic structure at low temperature $(\ensuremath{\theta}\ensuremath{\simeq}130\ifmmode^\circ\else\textdegree\fi{}).$ Above ${T}_{C}=118 \mathrm{K},$ it becomes a paramagnet with a huge effective magnetic moment ${\ensuremath{\mu}}_{\mathrm{eff}}=6.0{\ensuremath{\mu}}_{B},$ reflecting the presence of magnetoelastic polarons which are not affected by the magnetic field (up to 20 T) or the temperature ${1.2T}_{C}lTl{2.5T}_{C}.$ When $\ensuremath{\delta}$ is increased to $\ensuremath{\delta}=0.09,$ the system becomes fully ferromagnetic below $170 \mathrm{K}$ but remains insulating down to the lowest temperature.

http://export.arxiv.org/pdf/cond-mat/9803024

Gérard Chouteau

Papers

Charge, orbital, and magnetic order in Nd 0.5 Ca 0.5 MnO 3

Improving the energy product of hard magnetic materials

Coercivity and squareness enhancement in ball-milled hard magnetic-antiferromagnetic composites

Large coercivity and low-temperature magnetic reorientation in ε‐Fe2O3 nanoparticles

Magnetic and electric properties of La 1 − δ MnO 3