Room Temperature Magnetic Ordering Research Articles

Room temperature magnetic ordering and in vitro antibacterial potency of Nd3+ doped CeO2 against the pathogenic bacterial strains

In this study, 5% Nd3+ doped Cerium oxide (Ce0.95Nd0.05O2) was prepared by a modified solid-state reaction method. Crystallite size and lattice strain were determined from the Williamson-Hall (W-H) plot. The four distinct peaks in the photoluminescence (PL) spectra in the visible region signify the structural defects within the crystal lattice. Room temperature ferromagnetism (RTFM) was observed from the hysteresis loop, and the mathematical fitting of the hysteresis loop suggests ferromagnetic dominance (∼83%) in the magnetic response. The virgin M-H loop was fitted by the ferromagnetic Brillouin function, which suggests possible domain formation in the sample. The in vitro antibacterial activity of 5% Nd3+doped CeO2 was evaluated against two clinically isolated multidrug-resistant pathogenic bacterial strains, namely MLD 2 (Escherichia coli) and MLD 4 (Staphylococcus aureus), utilizing the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), disc agar diffusion (DAD) assays, etc. Notably, compared to the MLD 4 bacterial strain, the synthesized material revealed comparable better antibacterial results against the Gram-negative MLD 2 and in comparison, to the MLD 2 bacterial strain, a relatively higher concentration of the sample is required to completely eradicate the bacterial population of MLD 4. This implies that Ce0.95Nd0.05O2 can destroy the growth of the two tested bacterial strains. In the context of cytotoxicity, up to a certain concentration, the synthesized particle demonstrated no appreciable toxicity towards healthy PBMCs.

Pressure-controlled magnetism in 2D molecular layers

Long-range magnetic ordering of two-dimensional crystals can be sensitive to interlayer coupling, enabling the effective control of interlayer magnetism towards voltage switching, spin filtering and transistor applications. With the discovery of two-dimensional atomically thin magnets, a good platform provides us to manipulate interlayer magnetism for the control of magnetic orders. However, a less-known family of two-dimensional magnets possesses a bottom-up assembled molecular lattice and metal-to-ligand intermolecular contacts, which lead to a combination of large magnetic anisotropy and spin-delocalization. Here, we report the pressure-controlled interlayer magnetic coupling of molecular layered compounds via chromium-pyrazine coordination. Room-temperature long-range magnetic ordering exhibits pressure tuning with a coercivity coefficient up to 4 kOe/GPa, while pressure-controlled interlayer magnetism also presents a strong dependence on alkali metal stoichiometry and composition. Two-dimensional molecular interlayers provide a pathway towards pressure-controlled peculiar magnetism through charge redistribution and structural transformation.

Room temperature multiferroicity of hexagonal LuFeO3 and its enhancement by co-doping in Lu0.9Co0.1Fe0.9Ti0.1O3 nanoparticle system

Antiferromagnetic LuFeO3 can be good multiferroic by having ferroelectricity in its non-centrosymmetric hexagonal phase. But, it is hard to stabilize this metastable phase, preventing the stable orthorhombic phase. In this work, metastable hexagonal LuFeO3 (LFO) nanoparticle was stabilized in chemical sol-gel route in pure phase and co-doped with Co and Ti in the same route to synthesize Lu0.9Co0.1Fe0.9Ti0.1O3 (LCFTO) nanoparticles. Room temperature multiferroicity of bare LFO was established through relevant characterization. And motive behind the co-doping is to enhance the magnetoelectric behavior of the bare system to synthesize a new monophasic type II magnetoelectric multiferroic. Structural investigation by thorough Rietveld analyses of the recorded X-ray diffractograms, confirmed the formation of pure hexagonal (P63cm) phase of both bare and doped LFO. However, deviations in various structural & microstructural parameters were observed in the doped system, which is mainly responsible for the enhancement of magnetic and electric properties of the sample. Presence of antiferromagnetic transition at ∼604 K confirmed the room temperature magnetic ordering of bare LFO. Interestingly, LCFTO shows a drastic enhancement of magnetic property than the bare one in all concerns, where the maximum magnetization at the maximum applied field is enhanced by nearly 36 times at room temperature. Detailed high-temperature dielectric investigation shows, good dielectric strength (∼261) of LFO gets enhanced highly in LCFTO (∼1053) and a high relaxation time having negligible loss factor with an indication of ferro to paraelectric transition above room temperature. Current density vs. electric field (J-E) curve suggests the presence of polarization at room temperature with negligible leakage loss. Direct measurement of ferroelectric loop shows the ferroelectricity (Pmax∼0.064 µc/cm2) of bare LFO at room temperature and a well improvement in the doped LCFTO (Pmax∼0.151 µc/cm2). The presence of room temperature magnetoelectric coupling, confirmed by magnetocapacitance measurements, results in a high value (∼5 %) of magnetocapacitance in the doped system which is also much higher than the bare one (<∼1 %) as expected. All these properties confirm the magnetoelectric multiferroicity of bare h-LuFeO3 at room temperature. And, co-doping in hexagonal LuFeO3 nanoparticle system results in a considerable improvement in its magnetoelectric behavior, so this co-doped system can be a promising and potential magnetoelectric multiferroic for the future generation magnetoelectric devices.

Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe3GaTe2 with highly spin-polarized Fermi surfaces

Recently, van der Waals (vdW) magnetic heterostructures have received increasing research attention in spintronics. However, the lack of room-temperature magnetic order of vdW materials has largely impeded its development in practical spintronic devices. Inspired by the lately discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic order above room temperature and sizable perpendicular magnetic anisotropy, we investigate the basic electronic structure and magnetic properties of Fe3GaTe2 as well as tunneling magnetoresistance effect in magnetic tunnel junctions (MTJs) with structure of Fe3GaTe2/insulator/Fe3GaTe2 by using first-principles calculations. It is found that Fe3GaTe2 with highly spin-polarized Fermi surface ensures that such magnetic tunnel junctions may have prominent tunneling magnetoresistance effect at room temperature even comparable to existing conventional AlOx and MgO-based MTJs. Our results suggest that Fe3GaTe2-based MTJs may be the promising candidate for realizing long-waiting full magnetic vdW spintronic devices.

Topologically Frustrated Graphene Antidot Lattice Semiconductors with Room-Temperature Magnetism

Realizing graphene spintronics is intriguing due to the weak spin–orbital coupling; however, developing intrinsic room-temperature magnetic semiconductors in graphene is still a great challenge. Graphene antidot lattices (GALs), as a type of regular vacancy graphene, exhibit topology-dependent magnetism and offer an ideal platform to achieve room-temperature magnetic semiconductors. Recently, on-surface-synthesized open-shell [n]triangulene polymers as topologically frustrated graphene nanoflakes (GNFs) are the new building blocks to construct topologically frustrated GALs with robust magnetism. Herein, on the basis of the density functional theory calculations, we report seven magnetic GAL semiconductors by assembling two types of open-shell GNFs with topological frustration, that is, isomeric π-extended heptauthrene (cis triangulene dimer) and heptazethrene (trans triangulene dimer). Our results demonstrate that topologically frustrated GALs are semiconductors with either bipolar ferromagnetism or antiferromagnetism, inheriting the topologically frustrated magnetism from their building blocks. In particular, three ferromagnetic and two antiferromagnetic GALs exhibit above room-temperature magnetic order with their Curie or Néel temperatures varying from 507 to 527 or 366 to 391 K, respectively. This study provides a feasible route to obtain topologically frustrated GAL semiconductors with the above room-temperature magnetism from open-shell GNFs for graphene spintronics applications.

Revealing room temperature ferromagnetism in exfoliated Fe5GeTe2 flakes with quantum magnetic imaging

Van der Waals (vdW) material Fe5GeTe2, with its long-range ferromagnetic ordering near room temperature, has significant potential to become an enabling platform for implementing novel spintronic and quantum devices. To pave the way for applications, it is crucial to determine the magnetic properties when the thickness of Fe5GeTe2 reaches the few-layers regime. However, this is highly challenging due to the need for a characterization technique that is local, highly sensitive, artifact-free, and operational with minimal fabrication. Prior studies have indicated that Curie temperature T C can reach up to close to room temperature for exfoliated Fe5GeTe2 flakes, as measured via electrical transport; there is a need to validate these results with a measurement that reveals magnetism more directly. In this work, we investigate the magnetic properties of exfoliated thin flakes of vdW magnet Fe5GeTe2 via quantum magnetic imaging technique based on nitrogen vacancy centers in diamond. Through imaging the stray fields, we confirm room-temperature magnetic order in Fe5GeTe2 thin flakes with thickness down to 7 units cell. The stray field patterns and their response to magnetizing fields with different polarities is consistent with previously reported perpendicular easy-axis anisotropy. Furthermore, we perform imaging at different temperatures and determine the Curie temperature of the flakes at ≈300 K. These results provide the basis for realizing a room-temperature monolayer ferromagnet with Fe5GeTe2. This work also demonstrates that the imaging technique enables rapid screening of multiple flakes simultaneously as well as time-resolved imaging for monitoring time-dependent magnetic behaviors, thereby paving the way towards high throughput characterization of potential two-dimensional (2D) magnets near room temperature and providing critical insights into the evolution of domain behaviors in 2D magnets due to degradation.

Novel bipolar magnetic semiconductor materials formed by adsorption of methyl or halomethyles on the graphene: A spin-polarized density functional theory study

Exploring magnetic materials with electrically controlled spin polarization and room temperature magnetic ordering is of particular importance for applications in spintronic devices. In this study, we present a detailed theoretical study on the structural, electronic, and magnetic features of pristine graphene on which methyl(CH3) or a halomethyl (CH2F, CH2Cl, CH2Br, or CH2I) radical has been adsorbed. The framework of our calculations is dispersion-corrected density functional theory with due account of the spin degree of freedom within the Quantum-ESPRESSO package. The investigation starts with a complete discussion of the geometrical characteristics, followed by a thorough study of the manner of charge transfer and redistribution, electronic band structures, and density of states. The calculated adsorption energies and distances demonstrate the adsorption process to be of the chemisorption type. The adsorption of each radical on graphene is accompanied by a net charge transfer, changing the work function of the resulting compounds and modulating the electronic and magnetization characteristics of pristine graphene. Considerations of the calculated spin-distinct electronic band structure and density of states support the latter conclusion. The presence of unequal band gaps in the up and down spin channels also corroborates the aforementioned compounds' bipolar magnetic semiconductor nature.

Two-dimensional bipolar magnetic semiconductors with high Curie-temperature and electrically controllable spin polarization realized in exfoliated Cr(pyrazine)2 monolayers

Exploring two-dimensional (2D) magnetic semiconductors with room temperature magnetic ordering and electrically controllable spin polarization is a highly desirable but challenging task for nanospintronics. Here, through first principles calculations, we propose to realize such a material by exfoliating the recently synthesized organometallic layered crystal Li$_{0.7}$[Cr(pyz)$_2$]Cl$_{0.7}$0.25$\cdot$(THF) (pyz = pyrazine, THF = tetrahydrofuran) [Science 370, 587 (2020)]. The feasibility of exfoliation is confirmed by the rather low exfoliation energy of 0.27 J/m$^2$, even smaller than that of graphite. In exfoliated Cr(pyz)$_2$ monolayer, each pyrazine ring grabs one electron from the Cr atom to become a radical anion, then a strong $d$-$p$ direct exchange magnetic interaction emerges between Cr cations and pyrazine radicals, resulting in room temperature ferrimagnetism with a Curie temperature of 342 K. Moreover, Cr(pyz)$_2$ monolayer is revealed to be an intrinsic bipolar magnetic semiconductor where electrical doping can induce half-metallic conduction with controllable spin-polarization direction.

Room temperature magnetic ordering in very dilute Iron doped with and without selenium substitutions in antimony matrix

Mossbauer spectroscopy is one of the very sensitive tools to study the hyperfine interactions in alloys and compounds. The interaction of the probe with the local environment gives information like spin state, coordination number, magnetic and quadrupole interaction etc. In the present study, 57Fe Mossbauer spectroscopy was used to study the hyperfine interaction of the FexSb1-x-ySey bulk alloy with very dilute quantity of Fe, x = 0.002. The measurements were done at room temperature. Keeping the amount of Fe constant in the bulk alloy at x = 0.002, the concentration of Se was varied from y = 0.000, 0.004, 0.016 to 0.048. Additionally, to see the effect of extremely low concentration of Fe in Sb matrix alone, a sample with Fe concentration of 0.0015 was prepared without any Se substitution in Sb. The structural study was done using X-ray diffraction technique. Neutron depolarization study was done to see if clusters of Fe were present in the samples. The XRD spectra showed Sb peaks with no other compound phases. From Mossbauer spectroscopy, at y = 0.000, x = 0.002 one magnetic site (site A) with hyperfine magnetic field of ~312 kOe was observed. When the concentration of Fe was further reduced to x = 0.0015, there was no change in the hyperfine magnetic field of ~312 kOe. On introduction of Se into the system, we observed two magnetic sites (A and B). The value of hyperfine magnetic field (HMF) for both the sites (A and B) decreases with increases in Se concentration. At higher concentration of Se (y = 0.048) an additional nonmagnetic site (site C) with quadrupole splitting of 0.51 mm/s was also observed.

Study of magnetic and transport properties of Bi2Se3/FeSe2 bilayer thin films

Thin films of topological insulator (TI) Bi2Se3 were grown onto the surfaces of FeSe2 layers of different thicknesses on Si (100) substrates by magnetron sputtering, forming bilayer films with smooth surface. Magnetic and transport measurements indicate ferromagnetism in these bilayer samples. Large coercive fields at low-temperatures and a room-temperature magnetic order were observed. Moreover, nonsaturated high-filed linear magnetoresistance (MR) and weak anti-localization effect were found in these bilayer thin films. These results indicate that the bilayer samples could have both strong spin–orbit coupling and ferromagnetic proximity effect, which are the desired features.

Unveiling the interplay between induced native defects and room temperature magnetic ordering in titanium deficient disordered-TiO2 nanoparticles

Understanding the origin of magnetic ordering in an undoped semiconductor with native defects is an open question, which is being explored actively in research. In this investigation, the interplay between magnetic ordering and excess induced native defects in undoped anatase TiO2 nanoparticles is explained using an experimental and theoretical approach. It is demonstrated that structurally disordered TiO2 nanoparticles with a high concentration of native defects such as titanium interstitials and oxygen vacancies are synthesized using controlled atmospheric rapid cooling (i.e. quenching) process. The structural disorders in the lattice have been examined using various spectroscopic and microscopic analyses revealed the existence of Ti deficiency in both pristine and quenched TiO2 nanoparticles. A possible origin of magnetic ordering in titanium deficient anatase TiO2 system is elucidated based on first-principle calculations. It was found that the overall magnetic moment of Ti deficient TiO2 system is determined by the distance between Ti interstitials and its neighboring vacancies (i.e. either V Ti or V Os). However, quenched TiO2 nanoparticles possess excess Ti interstitials, Ti and O vacancies and therefore the net magnetic moment of the system is reduced due to anti-ferromagnetically coupled neighboring Tilattice ions.

Metal-organic frameworks: possible new two-dimensional magnetic and topological materials.

Finding new two-dimensional (2D) materials with novel quantum properties is highly desirable for technological innovations. In this work, we studied a series of metal-organic frameworks (MOFs) with different metal cores and discovered various attractive properties, such as room-temperature magnetic ordering, strong perpendicular magnetic anisotropy, huge topological band gap (>200 meV), and excellent spin-filtering performance. As many MOFs have been successfully synthesized in experiments, our results suggest realistic new 2D functional materials for the design of spintronic nanodevices.

Microstructural analysis, dielectric properties and room temperature magnetic ordering of Pr-doped ZnO nanoparticles

Praseodymium (Pr ion)-doped zinc oxide nanoparticles (Zn1−xPrxO, x = 0.00, 0.02, 0.05) were prepared by chemical co-precipitation method. The as-dried samples were annealed at 400 °C for 6 h duration in vacuum (10−2 mm of Hg). Crystallographic phase formation of each prepared sample is determined by matching the peak positions of the observed X-ray diffractograms with those of JCPDS file no. 76-0206. Rietveld refinement of the XRD data is also carried out to confirm the desired crystallographic phase. Analysis of FTIR spectroscopic data confirms that no unwanted chemical bonding related to impurity is present in the sample. Intrinsic defects are investigated by observing photoluminescence spectroscopy of each sample. Due to the presence of bound magnetic polaron interaction mediated by defects like oxygen vacancy and zinc vacancy, both 2 and 5% Pr-doped ZnO nanoparticles show unsaturated hysteretic magnetization versus magnetic field loop at room temperature along with the presence of paramagnetic contribution. The presence of paramagnetic and ferromagnetic contribution confirmed from the nature of variation of magnetization vs. temperature curves. Dielectric measurements of each sample show that the substitution of dopant enhances the dielectric constant of the host system of ZnO and reduces the dielectric loss. AC electrical conductivity of the doped sample is lowered compared to that of ZnO which indicates that the doped samples would be useful for dielectric applications. The improved magnetic and dielectric properties of the doped samples open a new area for application in spintronic device as dilute magnetic dielectric.

Optimization of catalytic active sites in non-collinear antiferromagnetic Mn3Pt bulk single-crystal

Electrons in non-collinear antiferromagnets exhibit abundant transfer properties of interest to next-generation innovative devices. As two of the most important properties of electrons, both charge and spin must be simultaneously transferred. This will certainly influence many surface reaction processes like the hydrogen evolution reaction (HER). We grow a Mn3Pt bulk single-crystal that having a room-temperature long-range magnetic order at the Mn sites, which showed Pt-like activity and excellent stability as a catalyst for HER. Experiments and density-functional-theory calculations reveal that the electronic structure can be modified owing to the spin polarization of the Mn atoms. This further affects the adsorption energy of the reaction intermediate by tailoring the arrangement and filling of d-electrons. With this strategy, a similar Gibbs free energy for hydrogen adsorption was obtained between Mn–Mn hollow sites and Pt sites. In other words, more actives sites beyond Pt are created. This study paves the way for the design of high-efficiency electrocatalysts through the interplay between the spin states and the adsorption-desorption behaviors.

Optimization of Catalytic Active Sites in Noncollinear Antiferromagnetic Mn₃Pt Bulk Single-Crystal

Electrons in non-collinear antiferromagnets exhibit abundant transfer properties of interest to next-generation innovative devices. As two of the most important properties of electrons, both charge and spin must be simultaneously transferred. This will certainly influence many surface reaction processes like the hydrogen evolution reaction (HER). We grow a Mn₃Pt bulk single-crystal that having a room-temperature long-range magnetic order at the Mn sites, which showed Pt-like activity, and excellent stability as a catalyst for HER. Experiments and density-functional-theory calculations reveal that the electronic structure can be modified owing to the spin polarization of the Mn atoms. This further affects the adsorption energy of the reaction intermediate by tailoring the arrangement and filling of d-electrons. With this strategy, a similar Gibbs free energy for hydrogen adsorption was obtained between Mn-Mn hollow sites and Pt sites. In other words, more actives sites beyond Pt are created. This study paves the way for the design of high-efficiency electrocatalysts through the interplay between the spin states and the adsorption-desorption behaviors.

Two-Dimensional Manganese Nitride Monolayer with Room Temperature Rigid Ferromagnetism under Strain

Developing low-dimensional spintronic materials with room temperature magnetic ordering and large spin polarization is the key for the fabrication of practical spintronic devices with a high circuit integration density and speed. Here, first-principles calculations were performed to systematically investigate a two-dimensional hexagonal MnN monolayer with room temperature magnetic ordering and 100% spin polarization. The MnN monolayer is thermally, dynamically, and mechanically stable, and intrinsically half-metallic with a very wide band gap. The Curie temperature of the MnN monolayer is estimated to be ∼368 K, which is higher than room temperature and insensitive to strain. The MnN monolayer shows half-metallic and excellent magnetic stability upon the external strain from −10 to 10%. Our calculations indicate that the MnN monolayer could be a promising material for room temperature spintronic devices.

Two-dimensional Janus transition-metal dichalcogenides with intrinsic ferromagnetism and half-metallicity

Searching experimental feasible two-dimensional (2D) ferromagnetic crystals with room-temperature magnetic order and high spin-polarization is one key for the development of next-generation spintronic devices. Inspired by the recent experimental achievement for the synthesis of Janus MoSSe monolayer with out-of-plane symmetry, here, by ab initio calculation, we demonstrate this feasibility with the discovery of intrinsic 2D ferromagnetic Janus TMDs monolayer (TMXX′, TM = V, Cr and Mn; X, X′ = S, Se and Te, X ≠ X′) with large spin-polarization and high Curie temperature. Particularly, the MnSSe monolayer show half-metal with 100% spin polarization and wide half-metallic gap. A Curie temperature as high as 400 K has been found for VSSe materials. The formation energy calculation for Janus TMDs can be comparable with the TMDs monolayer. The dynamical stability for these 2D crystals also have been confirmed by phonon spectrum calculation. Our study presents a new class of 2D magnetic materials for future spintronics and valleytronics.

Ba3Fe1.56Ir1.44O9: A Polar Semiconducting Triple Perovskite with Near Room Temperature Magnetic Ordering

The crystal chemistry and magnetic properties for two triple perovskites, Ba3Fe1.56Ir1.44O9 and Ba3NiIr2O9, grown as large, highly faceted single crystals from a molten strontium carbonate flux, are reported. Unlike the idealized A3MM2'O9 hexagonal symmetry characteristic of most triple perovskites, including Ba3NiIr2O9, Ba3Fe1.56Ir1.44O9 possesses significant site-disorder, resulting in a noncentrosymmetric polar structure with trigonal symmetry. The valence of iron and iridium in the heavily distorted Fe/Ir sites was determined to be Fe(III) and Ir(V) by X-ray absorption near edge spectroscopy (XANES). Density functional theory calculations were conducted to understand the effect of the trigonal distortion on the local Fe(III)O6 electronic structure, and the spin state of iron was determined to be S = 5/2 by Mössbauer spectroscopy. Conductivity measurements indicate thermally activated semiconducting behavior in the trigonal perovskite. Magnetic properties were measured and near room temperature magnetic ordering (TN = 270 K) was observed for Ba3Fe1.56Ir1.44O9.

Exploration of magnetically stable BiFeO3[sbnd]CoFe2O4 composites with significant dielectric ordering at room temperature

Present work demonstrates our attempts of enhancement of room temperature magnetic stability and dielectric ordering of BiFeO3 via perovskite-spinel composite approach. We selected CoFe2O4 spinel phase for the study. (1-x)BiFeO3(BFO)-xCoFe2O4(CFO) composites with compositions (x = 0, 20, 30, 40 wt%) were developed. Structure of the composite are ensured by Rietveld refinement of XRD patterns; which reveal rhombohedral (space group:R3c) symmetry for BFO and inverse spinel cubic (space group: Fd3¯m) symmetry for CFO. Microstructural backscattered electron image of sintered composites shows well distribution of CFO in BFO matrix with interaction of BFO and CFO phase at the interface. Remanent magnetization observed for composites is found to be 3 times higher than estimated value by using Vegard's law. Higher magnetic stability achieved in composites. Room temperature dielectric properties of BFO-CFO composites revealed higher dielectric constant with low loss. The enhancement in magnetic stability and dielectric ordering of composites might be useful in miniaturizing antenna system and electromagnetic shielding materials.

Room temperature magnetic ordering and analysis by bound magnetic polaron model of Yb3+ doped nanocrystalline zinc oxide (Zn0.98Yb0.02O)

Nanocrystalline ZnO and Yb-doped ZnO (Zn0.98Yb0.02O) are prepared by simple co-precipitation method. The pure crystallographic phases of ZnO and Zn0.98Yb0.02O are confirmed by Rietveld analyses of XRD patterns. Raman and photoluminescence spectra recorded at room temperature (RT) indicates that lattice defects and oxygen vacancy in Zn0.98Yb0.02O is more than that of ZnO. Magnetic measurements of ZnO and Zn0.98Yb0.02O are carried out from 300 to 5 K. Ferromagnetic ordering is observed in Zn0.98Yb0.02O at RT and the strength of the ordering increases with the lowering of temperature. Ferromagnetism of Zn0.98Yb0.02O is attributed to the oxygen vacancy introduced by annealing in vacuum. Magnetization vs. temperature curve is well fitted by the combination of 3D spin wave and Curie-Weiss law, which suggest simultaneous presence of para- and ferro-magnetic phases in Zn0.98Yb0.02O. Ferromagnetic ordering is successfully explained by vacancy mediated bound-magnetic polaron model.