Search

The tunnelling electric current passing through a magnetic tunnel junction (MTJ) is strongly dependent on the relative orientation of magnetizations in ferromagnetic electrodes sandwiching an insulating barrier, rendering efficient readout of spintronics devices1–5. Thus, tunnelling magnetoresistance (TMR) is considered to be proportional to spin polarization at the interface1 and, to date, has been studied primarily in ferromagnets. Here we report observation of TMR in an all-antiferromagnetic tunnel junction consisting of Mn3Sn/MgO/Mn3Sn (ref. 6). We measured a TMR ratio of around 2% at room temperature, which arises between the parallel and antiparallel configurations of the cluster magnetic octupoles in the chiral antiferromagnetic state. Moreover, we carried out measurements using a Fe/MgO/Mn3Sn MTJ and show that the sign and direction of anisotropic longitudinal spin-polarized current in the antiferromagnet7 can be controlled by octupole direction. Strikingly, the TMR ratio (about 2%) of the all-antiferromagnetic MTJ is much larger than that estimated using the observed spin polarization. Theoretically, we found that the chiral antiferromagnetic MTJ may produce a substantially large TMR ratio as a result of the time-reversal, symmetry-breaking polarization characteristic of cluster magnetic octupoles. Our work lays the foundation for the development of ultrafast and efficient spintronic devices using antiferromagnets8–10.

Rh-rich and Ir-poor erlichmanite–laurite OsS2–RuS2 solid solutions have been discovered at placers in Haraigawa, Misato-machi, Kumamoto, Japan. Microprobe analysis was performed to identify solid solutions containing few sub-components other than Rh. Approximately 10 at.% Rh was found to be present in the solid-solution samples. Structural refinement was performed using four natural samples: Os0.32Ru0.61Rh0.07S2, Os0.49Ru0.43Rh0.08S2, Os0.58Ru0.33Rh0.08S2 and Os0.81Ru0.09Rh0.10S2. The unit-cell parameters for the solid solutions containing Rh from Haraigawa varied from 5.61826(6) to 5.63142(8) Å. The (Os, Ru, Rh)–S distances in the Os1–x–yRu x Rh y S2 system were almost constant with a small variation of 0.001 Å. Conversely, the S–S distances varied significantly, with variations approaching 0.1 Å. Rh substitution of Os rather than Ru had a larger impact on the crystal structure. The atomic displacement ellipsoid of both cations and anions was almost spherical, and no elongation along the M–S and S–S bond directions was observed. The bulk Debye temperatures were estimated from the Debye–Waller factor for the sulfide site. The bulk Debye temperatures of pure OsS2 and RuS2 were 688 K and 661 K, respectively, which suggests that the melting point of erlichmanite is higher than that of laurite. The high Debye temperature of OsS2 is inconsistent with the crystallisation of laurite prior to erlichmanite from the primitive magma, which suggests that $f_{\rm S_2}$ , rather than temperature, is the main cause of the known crystallisation order. The presence of several percent Rh has a significant effect on the thermal stability of OsS2 and lowers the melting point of the erlichmanite solid solution compared to that of the laurite solid solution.

Some inorganic solids undergo phase transitions that result in the formation of "molecules" in their crystalline frameworks, which are frequently accompanied by dramatic changes in physical properties; the metal-insulator transition (MIT) in vanadium dioxide, for instance, is accompanied by the formation of dimer molecules with conventional two-center-two-electron bonding. We have discovered the creation of a linear ruthenium trimer with atypical three-center-four-electron bonding in ruthenium monophosphide at its MIT. Our detailed structural investigation and electronic structure calculations reveal that charge transfer from polymerized phosphorous to ruthenium automatically tunes the electron density to precisely four per trimer at the MIT, with all conduction electrons present at high temperatures being trapped by the trimer's molecular orbitals at low temperatures. Our results demonstrate that molecules are essential even in solid crystals, as they impact their electronic properties.

Electrical control of a magnetic state of matter lays the foundation for information technologies and for understanding of spintronic phenomena. Spin-orbit torque provides an efficient mechanism for the electrical manipulation of magnetic orders

Plastics are indispensable for our daily lives. However, since their excess use has caused serious environmental pollution, alternative materials are highly desired to realize a sustainable society...

Tetragonal FeAl2 is a high-pressure phase and is predicted to exhibit semiconductor-like behavior. We investigated the pressure and temperature synthesizing conditions of tetragonal FeAl2, supported by in situ X-ray diffractions, using synchrotron radiation during heating the sample under a pressure of 20 GPa. Based on the determined optimal conditions, we synthesized the bulk polycrystalline samples of tetragonal FeAl2 at 7.5 GPa and 873 K, using a multi-anvil press and measured its thermoelectric properties. The Seebeck coefficient of tetragonal FeAl2 showed a large negative value of – 105 μV/K at 155 K and rapidly changed to a positive value of 75 μV/K at 400 K. Although these values are the largest among those of Fe–Al alloys, the maximum power factor remained at 0.41 mW/mK2 because the carrier concentration was not tuned. A comparison of the Gibbs free energy of tetragonal FeAl2, triclinic FeAl2 and FeAl+Fe2Al5 revealed that tetragonal FeAl2 became unstable as the temperature increased, because of its smaller contribution of vibrational entropy., GRAPHICAL ABSTRACT

Substitution effects of Os for Ru in ��-RuCl3 are investigated in a wide composition range of 0 =< x =< 0.67 in Ru1-xOsxCl3 by X-ray and electron diffraction, magnetic susceptibility, heat capacity, and Raman spectroscopy measurements. Apart from the Kitaev physics with antiferromagnetic interactions increasing with x, a rich phase diagram is obtained, which includes an antiferromagnetic long-range order below 12 K for x =< 0.15, a dome-shaped spin-singlet dimer phase below 130 K for 0.15 =< x =< 0.40, and a magnetic short-range order for x > 0.40. A dimerization as similarly observed in ��-RuCl3 under high pressure occurs in the spin-singlet phase. It is suggested that Ru-Os pairs in the solid solutions tend to form dimers with short bonds and trigger the first-order transition in the presence of pseudo-threefold rotational symmetry for dimerization around a substituted Os atom only at low substitutions. This is a rare example of molecular orbital crystallization induced by elemental substitution in a highly disordered system. The short-range order at high substitutions may be related to a random-singlet state stabilized by bond disorder in the honeycomb net., 13 pages, 14 figures

The magnetic Weyl semimetallic state in the chiral antiferromagnet Mn3Sn has attracted interest for its potential in memory technology. Despite vanishingly small magnetization, the material exhibits large transverse responses that can be electrically manipulated, similar to ferromagnets. Through deposition on heated Si/SiO2 substrates, we have fabricated polycrystalline Mn3Sn films that have coarse surfaces, the thinner of which have a discontinuous structure comprised of grains with diameters of the order of 100 nm. We confirm that these grains retain the anomalous Hall effect arising in the time reversal symmetry broken chiral antiferromagnetic phase of Mn3Sn at room temperature by serially connecting the grains with an additional conducting layer. These results pave the path for the potential applications of nanoscale Mn3Sn systems, which could be useful in the development of energy efficient memory devices.

The Sm(Co,Fe)4B alloys were prepared by rapid quenching and subsequent heat treatment. As-rapidly quenched SmCo4-xFexB (x = 0–2) specimens mainly consisted of the amorphous phase. Subsequent annealing resulted in the formation of the SmCo4B or Sm(Co,Fe)4B phase. The annealed specimens exhibited high coercivity, with the value depending on the composition and annealing temperature. SmCo4-xFexB (x = 0.5–1.5) specimens annealed at 973 K consisted of the Sm(Co,Fe)4B phase and exhibited high coercivity, comparable to that of the high-performance rare-earth magnets.

Phase-pure Mo2AlB2 with a single Al layer, a possible precursor for MBenes, was synthesized topochemically by the removal of an Al layer from MoAlB. Ab initio calculations predicted the sequential staging transformation from MoAlB through Mo4Al3B4 (stage II) to Mo2AlB2 (stage I).

SmFe12-based magnets were successfully produced by the spark plasma sintering method from SmFe12-xTiX (x = 0–2) melt-spun ribbons. Although the SmFe12 magnet consisted of the SmFe7 and Fe phases and did not contain the SmFe12 phase, the SmFe12-xTiX (x = 0.5–2) magnets mostly consisted of the Sm(Fe,Ti)12 phase. The highest coercivity of 5.2 kOe was achieved in the SmFe11Ti magnet, which consisted solely of the Sm(Fe,Ti)12 phase. Magnetic measurements and a TEM study revealed that the SmFe11Ti magnet produced by the SPS method consisted of fine equiaxed grains and was magnetically isotropic.

The constitutional undercooling criterion of the Al3Ni intermetallic compound with nil solubility was established, which reveals that there is no constitutional undercooling when the initial Al-Ni alloy concentration is lower than 43 wt%. Meanwhile, the interface stability growth criterion for the Al3Ni was also established by considering the effects of pressure and superheating on diffusion coefficient, interface growth rate, interface energy, and kinetic coefficient. The results demonstrate that when the pressure is greater than 4.2 GPa, the Al3Ni phase will move forward with a planar interface without superheating. Under the combined effects of high pressure and superheating the transition point of Al3Ni planar growth decreases. For example, with a superheat of 600 K, the pressure for stable planar growth decreases to 2.7 GPa. In addition, the microstructure of hypo-peritectic Al-30 wt%Ni alloy solidified at different conditions was investigated. It shows that the Al3Ni phase growth interface is unstable at 2 and 4 GPa with no superheating. The microstructure of the sample synthesized at 2 GPa with the superheat degree 600 K is typically hypereutectic microstructure. While the whole sample can be divided into there regions (high pressure solid solution region, mushy zone, and fully melted region which consists of planar growth single phase Al3Ni area and hypoeutectic zone) at 3 GPa/600 K.

Severe structural damage in Cr- and V-bearing clinozoisite (Czo) from the Outokumpu copper mine, Finland, was discovered by Nagashima et al. (Eur J Miner 23:731–743, 2011). Single-crystal X-ray and electron diffraction patterns indicated moderate-to-very-poor structural coherency, suggesting a high density of faults in the translational symmetry. However, the poor crystallinity cannot be attributed to self-radiation due to negligible concentrations of radioactive elements. Annealing of Cr- and V-bearing Czo up to 750 °C only slightly improved crystallinity. To solve this enigma, polarized Raman spectroscopy was applied to gain further insights into the structural state of the Cr + V-bearing Finnish Czo. According to the parallel-polarized Raman spectra of Cr + V-rich (Czo-ts3), Cr + V-bearing (Czo-ts2), and Cr + V-free (Czo-ts1) Czo, the peaks broaden with the Cr + V content, indicating increasing density of structural defects. Spectra from a euhedral Cr + V-bearing Czo single-crystal evidence intact structural domains by strong polarization and orientation dependence. Thus, the structural state of Finnish Czo should be described in terms of defect-rich segmented domains with common crystallographic orientation. The incorporation of V and Cr into the clinozoisite structure strongly affects the Raman-active O–H bond stretching modes near 3343 cm−1 [(OH)a] and 3435 cm−1 [(OH)b], assigned to O10-H···O4 and O10-H···O2 hydrogen bridges, respectively. The H···O2 hydrogen bonding is strongly promoted when M3 is partially occupied by Cr + V, and as a result, the linkages between the M2O6- and (M1, M3)O6-chains are disturbed, leading to periodicity faults and size reduction of coherent structural domains. In the case of M3Fe3+ substitution for M3Al, the local stress imposed by the larger M3-site cation is relaxed within the distorted M3O6 octahedron. In the case of M3V3+ or M3Cr3+ substitution for M3Al, M3O6 octahedra are less distorted and local stress fields propagate farther than only to the first coordination sphere, thus disturbing the transitional symmetry. New high-resolution transmission electron microscopy (HRTEM) images indeed display nanocrystals of ca. 10 nm with common crystallographic orientation surrounded by amorphous regions. It is suggested that the segmentation of large coherent crystalline areas in Cr + V-rich Czo to nanocrystals may be triggered by a potential miscibility gap in combination with the sluggish diffusion behavior of Cr3+. Moreover, this study implies that nanostructures as commonly observed for metamict materials may also be caused by strain effects and/or exsolution phenomena precluded by tardy diffusion.

Three non-metamict chevkinite-subgroup minerals, space group P21/a, from Cape Ashizuri, Japan, (No. 1), Tangir Valley, Diamar District, Pakistan (No. 2) and Haramosh Mts., Skardu district, Pakistan, (No. 3) were studied by crystal chemical techniques. Powder X-ray diffraction and transmission electron microscopic observations confirmed well crystalline samples. Electron-microprobe analyses indicated the general composition [(REE, Ca)4Fe2+(Fe2+, Fe3+, Ti)2Ti2(Si2O7)2O8] known for chevkinite-(Ce). Site scattering values determined by single-crystal X-ray structure refinements suggested assignment of subordinate Nb to the octahedral M3 and M4 sites, minor Th to M1 for the Ashizuri sample and minor Mg to M1 for both samples from Pakistan. Neutron time-of-flight powder diffraction studies were applied to determine the Ti/Fe distribution among octahedral sites for all samples and Mossbauer spectroscopy served for the Fe valence assignment at the four octahedral sites. Combined results gave the simplified formulas with Ce as dominant REE: No. 1 A(REE,Ca)4M1(Fe2+,Ti)M2(Ti,Fe3+)2M3,M4(Ti,Fe2+,Nb)2(Si2O7)2O8, No. 2 A(REE,Ca)4M1(Fe2+,Fe3+,Mg)M2(Ti,Fe3+)2M3,M4(Ti,Fe2+)2(Si2O7)2O8 and No. 3 A(REE,Ca)4M1(Fe3+,Fe2+,Mg,Ti)M2(Ti,Fe3+)2M3,M4(Ti,Fe2+)2(Si2O7)2O8. The dominant iron valence at M1 of the Haramosh sample (No. 3) is ferric whereas for samples Nos. 1 and 2 iron is ferrous. The structure of chevkinite-subgroup minerals consists of octahedral layers (M2, M3 and M4) alternating with an intermediate layer containing disilicate groups, REE polyhedra and strongly distorted M1 octahedra. Increased O atomic displacement parameters within the intermediate layers indicate disorder and/or strain to fit the extension of the embracing octahedral layers. A statistical analysis of chevkinite-subgroup structures (space groups P21/a, C2/m and P21/m) indicates a positive correlation between bond length and M1 bond angle variance. A negative correlation is found between bond length and the disilicate bending angle Si–O–Si, varying between ca. 160° and 175°. Outliers of this trend are delhuyarite-(Ce) Ce4Mg(Fe3+2W)□(Si2O7)2O6(OH)2, mainly due to octahedral W6+ and vacancies in the octahedral layers associated with OH groups, and synthetic Nd end-members with strong bonds between Nd and the intersecting O of the disilicate group. The observed trends reflect the main mechanisms in the intermediate layer to adopt to the size of the embracing rigid octahedral layers formed by M2, M3 and M4 octahedra.

We study the lead rhenium oxide PbRe2O6 as a candidate spin–orbit-coupled metal (SOCM), which has attracted much attention as a testing ground for studying unconventional Fermi liquid instability associated with a large spin–orbit interaction. The compound comprises a stack of modulated honeycomb lattices made of Re5+ (5d2) ions in a centrosymmetric R–3m structure at room temperature. Resistivity, magnetic susceptibility, and heat capacity measurements using single crystals reveal two successive first-order phase transitions at Ts1 ​= ​265 ​K and Ts2 ​= ​123 ​K. At Ts1, the magnetic susceptibility is enormously reduced and a structural transition to a monoclinic structure takes place, while relatively small changes are observed at Ts2. Surprisingly, PbRe2O6 bears a close resemblance to another SOCM candidate Cd2Re2O7 despite crucial differences in the crystal structure and probably in the electronic structure, suggesting that PbRe2O6 is an SOCM.

This is the first report of the crystal structure of mukhinite, V-analogue clinozoisite, on the join Ca2Al3Si3O12(OH)–Ca2Al2V3+Si3O12(OH) synthesized at 1.5 GPa and 800 °C. The study was performed to clarify the distribution of V3+ among structurally independent octahedral M1, M2, and M3 sites, and the effect of V3+ on the crystal structure. Mukhinite and V3+-bearing clinozoisite in all run products are associated with zoisite, and also coexist with V-bearing phases such as vanadomalayaite, goldmanite, V-oxides, and unidentified Ca–Al-bearing vanadates. Mukhinite and V3+-bearing clinozoisite crystallized in the Run 20 product show a compositional gap between 0.33 and 0.74 V atoms per formula unit (apfu), and the V content attains 1.14 apfu. The coexistence of low V3+- and high V3+-clinozoisites indicates the presence of a miscibility gap at 1.5 GPa and 800 °C. Two mukhinite crystals with 0.75 and 0.83 V3+ apfu were used for X-ray single-crystal structure analysis. The unit-cell parameters are a = 8.8995(2), b = 5.6299(1), c = 10.1532(2) A, β = 115.327(1)°, and V = 459.81(2) A3 for the former, and a = 8.8999(1), b = 5.6357(1), c = 10.1499(1) A, β = 115.306(1)°, and V = 460.24(2) A3 for the latter. The resulting V3+ occupancies among the octahedral sites are M1(Al0.894(6)V0.106)M2(Al0.976(6)V0.024)M3(V0.621(6)Al0.379) for the former and M1(Al0.868(4)V0.132)M2(Al0.957(4)V0.043)M3(V0.652(2)Al0.348) for the latter. Site preference of V3+ at the octahedral sites is M3 > M1 > M2 as that of Fe3+ and Mn3+. The intracrystalline partition coefficient of V3+ and Al3+ between the M1 and M3 sites, KD = (V3+/Al)M1/(V3+/Al)M3, is 0.07–0.08, which is greater than those of Fe3+ and Al3+ (0.03–0.05) and of Mn3+ and Al3+ (0.04–0.06). Variations of the unit-cell parameters are strongly related to the variations of the M3−Oi and M1−Oi distances.

A series of gold nanoparticles (AuNPs) with controllable size were prepared from immobilized gold-containing ionic liquid on SBA-15 (AuCl_me-Im@SBA-15) at room temperature. AuNPs size and shape could be controlled inside porous SBA-15 in the presence of immobilized 1-methyl-3-(3-trimethoxysilyl- propyl)-imidazolium chloride by controlling a concentration and a feed rate of a reducing agent NaBH 4 . The smallest AuNPs with the average size of 1.6 nm was obtained at a fixed feed rate of 0.2 ml/min with 4 mM NaBH 4 . The transformation of AuNPs shape from spherical to capsule-like NPs was observed at low feed rate of 0.04 ml/min. The prepared AuNPs catalysts were characterized by TEM, XPS, FTIR, and XRD. The catalyst with the smallest NPs, AuNP(1.6 nm)_me-Im@SBA-15, exhibited the highest catalytic performance in p -nitrophenol hydrogenation reaction at room temperature. Moreover this catalyst was reusable up to four recycle processes.

Electric resistivity, magnetic susceptibility, and x-ray diffraction measurements under high pressure are performed in both $\ensuremath{\alpha}$-${\mathrm{Sr}}_{2}{\mathrm{VO}}_{4}$ and $\ensuremath{\alpha}$-${\mathrm{Sr}}_{2}{\mathrm{CrO}}_{4}$, which are carefully prepared with regard to their stoichiometry. These measurements reveal contrasting and peculiar metallization processes of these compounds with increasing pressure. In contrast to a previously reported one in a V compound, we find two kinds of pressure-induced metallic states at low- ($Tl50\text{ }\text{ }\mathrm{K}$) and high-temperature ($Tg100\text{ }\text{ }\mathrm{K}$) regions. The high-temperature one seems to emerge beyond the pressure-induced Mott transition. The low-temperature one might imply a topological nature of the V compound, which is expected in the spin-orbit coupled $3{d}^{1}$ state that arises from their degenerated ${d}_{zx}$ and ${d}_{yz}$ orbits.

Overgrowths of whiskers of hedenbergite (Ca(Fe2+,Mg)Si2O6) on the hydrous pyroxenoid babingtonite (Ca2Fe2+Fe3+[Si5O14(OH)]) have been observed at Arvigo in Switzerland and Kreimbach/Kaulbach in Germany, and we have studied them with transmission electron microscopy in order to understand their structural relationships and formation. The boundaries between babingtonite and hedenbergite are sharply defined, and the two minerals are in direct contact with no additional phases present. The relationships of babingtonite (Bab) and hedenbergite (Hd) were determined as Bab[100]//Hd[112] in the Arvigo specimen and Bab[$\bar 1$00]//Hd[1$\bar 1$2] in the Kreimbach/Kaulbach specimen. Diffraction derived from Bab(031) and Hd(02$\bar 1$) in the Arvigo samples and Bab(031) and Hd(021) in the Kreimbach/Kaulbach samples were observed in identical positions. The reciprocity between the babingtonite and hedenbergite structures is governed by the direction of the SiO4-tetrahedral chains, and the related configuration of octahedra. Thus, hedenbergite is apparently an epitaxial phase grown on a base of {010} plates of babingtonite. The defined orientation relationship is also consistent with that shown in topotaxial intergrowths of other clinopyroxenes and pyroxenoids. The topotaxial intergrowths may result from diffusion-controlled solid-state reactions, whereas rapid whisker growth is characteristic of supersaturated solutions or a vapour medium. The epitaxial growth of hedenbergite whiskers on babingtonite with an abrupt but coherent change of structure at the interface represents an ideal example where the similar chemical compositions of host and guest contribute strongly to the close structural relationship.