Abstract
Giant magnetocaloric materials are highly promising for technological applications in magnetic refrigeration. Although giant magnetocaloric effects were discovered in first-order magnetic ...transition materials, it is accompanied by some non-desirable drawbacks, such as important hysteretic phenomena, irreversibility of the effect, or poor mechanical stability, which limits their use in applications. Here, we report the discovery of a giant magnetocaloric effect in commercialized Ho
2
O
3
oxide at low temperature (around 2 K) without hysteresis losses. Ho
2
O
3
is found to exhibit a second-order antiferromagnetic transition with a Néel temperature of 2 K. At an applied magnetic field change of 5 T and below 3.5 K, the maximum value of magnetic entropy change
$$(-\Delta {{\rm{S}}}_{M}^{max})$$
(
-
Δ
S
M
max
)
, the refrigerant capacity (RC) were found to be 31.9 J.K
−1
.kg
−1
and 180 J.K
−1
, respectively.
Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer ...exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.
We present a detailed investigation on the effects of C-implantation on low temperature magnetic behavior in Fe93Zr7 amorphous films using spin wave theory, law of approach to saturation, and Alben ...and Becker's theory. Significant increase in Curie temperature with a decrease in coercivity were observed upon C-implantation. Bloch's law was used to analyze the temperature dependence of magnetization, and several important parameters were extracted such as the stiffness constant of the spin wave, and the exchange constant. The local random anisotropy constant decreases from 0.35 to 0.19 MJ/m3 with increasing carbon concentration from 0 to 11%. The ferromagnetic correlation length for which the anisotropy directions are assumed to be arbitrarily oriented increases significantly with increasing carbon content. By the use of the theory of Alben and Becker, we also extracted the local anisotropy from coercivity, and reasonable agreement was found with random magnetic anisotropy approach.
Current research is in constant evolution, regularly revealing surprises that challenge our current understanding. Introducing magnetism into non-magnetic materials like ZnO is motivated by the ...desire to create new properties and develop innovative technological applications. In this work, magnetization is generated in O-polar ZnO by implanting krypton ions. Krypton is chemically unreactive and does not engage in chemical bonding within the compound; magnetization results from the radiation damage caused by the implantation process. The Kr implantation increases the lattice parameters and defect density. Large magnetization values of approximately 186 emu cm
−3
were observed upon implantation. To discern the mechanism leading to the induced magnetism, we have performed ab initio calculations. We modeled the effects caused by beam damage by simulating mechanical constraints and introducing Zn and O vacancies. The calculations clearly show that the magnetism in pristine ZnO was attributed to Zn vacancies, where a magnetic moment of around 2µ
B
was observed. Oxygen defects lead to negligible magnetization within the cell (10
−5
µ
B
). The effects of strain on the observed magnetism were also negligible. The introduction of Zn vacancies in the ZnO matrix leads to localized unpaired electrons, creating large local magnetic moments. This disruption of the electronic structure results in an asymmetry between spin-up and spin-down states, promoting magnetic alignment. Interaction between these magnetic moments near the vacancies establishes a pronounced magnetic region with a reduced charge density, while the regions far away from the vacancy were found to be non-magnetic with a higher charge density, shedding light on the induced magnetism in the material. Our research is of crucial importance in shedding light on the fundamental mechanisms of magnetism induced in ZnO.
We have studied the effects of uniaxial strain on the electronic and optical properties in CsPbI
3
perovskite using density functional theory. The unstrained CsPbI
3
has a band gap energy of 1.63 eV. ...We have applied a compressive and tensile strain (− 5% to 5%) in each of the three crystallographic directions independently. We have observed an anisotropic behavior in the variation of the band gap energy in the case of a tensile strain along the
c
-direction, where the band gap varies differently compared to the case of a tensile strain along the
a
- and
b
-directions. This unusual behavior appears up to a tensile strain of 3.5%, where the band gap energy reaches a value of 1.74 eV. The key factor of this atypical behavior was attributed to the distortion of the structure caused by the inclination of the PbI
6
octahedral, the deviation of the Pb-I-Pb angle from the ideal angle of 180°. Furthermore, through ab initio calculations, we found that CsPbI
3
has several interesting optical properties related to the strain, remarkable optical absorption (about 10
5
cm
−1
), refractive index (2.25) and excellent optical conductivity. These properties make CsPbI
3
a very promising candidate for Optoelectronics applications.
Ruddlesden-Popper Perovskite Ca3Ti2-xFexO7-δ (x = 0.0, 0.02, 0.04, 0.06, and 0.08 (CTFxO)) powders were synthesized by the sol-gel route. The crystal structure was examined using X-ray diffraction ...(XRD) and shows that the Fe doping induces a negligible structural change without perturbing their original crystal structure. The optical properties were investigated using UV–visible spectroscopy. The results indicate that x = 0.08 of Fe doping at the B-site in Ca3Ti2O7-δ (CTO) reduces the optical band gap from 3.61 to 2.23 eV. Hence, Fe substitution induces disorder and broadens the gap edge of absorption significantly that can makes these materials as promising candidate in photovoltaic applications. Furthermore, different fundamental optical properties such as the transmittance, optical band tail, refractive index, optical conductivity, and dielectric coefficient were determined and correlated to the variation of Fe content. Moreover, we have examined the influence of Fe doping on the nonlinear optical (NLOp) properties of the studied compounds and they exhibit an enhanced nonlinear optical behavior with increasing Fe content.
•Ruddlesden-Popper Perovskite Ca3Ti2-xFexO7-δ powders were prepared by sol-gel route.•The samples were investigated using X-ray diffraction and UV–visible spectroscopy.•The results indicate that Fe doping reduces the optical band gap.•Fe doping improved the linear and nonlinear optical parameters of Ca3Ti2-xFexO7-δ.
Fe
2−
x
Ru
x
O
3
(0 ≤
x
≤ 0.08) powders were prepared by solid-state method. X-ray diffraction patterns revealed that the Fe
2
O
3
powders crystallize in a hexagonal structure typical of
α
-Fe
2
O
3
...phase (hematite). The crystallite size was found to decrease from 141 to 84 nm with increasing Ru content from 0 to 0.08, respectively. UV–visible absorption study was performed at room temperature. The direct energy band gap of un-doped
α
-Fe
2
O
3
was 2.22 eV and found to increase with increasing Ru concentration to reach 2.45 eV for
x
= 0.08. This increase in band gap was attributed to the decrease in oxygen vacancies with increasing Ru as indicated by calculations of the oxygen occupancy rate using Rietveld refinement. Other properties such as the absorption coefficient, refractive index, the extinction coefficient, real and imaginary dielectric constant, real and imaginary electrical conductivity were calculated using spectrophotometric measurements.
Nano-crystalline (BaTiO3)0.95 - (LaFeO3)0.05 (BTO-LFO5%) solid solution was synthesized using sol-gel method. X-ray diffraction (XRD) measurements show that BTO-LFO5% ceramics crystallize in a ...tetragonal structure. Impedance relaxation was studied in large windows of frequency and temperature. The electrical properties were found to be significantly dependent on temperature. From Cole-Cole (Nyquist) plots, we demonstrate that the grain bulk and grain boundaries are responsible for the conduction regime at high temperature (T > TC). The grain bulk and grain boundary activation energies were determined using impedance and modulus spectroscopy. The activation energy magnitudes indicate that the conduction mechanism could be attributed to structural defects and charge carriers.
•(BaTiO3)0.95 - (LaFeO3)0.05 solid solutions were prepared using DCS sol-gel method.•(BaTiO3)0.95 - (LaFeO3)0.05 ceramics crystallize in a tetragonal structure.•Grain bulk and grain boundaries are responsible for conduction at high temperature.•Conduction can be attributed to both structural defects and charge carriers.
•RFe11Ti (R= Y, Pr) intermetallic compounds were prepared by arc-melting technique with a subsequent annealing at 1100 °C.•Ti atoms preference to occupy the 8i site was demonstrated by means of XRD, ...DFT and M?ssbauer spectrometry.•Ab initio calculations are in good agreement with the experimental data of M?ssbauer and magnetization
RFe11Ti (R = Y, Pr) intermetallic compounds were successfully synthesized by arc-melting method. The correlation between their structural and magnetic properties has been investigated by means of X-ray diffraction analysis (XRD), Mössbauer spectrometry and magnetic measurements. The combination of these methods allowed to determine unambiguously the preferred inequivalent crystallographic site of titanium atoms. PrFe11Ti presents a weighted average hyperfine field higher than YFe11Ti compound. For both compounds, the hyperfine field follows this sequence: HHF{8i}>HHF{8j}>HHF{8f}. First principles calculations of RFe11Ti were performed utilizing the density functional theory (DFT) based on the full potential linearized augmented plane wave (FLAPW). These calculated data were found to be in good agreement with the experimental magnetic results.
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