Magnetic Behavior Research Articles

Simulating magnetism in Borospherene-like nanostructure: a Monte Carlo exploration

ABSTRACT This study employs a Monte Carlo approach to investigate the magnetic properties and thermal behaviour of the Borospherene-like nanostructure, yielding insightful information. The analysis delves into the blocking temperature (TB ) concerning external magnetic field (H), biquadratic coupling interaction (K), linear coupling interaction (JSS ), and crystal field (Δ). Results highlight the impact of JSS , K, and |Δ| on coercive field (Hc) and hysteresis loop. A distinct magnetisation plateau is observed at |Δ|=−5, underscoring the crucial roles of JSS , K, and |Δ| in dynamic magnetic behaviour. The current research provides a comprehensive understanding of the system's magnetic dynamics, offering valuable insights for potential applications in nanotechnology.

Characterization of the microstructural, magnetic, and thermal behaviors of boron-doped Fe–Co–Ni alloys produced via mechanical alloying

FeCoNi alloys, both doped and undoped, were synthesized into nanocrystalline forms using a high-energy mechanical milling technique. The study used the x-ray diffraction technique to examine the microstructure characteristics of powder materials. The identified patterns were examined using Maud software. It was found that mechanical alloying produced solid solutions with BCC and FCC structures and crystallite sizes in the range of 25 nm after 100h of milling. The BCC-Fe(Co,Ni,B) and orthorhombic-Fe3B phases were refined for the alloy doped with amorphous boron, while only the bcc-Fe(Co,Ni,B) phase was identified for the alloy doped with crystalline boron. Meanwhile, the FeCoNi alloy revealed a mixture of FCC-Co and BCC-FeCoNi phases. This sample has a soft ferromagnetic behavior, whereas the doped ones have hard ferromagnetic behaviors. The squareness ratios (Mr/Ms) are typically low. The microstructural variations were associated with magnetic characteristics. The thermal stability of the alloyed powder mixtures was investigated by the DSC technique from 25 to 700 °C for 2h. The alloyed samples were first annealed at selected temperatures and then analyzed using x-ray diffraction. The obtained x-ray diffraction results proved that at temperatures below 230 °C, the initial heavy deformed structure’s structural relaxation followed by the recrystallization of the fcc-Co phase and, at higher temperatures, the recrystallization of new phases, such as α-FeCo, fcc-FeNi, fcc-Ni3Fe, and borides of the (FeNi)23B6, -(FeCo)23B6 types. The stability of the crystalline phases that are formed and their magnetic characteristics can be regulated through a carefully calibrated annealing process.

Crossover from relativistic to non-relativistic net magnetization for MnTe altermagnet candidate

Abstract We experimentally study magnetization reversal curves for MnTe single crystals, which is the altermagnetic candidate. Above 85 K temperature, we confirm the antiferromagnetic behavior of magnetization M, which is known for α–MnTe. Below 85 K, we observe anomalous low-field magnetization behavior, which is accompanied by the sophisticated M(α) angle dependence with beating pattern as the interplay between M(α) maxima and minima: in low fields, M(α) shows ferromagnetic-like 180° periodicity, while at high magnetic fields, the periodicity is changed to the 90° one. This angle dependence is the most striking result of our experiment, while it can not be expected for standard magnetic systems. In contrast, in altermagnets, symmetry allows ferromagnetic behavior only due to the spin-orbit coupling. Thus, we claim that our experiment shows the effect of weak spin-orbit coupling in MnTe, with crossover from relativistic to non-relativistic net magnetization, and, therefore, we experimentally confirm altermagnetism in MnTe.

Enhancement the physical properties of V2O5/Ni0.1Fe2.9O4 nanocomposite

AbstractNanocomposite containing vanadium oxide (V2O5) and magnetite (Fe3O4) doped with nickel (Ni) ion were synthesized according to the formula of Ni0.1Fe2.9O4 /V2O5. The obtained composition was characterized by XRD, FTIR, FESEM. The FESEM micrograph shows that the existence of two different phases related to V2O5 and Ni-Magnetite. Moreover,the roughness parameters have values of 281, 85 and 385nm for roughness average Ra, root mean square roughness Rq, Maximum height of roughness RT respectively. Moreover, the magnetic behavior of the sample was studied, and we found that by adding V2O5 to Ni dopped magnetite, the curie temperature value was lowered from 750 oC to 625 oC. The activation energy was calculated and found to be 0.22 eV and 0.08 eV for 1000 Hz and 3MHz respectively.

Interacting Trimagnetic Ensembles for Enhanced Magnetic Resonance Transverse Relaxivity.

An ensemble of nanosystems can be considered to improve magnetic resonance imaging (MRI) transverse relaxivity. Herein, an interacting superparamagnetic competing structure of an isotropic-anisotropic trimagnetic hybrid nanosystem, γ-Fe2O3@δ-MnO2@NiFe2O4, is considered for MRI relaxivity exploration. The interacting superparamagnetic system reveals fascinating dynamic magnetic behavior, where flower-shaped two-dimensional flakes are decorated over nanoparticles. The hybrid nanosystem exhibits modulated shape anisotropy with spin blocking and energy barrier broadening, which help in achieving faster MR transverse relaxivity. The hierarchical architecture ensemble of the trimagnetic landscape shows effective MR transverse relaxivity with a transverse (r2)/longitudinal (r1) relaxivity of 61.5 and potential cell viability. The competing trimagnetic system with regulated activation energy is found to be the underlying reason for such signal enhancement in MRI contrast efficiency. Hence, this study displays a novel pathway correlating MR transverse relaxivity with dynamic magnetic behavior and competing landscape of hierarchical trimagnetic ensembles.

The electronic, magnetic, and optical behaviors of graphyne modulated by metal atoms adsorption: A first-principles study

Abstract The electronic, magnetic, and optical behaviors of graphyne modulated by various adsorbed metal atoms (Li, Na, K, Mg, Ca, Al, and Zn) from typical metal-ion batteries are studied by first-principles calculation. Notably, Mg and Zn adsorption systems are deemed unstable. In contrast, Li, Na, K, Ca, and Al systems exhibit two preferential adsorption sites, with the optimal position being the hollow center site within the large acetylenic ring. Upon the adsorption of these metal atoms, except for Ca adsorption systems exhibit semi-metallic behavior, while the other metal adsorption systems induced a transition from p-type to n-type semiconductors with decreased band gaps. Intriguingly, the inherent magnetism of the metal atoms vanished, resulting in a total magnetic moment of 0 μB for the adsorption systems. Furthermore, the optical absorption and reflectivity peak positions for Ca adsorption systems show a significant redshift from violet to green and blue light regions. Conversely, other adsorption systems exhibit new absorption and reflection peaks in the infrared range, accompanied by an increase in both absorption coefficient and reflectivity across various spectral regions. These findings are conducive to the application in the field of novel optoelectronics and optical films.

The electronic, magnetic, and optical behaviors of graphyne modulated by metal atoms adsorption: A first-principles study

The electronic, magnetic, and optical behaviors of graphyne modulated by metal atoms adsorption: A first-principles study

TCAD Modelling of Magnetic Hall Effect Sensors

In this paper, a gallium nitride (GaN) magnetic Hall effect current sensor is simulated in 2D and 3D using the TCAD Sentaurus simulation toolbox. The model takes into account the piezoelectric polarization effect and the Shockley–Read–Hall (SRH) and Fermi–Dirac statistics for all simulations. The galvanic transport model of TCAD Sentaurus is used to model the Lorentz force and magnetic behaviour of the sensor. The current difference, total current, and sensitivity simulations are systematically calibrated against experimental data. The sensor is optimised using varying geometrical and biasing parameters for various ambient temperatures. This unintentionally doped ungated current sensor has enhanced sensitivity to 16.5 %T−1 when reducing the spacing between the drains to 1 μm and increasing the source to drain spacing to 76 μm. It is demonstrated that the sensitivity degrades at 448 K (S = 12 %T−1), 373 K (S = 14.1 %T−1) compared to 300 K (S = 16.5 %T−1). The simulation results demonstrate a high sensitivity of GaN sensors at elevated temperatures, outperforming silicon counterparts.

Role of Co and Ni ferrites in the fabrication of Saccharum officinarum bioadsorbents for removing As(III)

Removal of arsenic from drinking water is one of the most significant worldwide concerns. Adsorptive removal of arsenic is highly practical and efficient among the various methods. The green synthesis using sugarcane extract was eco-friendly, and cost-effective and resulted in adsorbents having magnetic behavior and a high capacity for arsenic. In the present study, activated carbon (ACs) of sugarcane and its surface, functionalized with nickel ferrite (AC/NFO) and cobalt ferrite (AC/CFO) were used as biosorbents for the removal of As(III) from aqueous medium. The functionalization was undertaken in a controlled hydrothermal method using Saccharum officinarum (sugarcane) extract as a green source. The morphology, functionality, thermal stability, structure, magnetic behavior, surface area and porosity of adsorbents were confirmed by SEM, FTIR, TGA, XRD, VSM, BJH and AFM. The sorption behavior was determined with the effect of pH, time, concentration, temperature and dose. Pseudo-second order and Langmuir models were found suitable to validate the sorption data. Thermodynamics of the sorption process and the desorption studies suggested that the governing mechanism is chemisorption. The adsorption capacities for AC2, AC2C2 and AC2N2 were 961 µg/g, 1103 µg/g and 1000 µg/g respectively. Among the studied samples, AC2C2 was found as a potential candidate due to its high adsorptive efficiency of 97 % for As(III).

Synthesis, Structures, and Magnetic Investigations of Nickel Phosphates: Ni2(PO4)(OH), Ni7(PO4)3(HPO4)(OH)3, and NaNiPO4 Including Potential Haldane Behavior.

Three novel nickel-phosphate structures are reported, Ni2(PO4)(OH) (I), Ni7(PO4)3(HPO4)(OH)3 (II), and NaNiPO4 (III). Each new system was prepared via a high-temperature hydrothermal synthesis at 600-650 °C. All three compounds are built of quasi-one-dimensional (quasi-1-D) Ni2+ containing chains with varying phosphate bridging modes and were characterized by single crystal X-ray diffraction and magnetic susceptibility. All three compounds display very different magnetic behavior. Anisotropic magnetic data is reported for Ni2(PO4)(OH) (I) exhibiting slow antiferromagnetic ordering in the high-temperature regime with substructures that begin to form below 32 K at different field strengths. These characteristics affirm I as being one of the few Haldane-like material candidates. The Ni7(PO4)3(HPO4)(OH)3 (II) material is a member of the unusual ellenbergerite structural family and displays complex inter- and intrachain magnetic interactions while NaNiPO4 (III) shows antiferromagnetic ordering near 18 K. This magnetic behavior is correlated with their structures.

Magnetic response of Ho3+ doped Ni0.4Cu0.6HoyFe2-yO4 spinel ferrites and their correlation with crystallite size

This study investigates the magnetic response of Ho3+ doped Ni0.4Cu0.6HoyFe2-yO4 (y = 0.0, 0.02, 0.04, 0.06, and 0.08) spinel ferrites (SFs) and their correlation with crystallite size. The synthesis was achieved using a sol-gel auto-combustion (SGAC) route and performed different characterizations, including X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy dispersive x-ray (EDX), Inductively coupled plasma atomic emission spectroscopy (ICP-AES), and vibrating sample magnetometer (VSM) analysis. The cubic spinel phase was verified via XRD in pure NCF and Ho3+ doped NCF samples. The lattice constant (a) was improved from 8.344 Å to 8.378 Å. The substitution of Ho3+ ions led to a decrease in porosity from 42.22 % to 39.54 %. The introduction of Ho3+ ions also reduced the crystallite size (D) from 37.05 nm to 27.72 nm. The specific surface area (S) was increased from 27.44 g/cm2 to 36.14 g/cm2 with the doping of Ho3+. The average particle size (DS) was decreased from 54 nm to 35 nm. The EDX and ICP-AES analyses confirmed the good agreement with the theoretical composition. The VSM measurements provided insights into their magnetic properties. Furthermore, the doping of Ho3+ ions enhanced coercivity (HC), while reducing saturation magnetization (MS) from 64.35 emu/g to 16.22 emu/g. The decrease in crystalline anisotropy (K) observed at higher concentrations of Ho3+ may result from the increase in coercivity, potentially attributable to the smaller crystallite size of the single-domain SFs particles. The single-phase matrix and their magnetic behaviour showed that the Ho3+ doped Ni–Cu SFs samples are suitable for high-frequency applications.

Investigations of the physical behavior of Cr2PX (X = C and N) MAX phases through first-principles calculations

MAX phases display an exclusive combination of ceramic and metallic characteristics, which makes them highly promising for various technological applications. This study investigated MAX phases of 211-type based on Cr2PX (X = C and N) by focusing on their physical properties, mainly the magnetic, electronic, and optical behaviors. The results obtained using the “density functional theory (DFT) based full-potential linearized augmented plane wave (FP-LAPW) method” matched those reported in the literature, indicating the reliability of the adopted methodology. The stabilities of the Cr2PX were validated by calculating their cohesive energies and phonon band structures. These compounds demonstrate identical energies for nonmagnetic, ferromagnetic, and antiferromagnetic phases and exhibit symmetrical arrangements of the “density of states (DOS)” for both up and down spins. Moreover, these MAX phases exhibit high optical absorption (∼10−6cm−1) and anisotropic reflectivity spectra, emphasizing the role of crystallographic orientation and their potential for applications in photovoltaics and other optical devices. These findings will provide valuable insights into the properties and behaviors of Cr2PX-based 211-MAX phases, thereby establishing the foundation for further research and potential applications across diverse areas.

DFT analysis of electronic, magnetic and elastic behavior in SmMnO3

DFT analysis of electronic, magnetic and elastic behavior in SmMnO3

Harnessing ion beam erosion engineering for controlled self-assembly and tunable magnetic anisotropy in epitaxial films

The engineering of the surface morphology and the structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study presents an easy and handy approach to tailor the surface structure of epitaxial thin films utilizing low-energy ion beam. Here, we investigate the evolution of the surface structure and magnetic anisotropy (MA) in epitaxial Fe/MgO (001) model systems subjected to multiple cycles of ion beam erosion (IBE) after thin film growth. The growth of Fe film occurs in the form of three–dimensional islands and exhibits intrinsic biaxial MA. Following a few cycles of IBE, an induced uniaxial magnetic anisotropy leads to a split in the hysteresis loop, and the film displays almost uniaxial magnetic switching behavior. More distinctly, we present a clear and conclusive evidence of (2 × 2) reconstruction of the Fe surface due to the atomic rearrangement by IBE. Furthermore, 57Fe isotope sensitive nuclear resonance scattering measurement provides insight into the depth-resolved magnetic information due to the modified surface topography. We also demonstrate that thermal annealing can reversibly tune the surface reconstruction and induced UMA. The feasibility of the IBE technique by adequately selecting IBE parameters for surface structure modification has been highlighted apart from conventional tailoring of the morphology for the tuning of UMA and introduces a new dimension to our understanding of self-assembled surface morphology evolution by IBE.

Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 μm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

Transitions in magnetic behavior at the substellar boundary

We aim to advance our understanding of magnetic activity and the underlying dynamo mechanism at the end of the main sequence. To this end, we have embarked on collecting simultaneous X-ray and radio observations for a sample of M7..L0 dwarfs in the solar neighborhood using XMM-Newton jointly with the Jansky Very Large Array (JVLA) and the Australia Telescope Compact Array (ATCA). We supplemented the data from these dedicated campaigns with X-ray data from the all-sky surveys of the ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission (SRG). Moreover, we complement this multiwavelength data set with rotation periods that we measured from light curves acquired with the Transiting Exoplanet Survey Satellite (TESS). We limited the sample to objects with rotation period of < 1 day, focusing on the study of a transition in magnetic behavior suggested by a drastic change in the radio detection rate at υ sin i ≈ 38 km s−1, corresponding to Prot ≈ 0.2 day for a typical ultracool dwarf (UCD) radius of R★ = 0.15 R⊙. Finally, to enlarge the target list, we have compiled archival X-ray and radio data for UCDs from the literature, and we have analyzed the abovementioned ancillary eROSITA and TESS observations for these objects’ analogous to the targets from our dedicated X-ray/radio campaigns. We compiled the most up to date radio/X-ray luminosity (LR,ν − Lx) relation for 26 UCDs with rotation periods (Prot) lower than 1 day, finding that rapid rotators lie the furthest away from the “Güdel-Benz” relation previously studied for earlier-type stars. Radio bursts are mainly (although not exclusively) experienced by very fast UCDs (Prot ≤ 0.2 day), while X-ray flares are seen by objects spanning the whole range of rotation. Finally, we examined the Lx/Lbol versus Prot relation, where our sample of UCDs spans a large activity level range, that is log(Lx/Lbol) = −5.5 to log(Lx/Lbol) = −3. Although they are all fast rotating, X-ray activity evidently decouples from that of normal dynamos. In fact, we found no evident relation between the X-ray emission and rotation, reinforcing previous speculations on a bimodal dynamo across late-type dwarfs. One radio-detected object, 2MJ0838, has a rotation period consistent with the range of auroral bursting sources; while it displays moderately circularly polarized emission, there is no temporal variation in the polarized flux. A radio flare from this object is interpreted as gyrosynchrotron emission, and it displays X-ray and optical flares. Among the ten UCDs observed with the dedicated X-ray/radio campaigns, we found a slowly rotating apparent auroral emitter (2MJ0752) that is also one of the X-ray brightest radio-detected UCDs. We speculate that this UCD is experiencing a transition in its magnetic behavior since it produces signatures expected from higher-mass M dwarfs along with emerging evidence of auroral emission.

Enhanced magnetic behavior of LaFeO3 by co-doping with Nd3+ and V5+ substitution (La0.8Nd0.2Fe0.95V0.05O3)

To enhance the quality of applications of LaFeO3 (LFO) as a magnetoelectric multiferroic through the improvement of magnetic behaviour, co-doping of Nd3+ (20 %) and V5+ (5 %) was considered for partial substitution in place of La3+ and Fe3+, respectively. Co-doped sample of La0.8Nd0.2Fe0.95V0.05O3 (LNFVO) was prepared by solid state reaction method. Rietveld analysis of X-ray diffractograms confirmed the formation as well as successful incorporation of dopants (Nd3+ and V5+) in La3+ and Fe3+ sites of the distorted perovskite structure with Pbnm space group. Morphological features including information related to crystallographic phase were examined by TEM. Distortion due to co-doping helped to achieve the stated objectives. Valence states of dopants and host cations were explored by analyzing XPS observations. Detailed magnetic measurements in the temperature range starting from 300 K down to 2 K suggested that magnetic property was drastically enhanced compared to that of the undoped, which was attributed to mismatch of valence states, ionic diameters etc. between dopants with host cations. The doped sample showed antiferromagnetic to ferromagnetic transition at and below 19 K. All such findings related to magnetic property would be quite attractive for the improvement of multiferroic applications as the low value of magnetization of pristine sample of LFO restrict it to become a good magnetoelectric multiferroic.

Direct and inverse magnetocaloric effects in magnetostrictive GdMn2Ge2 with field-induced metamagnetic transition

Heavy rare-earth-based ternary intermetallic compounds with the formula RT2X2 have drawn great interest because of their multiple magnetic transitions and various magnetic structures. Here, anisotropic magnetic behaviors, magnetocaloric effects (MCEs), and magnetostriction effects in single-crystalline GdMn2Ge2 are studied in two different directions. Experiments show a magnetic transition characterized by a sudden decrease in magnetization for μ0H//a and a sharp increase for μ0H//c at Tt. The transition is driven by lower temperatures for μ0H//a, contrasting that for μ0H//c with an increase in the magnetic field. An inverse MCE is observed for μ0H//a with a maximum magnetic entropy change (−ΔSMmax) of −7.4 J kg−1 K−1 (μ0ΔH = 6 T), while a direct MCE is obtained for μ0H//c with an −ΔSMmax of 8.0 J kg−1 K−1 under the same magnetic field change. Moreover, a remarkable field-induced metamagnetic transition and a magnetostriction effect are observed simultaneously at Tt, indicating strong magneto-lattice coupling. The T-μ0H phase diagrams are constructed based on the magnetic properties. The coexistence of direct and inverse MCEs is discussed and is due to the spin-flop of Mn and anisotropic magnetic properties under magnetic fields in different directions.

Experimental evidence of magnetism in a 2D electron gas at the CoO/Co3O4 interface by employing EMCD

In the present study we investigate the CoO/Co3O4 interface in order to determine its intriguing magnetic behavior, which can be utilized for tailoring magnetic properties, enabling spin transport, enhancing magnetic coupling, tuning device functionalities, and realizing miniaturized magnetic devices for various technological applications. We decipher the magnetic properties of the CoO/Co3O4 interface from first principles calculations using Wien2k and probe them experimentally by employing electron energy-loss magnetic chiral dichroism (EMCD), which is an electron-energy loss spectrometry (EELS) based technique in the transmission electron microscope (TEM). Both, theory and experiment, are in perfect agreement and result in a ferromagnetic 2D-electron gas of 5Å thickness directly at the interface.

Origin of the metamagnetic transitions in Y0.9Tb0.1Fe2D4.3

Deuterium insertion was used to tune the magnetic properties of Y0.9Tb0.1Fe2 Laves phase towards an itinerant electron metamagnetic (IEM) behavior. The latter is highly sensitive to chemical changes and external parameters. The structural and magnetic properties of Y0.9Tb0.1Fe2D4.3 were investigated using various neutron powder diffraction experiments in addition to magnetic measurements under steady and pulsed high magnetic fields up to 60 T. The deuteride crystallizes in a monoclinic structure (Pc space group) with 4.3 D atoms located in 18 tetrahedral interstitial sites. At zero field, it undergoes a ferrimagnetic-antiferromagnetic (FiM-AFM) transition at TM0 = 90 K, accompanied by an anisotropic magnetostriction and a negative cell volume expansion of 0.6%. A second AFM-PM transition is observed at 146 K. Under pulsed magnetic field at 4.2 K, the deuteride displays a multistep magnetic behavior from ferrimagnetic to a ferromagnetic state, which can be attributed to a stepwise rotation of the Tb moments. The ZFC-FC magnetization curves at low fields exhibit an irreversibility below 90 K, followed by a sharp decrease in magnetization at the FM-AFM transition. Between 90 K and 130 K, the magnetization curves display an IEM behavior, with the transition field increasing linearly with temperature.