Thermomagnetic Measurements Research Articles

Effects of inserted ultrathin Pt buffer on perpendicular magnetic properties of Ta/TbFeCo/Ta layered structures

We investigated effects of inserted ultrathin Pt buffer on the perpendicular magnetic properties of Ta/TbFeCo/Ta layered structures. For Tb-rich TbFeCo films buffered with Ta and Ta/Pt a compensation thickness is observed at ∼ 6 nm, where the net saturation magnetization vanishes. The perpendicular magnetic anisotropy properties of two structures are found to be governed by a competition of a perpendicular bulk anisotropy and an in-plane interface anisotropy. Compared with Ta-buffered TbFeCo films, the counterparts with insertion of Pt buffer exhibits a larger negative interface anisotropy. A large variation of saturation magnetization and perpendicular magnetic anisotropy with increasing inserted thickness of Pt buffer is observed in the Ta/Pt/TbFeCo/Ta structure. This can be ascribed to the interface-driven variation of exchange interaction between Tb and FeCo at the interface, confirmed by thermomagnetic measurements. A clear correlation between the interface-driven variation of exchange interaction and perpendicular magnetic properties of the TbFeCo films is identified. Our results show the interface plays an important role in the perpendicular magnetic properties of TbFeCo films, which is critical for the application in spintronic devices.

Iron Age ceramics from Thracian rock-cut complexes from Bulgaria – Mineral magnetic relics of technological production and use

The Gluhite kamani Thracian rock-cut complex in the Eastern Rhodopes Mountain is famous with its more than 500 rock niches carved in the rock at heights up to 20 m. Continuous habitation starting from the final Chalcolithic (the second quarter of the 4th millenium BCE) until the Late Classical – Early Hellenistic period (late 5th – 4th century BCE) provides unique opportunity for studying diachronic changes in pottery production and use. In this contribution, systematic analysis of a collection of 135 ceramic sherds from five archaeological periods at the site was carried out using a combined mineral magnetic and geochemical approach. Magnetic susceptibility (χ), frequency-dependent magnetic susceptibility (χfd%) and firing temperature (Tfire), determined using the magnetic susceptibility method, were combined with data from elemental XRF analyses. Thermomagnetic measurements, employed for identification of magnetic minerals revealed the dominant presence of (titano)magnetite with low Ti-content and/or a fraction of single-domain magnetite and in few cases hematite. Although varying in a wide range, median χ values of ceramic sherds from the Early Iron Age (EIA) periods show similar distribution, while for Late Iron Age (LIA) with the introduction of the wheel-thrown pottery, χ values are higher, presumably due to decreased amount of silica-rich clastics in the clay. Concurrently, χfd% values decrease in ceramics from the LIA, indicating predominant presence of stable single-domain magnetite in the iron oxide composition of the ceramics. Firing temperatures (Tfire) estimations display a systematic pattern of two groups – higher (Tfire between 760 and 800 °C) and lower (Tfire ∼ 400–––600 °C). During the EIA periods both Tfire groups are present, characterized by systematic gradual decrease of the median value of the low Tfire when going from EIA1 towards the EIA2. Wheel-thrown pottery from the LIA show low Tfire ∼ 400 °C only. Based on the differences in thermomagnetic properties of ceramics, their magnetic parameters and Tfire estimates, two possible hypotheses are suggested to explain the observed changes in EIA ceramic characteristics: i) utilization of two differently sourced clay materials (illite-dominated and montmorillonite-dominated) for production of ceramics fired at higher and lower temperatures, respectively; and ii) utilization of one raw clay source, while using two firing regimes – firing at higher temperature for prolonged time, and fast firing to high temperature with successive stage of longer firing at lower temperature. Differences in thermomagnetic properties of wheel-thrown pottery from the LIA period leads to the assumption for utilization of diverse clay source for their production, as compared clay sources for the Early Iron Age periods.

Thermomagnetic analysis applied for identification of lithogenic and pedogenic iron oxides in topsoils from Bulgaria

Identification of magnetic minerals, which determine the magnetic properties of natural rocks, sediments and soils, is of crucial importance for any further interpretation of their magnetic signature in environmental or paleogeographical context. One of the major and widely used methods for determination of kind of magnetic phases in natural materials is by obtaining the Curie/Neel temperature of the respective magnetic mineral. In this contribution, we report a set of thermomagnetic measurements of high-temperature behavior of magnetic susceptibility for topsoils from the territory of Bulgaria, aiming to reveal the pedogenic and lithogenic signature. The data are considered and reported in respect to the parent rock type. Our results suggest that pedogenic magnetic minerals are represented mainly by fine-grained maghemite and/or hematite with possible Al-substitutions in the crystal lattice. This phase is expressed on the heating run of the thermomagnetic curve as a “hump” with a maximum at 250–300 °C. Coarse-grained magnetite is identified as a dominant lithogenic magnetic mineral. Hematite’s presence in a sub-set of red-colored soils is confirmed by additional analyses of isothermal remanence acquisition curves. Two hematite coercivity components were identified, related to pedogenic and lithogenic origin, respectively.

Magnetite crystallization in a sodium-calcium-silicate glass with high iron oxide concentration–Effect on the magnetic properties

Glasses with mol% composition 16 Na2O∙10 CaO∙54 SiO2∙20 Fe2O3 were prepared by the melt-quenching technique. Heat treatment at 580 °C for 1 and 3 h resulted in the crystallization solely of magnetite and additionally, of hematite for longer times. Transmission electron microscopy shows growth mainly of cubic magnetite with crystallite sizes ≤ 16 nm. X-ray photoelectron spectroscopy reveals the presence of Fe3+ and Fe2+ ions in both the glass and the glass-ceramics. Mössbauer spectroscopy of the glass detects octahedrally and tetrahedrally coordinated Fe3+, while Fe2+ solely occurs in octahedral coordination. In the glass-ceramics, magnetite was detected as well as Fe3+ in both tetrahedral and octahedral coordination. Magnetization curves of the heat-treated samples recorded at room temperature and below show ferrimagnetic behaviour. From the thermomagnetic curves recorded in the temperature range from 300 to 900 K, the Curie and superparamagnetic blocking temperatures are determined. Thermomagnetic measurements in the range from 5 to 300 K reveal the nanoparticle size dependence of the observed Verwey transition.

Thickness dependence of structural and magnetic properties of electrodeposited Co2FeSn films

Co2FeSn films have been electrochemically deposited on polycrystalline Cu substrates in potentiostatic mode. Processed films with thicknesses of 320 nm, 780 nm, and 1400 nm exhibited highly ordered L21 type crystal structure with saturation magnetizations of 1023.38 kA/m (5.08 ± 0.04 μB/f.u.), 1035.31 kA/m (5.14 ± 0.04 μB/f.u.) and 1044.34 kA/m (5.18 ± 0.04 μB/f.u.) at 5 K and 965.00 kA/m (4.79 ± 0.04 μB/f.u.), 967.75 kA/m (4.81 ± 0.04 μB/f.u.), and 1003.52 kA/m (4.97 ± 0.04 μB/f.u.) at 300 K, respectively. The soft ferromagnetic films possess coercivity of ∼ 15.92 kA/m (200 Oe) with a high effective anisotropy constant of ∼ 105 J/m3. Thermo-magnetization measurements yielded high Curie temperatures of 995 K, 1005 K, and 1123 K for films of thicknesses 320 nm, 780 nm, and 1400 nm, respectively. Tailoring the thickness from 320 to 1400 nm could be achieved by merely varying the electrodeposition time without appreciable departure from chemical stoichiometry or compromise in crystalline order or magnetic properties. This establishes a methodology to prepare high quality L21 ordered Co2FeSn films with a few hundred nanometers thickness by electrodeposition. Electrodeposited Co2FeSn films with high magnetic moment, high Keff value, and high Curie temperature are potential candidates for fabricating nanomagnetic devices.

Enhancement of magnetocaloric effect by partial substitution of Bi in La0.60Dy0.10Sr0.30Mn(1−x)BixO3 manganites (x = 0, 0.01, 0.03, and 0.10)

In this study, the effects of Bi substitution for Mn on the magnetic and magnetocaloric properties of La0.60Dy0.10Sr0.30Mn(1−x)BixO3 manganites (x = 0, 0.01, 0.03, and 0.10) synthesized using the sol–gel method ​​were investigated. The samples x = 0, 0.01, and 0.03 had been indexed in an orthorhombic structure (space group Pnma), while sample x = 0.10 had been indexed in a hexagonal structure (space group R3c). The thermomagnetic measurements showed an increase in the Curie temperature (TC) with increasing Bi content, as well as an increase in magnetization at low temperatures. The TC values were determined as 322, 318, 327, and 360 K for x = 0, 0.01, 0.03, and 0.10 samples, respectively. Maximum magnetic entropy change (-ΔSMmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{M}^{max}$$\\end{document}) values ​​obtained from isothermal magnetization measurements showed an increase with the amount of Bi. The -ΔSMmax\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta {S}_{M}^{max}$$\\end{document} value of 3.80 Jkg−1K−1 at 5 T for the x = 0 sample increased to 4.12 Jkg−1K−1 for the x = 0.10 sample with the highest Bi content. From the Arrott curves, it was observed that all samples exhibited a second-order magnetic phase transition. The obtained values of relative cooling power (RCP), which is an important factor in determining the performance of cooling material, are in the range of 282, 262, 251, and 232 Jkg−1 for x = 0, 0.01, 0.03, and 0.10, respectively.

Pressure control of magnetic order and excitations in the pyrochlore antiferromagnet MgCr2O4

MgCr2O4 is one of the best-known realizations of the pyrochlore-lattice Heisenberg antiferromagnet. The strong antiferromagnetic exchange interactions are perturbed by small further-neighbor exchanges such that this compound may in principle realize a spiral spin liquid (SSL) phase in the zero-temperature limit. However, a spin Jahn-Teller transition below TN≈13 K yields a complicated long-range magnetic order with multiple coexisting propagation vectors. We present neutron scattering and thermomagnetic measurements of MgCr2O4 samples under applied hydrostatic pressure up to P=1.7 GPa demonstrating the existence of multiple close-lying nearly degenerate magnetic ground states. We show that the application of hydrostatic pressure increases the ordering temperature by around 0.8 K per GPa and increases the bandwidth of the magnetic excitations by around 0.5 meV per GPa. We also evidence a strong tendency for the preferential occupation of a subset of magnetic domains under pressure. In particular, we show that the k=(0,0,1) magnetic phase, which is almost negligible at ambient pressure, dramatically increases in spectral weight under pressure. This modifies the spectrum of magnetic excitations, which we interpret unambiguously as spin waves from multiple magnetic domains. Moreover, we report that the application of pressure reveals a feature in the magnetic susceptibility above the magnetostructural transition. We interpret this as the onset of a short-range ordered phase associated with k=(0,0,1), previously not observed in magnetometry measurements. Published by the American Physical Society 2024

Nanocrystallization Behaviour of Amorphous Co<sub>67</sub>Fe<sub>4</sub>Cr<sub>7</sub>Si<sub>8</sub>B<sub>14</sub> Alloy

The investigation addresses the structure of a Co-based alloy and its magnetic properties. The major applications of these materials are in the development of different sensors, which require materials with high permeability. The structure evolution processes need to be explored to clarify the main parameters determining the time-temperature stability. In the present paper, a nanocrystallization behavior of Co67Fe4Cr7Si8B14 amorphous alloy manufactured in the form of a ribbon was studied using X-ray diffraction and sample vibromagnetometry methods. The structure evolution induced by the 30min isothermal annealing at a temperature range of 450 - 700 °C was studied by the X-ray diffraction method, and crystallization with hcp-Co, fcc-Co, and Co2B nanophases was revealed depending on the annealing temperature. According to thermomagnetic measurements, the nanocrystallization process corresponds to a three-stage crystallization model. The crystallization onset temperature of the amorphous alloy was observed to be to equal540 °C. The Curie point and saturation magnetization of the as-quenched alloy were defined as 305 °C and 76 Am2/kg, respectively.

Strewn field, mineralogy, and petrology of Al Haggounia 001: A unique enstatite chondrite

AbstractIn this work, we investigate macroscopic characteristics, magnetic susceptibility, mineralogy, and mineral composition of Al Haggounia 001. The samples were collected during eight field missions in the period between 2015 and 2019. In the strewn field of about 65 km in length, the specimens are found either on the surface or shallowly buried in loose sediments, which rules out the previous suggestions that this meteorite is a fossil meteorite. Macroscopically, the samples exhibit three major lithologies with various colors, porosities, and distributions of oxidized veins. The data obtained using transmitted and reflected light microscopy, scanning electron microscopy, and electron microprobe analysis confirm the macroscopic observations and show a heterogenous distribution of silicates and metal sulfides. Al Haggounia 001 is composed of enstatite, plagioclase, kamacite, taenite, schreibersite, daubreelite, troilite, graphite, sinoite, and silica polymorphs. We identified a new type of chondrules that are flattened and composed of rods of albite and enstatite, as well as elongated nodules of metal and sulfides, in addition to compression fractures in the form of subparallel veinlets. These features presumably reflect the deformation caused by shock. The magnetic susceptibility of Al Haggounia 001 (4.39 ± 0.20) is much lower than that of usual EH (5.48 ± 0.16) and EL (5.46 ± 0.04) chondrites but is in the range of E finds (5.05 ± 0.43). The thermomagnetic and hysteresis measurements are controlled by type, size, distribution of metal‐sulfide nodules, arrangement of oxyhydroxide veins, and weathering. Al Haggounia 001 is an anomalous meteorite with a polymict nature. It records multiple events revealing its unique origin which expends the groups of enstatite chondrites and provides insights into the complex formation and evolution history of their parent body.

Rock magnetic analyses as a tool to investigate diversity of drift pumice clasts: An example from Japan's 2021 Fukutoku‐Oka‐no‐Ba (FOB) eruption

AbstractThe crystallization of nanolites within magma chambers has recently raised a strong interest due to their impact on increasing melt viscosity and triggering magmatic eruptions. In 2021, the Fukutoku‐Oka‐no‐Ba (FOB) underwater eruption produced large quantities of pumices that eventually formed rafts drifting at the surface of the ocean to the East coasts of Japan. Pumices collected along the shore shortly after grounding show various colors, microscopic and Raman analyses made by Yoshida et al. (Island Arc, 31, 1, 2022) revealed the presence of magnetite nanolites in some of them. In this study, we explore the magnetic properties of a batch of pumices of different colors from the FOB eruption, aiming to refine characterization of iron oxide nanolites. We used various analytical techniques such as SEM and FEG‐SEM observations, EDS‐X analyses, and rock magnetic experiments, including thermomagnetic analyses, hysteresis curves, coercivity analyses and FORC measurements. Our findings reveal that the iron oxides present in the FOB samples are Ti‐magnetite, with minor amounts of Mg and Al. The magnetic crystals show a wide range of sizes, from extra small iron oxide nanolites (ESION) in the pumices with the lighter colors, to more bulky grains reaching the micrometer size in some of the dark color samples, significant diffusion is inferred in that case. Consequently, the magnetic characterization of iron oxide crystals within the Fukutoku‐Oka‐no‐Ba pumices reveals varying stages of nucleation, dissolution, growth, and diffusion processes, providing evidences for the heterogeneous state of the magma during the eruption.

Unmixing the hydrothermal and detrital components from a metalliferous sediment core from the eastern Southwest Indian Ridge – Insights from mineral magnetism

Mineral magnetic and geochemical investigations were carried out on a short sediment core collected from the eastern Southwest Indian Ridge (ESWIR) to study the variations in the source components. The magnetic concentration parameter χarm (representing the concentration of stable single domain (SSD) sized grains), magnetic grain size ratios χarm/χlf, χarm/SIRM, geochemical ratios Fe/Ti, Co/Zn, and Zn/Fe and Ba content serve as hydrothermal indicators, all of which show a distinct top - bottom variability. The magnetomineralogical parameters S-ratio and coercivity (Hc) also follow these variations, suggesting an increased contribution of hydrothermal components in the top 15 cm of the core. Significant enrichments of Fe, Mn, and Mg in the samples, along with depletions of detrital elements Al, Si, Rb, Zr, Hf, and Nb in the element/Upper Continental Crust (UCC) values, show that the majority of the detrital component is locally sourced. Thermomagnetic measurements of samples indicate that the major remanence carrier is magnetite in the core, along with minor contributions from titanomagnetite, hematite, and iron sulfides.

A detailed magnetic characterization of combustion products from various metamorphic grade coals

The magnetic properties of combustion products from various metamorphic grade coals including lignite, flame coal, gas coal, fat coal, baking coal and lean coal and anthracite coal, were analyzed. This study was carried out by means of basic magnetic parameters, thermomagnetic and hysteresis measurements. The mass magnetic susceptibility (χ) values ranged from 327 × 10−8 m3/kg to 1722 × 10−8 m3/kg, with an average value of 892 × 10−8 m3/kg, demonstrating a considerable amount of ferrimagnetic minerals in these burned coal samples. The lower χ and SIRM values for the burned lignite were probably due to the lower content of magnetite. A characteristic feature of combustion products was their high values of frequency dependent susceptibility (χfd%), indicating the presence of a large amount of superparamagnetic grains of ferrimagnetic minerals within the combustion products. Thermomagnetic analyses of various combustion products showed the dominant role of magnetite-like phase. Moreover, a significant amount of hematite was also only identified in the combustion product from Flame coal. While the combustion products from Flame coal and Fat coal were characterized by a relatively narrow loop, characteristic of magnetically soft ferrimagnetic minerals, other combustion products including lignite, gas coal, baking coal, lean coal and anthracite coal displayed wasp-waisted loops, indicating the presence of two or more coercivity fractions.

Crystal structure, critical phenomena and magnetocaloric properties of Ni-substituted ferromagnetic Pr2Fe17 intermetallic compound around room temperature

The structural, critical behavior and magnetocaloric properties of Pr2Fe16.9Ni0.1 alloy have been studied. Rietveld's refinement of the X-ray powder diffraction patterns shows that the sample crystallizes in the rhombohedral structure with an R3¯m space group. Based on thermomagnetic measurements, critical behavior was investigated using the modified Arrott plot, Kouvel-Fisher methods, and critical isotherm analysis. The critical exponents (β, γ, and δ) were found to be similar to the 3D-Ising type indicating that the magnetic interactions extend beyond the nearest neighbors. Furthermore, Pr2Fe16.9Ni0.1 exhibits a direct magnetocaloric effect around room temperature with moderate magnetic entropy change (−ΔSMmax = 6.2J.kg−1.K−1 at μ0ΔH=5T) and a wide working temperature range. Additionally, the Relative Cooling Power (RCP) is about 89% of the well-known gadolinium (Gd) for μ0ΔH=2T. The good magnetocaloric response of this compound is comparable or even better than that of many other intermetallic alloys.

Quantum paramagnetism in a non-Kramers rare-earth oxide: Monoclinic Pr2Ti2O7

Little is so far known about the magnetism of the ${A}_{2}{B}_{2}{\mathrm{O}}_{7}$ monoclinic layered perovskites that replace the spin-ice supporting pyrochlore structure for ${r}_{A}/{r}_{B}>1.78$. We show that high quality monoclinic ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ single crystals with a three-dimensional network of non-Kramers ${\mathrm{Pr}}^{3+}$ ions that interact through edge-sharing superexchange interactions, form a singlet ground-state quantum paramagnet that does not undergo any magnetic phase transitions down to, at least, 1.8 K. The chemical phase stability, structure, and magnetic properties of the layered perovskite ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ were investigated using x-ray diffraction, transmission electron microscopy, and magnetization measurements. Synthesis of polycrystalline samples with the nominal compositions of ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2+x}{\mathrm{O}}_{7}$ ($\ensuremath{-}0.16\ensuremath{\le}x\ensuremath{\le}0.16$) showed that deviations from the ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ stoichiometry lead to secondary phases of related structures including the perovskite phase ${\mathrm{Pr}}_{2/3}{\mathrm{TiO}}_{3}$ and the orthorhombic phases ${\mathrm{Pr}}_{4}{\mathrm{Ti}}_{9}{\mathrm{O}}_{24}$ and ${\mathrm{Pr}}_{2}{\mathrm{TiO}}_{5}$. No indications of site disordering (stuffing and antistuffing) or vacancy defects were observed in the ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ majority phase. A procedure for growth of high-structural-quality stoichiometric single crystals of ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ by the traveling solvent floating zone method is reported. Thermomagnetic measurements of single-crystalline ${\mathrm{Pr}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ reveal an isolated singlet ground state that we associate with the low-symmetry crystal electric-field environments that split the ($2J+1=9$)-fold degenerate spin-orbital multiplets of the four differently coordinated ${\mathrm{Pr}}^{3+}$ ions into 36 isolated singlets resulting in an anisotropic temperature-independent van Vleck susceptibility at low $T$. A small isotropic Curie term is associated with 0.96(2)% noninteracting ${\mathrm{Pr}}^{4+}$ impurities.

Controlling the magnetic structure in W-type hexaferrites.

W-type hexaferrites with varied Co/Zn ratios were synthesized and the magnetic order was investigated using neutron powder diffraction. In SrCo2Fe16O27 and SrCoZnFe16O27 a planar (Cm'cm') magnetic ordering was found, rather than the uniaxial ordering (P63/mm'c') found in SrZn2Fe16O27 which is common in most W-type hexaferrites. In all three studied samples, non-collinear terms were present in the magnetic ordering. One of the non-collinear terms is common to the planar ordering in SrCoZnFe16O27 and uniaxial ordering in SrZn2Fe16O27, which could be a sign of an imminent transition in the magnetic structure. The thermomagnetic measurements revealed magnetic transitions at 520 and 360 K for SrCo2Fe16O27 and SrCoZnFe16O27, and Curie temperatures of 780 and 680 K, respectively, while SrZn2Fe16O27 showed no transition but a Curie temperature at 590 K. This leads to the conclusion that the magnetic transition can be adjusted by fine-tuning the Co/Zn stoichiometry in the sample.

Structural, magnetic, and transport properties of Co2CrAl epitaxial thin film

We report the physical properties of Co2CrAl Heusler alloy epitaxial thin films grown on a single-crystalline MgO(001) substrate using a pulsed laser deposition technique. The x-ray diffraction pattern in the θ-2θ mode showed the film growth in a single phase B2-type ordered cubic structure with the presence of (002) and (004) peaks, and the film oriented along the MgO(001) direction. The ϕ scan along the (220) plane confirms the fourfold symmetry, and the epitaxial growth relation is found to be Co2CrAl(001)[100]||MgO(001)[110]. The thickness of about 12 nm is extracted through the analysis of x-ray reflectivity data. The isothermal magnetization (M–H) curves confirm the ferromagnetic (FM) nature of the thin film having significant hysteresis at 5 and 300 K. From the in-plane M–H curves, the saturation magnetization values are determined to be 2.1 μB/f.u. at 5 K and 1.6 μB/f.u. at 300 K, which suggest the soft FM behavior in the film having the coercive field ≈522 Oe at 5 K. The thermomagnetization measurements at 500 Oe magnetic field show the bifurcation between field-cooled and zero-field-cooled curves below about 100 K. The normalized field-cooled magnetization curve follows the T2 dependency, and the analysis reveals the Curie temperature around 335±11 K. Moreover, the low-temperature resistivity indicates semiconducting behavior with the temperature, and we find a negative temperature coefficient of resistivity (5.2×10−4/K).

Investigation of Mn-Fe magnetic interaction in mechanically alloyed Fe doped-MnAlC by 57Fe Mössbauer spectrometry

Four samples γ2-Mn40Fe0.5Al59.5, β-Mn60Fe0.5Al39.5, and ε-Mn50.5Fe0.5Al47C2, τ-Mn50.5Fe0.5Al47C2 were synthesized by mechanical alloying method. X-ray diffraction results showed high purity of the γ2, β, ε, and τ phases in each sample. Mössbauer measurement at room temperature showed non-ferromagnetic characteristic of the γ2-Mn40Fe0.5Al59.5, β-Mn60Fe0.5Al39.5, and ε-Mn50.5Fe0.5Al47C2. Interestingly, τ-Mn50.5Fe0.5Al47C2 showed a complex magnetic hyperfine splitting, indicating magnetic ordered structure. The hyperfine interaction in τ-Mn50.5Fe0.5Al47C2 was found dependent with temperature, in which isomer shift (IS) and magnetic hyperfine field (Bhf) decreased with increasing temperature. From the IS temperature dependence curve, the Debye temperature (θD) is determined to be 422 ± 80 K. The temperature dependence of Bhf values and the thermomagnetic measurement yielded a Curie temperature (Tc) values of 560 ± 13 K and 565 ± 2 K respectively. In order to investigate the magnetic interaction between Fe and Mn atoms in τ-Mn50.5Fe0.5Al47C2, local magnetic order of τ-Mn50.5Fe0.5Al47C2 was probed by using in-field 57Fe Mössbauer spectrometry. The obtained results showed that Fe and Mn formed a non-collinear magnetic structure with magnetic moments of Fe at different sites showing different canting angles with neighboring Mn atoms.

Nature inspired synthesis of magnetite nanoparticle aggregates from natural berthierine.

We investigate the origin of the magnetite nanoparticle aggregates (MNAs) from the Peña Colorada iron-ore mining district (Mexico) to devise a nature inspired synthesis process. Three types of samples were used: natural MNAs recovered from the mine, concentrated magnetite microparticles as reference material, and thin berthierine films used to synthesize MNAs. The chemical, mineralogical, crystallographic and rock magnetic properties were determined by polarized microscopy, high-resolution transmission electron microscopy, electron microprobe, X-ray diffraction, Mössbauer spectroscopy, and thermomagnetic and hysteresis measurements. MNAs were synthesized in the lab with the following steps. We start with berthierine thin films, which are heated to temperatures between 495 and 510 °C leading to formation of numerous stable magnetite nanocrystals. They grow at a temperature above 650 °C. Space restrictions lead to the formation of dense MNAs. Smaller MNAs, <200 nm, with a Curie temperature of 650 °C, shows superparamagnetic behavior. While larger MNAs, >7 μm, show Curie temperature of 578 °C and ferromagnetic behavior. Based on present observations, we suggest that MNAs in the Peña Colorada iron-ore formed in a marine environment, where berthierine formation was accelerated by Fe-rich hydrothermal springs that supplied iron and increased the temperature. Most notably, our laboratory experiments mimicked natural conditions and were able to successfully nucleate and grow magnetite nanoparticles which developed into MNAs. These MNAs were similar to those recovered from the Peña Colorada iron-ore deposit. This study, thus, provides a nature inspired method for synthesis of magnetite nanoparticles and its aggregates.

Realization of Enhanced Refrigeration Capacity with Non-Hysteretic Behavior in Ni40Gd5Co5Mn37In12Si1 Alloy Near Room Temperature at 2T

Ni–Co–Mn–In–Si-based Heusler alloys have recently attracted a lot of attention because of their superior magnetocaloric properties around the second-order magnetic transformation near room temperature. In this paper, the effects of Gd substitution (Ni45–xGdxCo5Mn37In12Si1; x = 0 and 5) and Gd addition (Ni45Co5Mn37In12Si1 + Gdx; x = 0 and 5) on thermal and magnetic hysteretic behavior of temperature- and field-dependent magnetization of Ni45Co5Mn37In12Si1 Heusler alloy were investigated. The as-prepared Ni45–xGdxCo5Mn37In12Si1 Heusler alloys crystalize into a high-temperature austenite cubic L21 crystal structure, confirmed by powder X-ray diffraction. Microstructural and elemental composition analyses from field emission scanning electron microscopy reveal that parent Ni45Co5Mn37In12Si1 alloy shows single phase with larger grains in its as-cast form, whereas the Gd-doped Ni45Co5Mn37In12Si1 sample possess some dendritic well-distinguishable Gd-rich and deficient regions. Thermomagnetic measurements show that substitution of Gd at the Ni site in Ni45Co5Mn37In12Si1 notably reduces the Curie temperature, TC, from 333 to 317 K. Thermodynamic analyses of isothermal field-dependent magnetization result in significantly large magnetic entropy change, ΔSM = −0.842 J kg–1 K–1 under an applied field change, ΔH = 2 T at 305 K across the austenite regime for Ni40Gd5Co5Mn37In12Si1. Furthermore, the maximum refrigeration capacity of ∼47 J kg–1 was achieved for the composition of Ni40Gd5Co5Mn37In12Si1 at 305 K.

Chemical Pressure Tuning Magnetism from Pyrochlore to Triangular Lattices.

Geometrically frustrated lattices combined with magnetism usually host quantum fluctuations that suppress magnetic orders and generate highly entangled ground states. Three-dimensionally (3D) frustrated magnets generally exist in the diamond and pyrochlore lattices, while two-dimensionally (2D) frustrated geometries contain Kagomé, triangular, and honeycomb lattices. In this work, we reported using chemical pressure to tune the magnetism of the pyrochlore lattice in LiYbSe2 into a triangular lattice by doping Ga or In. Li3-xGaxYb3Se6 and Li3-xInxYb3-yInySe6/Li3-xInxYb3-y□ySe6 crystallize in a trigonal α-NaFeO2 structure-type (space group R3̅m) and can be synthesized using either LiCl or Se flux. In Li3-xGaxYb3Se6, Ga3+ and Li+ are mixed, leaving Yb3+ on the triangular plane. Instead of just Li+ being replaced in Li3-xGaxYb3Se6, In3+ was observed in both the Li+ and Yb3+ layers in Li3-xInxYb3-yInySe6 depending on the reaction conditions. Dominant antiferromagnetic interactions are revealed by magnetic measurements in both Li3-xGaxYb3Se6 and Li3-xInxYb3-yInySe6/Li3-xInxYb3-y□ySe6. However, no long-range magnetic order is detected in thermomagnetic measurements above 1.8 K due to geometrical frustration. Thus, Li3-xGaxYb3Se6, Li3-xInxYb3-yInySe6/Li3-xInxYb3-y□ySe6, and the LiYbSe2 previously discovered by our group provide an ideal platform to understand the complex structure-magnetism correlations from 3D to 2D frustrated lattices.