High Magnetic Field Properties Research Articles

Magnetic properties of the Co-doped MnNiGe system in high magnetic field

High-field magnetic properties of the Co-doped MnNiGe system, Mn0.9Co0.1NiGe, which undergoes a ferromagnetic and structural phase transition at Tt= 215 K, were investigated. Additionally, first-principles calculations were performed on Mn0.875Co0.125NiGe. The magnetic field, μ0H, dependence of magnetization, M(μ0H), of Mn0.9Co0.1NiGe saturates at ∼73 A⋅m2⋅kg−1 below Tt and shows significant hysteresis in the range of 215 ≤T≤ 230 K due to the magnetic-field-induced structural phase transition. The isothermal magnetic entropy change, ΔS, peaks around Tt, reaches -79.7 J⋅K−1⋅kg−1 for Δμ0H = 30 T. The density of states (DOS) calculated for Mn0.875Co0.125NiGe in the paramagnetic-hexagonal phase (Tt<T) exhibits a peak at the Fermi energy, EF, with significant contributions from the Mn 3d orbitals. In the ferromagnetic-orthorhombic phase, DOS at EF is suppressed, indicating that the structural phase transition at Tt in this system is primarily driven by the band Jahn-Teller effect.

Contractional deformation between extensional dome exhumation in Central Pamir at 17–15 Ma constrained by metamorphic and paleomagnetic data from the Bartang volcanic rocks, Tajikistan

The debated mechanism and timing of formation of the Pamir orogenic salient provides an ideal case to combine paleomagnetic and metamorphic analyses. Opposing views argue for either oroclinal bending of the Pamir since the India-Asia collision or for an originally arcuate shape, which can be tested using paleomagnetism to estimate vertical-axis rotations. Furthermore, Pamir deformation can be dated and characterized by the analysis of a well-expressed regional metamorphism. However, paleomagnetism is seldom applied to metamorphic rocks such that the significance of their rock magnetic signal with respect to deformation remains poorly understood. We studied a > 2 km thick sequence of slightly metamorphosed Cretaceous-Paleogene volcanic and volcaniclastic rocks from the western Central Pamir Mountains using metamorphic petrology, geochronology, and paleomagnetic analyses. These rocks present a medium-grade metamorphism and have undergone fine grained recrystallisation of biotite due to NW-SE compression. 40Ar/39Ar and Rb/Sr ages (∼17 to 15 Ma) on whole rock and biotite, confirm that the greenschist facies metamorphism is related to the coeval exhumation of Pamir gneiss domes during the Middle Miocene. The rocks generally show homogenous magnetic properties. High field magnetic properties and SEM/EDS data show that the main magnetic remanent carrier is titano-hematite. Thermal demagnetizations yield complex characteristic remanent magnetization with site-mean directions obtained for only 14 of the 44 studied sites but scattered mainly within the foliation plane defined by the anisotropy of magnetic susceptibility (AMS). These rocks have also unusual magnetic characteristics where strong-field isothermal remanent magnetizations induce an AMS fabric, likely related to the specific composition and structure of the metamorphic titano-hematite but independent of the original anisotropy fabrics. Combined paleomagnetic and geochronological data from the Bartang volcaniclastics rocks enable us to identify a ∼ 17–15 Ma compressive deformation event contemporaneous with the emplacement of the gneiss domes and suggest no oroclinal bending since that event.

High-field magnetic and magnetocaloric properties of pseudo-binary Er1−xHoxNi2 (x = 0.25–0.75) solid solutions

Hydrogen is quickly becoming a desired type of fuel, however, the energy and cost required for liquefaction using today’s cooling technology is excessively high. Magnetic cooling based on the magnetocaloric effect is an energy-efficient and environmentally friendly alternative to commonly used vapor compression, but improvements in refrigerants are crucial for this technology to succeed. Polycrystalline Er1−xHoxNi2 (x = 0.25, 0.5, 0.75) Laves-phase solid solutions obtained by the arc-melting method have been investigated due to their potential for low-temperature refrigerants. Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2 crystallize in cubic Laves phase superstructure (space group F-43 m), while Er0.25Ho0.75Ni2, similarly to the initial ErNi2 and HoNi2 binary compounds, crystallizes with the formation of the regular cubic C15 structure (space group Fd-3 m). To evaluate how the structure affects magnetic and magnetocaloric properties, studies in a wide magnetic field range, up to 14 T, were conducted. Measurements show all samples obey the second-order magnetic phase transition from ferromagnetic to paramagnetic state, and their Curie temperatures increase with increasing Ho content from 8 K for Er0.75Ho0.25Ni2 to 12.3 K for Er0.25Ho0.75Ni2. At higher temperatures, all solid solutions are Curie-Weiss paramagnets. However, it has been observed that the formation of the superstructure with lower translational symmetry seems to affect magnetic moments and magnetic entropy values. Er0.25Ho0.75Ni2, with the regular cubic C15 structure, showed the highest entropy changes of 43.5 J/kgK around 12 K, while Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2, with cubic superstructure, provided ∼30 % lower results of 30.3 and 35.1 J/kgK, around 8 and 10 K, respectively, for magnetic field change of 14 T. Nevertheless, relatively large and reversible values of magnetic entropy prove that these compounds can be promising candidates for magnetic cooling operating within the low-temperature range needed for hydrogen liquefaction.

Structural and high-field magnetic properties of Laves phase RFe2-H hydrides

The crystal structure and magnetic properties of the multicomponent compounds (Tb1−xYx)0.8Sm0.2Fe2Hz (x = 0, 0.2, 0.4, 0.6, 0.8, 1; z = 0 and 3.7) are investigated. The compounds crystallize in the MgCu2 type of structure. While the parent compounds Tb0.8Sm0.2Fe2 and Y0.8Sm0.2Fe2 are single phase, we detect 5%–8% of a second phase with a crystal structure of the PuNi3 type (space group R3m) in the alloys with 0.2 ≤ x &amp;lt; 0.8. Hydrogen absorption does not change the space group of the (Tb,Y,Sm)Fe2 compounds but boosts significantly the lattice parameter a. A large volume change of ΔV/V ∼ 28% upon hydrogen absorption is observed. By applying high magnetic fields up to 58 T, we observed rotations of the magnetic sublattices and hence we were able to determine the critical transition fields, H, from the ferrimagnetic to the ferromagnetic state and the inter-sublattice exchange parameter λ. The magnetic compensation occurs at x ≈ 0.6 and 0.2 in (Tb1−xYx)0.8Sm0.2Fe2Hz at z = 0 and 3.7, respectively. While maintaining the collinear magnetic structure, the phenomenon of compensation in hydrides should be observed at x ≈ 0.4.

Magnetocaloric effect in the Laves-phaseHo1−xDyxAl2family in high magnetic fields

Hydrogen has the largest gravimetric energy density among all chemical fuels. At the same time, the density of gaseous ${\mathrm{H}}_{2}$ is extremely low, which makes its compression to high pressures, liquefaction, or solid-state storage necessary for transport purposes. Liquid hydrogen ($\mathrm{L}{\mathrm{H}}_{2}$) can be transported in a dewar under atmospheric pressure, but this requires energy-intensive cooling down to $20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Magnetocaloric materials have great potential to revolutionize gas liquefaction to make $\mathrm{L}{\mathrm{H}}_{2}$ more competitive as fuel. In this paper, we investigate a series of Laves-phase materials regarding their structural, magnetic, and magnetocaloric properties in high magnetic fields. The three compounds $\mathrm{Ho}{\mathrm{Al}}_{2}$, ${\mathrm{Ho}}_{0.5}{\mathrm{Dy}}_{0.5}{\mathrm{Al}}_{2}$, and $\mathrm{Dy}{\mathrm{Al}}_{2}$ are suited for building a stack for cooling from liquid-nitrogen temperature ($77\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) down to the boiling point of hydrogen at $20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This is evident from our direct measurements of the adiabatic temperature change in pulsed magnetic fields, which we compare with calorimetric data measured in a static field. With this methodology, we are now able to study the suitability of magnetocaloric materials down to low temperatures up to the highest magnetic fields of 50 T.

Competing magnetic states in multiferroic BaYFeO4 : A high magnetic field study

Spin-driven ferroelectricity phenomena have drawn great interest in the scientific community due to potential application in spintronics and their complex physical mechanisms. A noticeable example of this is multiferroic $\mathrm{BaYFe}{\mathrm{O}}_{4}$ that exhibits an unconventional magnetoelectric (ME) coupling due to the uncorrelated behavior of the ferroelectric and cycloidal states under an applied magnetic field. To shed more light on this spin-driven ME effect, a high-quality sample of $\mathrm{BaYFe}{\mathrm{O}}_{4}$ was synthesized by a standard solid-state reaction method, and its high-field (up to 9 T) magnetic properties have been systematically investigated by means of magnetometry, magnetocaloric effect, and M\"ossbauer measurements over a wide temperature range (5--400 K). In addition, its crystal and magnetic structures have been studied using x-ray and neutron powder diffraction. Results obtained indicate that Fe spins form a long-range spin density wave (SDW) antiferromagnetic (AFM) order at ${T}_{\mathrm{N}1}\ensuremath{\sim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which transforms into the cycloidal AFM order at ${T}_{\mathrm{N}2}\ensuremath{\sim}35\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. A spin-glass-like state emerges below ${T}^{*}\ensuremath{\sim}17\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and coexists with the long-range cycloidal AFM one in this temperature range. Magnetocaloric and M\"ossbauer measurements consistently confirm the robustness of both the long-range SDW and cycloidal AFM orders under applied magnetic fields up to 6 T, whereas the spin-glass state is converted into the ferromagnetic (FM) state when the applied magnetic field exceeds 1 T. These findings pinpoint the fact that the magnetic field evolution of spin correlations from the AFM to FM character in the spin-glass state is responsible for the magnetic field dependence of ferroelectricity in $\mathrm{BaYFe}{\mathrm{O}}_{4}$.

High magnetic field properties in Ru2−xFexCrSi with antiferromagnetic and spin-glass states

We report experimental studies on ${\mathrm{Ru}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}\mathrm{CrSi}$ focusing on properties related to antiferromagnetism in ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ and spin glass (SG) in ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$. By measuring the temperature dependence of magnetization $M(T)$, specific heat $C(T)$, electrical resistivity $\ensuremath{\rho}(T)$, and muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), we observed that ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ exhibited an antiferromagnetic (AF) transition at a temperature ${T}_{N}$ of $\ensuremath{\sim}13$ K, and ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$ showed SG properties that could be interpreted as successive SG transitions, where the spin-freezing occurred at temperature ${T}_{g}$, and below that strong irreversibility in $M(T)$ and a gradual peak of $M(T)$ at ${T}^{*}\phantom{\rule{4pt}{0ex}}(&gt;{T}_{g})$ appeared. When the data for $0\ensuremath{\le}x\ensuremath{\le}0.1$ were compared, by substituting Fe the AF order was rapidly destroyed and it appeared to change to two anomalies at ${T}^{*}$ and ${T}_{g}$. With increasing $x$, there was a slight change in ${T}_{g}$ from ${T}_{N}$ for $x=0$; however, ${T}^{*}$ increased, suggesting that the AF and the SG states are closely related. Furthermore, the results of specific heat, resistivity, and magnetization in high fields were presented and compared. For ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ in specific heat under high magnetic fields up to 14 T, the peak shape around ${T}_{N}$ and the ${T}_{N}$ value were constant. The resistivity and magnetization in pulsed fields suggested that ${T}_{N}$ of ${\mathrm{Ru}}_{2}\mathrm{CrSi}$ was constant up to over 50 T. These results demonstrated the unusual robustness of the AF transition to magnetic fields. In ${\mathrm{Ru}}_{1.9}{\mathrm{Fe}}_{0.1}\mathrm{CrSi}$, unusual hysteresis in magnetoresistance was observed in static and pulsed magnetic fields, although their appearances differed. These hystereses were considered a manifestation of the curious properties of the SG state with strong irreversibility.

High-field spin-flop state in green dioptase

The high-field magnetic properties and magnetic order of the gem mineral green dioptase Cu$_6[$Si$_6$O$_{18}]\cdot 6$H$_2$O have been studied by means of single-crystal neutron diffraction in magnetic fields up to $21~$T and magnetization measurements up to $30~$T. In zero field, the Cu$^{2+}$-moments in the antiferromagnetic chains are oriented along the $c$-axis with a small off-axis tilt. For a field applied parallel to the $c$-axis, the magnetization shows a spin-flop-like transition at $B^*=12.2~$T at $1.5~$K. Neutron diffraction experiments show a smooth behavior in the intensities of the magnetic reflections without any change in the periodicity of the magnetic structure. Bulk and microscopic observations are well described by a model of ferromagnetically coupled antiferromagnetic $XXZ$ spin-$\frac{1}{2}$ chains, taking into account a change of the local easy-axis direction. We demonstrate that the magnetic structure evolves smoothly from a deformed N\'eel state at low fields to a deformed spin-flop state in a high field via a strong crossover around $B^*$. The results are generalized for different values of interchain coupling and spin anisotropy.

Microstructure and High-Field Magnetic Properties of Fe-Based Bulk Amorphous Alloys

In this paper the results of the structural and magnetic properties for bulk amorphous alloys Fe65Co10Y5B20 and Fe63Co10Y7B20 were presented. For the structural investigation was performed by X-ray diffractometry and Mossbauer spectroscopy. It was found that investigated samples were amorphous in the as-cast state. The magnetisation was measured within magnetic fields ranging from 0 to 2T using a vibrating sample magnetometer (VSM). On the basis of the hysteresis loops, the saturation magnetization value and the coercive field were determined.The investigation of the �magnetisation in the area close to ferromagnetic saturation� showed that the magnetisation process in strong magnetic fields is connected with point defects and Holstein-Primakoff paraprocess. Analysis of the high-field magnetization curves has facilitated the calculation of the spin wave stiffness parameter.

Evolutions of different crystalline textures in Sm-Fe film fabricated under high magnetic field and subsequent tuning magnetic properties

In order to tune the crystalline texture evolution and magnetic properties of the Sm-Fe film, molecular beam vapor deposition method is used to fabricate the Sm-Fe films. Sm content, thickness, and high magnetic field are used to affect the crystalline texture and magnetic properties. X-ray diffraction is used to analyze the texture evolution. Atomic force microscope is used to observe the surface morphology and roughness. Energy-dispersive X-ray spectroscopy is used to measure the compositions of the film. Vibrating sample magnetometer is used to test the magnetic properties. The results show that the crystalline textures are tuned through the Sm content. The crystalline texture evolution and high magnetic field have significant effect on the magnetic properties of the Sm-Fe film. The Sm-Fe film with 5.8% atomic content is of bcc crystal structure and is of amorphous structure with 33.0% Sm. Neither the thickness nor the high magnetic field has an influence on the crystalline texture. The surface roughness and particle size on the surface of the amorphous film are smaller than those of the crystal film. A 6 T high magnetic field increases the surface particle size and reduces the surface roughness. Saturation magnetization Ms of the amorphous film is 47.6% lower than that of the crystal film (1466 emu/cm3, 1 emu/cm3=410-10 T). The 6 T high magnetic field reduces the Ms of crystal and amorphous film by about 50%. The coercivity Hc values of the Sm-Fe films are in a range of 6-130 Oe (1 Oe=103/(4) A/m). The Hc of the amorphous film is higher than that of the crystal film. The 6 T high magnetic field increases the Hc of the crystal film and reduces the Hc of the amorphous film. The highest reduction is 95%. The anisotropy of the crystal film transforms to isotropy of the amorphous film. High magnetic field increases the anisotropy of the crystal film. The squareness of the crystal film is much higher than that of the amorphous film. High magnetic field has a significant effect on the measured magnetic field to obtain saturation magnetization in the film. This measured saturation magnetic field increases in the amorphous film and decreases in the crystal film after the high magnetic field has been exerted during the film growth. These results indicate that the Sm content and high magnetic field can be used to tune the crystal textures and magnetic properties of the Sm-Fe films.

Superconducting properties and microstructures for Ba2SmNbO6 and BaHfO3 co-doped SmBa2Cu3Oy thin films

Recently, we observed that Ba2SmNbO6 (BSNO), which has a double perovskite structure, forms wide nanorods in a SmBa2Cu3Oy (SmBCO) film when compared with BaHfO3 (BHO) nanorods. These wide nanorods can trap flux quanta effectively in low magnetic fields; on the other hand, narrow nanorods can trap flux quanta in high magnetic fields. In this paper, we doped SmBCO films with BSNO and BHO with the aim of introducing both wide and narrow nanorods and bringing out the flux pinning properties in low and high magnetic fields simultaneously. We investigated their microstructures and superconducting properties, and as a result, we confirmed that wide and narrow nanorods could coexist in the SmBCO films. The wide and narrow nanorods trapped the flux quanta in different magnetic fields. We also explored the optimal composition for BSNO + BHO co-doped SmBCO films. These findings indicate that flux pinning properties can be tuned by the multiple doping of BMO materials.

Experimental study on a conduction cooling system for a HTS NMR magnet

A nuclear magnetic resonance (NMR) magnet composed of a high-temperature superconductor (HTS) is expected to contribute to a smaller size and a higher magnetic field (>1 GHz) of the NMR magnet due to its high critical current density under high magnetic field and better mechanical properties. The high operating temperature of HTS NMR magnets also makes conduction cooling by a cryocooler available. The conduction cooling system combined with a cryocooler is compact and user-friendly but has critical issues about the design of conduction cooling passages and the mechanical vibration. The small-scale HTS magnet with the conduction cooling system is fabricated and tested to check the issues and establish the design basis as a preliminary step for the development of a 400-MHz HTS NMR magnet. Thermal analysis for heat loads and thermal resistances at main joints is performed from the temperature distribution of the cooling system. The vibration levels at the crycooler and the vacuum chamber are discussed in comparison to the vibration criterion of NMR magnets. In addition, the design approach to the conduction cooling system for the HTS NMR magnet is discussed.

Vpliv strukturnih napak na magnetne lastnosti masivne amorfne zlitine Fe60Co10Mo2WxY8B20-x (x = 1, 2), izdelane z metodo litja z vbrizgavanjem

This paper presents the results of research pertaining to high-field magnetic properties, in relation to the theory of H. Kronmuller. Studies were performed on bulk amorphous alloys featuring composition Fe60Co10Mo2WxY8B20-x (x = 1, 2). Samples were produced in the form of plates with a thickness of 0.5 mm; they were prepared by injecting the molten alloy into a water-cooled copper mould. The influence of structural defects on the magnetization process was investigated within high magnetic fields known as the area of the approach to ferromagnetic saturation. For the investigated samples, the studies showed that, in the process of magnetization in high magnetic fields, rotation of the magnetization vector was mainly due to the presence of linear defects in the structure, i.e., quasidislocational dipoles. The density of quasidislocational dipoles in a sample with an addition of 1 % W was nearly twice as high as that of an alternative alloy.

Anisotropic thermodynamic and transport properties of single-crystallineCaKFe4As4

Since 2008, iron-based superconductors have been the focus of intense research. Unfortunately, the higher transition temperatures and most promising high-magnetic field properties have been associated with compounds that have to be chemically disordered, making it hard to fully understand their intrinsic properties. A fully ordered compound with near optimal properties would be ideal and CaKFe${}_{4}$As${}_{4}$ appears to be that compound. In this work, the authors present detailed anisotropic, structural, thermodynamic, and transport measurements that, in addition to revealing high upper critical fields, also provide the basis for further understanding of this fully ordered, high-${T}_{c}$, iron-based superconductor. It is shown that CaKFe${}_{4}$As${}_{4}$ has exceptionally large upper critical fields (in excess of 650 kOe and possibly as high as 900 kOe) as well as high ${T}_{c}$ values (35 K), which can be obtained and studied without any disorder-related effects obscuring or complicating the results.

Spin-Driven Multiferroic Properties of PbMn7O12 Perovskite

We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) conditions and investigate its structural, magnetic, dielectric, and ferroelectric properties. We find that PbMn7O12 exhibits rich physical properties from interplay among charge, orbital, and spin degrees of freedom and rich structural properties. PbMn7O12 crystallizes in space group R3̅ near room temperature and shows a structural phase transition at TCO = 397 K to a cubic structure in space group Im3̅; the Im3̅-to-R3̅ transition is associated with charge ordering. Below TOO = 294 K, a structural modulation transition associated with orbital ordering takes place. There are two magnetic transitions with Néel temperatures of TN1 = 83 K and TN2 = 77 K and probably a lock-in transition at TN3 = 43 K (on cooling). There is huge hysteresis on specific heat (between ∼37 and 65 K at 0 Oe), dielectric constant (between ∼20 and 70 K at 0 Oe), and dc and ac magnetic susceptibilities around the lock-in transition. Sharp dielectric constant, dielectric loss, and pyroelectric current anomalies are observed at TN2, indicating that electric polarization is developed at this magnetic transition, and PbMn7O12 perovskite is a spin-driven multiferroic. Polarization of PbMn7O12 is measured to be ∼4 μC/m(2). Field-induced transitions are detected at ∼63 and ∼170 kOe at 1.6-2 K; similar high-magnetic field properties are also found for CdMn7O12, CaMn7O12, and SrMn7O12. PbMn7O12 exhibits a quite small magnetodielectric effect, reaching approximately -1.3 to -1.7% at 10 K and 90 kOe.

Tuning the critical magnetic field of the triplon Bose–Einstein condensation in Ba3-xSrxCr2O8

The structure and magnetic interactions of the triplon Bose–Einstein condensation candidates Ba3Cr2O8 and Sr3Cr2O8 have been studied thoroughly in the literature, but little is known about a possible triplon condensation in the corresponding solid solution SrxCr2O8. We have prepared various members of this solid solution and systematically examined their magnetic properties in high magnetic fields up to and at low temperatures down to , by means of pulsed field and cantilever magnetometry. From these experiments for , we find that the critical fields of SrxCr2O8 decrease monotonically with decreasing Sr content x. This change is in good agreement with the earlier reported variation of the magnetic interactions in these compounds.

Superconducting Properties in SmBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;y&lt;/sub&gt; Films With High Density of BaHfO&lt;sub&gt;3&lt;/sub&gt; Nanorods Fabricated With a Seed Layer

A high density of BaMO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BMO) nanorods within a REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (REBCO) film can be generated by heavy doping of the BMO. This is very effective in improving superconducting properties in high magnetic fields. However, heavy doping causes a significant T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> reduction. Introduction of a high density of BMO nanorods into REBCO films without reduction in T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is required. To this end, we deposited SmBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (SmBCO) films with various amount of BaHfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BHO) by a pulsed laser deposition (PLD) method using a seed-layer technique and a low-temperature growth (LTG) technique. Using this technique, we can fabricate a purely c-axis-oriented SmBCO film even at low substrate temperatures T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The SmBCO films with BHO were fabricated at low T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> of 750 °C without heavy doping of BHO. As a result, the BHO nanorods became thinner and denser than those within SmBCO films fabricated by conventional PLD methods at high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The maximum density was 4780/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">φ</sub> of the film reached 9.9 T. These samples showed high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (> 90 K). We have therefore successfully fabricated high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> SmBCO films with high densities of BHO nanorods using the LTG technique.

Characteristics of REBCO Coated Conductors for 25 T Cryogen-Free Superconducting Magnet

A 25 T cryogen-free superconducting magnet is under development at the High Field Laboratory for Superconducting Materials (HFLSM), Institute for Materials Research (IMR), Tohoku University. Fujikura has manufactured and supplied REBCO coated conductors for the 25 T cryogen-free superconducting magnet. In-field critical current (I c ) properties in high magnetic fields at lower temperatures below 20 K and mechanical properties are important for design of these superconducting magnets. However, there is insufficient data of I c properties in high magnetic fields above 15 T. In this work, in-field I c properties at 20 K, 15 T of several samples cut from commercial coated conductors are evaluated at HFLSM, IMR, Tohoku University. The correlations between I c at 20 K, 15 T and I c at 77.3 K are compared. As a result, it is confirmed that I c at 20 K, 15 T have a stronger correlation with in-field I c at 77.3 K rather than I c at 77.3 K, self-field. In addition, tensile strengths at 77.3 K of more than 30 samples of coated conductors are also evaluated.

Low Temperature and High Magnetic Field Dependence and Magnetic Properties of Nanocrystalline Cobalt Ferrite

The DC magnetic hysteresis loop measurements were carried out for temperatures varying from 5 to 300 K over a field range of ±10 T on nanocrystalline (∼35 nm) cobalt ferrite samples (crystallized to \(Fd\bar {3} m\) space group with cubic symmetry) to validate the law of approach at low temperature for the nanocrystalline cobalt ferrite. A magnetocrystalline anisotropy constant and saturation magnetization have been obtained by analyzing the magnetization curve in saturation using the “law of approach (LA) to saturation.” The magnetocrystalline anisotropy constant is found to be almost constant in the temperature range of 5 to 150 K due to the freezing of spin at low temperature. Also, spin freezing leads to a decrease of coercivity with the increase in the temperature.

Analysis on high-field magnetic properties of aluminum substituted rare-earth iron garnet at low temperatures

Magnetic properties of aluminum substituted erbium and holmium iron garnets (Er3Fe4.65Al0.35O12, Er3Fe4.45Al0.55O12 and Ho3Fe4.55Al0.45O12) are theoretically investigated by a three-sublattice model in high magnetic fields up to 200kOe applied along the three principal crystallographic directions [100], [110] and [111] at low temperatures (4.2K and 30K). The effect of the substitution of the diamagnetic Al3+ ion, located in tetrahedral site, on the exchange interaction in rare-earth iron garnets is analyzed. The temperature and field dependence of the magnetization in a, c and d sublattices, labeled as Ma, Mc and Md, are analyzed, where obvious anisotropies are revealed. Correspondingly, it is further pointed out that the anisotropy of magnetic properties mainly arises from the contribution of exchange interaction. Excellent fits to the experimental magnetization are carried out, from which the parameters αi (i=a, c, d) associated with the exchange interaction and the effective magnetic susceptibility are determined. At a certain temperature, the parameters conform to the expression αi=P1+P2He−1+P3He−2, where P1, P2 and P3 are the coefficients, He is the external magnetic field.