Reduction Of Magnetic Moment Research Articles

Single-molecule Magnets (SMM) spin channels connecting FeMn antiferromagnet and NiFe ferromagnetic electrodes of a tunnel junction

The integration of single-molecule magnets (SMMs) into magnetic tunnel junctions (MTJs) offers significant potential for advancing molecular spintronics, particularly for next-generation memory devices, quantum computing, and energy storage technologies such as solar cells. In this study, we present the first demonstration of SMM-induced spin-dependent properties in an antiferromagnet-based MTJ molecular spintronic device (MTJMSD). We engineered cross-junction-shaped devices comprising FeMn/AlOx/NiFe MTJs. The AlOx barrier thickness where the exposed junction edges meet was comparable to the SMM length, facilitating the incorporation of SMM molecules as spin channels for spin-dependent transport. The SMM channels enabled long-range magnetic moment ordering around molecular junctions, which were precisely engineered via fabrication processes. The SMM, composed of a [Mn6(μ3-O)2(H2N-sao)6(6-atha)2(EtOH)6] (H2N-saoH = salicylamidoxime, 6-atha = 6-acetylthiohexanoate) complex, featured thioester groups at the ends that upon hydrolysis they form bonds with the magnetic electrodes. SMM-treated junctions demonstrated a significant current enhancement, reaching up to 7 μA at an input voltage of 60 mV. Furthermore, SMM-doped junctions exhibited current stabilization in the μA range at lower temperatures, whereas the bare electrodes showed current suppression to the picoampere range. Magnetization measurements conducted at 55 K and 300 K on pillar-shaped devices revealed a reduction in magnetic moment at low temperatures. Additionally, Kelvin probe atomic force microscopy (KPAFM) measurements confirmed that SMM integration transformed the electronic properties over long ranges.These findings are attributed to the spin channels formed between magnetic metal electrodes, which enhance spin polarization at each magnetic electrode. Our research highlights the potential of using antiferromagnetic materials, characterized by minimal stray fields and zero net magnetization, to transform MTJMSD devices.

The study of electronic structure and magnetic properties of ferromagnetic Kondo-lattice CePd2P2 from the first-principles

The electronic structure of ferromagnetic CePd2P2 Kondo lattice crystallizing in the tetragonal ThCr2Si2-type structure is investigated by means of the Density Functional Theory (DFT) and Time-Depedent DFT (TDDFT) methods. The calculated electronic properties from DFT are presented and compared to those of the non-magnetic LaPd2P2 compound. The differences in the FS topologies upon changing magnetic states (paramagnetic → ferromagnetic) is also examined. Including the relativistic effects of without or with spin-orbit coupling, and Hubbard corrections in the calculations, ferromagnetic ground state with an ordered magnetic moment of ∼ 0.8-0.9 μB is corroborated. Meaningful changes in the magnetic moment and electronic properties of CePd2P2 are discussed in terms of effects brought by the Coulomb interaction (U), and the Hund coupling (J). In particular, the reduction in magnetic moment and simultaneously enhancement of DOS at the Fermi energy due to decreasing J are in quantitative concordance with the Kondo lattice characteristic. Furthermore, dynamical model used in TDDFT calculations exhibits that 4 f electrons in CePd2P2 tend to be delocalized. The frequency-temperature behavior of response function allows to estimate the Kondo temperature to amount 19 K.

Study of ferromagnetism and thermoelectric behaviour of thiospinels MgFe2(S/Se)4 for spintronics and energy harvesting

Magnesium-based spinel chalcogenides are remarkable materials for spintronic and energy harvesting applications. Therefore, the electronic, ferromagnetism, and thermoelectric characteristics of MgFe2(S/Se)4 spinels are addressed comprehensively by modified Becke Johnson potential (TB-mBJ). The stability of cubic phase has been illustrated by formation energy and energy released during optimization. The Curie temperature and spin polarization have been calculated by Heisenberg model and density of states at Fermi level. Ferromagnetism has been studied by exchange energies, double exchange mechanism, exchange constants, and hybridization process. The reduction of magnetic moment of Fe and its shifting on nonmagnetic (Mg, S/Se) sites shows the ferromagnetism is due to the exchange of electrons spin rather than the clustering effect of internal magnetic of Fe atoms in the structure. Moreover, thermoelectric analysis of studied spinels has been illustrated by electrical and thermal conductivities, Seebeck coefficient (S), and power factor.

Spin-Orbit Torque in Structures With Magnetization-Compensated MnGa/Co2MnSi Bilayer

We have systematically investigated the spin-orbit torque (SOT)-induced effective magnetic field in a structure consisting of a Ta heavy metal layer and an antiferromagnetically coupled Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.8</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> MnSi (CMS) bilayer around the magnetization compensation point by varying CMS film thickness. The efficiency of SOT generation takes the maximum around the compensation point, and it is approximately six times as large compared with that in the devices with a MnGa single structure. The enhancement of SOT efficiency can be explained mainly by the reduction in saturation magnetic moment around the compensation point. Moreover, a significant enhancement of the effective spin Hall angle was observed around the compensation point because of the inversion of the magnetization configuration before and after the compensation point.

Understanding the Interaction Between Fullerene and Graphene Nanoribbons Using Density Functional Theory

Carbon based heterostructures are extremely important in the field of material science as the junction of two carbon nanomaterials strongly influence the properties of a material. In present work, the structural, electronic and magnetic properties of covalently attached C60 cage with armchair and zigzag GNRs have been investigated using density functional theory. AGNR-nanobuds don't form stable structures, owing to their positive values of the interaction energy. However, pure and N/B doped ZGNR-nanobud form stable structures with [2+2]hhT mode, hence presenting the possibility of their formation. Average diameter for N doped ZGNR-nanobuds decreases as the C-N bond length is lower than the C-C bond length whereas average diameter for doped ZGNR increases due to the large C-B bond length. The considered complexes are magnetic in nature having a finite value of total magnetic moment. Increase in total magnetic moment is due to the induced localized magnetic moments near dopant sites, whereas decrease in the total magnetic moments is due to the reduction in magnetic moments at C-sites near connecting bond atoms. The significant variation in electronic density of states near the Fermi level leads to change in the metallic behaviour of ZGNR-nanobuds. Mulliken charge analysis shows that in N-doped nanobud, there is a transfer of charge from N to surrounding C atoms due to their electronegativity difference, and there is a gain in charge of B from surrounding C atoms. The unique electronic and magnetic properties of nanobuds can lead to the possible applications in the field of magnetic nano devices.

Atomic Scale Control of Spin Current Transmission at Interfaces.

Ferromagnet/heavy metal bilayers represent a central building block for spintronic devices where the magnetization of the ferromagnet can be controlled by spin currents generated in the heavy metal. The efficiency of spin current generation is paramount. Equally important is the efficient transfer of this spin current across the ferromagnet/heavy metal interface. Here, we show theoretically and experimentally that for Ta as heavy metal the interface only partially transmits the spin current while this effect is absent when Pt is used as heavy metal. This is due to magnetic moment reduction at the interface caused by 3d–5d hybridization effects. We show that this effect can be avoided by atomically thin interlayers. On the basis of our theoretical model we conclude that this is a general effect and occurs for all 5d metals with less than half-filled 5d shell.

Spin-orbit coupling induced demagnetization in Ni: Ab initio nonadiabatic molecular dynamics perspective

Spin-orbit coupling (SOC), which can induce spin flip during the relaxation of photoexcited charge carrier, plays a crucial role in spin dynamics. In this work, we have used time-domain ab initio nonadiabatic molecular dynamics (NAMD) method to study the SOC induced ultrafast demagnetization in Ni at $300\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The spin-diabatic representation using spin-polarized Kohn-Sham (KS) basis sets and spin-adiabatic representation using spinor basis sets have been applied, and both of them achieve demagnetization in Ni with a timescale around $100\phantom{\rule{0.16em}{0ex}}\mathrm{fs}$. The spin-diabatic representation suggests a picture that the electron-phonon coupling (EPC) provides direct energy relaxation channel among the same-spin states, while the SOC can induce spin flip. After photoexcitation, it is found the spin-minority electrons relax to the same-spin states rather than the opposite-spin states, since EPC is larger than SOC by one order of magnitude. By contrast, for the spin-majority electrons, spin flip occurs since there are no empty same-spin states as electron acceptor above the Fermi level. The different relaxation pathways for spin-majority and spin-minority electrons induce the demagnetization. The spin-adiabatic representation provides an Elliott-Yafet spin-phonon scattering picture. The SOC induced reduction of magnetic moment in Ni may induce magnon to drive further demagnetization. The ab initio NAMD simulation provides a critical angle to understand how the SOC and EPC affect demagnetization process in Ni.

Crystal and magnetic structures of R 2Ni1.78In compounds (R = Tb, Ho, Er and Tm)

The crystal and magnetic structures in R 2Ni1.78In (R = Ho, Er and Tm) have been studied by neutron diffraction. The compounds crystallize in a tetragonal crystal structure of the Mo2FeB2 type (space group P4/mbm). At low temperatures, the magnetic moments, localized solely on the rare earth atoms, form antiferromagnetic structures described by the propagation vector k = [kx , kx , ½], with kx equal to ¼ for R = Er and Tm or 0.3074 (4) for R = Ho. The magnetic moments are parallel to the c axis for R = Ho or lie within the (001) plane for R = Er and Tm. The obtained magnetic structures are discussed on the basis of symmetry analysis. The rare earth magnetic moments, determined from neutron diffraction data collected at 1.6 K, are 6.5 (1) μB (Er) and 6.09 (4) μB (Tm), while in the incommensurate modulated magnetic structure in Ho2Ni1.78In the amplitude of modulation of the Ho magnetic moment is 7.93 (8) μB. All these values are smaller than those expected for the respective free R 3+ ions. A symmetry analysis of the magnetic structure in Tb2Ni1.78In is also included, as such information is missing from the original paper [Szytuła, Baran, Hoser, Kalychak, Penc &amp; Tyvanchuk (2013). Acta Phys. Pol. A, 124, 994–997]. In addition, the results of magnetometric measurements are reported for Tm2Ni1.78In. The compound shows antiferromagnetic ordering below the Néel temperature of 4.5 K. Its magnetic properties are found to originate from magnetic moments localized solely on the thulium atoms (the nickel atoms remain non-magnetic in Tm2Ni1.78In). The reduction of rare earth magnetic moments in the ordered state in R 2Ni1.78In (R = Tb, Ho, Er and Tm) and the change in direction of the moments indicate the influence of the crystalline electric field (CEF) on the stability of the magnetic order in the investigated compounds.

First principles study of nearly strain-free Ni/WSe2 and Ni/MoS2 interfaces

Metal/transition metal dichalcogenide interfaces are the subject of active research, in part because they provide various possibilities for interplay of electronic and magnetic properties with potential device applications. Here, we present results of our first principles calculations of nearly strain-free Ni/WSe2 and Ni/MoS2 interfaces in thin-film geometry. It is shown that while both the WSe2 and MoS2 layers adjacent to Ni undergo metallic transition, the layers farther from the interface remain semiconducting. In addition, a moderate value of spin-polarization is induced on interfacial WSe2 and MoS2 layers. At the same time, the electronic and magnetic properties of Ni are nearly unaffected by the presence of WSe2 and MoS2, except a small reduction of magnetic moment at the interfacial Ni atoms. These results can be used as a reference for experimental efforts on epitaxial metal/transition metal dichalcogenide heterostructures, with potential application in modern magnetic storage devices.

Doping and pressure-driven structural transition in BiMnO[formula omitted] from first principles

We investigate the changes in the electronic structure and magnetic properties of BiMnO3+δ accompanied the phase transition C2∕c→P21∕c which occurs either with an increase in the oxygen content or with external pressure applied. We have established that although both factors lead to similar structural changes, their mechanisms have reverse causal relationships. The application of pressure leads to the change in the volume of MnO6 octahedra. The latter, due to strong p-d hybridization, leads to a decrease in the localization degree of manganese electrons, which causes the reduction in Mn magnetic moments. Meanwhile, when there is excess oxygen in the system, the reverse process occurs wherein the charge density redistribution leads to a decrease in the occupation number of the Mn-eg states causing the drop in the value of the local magnetic moments and, as a consequence, to the contraction in the lengths of the Mn-O bonds.

Determination of Dy substitution site in Nd2\u2212xDyxFe14B by HAADF-STEM and illustration of magnetic anisotropy of \u201cg\u201d and \u201cf\u201d sites, before and after substitution

Nd2Fe14B and Nd2−xDyxFe14B (x = 0.25, 0.50) particles were prepared by the modified co-precipitation followed by reduction–diffusion process. Bright field scanning transmission electron microscope (BF-STEM) image revealed the formation of Nd–Fe–B trigonal prisms in [− 101] viewing zone axis, confirming the formation of Nd2Fe14B/Nd2−xDyxFe14B. Accurate site for the Dy substitution in Nd2Fe14B crystal structure was determined as “f” site by using high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It was found that all the “g” sites are occupied by the Nd, meanwhile Dy occupied only the “f” site. Anti-ferromagnetic coupling at “f” site decreased the magnetic moment values for Nd1.75Dy0.25Fe14B (23.48 μB) and Nd1.5Dy0.5Fe14B (21.03 μB) as compared to Nd2Fe14B (25.50 μB). Reduction of magnetic moment increased the squareness ratio, coercivity and energy product. Analysis of magnetic anisotropy at constant magnetic field confirmed that “f” site substitution did not change the patterns of the anisotropy. Furthermore, magnetic moment of Nd2Fe14B, Nd2−xDyxFe14B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0° and 180°.

Pressure-induced large increase of Curie temperature of the van der Waals ferromagnet VI3

Evolution of magnetism in single crystals of the van der Waals compound VI3 in external pressure up to 7.3 GPa studied by measuring magnetization and ac magnetic susceptibility is reported. Four magnetic phase transitions, at T1 = 54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed at ambient pressure. The first two have been attributed to the onset of ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is characterized by the magnetic ordering transition at Curie temperature TC and the transition between two different ferromagnetic phases TFM, accompanied by a structure transition from monoclinic to triclinic symmetry upon cooling. The pressure effects on magnetic parameters were studied with three independent techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa whereas TFM increases rapidly with increasing pressure and reaches TC at a triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase transition is observed moving to higher temperatures with increasing pressure to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa) suggesting a possible pressure-induced reduction of vanadium magnetic moment. We discussed these results in light of recent theoretical studies to analyze exchange interactions and provide how to increase the Curie temperature of VI3.

Probing photoinduced rearrangements in the NdNiO3 magnetic spiral with polarization-sensitive ultrafast resonant soft x-ray scattering

We use resonant soft X-ray diffraction to track the photo-induced dynamics of the antiferromagnetic structure in a NdNiO$_{3}$ thin film. Femtosecond laser pulses with a photon energy of 0.61 eV, resonant with electron transfer between long-bond and short-bond nickel sites, are used to excite the material and drive an ultrafast insulator-metal transition. Polarization sensitive soft X-ray diffraction, resonant to the nickel L$_{3}$-edge, then probes the evolution of the underlying magnetic spiral as a function of time delay with 80 picosecond time resolution. By modelling the azimuthal dependence of the scattered intensity for different linear X-ray polarizations, we benchmark the changes of the local magnetic moments and the spin alignment. The measured changes are consistent with a reduction of the long-bond site magnetic moments and an alignment of the spins towards a more collinear structure at early time delays.

Study of combined effect of partial Bi doping and particle size reduction on magnetism of La0.7Sr0.3MnO3

La0.7Sr0.3MnO3 has been subjected to simultaneous partial bismuth substitution and particle size reduction to understand the mechanism controlling the magnetic properties. Nanosized samples of 10% Bi doped La0.7Sr0.3MnO3 samples were prepared by high energy planetary ball milling. Compared to pristine La0.7Sr0.3MnO3, 10% Bi doping results in the reduction of saturated magnetic moment and Curie temperature. Using the ‘top-down approach’ through high energy planetary ball milling, particle size reduces from 250 nm for bulk to 26 nm for 48 h ball milled sample. Correspondingly, the magnetic properties show the direct influence of size reduction, as the observed magnetic moment shows drastic decrease as particle size reduces. It is interesting to note that 10% Bi doping in La0.7Sr0.3MnO3 plays important role in controlling the size with respect to milling time. In the present work, we discuss the magnetic properties of nanostructured La0.6Bi0.1Sr0.3MnO3 samples. The observed magnetization behaviour can be described using the core-shell model for nanoparticles.

Thermal decomposition of ThMn12-type phase and its optimum stabilizing elements in SmFe12-based alloys

We investigated the phase stability of SmFe12-based compounds by experimental and computational first-principles approaches. The effect of particle size and alloy composition on the thermal decomposition rate is addressed. We show that decomposition begins with Sm evaporation from particle surface, resulting in the formation of α-Fe and Fe2Ti phases. The decomposition rate scales inversely with particle size. A significant stabilizing effect can be realized by substituting Fe with phase stabilizing elements such as V or Ga. According to ab initio calculations, Ti, V, and Ga lower the formation energies. However, when the reduction in magnetic moment is considered, the most effective stabilizing element that can minimize the reduction of μ0M is Ga. These findings present a useful insight on the potential solutions for the development of bulk Sm(Fe0·8Co0.2)12-based magnets.

Tunable first order transition in La(Fe,Cr,Si)13 compounds: Retaining magnetocaloric response despite a magnetic moment reduction

Materials with a large magnetocaloric response require a large magnetic moment. However, we show in this paper that it is possible to retain both the isothermal entropy change and the adiabatic temperature change even using dopants that reduce the magnetic moment of the parent alloy, provided that the first order character of the transition is enhanced. In this work, a combination of first-principles calculations, experimental determination of the magnetocaloric response (direct and indirect) as well as a new criterion to determine the order of the phase transition are applied to Cr-doped La(Fe,Si)13 compounds. Despite a reduction in magnetic moment, the magnetocaloric response is retained up to x ≈ 0.3 in LaFe11.6-xCrxSi1.4. Unlike other transition metal dopants, Cr occupy 8b sites and couple antiferromagnetically to Fe atoms. The cross-over of first to second order transition is achieved for a Cr content of x = 0.53, larger in comparison to other dopants (e.g. Ni or Mn). A direct relation between the first order character and the hysteresis is observed.

Evolution of electronic and magnetic properties of nominal magnetite nanoparticles at high pressure probed by x-ray absorption and emission techniques

We present a study of electronic and magnetic properties of nominal magnetite nanoparticles (NPs) (~6 nm) at high pressure in the presence of silicon pressure medium using x-ray absorption near edge structure (XANES), x-ray magnetic circular dichroism (XMCD) and non-resonant x-ray emission spectroscopy (XES). XANES data show a reduction of Fe charge state, a change in local environment around Fe at tetrahedral sites, and a reduced occupation of Fe 4p orbitals, not seen in previous pressure studies of bulk magnetite. XMCD data show a continuous magnetic moment reduction of ~50% between ambient pressure and 20 GPa, similar to what was observed in previous bulk magnetite studies. XES spectra of NPs indicate a gradual change in spin configuration away from the high-spin state consistent with a postulated charge transfer from Fe 4p to 3d states and the observed reduction in XMCD signal. Taken together, the results point to substantial differences in the response of electronic and magnetic properties of the nano-counterparts of bulk magnetite at high pressure.

Structural and magnetic properties of La3+ ion doped Ni–Cu–Co nano ferrites prepared by sol–gel auto-combustion method

Lanthanum doped Ni–Cu–Co nano ferrites with the chemical composition Ni0.2Cu0.1Co0.7Fe2−xLaxO4 (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared by sol–gel auto-combustion technology. All samples were sintered at a temperature of 950 ℃. The X-ray diffraction (XRD) analysis verifies that all the samples of the formation of the cubic spinel structure. It turns out that with the addition of La3+ ions, the lattice constant decreases, and with the addition of La3+ ions, the lattice constant increases. The obtained Fourier transform infrared (FT-IR) measurement also confirms the formation of the spinel structure. With the increase in La, the higher frequency ν1 is slightly moving toward the high-frequency side. Transmission electron microscopy (TEM) images show the presence of particles, which are spherically cubic shaped crystallites. The presence of constituent’s, i.e., the presence of ingredients, namely, Ni, Cu, Co, Fe and La were authenticated by energy dispersive X-ray analysis (EDX). It was confirmed La3+-doping was successfully achieved. The magnetic parameters were measured by Vibrating sample magnetometer (VSM). The saturation magnetization, remanent magnetization, coercivity, anisotropy constant first increase and then decrease with the La content increases. The sample had the best magnetic properties when the doping content of La at x = 0.025. This indicates that appropriate doping can improve the magnetic properties of the samples. The reduction of the magnetic moment can be attributed to non-magnetic La3+ ions in place of Fe3+ ions (5µB), which results in a reduction of net total magnetic moment.

Structural transformation, Griffiths phase and metal-insulator transition in polycrystalline Nd2−xSrxNiMnO6 (x = 0, 0.2, 0.4, 0.5 and 1) compound

Polycrystalline double perovskite Nd2−xSrxNiMnO6 (x = 0, 0.2, 0.4, 0.5 and 1) samples were synthesized using the solid state reaction method. There occurs a structural transformation from monoclinic (P21/n, for x = 0 to x = 0.5) to cubic (Fmm, for x = 1) with increasing Sr doping. Raman spectroscopy reveals the increase in static disorder with doping. The Curie temperature (TC) shows a small increase from x = 0 to 0.5 (TC ~ 200 K), but for x = 1, TC increases drastically upto ~264 K. The deviation of 1/χ(T) from Curie–Weiss behaviour for doped samples with exponent less than one, indicates a development of the Griffiths phase with doping. The systematic reduction in magnetic moment at 5 K suggests an increase in anti-site disorders with doping. Mn 3s x-ray photoemission spectra show an increase in exchange splitting, indicating a decrease in the valency of Mn. The x-ray absorption spectra at Ni and Mn 2p edges show that the formal valence remains 2+ (Ni) and 4+ (Mn) for all the samples, with changes in spectral weights. Ni 2p x-ray photoemission spectra show characteristic feature similar to Ni3+ systems, only for x = 1 sample. Our GGA-based calculations for the ordered supercell, predict half metallic character for doping (x > 0) samples due to delocalization of Ni eg orbitals. The calculations with anti-site disorders yield drastic reduction in Ni moments, with the disordered anti-ferromagnetic phase having lowest energy at maximum doping. Temperature dependent resistivity measurements exhibit a clear metallic region for x = 0.2 sample, while for higher dopings (x > 0.2), the metallicity gets suppressed due to increase in anti-site disorders in these samples.

Effect of magnetic fullerene on magnetization reversal created at the Fe/C60 interface

Probing the hybridized magnetic interface between organic semiconductor (OSC) and ferromagnetic (FM) layers has drawn significant attention in recent years because of their potential in spintronic applications. Recent studies demonstrate various aspects of organic spintronics such as magnetoresistance, induced interface moment etc. However, not much work has been performed to investigate the implications of such OSC/FM interfaces on the magnetization reversal and domain structure which are the utmost requirements for any applications. Here, we show that non-magnetic Fullerene can obtain non-negligible magnetic moment at the interface of Fe(15 nm)/C60(40 nm) bilayer. This leads to substantial effect on both the magnetic domain structure as well as the magnetization reversal when compared to a single layer of Fe(15 nm). This is corroborated by the polarized neutron reflectivity (PNR) data which indicates presence of hybridization at the interface by the reduction of magnetic moment in Fe. Afterwards, upto 1.9 nm of C60 near the interface exhibits magnetic moment. From the PNR measurements it was found that the magnetic C60 layer prefers to be aligned anti-parallel with the Fe layer at the remanant state. The later observation has been confirmed by domain imaging via magneto-optic Kerr microscopy.