Low-temperature Magnetization Research Articles

Spin stiffness of chromium-based van der Waals ferromagnets

Low temperature magnetization of CrI3, CrSiTe3 and CrGeTe3 single crystals were systematically studied. Based on the temperature dependence of extrapolated spontaneous magnetization from magnetic isotherms measured at different temperatures, the spin stiffness constant (D) and spin excitation gap (Δ) were extracted according to Bloch’s law. For spin stiffness, D is estimated to be 27 ± 6 meV Å2, 20 ± 3 meV Å2 and 38 ± 7 meV Å2 for CrI3, CrSiTe3 and CrGeTe3 respectively. Spin excitation gaps determined via Bloch’s formulation have larger error bars yielding 0.59 ± 0.34 meV (CrI3), 0.37 ± 0.22 meV (CrSiTe3) and 0.28 ± 0.19 meV (CrGeTe3). Among all three studied compounds, larger spin stiffness value leads to higher ferromagnetic transition temperature.

Structural and low-temperature magnetic properties of as-quenched and annealed Ni–Si–B alloys produced by rapid solidification

Structural characterization (differential scanning calorimetry, DSC, and X-ray diffraction, XRD) and temperature dependence of the magnetization are reported in Ni80Si10B10 and Ni75Si15B10 alloy ribbons produced by rapid solidification. XDR and DSC measurements lead to confirm the amorphous character of Ni75Si15B10 alloy while the Ni80Si10B10 alloy presents a mixture of amorphous and crystalline (Nickel face-centered cubic) phase. Low-temperature magnetization dependencies were analyzed in terms of spin-wave excitation and fluctuations of the exchange interaction. While both mechanisms are relevant for the high Ni-content alloy, fluctuations of exchange could be ascribed as mechanism for low Ni-content alloy. The effect of annealing (523 and 623 K during 1 h) on the magnetic behavior is also presented. Thus, annealing of Ni75 sample at 623 K also results in appearance of highly magnetic Ni phase.

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.

Magnetic properties and spin glass behavior in an antiferromagnet KFeO2

We report the inhomogeneous magnetic state with the characteristics of spin-glass like behavior in KFeO2 from the low temperature magnetization and magnetization relaxation of zero field cooled measurements. The results reveal a possible spin glass state below the typical glass transition temperature (Tg). The low temperature isothermal hysteresis loops reveal a spin configuration consisting of a small ferromagnetic component within an antiferromagnetic ground state. The observation of spin-glass state in KFeO2 may be attribute to the competition between ferromagnetic and antiferromagnetic component. And the ferromagnetic component might origin from the frustration effect or nonstoichiometric caused mixed valence state of Fe ions in KFeO2. Hence, we expect that a similar phenomenon would exist in related AFeO2 (A: alkali metal) family with strong super-exchange interactions.

Influence of low-spin Co3+ for high-spin Fe3+ substitution on the structural, magnetic, optical and catalytic properties of hematite (α-Fe2O3) nanorods

Pure hematite nanorods and very long and thin cobalt-doped hematite nanorods (nanoneedles) were prepared by a combined precipitation and annealing method. The influence of the level of cobalt doping on different properties of hematite nanorods was investigated. Incorporation of cobalt in the form of low-spin Co3+ ions into the structure of hematite by substitution for high-spin Fe3+ ions was proved by determination of a significant unit cell contraction by powder X-ray diffraction (PXRD) and characteristic positions of the absorption edge in X-ray absorption near edge structure (XANES) spectra and peaks in X-ray emission (XES) spectra. Cobalt doping caused a gradual elongation and thinning of hematite nanorods – very long and thin 1D nanoparticles (nanoneedles) were formed in the presence of 10 and 12 mol% Co. Magnetic measurements showed a strong increase in low-temperature remanent magnetization and coercivity upon cobalt doping, as well as a disappearance of the Morin transition, which was also confirmed by Mössbauer spectroscopy. Cobalt doping significantly affected optical properties of hematite nanorods – absorption in the visible and NIR ranges increased, which was accompanied by narrowing of the optical band gap. Compared with pure hematite nanorods cobalt-doped hematite nanoneedles showed a significantly better electrocatalytic activity for the oxygen evolution reaction (OER).

Magnetostratigraphy of the Hominin Sites and Paleolakes Drilling Project (HSPDP) Baringo-Tugen Hills-Barsemoi core (Kenya)

The principal objective of the Hominin Sites and Paleolakes Drilling project (HSPDP) is to study the relationship between climate and environmental change and the implications on human evolution in eastern Africa. For this purpose, HSPDP has recovered a 228 m core in the Chemeron Formation of the Baringo Basin (Kenya). The Chemeron Formation spans approximately 3.7 Myr, from around 1.6 to 5.3 Ma, and has yielded many vertebrate fossils, including fossil hominins. The magnetostratigraphy of the Baringo core contributes to the chronological framework. A total of 567 individual paleomagnetic samples were collected from 543 levels at regular intervals throughout the core and 264 were processed using thermal and alternative field stepwise demagnetizations. In most samples, distinct Low-Temperature (LT; 20–150 °C) and High-Temperature (HT; 150–550 °C) Characteristic Remanent Magnetization (ChRM) could be determined. Typical demagnetization behaviors and some rock magnetic experiments suggest titanomagnetite acts as the main carrier of the HT ChRM with pervasive secondary overprints in normal polarity expressed by the LT component. Normal and reversed polarities were identified based on the secondary overprints LT ChRM directions, either parallel or antiparallel to the HT ChRM directions respectively. Our study identified four paleomagnetic reversals interpreted as the Matuyama-Gauss, Gauss-Kaena, Kaena-Gauss and the Gauss-Mammoth transitions. These boundaries provide chronostratigraphic tie-points that can be combined with those derived from 40Ar/39Ar dating of tuffs (Deino et al., 2020) and together indicate that the HSPDP Baringo core has an age range of ~3.3 Ma to ~2.6 Ma. The consistent paleomagnetic and radioisotopic age constraints are incorporated into a Bayesian age model of the core (Deino et al., 2020).

Metastable and localized Ising magnetism in α−CoV2O6 magnetization plateaus

$\alpha$-CoV$_{2}$O$_{6}$ consists of $j_{\mathrm{eff}}={1 \over 2}$ Ising spins located on an anisotropic triangular motif with magnetization plateaus in an applied field. We combine neutron diffraction with low temperature magnetization to investigate the magnetic periodicity in the vicinity of these plateaus. We find these steps to be characterized by metastable and spatially short-range ($\xi\sim$ 10 $\r{A}$) magnetic correlations with antiphase boundaries defining a local periodicity of $\langle \hat{T}^{2} \rangle =\ \uparrow \downarrow$ to $\langle \hat{T}^{3} \rangle =\ \uparrow \uparrow \downarrow$, and $\langle \hat{T}^{4} \rangle=\ \uparrow \uparrow \downarrow \downarrow$ or $\uparrow \uparrow \uparrow \downarrow$ spin arrangements. This shows the presence of spatially short range and metastable/hysteretic, commensurate magnetism in Ising magnetization steps.

Insights into Nature of Magnetization Plateaus of a Nickel Complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 from a Spin-1 Heisenberg Diamond Cluster

Magnetic and magnetocaloric properties of a spin-1 Heisenberg diamond cluster with two different coupling constants are investigated with the help of an exact diagonalization based on the Kambe’s method, which employs a local conservation of composite spins formed by spin-1 entities located in opposite corners of a diamond spin cluster. It is shown that the spin-1 Heisenberg diamond cluster exhibits several intriguing quantum ground states, which are manifested in low-temperature magnetization curves as intermediate plateaus at 1/4, 1/2, and 3/4 of the saturation magnetization. In addition, the spin-1 Heisenberg diamond cluster may also exhibit an enhanced magnetocaloric effect, which may be relevant for a low-temperature refrigeration achieved through the adiabatic demagnetization. It is evidenced that the spin-1 Heisenberg diamond cluster with the antiferromagnetic coupling constants J1/kB = 41.4 K and J2/kB = 9.2 K satisfactorily reproduces a low-temperature magnetization curve recorded for the tetranuclear nickel complex [Ni4(μ-CO3)2(aetpy)8](ClO4)4 (aetpy = 2-aminoethyl-pyridine) including a size and position of intermediate plateaus detected at 1/2 and 3/4 of the saturation magnetization. A microscopic nature of fractional magnetization plateaus observed experimentally is clarified and interpreted in terms of valence-bond crystal with either a single or double valence bond. It is suggested that this frustrated magnetic molecule can provide a prospective cryogenic coolant with the maximal isothermal entropy change −ΔSM=10.6 J·K−1·kg−1 in a temperature range below 2.3 K.

Spin-1/2 Ising–Heisenberg Cairo pentagonal model in the presence of an external magnetic field: effect of Landé g-factors

In the present paper, a study of the magnetic properties of a spin-1/2 Ising-Heisenberg Cairo pentagonal structure is presented. The model has been investigated in Ref. [34] in the absence of external magnetic field. Here, we consider the effects of an external tunable magnetic field. By using the transfer matrix approach, we investigate the magnetic ground-state phase transition, the low-temperature magnetization process, and how the magnetic field influences the various thermodynamic parameters such as entropy, internal energy and specific heat. It is shown that the model exhibits intermediate magnetization plateaux accompanied by a double-peak in the specific heat curve versus temperature. The position of each magnetization jump is in accordance with the merging and/or separation of the two peaks in the specific heat curve. Considering different g-factors for the nodal Ising spins and spin dimers also results in arising different intermediate plateaux and to remarkable alterations of the thermodynamic properties of the model.

Effects of Cr substitution on the low temperature magnetization behavior in amorphous Fe68+xCr12-xSi8B12 ribbons

Amorphous Fe68+xCr12-xSi8B12 alloys (x=0, 2, 4, 6, 8 and 10) were prepared using single wheel melt spinning technique. Magnetic measurements were carried out in the temperature range from 5–300 K and at an external applied field of 30 kOe. The Curie temperature was found to increase by substituting Cr by Fe. The magnetic behavior at low temperature was analyzed using spin wave theory. The low temperature magnetization curve was found to obey Bloch's T3/2 law. Some parameters are extracted like the spin wave stiffness constant (D) and mean square range of exchange interaction for the different compositions. The values of spin waves constant (D) determined were found to increase with substitution the Cr by Fe. The values of the mean square range of exchange interaction were found to be characteristic of amorphous ferromagnets. The local random anisotropy constant KL was derived from the approach of saturation in the magnetization. KL increases as Cr concentration decreases.

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6.

SummaryThe finding of bulk quantum oscillations in the Kondo insulator SmB6 proved a considerable surprise. Subsequent measurements of bulk quantum oscillations in other correlated insulators including YbB12 lent support to our discovery of a class of bulk unconventional insulators that host bulk quantum oscillations. Here we perform a series of experiments to examine evidence for the intrinsic character of bulk quantum oscillations in floating zone-grown single crystals of SmB6 that have been the subject of our quantum oscillation studies. We present results of thermodynamic, transport, and composition analysis experiments on pristine floating zone-grown single crystals of SmB6 and compare quantum oscillations with metallic LaB6 and elemental aluminum. These results establish the intrinsic origin of quantum oscillations from the insulating bulk of floating zone-grown SmB6. The similarity of the Fermi surface in insulating SmB6 with the conduction-electron Fermi surface in metallic hexaborides is at the heart of a theoretical mystery.

Effect of B-Site Ordering on the Magnetic Order in Multifunctional La2NiMnO6 Double Perovskite**Supported by the National Natural Science Foundation of China (Grant Nos. 51702289, 21801054 and 11604067), and the Natural Science Foundation of Zhejiang Province (Grant No. LQ20E020006).

To obtain various Ni/Mn orderings, we use a low-temperature synthesized method to modulate the Ni/Mn ordering of the ferromagnetic-ferroelastic La2NiMnO6 compound, and the Ni/Mn ordering is estimated by the low-temperature saturation magnetism. The microstructures, crystal structures and magnetic properties are investigated, and the Landau theory are used to describe the form and magnitude of the coupling effects between Ni/Mn ordering and magnetic order parameters. It is predicted that the Ni/Mn ordering would be a strong coupling effect with the Curie transition temperatures if the La2NiMnO6 sample stoichiometry is close.

Performance Evaluation of Current Leads for a 5 Tesla Electromagnetic Properties Measurement System

The development of the Electromagnetic Property Measurement System is underway at the Korea Basic Science Institute. The Electromagnetic Property Measurement System is used for electrical, thermal, and magnetic specimen property measurements in variable magnetic fields and temperatures with a low-temperature superconducting magnet. To activate low-temperature superconducting magnet that operates with liquid helium, we propose the use of vapor-cooled current leads. The low-temperature superconducting magnet is connected to the power supply at room temperature through a pair of current leads. Accordingly, heat inflows through the current leads and represents one of the major contributory factors of the entire heat inflow. Therefore, design optimization and evaluation of the current leads is necessary to minimize heat and liquid helium consumption. Vapor-cooled, and hybrid current leads were designed and fabricated, and testing in liquid helium cryostat was conducted. The low-temperature superconducting magnet was charged with electrical current up to the operating level, and the liquid helium boil-off rate was measured with respect to the supplied electrical current level. The performances of the two current leads were accessed based on the thermal load and boil-off rate of the liquid helium. The experimental and analyzed liquid helium boil-off rates associated with the current leads were in close agreement.

Demonstration of engineering current density exceeding 1 kA mm−2 in ultra-thin no-insulation, soldered coil windings using NbTi/Cu wires with CuNi cladding

The no-insulation, or more precisely, controlled-resistance coil winding method, nowadays being exclusively used for high-temperature superconducting solenoids, has proven its effectiveness for improving quench protection. When considering low-temperature superconductor magnet technology, which is mostly focused on stability and training issues, controlled-resistance insulation windings are directly addressing these aspects as well. Fully soldered coil windings of non-insulated turns can also show superior mechanical properties and feature simplified manufacturing when compared to epoxy impregnated coil windings and are of high practical interest for quasi-stationary magnets provided the related charging time constant can be controlled and kept low enough. For demonstrating the principle feasibility two demonstrator coils were developed using NbTi/Cu wire with CuNi cladding of 1 mm diameter. The wire performance is reported including critical current and n-values at 4.2 K and background magnetic fields from 0 to 9 T, as well as effective transverse resistivity at room temperature and 77 K. Two solenoids with fully soldered windings comprising one layer on a 50 mm bore and three layers on a 100 mm bore, respectively, were manufactured and tested in liquid helium. Their performance is directly compared to data obtained on short wire samples. The drastically enhanced stability of the coils against thermal disturbances allows to avoid any training and enables to operate the coils up, or even slightly beyond, the short-sample critical current, resulting in generated magnetic fields of 2.2 and 3.8 T and time constants of 5 and 55 s, respectively. When initiating a quench deliberately by excessive heating or spontaneously at their limiting currents, the coils entirely switch to the normal state almost instantly, thus requiring no quench protection system. Design, manufacturing and test experiences with the two super stable coils are reported and their use and design constraints for certain applications discussed.

The influence of self-doping of stibnite ore with impurities on the preparation, heat capacity, magnetic and transport properties of tetrahedrite Cu12Sb4S13

Abstract Stibnite mineral (mainly Sb2S3) has been employed for the synthesis of tetrahedrite Cu12Sb4S13 bulk material by spark plasma sintering. High purity Cu12Sb4S13 can be quickly obtained by two sintering procedures at temperatures from the range of 420 °C to 440 °C for 1 h. Appropriate reduction of Cu content (Cu12+xSb4S13, x ⩽ –0.05) or CuS content (Cu12−ySb4S13−y, y = 0.1 or 0.3) was beneficial to fabricate Cu12Sb4S13. The secondary resintering improved the purity of Cu12Sb4S13 material. The first-order magnetic phase transformation with magnetic hysteresis effect was confirmed by the behavior of susceptibility, heat capacity and resistivity. The magnetization showed a linear increase with increasing field (up to 7 T) and non-saturation behavior was observed. The impurities in stibnite mineral Sb2S3 had a weak influence on the transformation temperature but affected the low-temperature magnetization value (~0.15, close to natural tetrahedrite). Similar transformation was observed by the analysis of heat capacity. The properties such as electrical resistivity, Seebeck coefficient and thermal conductivity were also measured for Cu11:9Sb4S13 and Cu11:9Sb4S12:9. The maximum figure of merit ZT of Cu11:9Sb4S12:9 was 0.22 at 367 K.

Dimensional crossover in Cr-doped Co3BO5

The crystal structure and the magnetic properties of the ${\mathrm{Co}}_{2.5}{\mathrm{Cr}}_{0.5}{\mathrm{BO}}_{5}$ ludwigite have been investigated by x-ray diffraction, magnetization, and specific heat experiments. Cr ions mainly occupy sites 4 of the ludwigite lattice, substituting approximately half of the ${\mathrm{Co}}^{3+}$. It changes the interatomic distances and favors a high spin state for the remaining ${\mathrm{Co}}^{3+}$ ions. Doping the homometallic ${\mathrm{Co}}_{3}{\mathrm{BO}}_{5}$ with magnetic Cr drastically increases the magnetic transition temperature from 42 K, for the undoped compound, to 76 K for ${\mathrm{Co}}_{2.5}{\mathrm{Cr}}_{0.5}{\mathrm{BO}}_{5}$. The latter contains three different magnetic ions, ${\mathrm{Co}}^{2+}, {\mathrm{Co}}^{3+}$ and ${\mathrm{Cr}}^{3+}$ in high spin states, as evidenced by magnetization measurements. The specific position of Cr in the structure (sites 4) gives rise, according to calculations of the exchange interactions and the Goodenough-Kanamori rules, to a few frustrated magnetic interactions. This is responsible for the high ferrimagnetic ordering temperature of 76 K, when compared to that of the pure compound. The experimental results imply a magnetic structure for the system that we show is consistent with the known interactions and the Goodenough-Kanamori rules. Low temperature specific heat and magnetization measurements reveal that the two-dimensional nature of the magnetism ${\mathrm{Co}}_{3}{\mathrm{BO}}_{5}$ when doped with Cr acquires a three-dimensional character with a high temperature ferrimagnetic order.

A Robust Metal Oxide Thin Film with Cryogenic Saturation Magnetization Exceeding 2 Tesla

Summary High saturation magnetization, hysteresis-less long linear response range, and resistance to device fabrication conditions are figures of merit for magnetic materials. Despite advances in materials research, many high-saturating micro- and nanomagnetic materials are hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in device inefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications. Holmium oxide is a promising material because of its high magnetic susceptibility, but synthetic options are limited, with low-temperature magnetism incompletely characterized. Here, we present physical vapor deposition synthesis and material characterization of polycrystalline holmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla, linear range (μ0H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistance to harsh processing conditions including oxygen plasma and concentrated hydrofluoric acid etching, making these thin films ideal for fabricating next-generation nanoscale magnetic devices in advanced scientific and engineering applications.

Nature of intermediate magnetization plateaus of a spin-1/2 Ising-Heisenberg model on a triangulated Husimi lattice resembling a triangulated kagome lattice.

The spin-1/2 Ising-Heisenberg model on a triangulated Husimi lattice is exactly solved in a magnetic field within the framework of the generalized star-triangle transformation and the method of exact recursion relations. The generalized star-triangle transformation establishes an exact mapping correspondence with the effective spin-1/2 Ising model on a triangular Husimi lattice with a temperature-dependent field, pair and triplet interactions, which is subsequently rigorously treated by making use of exact recursion relations. The ground-state phase diagram of a spin-1/2 Ising-Heisenberg model on a triangulated Husimi lattice, which bears a close resemblance with a triangulated kagomé lattice, involves, in total, two classical and three quantum ground states manifested in respective low-temperature magnetization curves as intermediate plateaus at 1/9, 1/3, and 5/9 of the saturation magnetization. It is verified that the fractional magnetization plateaus of quantum nature have character of either dimerized or trimerized ground states. A low-temperature magnetization curve of the spin-1/2 Ising-Heisenberg model on a triangulated Husimi lattice resembling a triangulated kagome lattice may exhibit either no intermediate plateau, a single 1/3 plateau, a single 5/9 plateau, or a sequence of 1/9, 1/3, and 5/9 plateaus depending on a character and relative size of two considered coupling constants.

Low-temperature study of an Er2Ti2O7 single crystal synthesized by floating zone technique and simplified feed rod preparation route

A new simplified synthesis of an Er2Ti2O7 single crystal is presented. The single crystal was prepared by a floating zone technique from the unreacted stoichiometric mixture of starting oxides Er2O3 and TiO2. No intermediate reactions of constituent oxides were conducted in contrast to previous studies. We demonstrate a good quality of prepared single crystal by both thorough (microscopic) chemical and structural characterization of the material and measurements of previously reported low-temperature properties: An Er2Ti2O7 single crystal was characterized by means of X-ray, electron and neutron diffraction techniques, and magnetization and specific heat measurements. The low-temperature magnetization was investigated by indirect measurement employing pre-calibrated Hall probes. The obtained low-temperature data are well comparable with previous reports and document a high quality of the prepared single crystal. Presented single crystal synthesis from an unreacted precursor is prospectively applicable to other rare-earth RE2Ti2O7 pyrochlores.

Partitioning of transition metals during magnetization of oxidized pyrrhotite tailings

Low-temperature magnetization using reducing gas derived from biomass pyrolysis is being explored as an option to recover Fe from oxidized waste generated during Ni extraction from bio-leaching of pyrrhotite-rich tailings. The study investigates the potential sequestration of the main transition metal contaminants - Cu and Ni - into the magnetic phases. In the original oxidized pyrrhotite tailings, Ni and Cu were associated with goethite. Magnetization at 460 °C led to full conversion of goethite and jarosite into magnetite through solid-state transformation. 93% of the magnetite was recovered in the magnetic fraction by magnetic separation. Nickel and Cu accumulation was respectively 4 times and 2 times greater in the magnetic than nonmagnetic fraction, indicating that the magnetic fraction acted as a sink for these transition metals. Metal fractionation of the magnetic fraction showed that a greater proportion of total Ni resided with the crystalline and refractory phases compared to Cu (47% of total Ni vs. 29% of total Cu). The greater affinity for Ni to incorporate into magnetite was further demonstrated using magnetized goethites co-precipitated with 100 mmol Cu or Ni kg−1: most Ni was associated with the amorphous and crystalline Fe whereas 60% of total Cu was extracted as a sorbed/exchangeable species. The greater Cu mobility during sequential extraction of magnetite is likely attributable to its monovalent state in this reducing system. Low-temperature magnetization coupled with biomass pyrolysis may represent a viable option to manage iron and leftover transition metals in oxidized, (bio)leached pyrrhotite wastes as a way to produce much smaller volumes of inert wastes.