Strain-mediated Ferromagnetism and Low-field Magnetic Reversal in Co Doped Monolayer W S2

Strain-mediated magnetism in 2D materials and dilute magnetic semiconductors hold multi-functional applications for future nano-electronics. Herein, First principles calculations are employed to study the influence of biaxial strain on the magnetic properties of Co-doped monolayer W S2. The non-magnetic W S2 shows ferromagnetic signature upon Co doping due to spin polarization, which is further improved at low compressive (-2 %) and tensile (+2 %) strains. From the PDOS and spin density analysis, the opposite magnetic ordering is found to be favourable under the application of compressive and tensile strains. The double exchange interaction and p-d hybridization mechanisms make Co-doped W S2 a potential host for magnetism. More importantly, the competition between exchange and crystal field splittings, i.e. (∆ ex > ∆ c f s), of the Co-atom play pivotal roles in deciding the values of the magnetic moments under applied strain. Micromagnetic simulation reveals, the ferromagnetic behavior calculated from DFT exhibits low-field magnetic reversal (190 Oe). Moreover, the spins of Co-doped W S2 are slightly tilted from the easy axis orientations showing slanted ferromagnetic hysteresis loop. The ferromagnetic nature of Co-doped W S2 suppresses beyond ±2 % strain, which is reflected in terms of decrease in the coercivity in the micromagnetic simulation. The understanding of low-field magnetic reversal and spin orientations in Co-doped W S2 may pave the way for next-generation spintronics and straintronics applications.

The structural, magnetic and electrical transport properties of perovskite La0.67Sr0.33Mn1−x(VMn)xO3: The B-sites vacancies as a rapier

The polycrystalline samples of manganites perovskite [Formula: see text] with B-sites vacancies were synthesized using the conventional solid-state reaction method. The results based on the X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analyses show that the samples with [Formula: see text] have a secondary phase of lanthanum oxides. It indicates there is a maximum vacancy content at the B-sites with [Formula: see text]. By X-ray Photoelectron Spectra (XPS), the ionicities of oxygen were determined to be 0.762, 0.842, and 0.886, corresponding to [Formula: see text], 0.03, and 0.05, respectively. The B-sites vacancy plays an important role in magnetic performances: (i) B-sites vacancy changes the contents and the average cant angle of Mn cations, and makes the specific saturation magnetization at 100 K and 300 K increase, and then decrease rapidly. (ii) The Curie temperature changes in a small range from 363.93 K to 366.00 K, resulting from both the double exchange interaction increasing and the double exchange path destroyed by the vacancies. (iii) The magnetoresistance (MR) at room temperature achieves 6.97% in the [Formula: see text] sample, whose value is larger than that of [Formula: see text] sample.

Localized electronic vacancy level and its effect on the properties of doped manganites

Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites $$\text {La}_{(1-\text {x})} \text {Sr}_{\text {x}} \text {MnO}_{3}$$ La ( 1 - x ) Sr x MnO 3 , varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range ($$0.2\,<\,\text {x}\,<\,0.5$$ 0.2 < x < 0.5 ). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites ($$\text {x}\,\sim \,1/3$$ x ∼ 1 / 3 ), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds.

Modification of pseudobrookite Fe1.7Mn0.3-xNixTiO5: Influence of Ni-substitution on the magnetic properties

In this study, the synthesis of pseudobrookite Fe1.7Mn0.3-xNixTiO5 with variations in composition (x = 0.01, 0.05, 0.1, and 0.15) using a mechanical milling technique has been performed. High purity powder of α-Fe2O3, TiO2, MnCO3, and NiO were prepared as raw materials. The mixture was milled for 5 hours using high energy milling equipment, and sintered at 1000 °C for 5 hours. The refinement result of X-ray diffraction profile shows that the all of pseudobrookite Fe1.7Mn0.3-xNixTiO5 samples have a single phase with particle size of less than 1 μm. The VSM result shows all the samples were ferromagnetic behavior. We concluded that the substitution Ni into Mn on the pseudobrookite Fe1.7Mn0.3-xNixTiO5 can change the magnetic properties of the material from paramagnetic to ferromagnetic through a mechanism of double exchange interaction.

Structural and Morphological La0.85-xBaxNa0.15MnO3 (x = 0, 0.05, 0.10 and 0.15) Perovskite Manganite

Bulk polycrystalline samples La0.85-xBaxNa0.15MnO3 (x = 0, 0.05, 0.10 and 0.15) manganites were synthesized by the sol-gel route. The effect of Barium (Ba) existence on the structural and morphological was investigated by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The structural parameters were obtained using Rietveld refinement of the XRD pattern. It was revealed the structures of compounds have rhombohedral with R-3c space group without any impurities phase. Furthermore, several changes are found to exist due to Ba substitution such as the lattice parameter, unit cells volume, average crystallite size, average Mn-O bond length (<Mn – O>) and average Mn-O-Mn bond angle (<Mn – O – Mn>). The changes in <Mn – O> and <Mn – O – Mn> due to Ba substitution, affects the double exchange interaction of the samples. SEM images reveal the existence of Ba also affects the morphology of the studied samples, which consisted of polygonal grains with homogeneous chemical composition.

Effect of Different Synthesis Methods on Structural, Morphological and Magnetic Properties of La0.7Ba0.25Nd0.05MnO3

La0.7Ba0.25Nd0.05MnO3 (LBNMO) compounds were synthesized using two different methods, namely are solid-state reaction (SS) and sol-gel (SG). All samples were heat-treated at 1200 °C for 12 hours. The investigation on structural, morphological, and magnetic properties was carried out by X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and Vibrating Samples Magnetometer (VSM) at room temperature. From the Rietveld refinement, both samples have formed a rhombohedral structure with an R-3c (167) space group. The average crystallite size was calculated using the Scherrer formula and Williamson-Hall (W-H) method for comparison. It was shown that the crystallite size of the sample produced by the SG method has larger than the SS method. This result is fairly consistent with the result obtained from SEM analysis, which shows that the average grain for the SG sample is larger than of the grain of the SS samples. From the magnetic hysteresis curve, the magnetization saturation value for the SG was higher and sharper than that of the SS sample. These confirm the occurrence of the double exchange interaction in the samples, which is mainly associated with the reduction of bandwidth and grain size.

Double exchange interaction promoted high-valence metal sites for neutral oxygen evolution reaction

A unique double-exchange strategy is adopted to access active high-valent transition metal sites during neutral oxygen evolution reaction.

Room-Temperature Ferromagnetism in Mn-Doped CuCrO2 Nanopowders

(Cu1-xMnx)CrO2 (0≤ x ≤6 at%) and Cu (Cr1-yMny)O2 (0≤ y ≤6 at%) nanopowders were prepared by combining solid-state reaction and ball milling. The Mn concentration dependences of microstructure, morphology and magnetic properties were investigated. It is found that all the samples have a pure 3R-CuCrO2 delafossite structure. The lattice expansion supports the Mn entrance into the Cu and Cr sublattices, respectively, in (Cu1-xMnx)CrO2 and Cu (Cr1-yMny)O2, which is further proved by X-ray photoelectron spectroscopy to some degree. A-site Mn substitution brings about paramagnetic behavior. However, room-temperature ferromagnetism is achieved in B-site Mn-doped samples, originating from the hole-mediated Cr3+–Mn3+ double-exchange interaction. The saturation magnetization of this CuMO2 delafossite (M=Cr, Mn) is about an order of magnitude higher than literature values, and gradually decreased with the Mn addition due to the combined influence of the number of the M–M pairs, the M–M distances and the hole density.