اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدUnconventional superparamagnetic behavior in the modified cubic spinel compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$
118
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Structural, electronic, and magnetic properties of modified cubic spinel compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ are studied via x-ray diffraction, resistivity, DC and AC magnetization, heat capacity, neutron diffraction, $^7$Li nuclear magnetic resonance, magnetocaloric effect, magnetic relaxation, and magnetic memory effect experiments. We stabilized this compound in a cubic structure with space group $P4_{3}32$. It exhibits semiconducting character with an electronic band gap of $Delta/k_{rm B} simeq 0.4$ eV. The interaction within each Mn$^{4+}$ and Ni$^{2+}$ sub-lattice and between Mn$^{4+}$ and Ni$^{2+}$ sublattices is found to be ferromagnetic (FM) and antiferromagnetic (AFM), respectively which leads to the onset of a ferrimagnetic transition at $T_{rm C} simeq 125$~K. The reduced values of frustration parameter ($f$) and ordered moments reflect magnetic frustration due to competing FM and AFM interactions. From the $^7$Li NMR shift vs susceptibility plot, the average hyperfine coupling between $^7$Li nuclei and Ni$^{2+}$ and Mn$^{4+}$ spins is calculated to be $sim 672.4$~Oe/$mu_{rm B}$. A detailed critical behaviour study is done in the vicinity of $T_{rm C}$ using modified-Arrott plot, Kouvel-Fisher plot, and universal scaling of magnetization isotherms. The estimated critical exponents correspond to the 3D XY universality class. A large magneto-caloric effect is observed with a maximum isothermal change in entropy $Delta S_m simeq - 11.3$~J/Kg-K and a maximum relative cooling power $RCP simeq 604$~J/Kg for 9~T magnetic field change. The imaginary part of the AC susceptibility depicts a strong frequency dependent hump at $T=T_{rm f2}$ well below the blocking temperature $T_{rm b}simeq120$~K. The Arrhenius behaviour of frequency dependent $T_{rm f2}$ and the absence of ZFC memory confirm the existence of superparamagnetism in the ferrimagnetically ordered state.
قيم البحث
اقرأ أيضاً
In view of the recent experimental predictions of a weak structural transition in CoV$_{2}$O$_{4}$ we explore the possible orbital order states in its low temperature tetragonal phases from first principles density functional theory calculations. We
observe that the tetragonal phase with I4$_1/amd$ symmetry is associated with an orbital order involving complex orbitals with a reasonably large orbital moment at Vanadium sites while in the phase with I4$_1/a$ symmetry, the real orbitals with quenched orbital moment constitute the orbital order. Further, to study the competition between orbital order and electron itinerancy we considered Mn$_{0.5}$Co$_{0.5}$V$_{2}$O$_{4}$ as one of the parent compounds, CoV$_{2}$O$_{4}$, lies near itinerant limit while the other, MnV$_{2}$O$_{4}$, lies deep inside the orbitally ordered insulating regime. Orbital order and electron transport have been investigated using first principles density functional theory and Boltzmann transport theory in CoV$_{2}$O$_{4}$, MnV$_{2}$O$_{4}$ and Mn$_{0.5}$Co$_{0.5}$V$_{2}$O$_{4}$. Our results show that as we go from MnV$_{2}$O$_{4}$ to CoV$_{2}$O$_{4}$ there is enhancement in the electrons itinerancy while the nature of orbital order remains unchanged.
La$_{1.5}$Sr$_{0.5}$CoMn$_{0.5}$Fe$_{0.5}$O$_{6}$ (LSCMFO) compound was prepared by solid state reaction and its structural, electronic and magnetic properties were investigated. The material forms in rhombohedral $Rbar{3}c$ structure, and the presen
ce of distinct magnetic interactions leads to the formation of a Griffiths phase above its FM transition temperature (150 K), possibly related to the nucleation of small short-ranged ferromagnetic clusters. At low temperatures, a spin glass-like phase emerges and the system exhibits both the conventional and the spontaneous exchange bias (EB) effects. These results resemble those reported for La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ but are discrepant to those found when Fe partially substitutes Co in La$_{1.5}$Sr$_{0.5}$(Co$_{1-x}$Fe$_{x}$)MnO$_{6}$, for which the EB effect is observed in a much broader temperature range. The unidirectional anisotropy observed for LSCMFO is discussed and compared with those of resembling double-perovskite compounds, being plausibly explained in terms of its structural and electronic properties.
We present a structural and magnetic study on two batches of polycrystalline LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_2$ (commonly known as Li NMC 811), a Ni-rich Li ion battery cathode material, using elemental analysis, X-ray and neutron diffraction, mag
netometry, and polarised neutron scattering measurements. We find that the samples, labelled S1 and S2, have the composition Li$_{1-x}$Ni$_{0.9+x-y}$Mn$_y$Co$_{0.1}$O$_2$, with $x = 0.025(2)$, $y = 0.120(2)$ for S1 and $x = 0.002(2)$, $y = 0.094(2)$ for S2, corresponding to different concentrations of magnetic ions and excess Ni$^{2+}$ in the Li$^+$layers. Both samples show a peak in the zero-field cooled (ZFC) dc susceptibility at 8.0(2) K but the temperature at which the ZFC and FC (field-cooled) curves deviate is substantially different: 64(2) K for S1 and 122(2) K for S2. Ac susceptibility measurements show that the transition for S1 shifts with frequency whereas no such shift is observed for S2 within the resolution of our measurements. Our results demonstrate the sample dependence of magnetic properties in Li NMC 811, consistent with previous reports on the parent material LiNiO$_2$. We further establish that a combination of experimental techniques are necessary to accurately determine the chemical composition of next generation battery materials with multiple cations.
Interest for layered Ruddlesden-Popper strongly correlated manganites of Pr$_{0.5}$Ca$_{1.5}$MnO$_4$ as well as to their thin film polymorphs is motivated by the high temperature of charge orbital ordering above room temperature. We report on the tai
loring of the c-axis orientation in epitaxial RP-PCMO films grown on SrTiO$_3$ (STO) substrates with different orientations as well as the use of CaMnO$_3$ (CMO) buffer layers. Films on STO(110) reveal in-plane alignment of the c-axis lying along to the [100] direction. On STO(100), two possible directions of the in-plane c-axis lead to a mosaic like, quasi two-dimensional nanostructure, consisting of RP, rock-salt and perovskite building blocks. With the use of a CMO buffer layer, RP-PCMO epitaxial films with c-axis out-of-plane were realized. Different physical vapor deposition techniques, i.e. ion beam sputtering (IBS), pulsed laser deposition (PLD) as well as metalorganic aerosol deposition (MAD) are applied in order to distinguish between the effect of growth conditions and intrinsic epitaxial properties. For all deposition techniques, despite their very different growth conditions, the surface morphology, crystal structure and orientation of the thin films reveal a high level of similarity as verified by X-ray diffraction, scanning and high resolution transmission electron microscopy. We found that for different epitaxial relations the stress in the films can be relaxed by means of a modified interface chemistry. The charge ordering in the films estimated by resistivity measurements occurs at a temperature close to that expected in bulk material.
Spinel Li$_x$Mn$_2$O$_4$ is a key cathode material that is used extensively in commercial Li-ion batteries. A challenge with this material has been that the capacity of the battery fades with cycling, an effect that can be traced to the presence of a
n anti-ferromagnetic insulator phase in the fully lithiated LiMn$_2$O$_4$ (LMO) and the associated charge disproportionation that drives distortions of the MnO$_6$ octahedra. Here, by combining x-ray magnetic Compton scattering experiments with parallel first-principles computations, we show that the anti-ferromagnetic phase of LMO is surrounded by a robust ferrimagnetic metallic phase, which becomes stable when even a small amount of Li is removed from or added to the charge-ordered LMO. In this surprising ferrimagnetic state, charge-ordering and octahedral distortions are found to be strongly suppressed. We identify the nature of the ferrimagnetic orbitals involved through theoretical and experimental analyses of the magnetic Compton scattering spectra.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
