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We report on the highly efficient spin-orbit torque (SOT) generation in epitaxial SrIrO$_{3}$(SIO), which is grown on an orthorhombic DyScO$_{3}$(110) substrate. By conducting harmonic Hall measurement in Co$_{20}$Fe$_{60}$B$_{20}$ (CoFeB)/SIO bilayers, we characterize two kinds of the SOTs, i.e., dampinglike (DL) and fieldlike ones to find that the former is much larger than the latter. By comparison with the Pt control sample with the same CoFeB thickness, the observed DL SOT efficiency $\xi$$_{DL}$ of SIO ($\sim$0.32) is three times higher than that of Pt ($\sim$0.093). The $\xi$$_{DL}$ is nearly constant as a function of the CoFeB thickness, suggesting that the SIO plays a crucial role in the large SOT generation. These results on the CoFeB/SIO bilayers highlight that the epitaxial SIO is promising for low-current and reliable spin-orbit torque-controlled devices., Comment: arXiv admin note: text overlap with arXiv:2305.17887

We study spin Hall magnetoresistance (SMR) in Pt/ferrimagnetic insulator Y3Fe5O12 (YIG) bilayers by focusing on crystallinity, magnetization, and interface roughness by controlling post-annealing temperatures. The SMR in the Pt/YIG grown on Si substrate is comparable to that grown on widely used Gd3Ga5O12 substrate, indicating that the large SMR can be achieved irrespective of the crystallinity. We deduced the spin mixing conductance from the Pt thickness dependence of the SMR to find the high interface quality of the optimized Pt/YIG grown on Si in terms of spin current. We also clarified that the SMR correlates well with the magnetization, the interface roughness, and carrier density. These findings highlight that optimizing YIG properties is a key to control of magnetization by spin current, leading to the development of the low power consumption spintronic device based on the magnetic insulator.

The 5d transition-metal oxides are an intriguing platform to demonstrate efficient charge-to-spin-current conversion due to a unique electronic structure dominated by strong spin-orbit coupling. Here, we report on the stacking-order effect of spin-orbit torque (SOT), spin-Hall magnetoresistance, and magnetic anisotropy in bilayer ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$-5d iridium oxide, ${\mathrm{Ir}\mathrm{O}}_{2}$. While all ${\mathrm{Ir}\mathrm{O}}_{2}$ and $\mathrm{Pt}$ control samples exhibit large dampinglike SOT generation, stemming from the efficient charge-to-spin-current conversion, the magnitude of the SOT is larger in the ${\mathrm{Ir}\mathrm{O}}_{2}$($\mathrm{Pt})$ bottom sample than in the ${\mathrm{Ir}\mathrm{O}}_{2}$($\mathrm{Pt})$ top one. The fieldlike SOT has an even more significant stacking-order effect, resulting in an opposite sign in the ${\mathrm{Ir}\mathrm{O}}_{2}$ samples in contrast to the same sign in the $\mathrm{Pt}$ samples. Furthermore, we observe that the magnetic anisotropy energy density and the anomalous Hall effect are increased in the ${\mathrm{Ir}\mathrm{O}}_{2}$($\mathrm{Pt})$ bottom sample, suggesting enhanced interfacial perpendicular magnetic anisotropy. Our findings highlight the significant influence of the stacking order on spin transport and the magnetotransport properties of $\mathrm{Ir}$ oxide-ferromagnet systems, providing useful information for the design of SOT devices, including 5d transition-metal oxides.

We present a model compound with a spin-1/2 spatially anisotropic frustrated square lattice, in which three antiferromagnetic interactions and one ferromagnetic interaction are competing. We observe an unconventional gradual increase in the low-temperature magnetization curve reminiscent of the quantum critical behavior between gapped and gapless phases. In addition, the specific heat and electron spin resonance signals indicate one-dimensional characteristics. These results demonstrate quantum critical behavior associated with one dimensionalization caused by frustrated interactions in the spin-1/2 spatially anisotropic square lattice., Comment: 6 pages, 4 figures

Background: In this paper, we report on the topics of one-dimensional (1D) and two-dimensional (2D) functional materials. Single-Walled Carbon Nanotubes (SWCNTs) are seamless hollow cylinders made of hexagonal lattice graphite sheets. The SWCNTs have attracted considerable attention due to the applicability of their enclosed nanospaces to engineering, and many types of guest materials are encapsulated inside their 1D space, expecting unusual properties. The poly Transition Metal (TM) phthalocyanine, in which phthalocyanine units are extended in two dimensions by sharing benzene rings, is one of the examples of the TM containing 2D carbon materials. Because of strong correlation between localized d-electrons in the TM atom and delocalized π-electrons on the poly phthalocyanine frame, it is expected that spin-polarized conduction, which is useful for the spintronic applications. Objectives: The objective of the first work is to synthesize SWCNTs encapsulating oxygen molecules having spin one, whose O-O bond directions are aligned to the longitudinal direction of the SWCNTs. The objective of the second work is to synthesize Poly Cu Phthalocyanine (PCuPc) through a bottom-up method by using copper octacyanophthalocyanine as a building block and to elucidate its crystal structure and magnetic properties. Methods: SWCNTs with inner diameter of ca 0.8 nm were prepared by the CoMoCAT method, and encapsulated together with oxygen molecules (~400 Torr) into a high-purity quartz tube. To subtract the background signals of the SWCNTs and the quartz tube, we prepared the same SWCNTs inducing He gas after evacuating oxygen molecules. Magnetization measurements of these SWCNTs samples were conducted by means of a SQUID magnetometer and a pulse magnet using an induction method. PCuPc were synthesized by a solid state reaction of octacyanophthalocyanine, tetracyanobenzene, and CuCl2·2H2O in glass ampoules sealed after evacuation. The as-synthesized samples were characterized using XRD analysis and TEM microscopy. Magnetization measurement of the samples were done by using a SQUID magnetometer. Results: The intrinsic magnetization data from oxygen molecules inside the SWCNTs (temperature and magnetic field dependence) show magnetic properties typical of the spin-one Heisenberg antiferromagnet named a Haldane magnet. PCuPc and its half-filling counterpart were obtained by solid state reaction. Both magnetic susceptibility and magnetization of PCuPc are larger than those of half-filling PCuPc, but the magnitudes of the former sample are about 1.5 times larger than those of the latter one, which is expected to be twice from the geometric superlattice structure. Conclusion: We have studied magnetic properties (magnetic susceptibility and magnetization) of oxygen molecules encapsulated into Single Walled Carbon Nanotubes (SWCNTs) with diameters of about 0.8 nm, regarded as a 1D functional magnetic material, and Poly Copper Phthalocyanine (PCuPc) and poly half-filling copper phthalocyanine (half-filling PCuPc), regarded as 2D functional magnetic materials.

The magnetic properties of ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ single crystals were investigated by magnetic and thermal measurements. The crystal structure of ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ consists of a bilayer triangular lattice of ${\mathrm{Fe}}^{3+}$ ions. The analysis of magnetic susceptibility clarified that the intra- and interdimer interactions are comparable with each other, and ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ is regarded as a spin-5/2 ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ buckled honeycomb antiferromagnet with the ferromagnetic interlayer interaction ${J}_{3}$. The susceptibility for the magnetic field $H||c$ axis exhibits a sudden drop at the N\'eel temperature ${T}_{\mathrm{N}}=5.4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, indicating a first-order magnetic phase transition. One of the characteristic features is the linear temperature dependence below ${T}_{\mathrm{N}}$. Furthermore, ${\mathrm{Cs}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Cl}}_{9}$ undergoes successive magnetic phase transitions in high magnetic fields along the $c$ axis. We obtained a rich H-T phase diagram in which the ${M}_{\mathrm{s}}/2$ magnetization-plateau phase is included. These unique magnetic behaviors probably originate from the competition of magnetic interactions and the easy-axis anisotropy in the antiferromagnetic ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ buckled honeycomb network.

A very large negative magnetoresistance (LNMR) is observed in the insulating regime of the antiferromagnet ${\mathrm{BaMn}}_{2}{\mathrm{Bi}}_{2}$ when a magnetic field is applied perpendicular to the direction of the sublattice magnetization. A high perpendicular magnetic field eventually suppresses the insulating behavior and allows ${\mathrm{BaMn}}_{2}{\mathrm{Bi}}_{2}$ to reenter a metallic state. This effect is seemingly unrelated to any field-induced magnetic phase transition, as measurements of magnetic susceptibility and specific heat did not find any anomaly as a function of magnetic fields at temperatures above $2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The LNMR appears in both current-in-plane and current-out-of-plane settings, and Hall effects suggest that its origin lies in an extreme sensitivity of conduction processes of holelike carriers to the infinitesimal field-induced canting of the sublattice magnetization. The LNMR-induced metallic state may thus be associated with the breaking of the antiferromagnetic parity-time symmetry by perpendicular magnetic fields and/or the intricate multiorbital electronic structure of ${\mathrm{BaMn}}_{2}{\mathrm{Bi}}_{2}$.

The $5d$ transition-metal oxides have a unique electronic structure dominated by strong spin-orbit coupling and hence they can be an intriguing platform to explore spin-current physics. Here, we report on room-temperature generation of spin-orbit torque (SOT) from a conductive $5d$ iridium oxide, $\mathrm{Ir}{\mathrm{O}}_{2}$. By measuring second-harmonic Hall resistance of ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}/\mathrm{Ir}{\mathrm{O}}_{2}$ bilayers, we find both dampinglike and fieldlike SOTs. The former is larger than the latter, enabling easier control of magnetization. We also observe that the dampinglike SOT efficiency has a significant dependence on $\mathrm{Ir}{\mathrm{O}}_{2}$ thickness, which is well described by the drift-diffusion model based on the bulk spin Hall effect. We deduce the effective spin Hall angle of +0.093 \ifmmode\pm\else\textpm\fi{} 0.003 and the spin-diffusion length of 1.7 \ifmmode\pm\else\textpm\fi{} 0.2 nm. By comparison with control samples Pt and Ir, we show that the effective spin Hall angle of $\mathrm{Ir}{\mathrm{O}}_{2}$ is comparable to that of Pt and seven times higher than that of Ir. The fieldlike SOT efficiency has a negative sign without appreciable dependence on the thickness, in contrast to the dampinglike SOT. This suggests that the fieldlike SOT likely stems from the interface. These experimental findings suggest that the uniqueness of the electronic structure of $5d$ transition-metal oxides is crucial for highly efficient charge to spin-current conversion.

We investigated the Landau-level structure in Weyl semimetal NbAs, in which a pair of band degenerate points (Weyl points) exists inside an anisotropic crescent-shaped Fermi surface. Through phase analysis of quantum oscillations in various magnetic-field directions, we found that the phase took various values between zero and $\ensuremath{\pi}$, reflecting variations of the energy dispersion in the extremal area. The nontrivial phase value around $\ensuremath{\pi}$ is seen when the extremal plane was relatively far from the Weyl pairs and the double-minimum energy dispersion caused by the band inversion disappears inside the plane.

Unconventional features of relativistic Dirac/Weyl quasi-particles in topological materials are most evidently manifested in the 2D quantum Hall effect (QHE), whose variety is further enriched by their spin and/or valley polarization. Although its extension to three dimensions has been long-sought and inspired theoretical proposals, material candidates have been lacking. Here we have discovered valley-contrasting spin-polarized Dirac fermions in a multilayer form in bulk antiferromagnet BaMnSb$_2$, where the out-of-plane Zeeman-type spin splitting is induced by the in-plane inversion symmetry breaking and spin-orbit coupling (SOC) in the distorted Sb square net. Furthermore, we have observed well-defined quantized Hall plateaus together with vanishing interlayer conductivity at low temperatures as a hallmark of the half-integer QHE in a bulk form. The Hall conductance of each layer is found to be nearly quantized to $2(N+1/2)e^2/h$ with $N$ being the Landau index, which is consistent with two spin-polarized Dirac valleys protected by the strong spin-valley coupling., 14 pages, 4 figures. Accepted in Phys. Rev. B (Rapid Communication)

Topological properties in material science have recently received tremendous attention, as exemplified by topological insulators. As for quantum spin systems, the Haldane chain with integer spins is the best known example1. The realization of a topological quantum phase in the Haldane chain is an innovative research development related to the 2016 Nobel Prize in Physics. For mixed spin chains composed of two different spins, the appearance of a topologically quantized magnetization plateau is predicted by the Lieb-Mattis theorem2 in combination with the Oshikawa-Yamanaka-Affleck criterion3. However, the actual magnetization plateau in the mixed spin chain has not yet been observed. Here, we present a model compound forming a mixed spin-(1/2, 5/2) chain. We observe a clear Lieb-Mattis plateau and well explain it quantitatively. The present results demonstrate a quantum many-body effect based on quantum topology and provide a new stage in the search for topological properties in condensed matter physics.

Layered organic-inorganic hybrid magnets, Co(cin)0.8(OH)1.2 (cin = cinnamate) (1) and Cu(cin) (OH) (2), have been synthesized by using a low energy process that employs transition metal nitrates as inorganic precursors and a cin as an organic precursor. The X-ray diffraction patterns and TEM images for the reaction products suggest that they possess organic-inorganic layered structure, where a transition metal hydroxide inorganic monolayer alternates with double cinnamate organic layers along the stacking direction. The compound 1 exhibits a ferrimagnetic long-range ordering (TC = 47.5 K) and large hysteresis with the coercive field Hc = 38 kOe. In contrast, the compound 2 shows soft ferromagnetic properties at low temperatures and a ferromagnetic phase transition occurs at TC = 15 K.

We report on the syntheses, crystal structure, and magnetic properties of the transition metal coordination polymer [Co3(SBA)2(OH)2(H2O)2]n, (SBA = 4-sulfobenzoate) in which CoO6 octahedra are linked through their edges, forming one-dimensional (1D) Co(II) arrays running along the crystal a-axis. These arrays are further perpendicularly bridged by SBA ligand to construct a three-dimensional framework. Its magnetic properties have been investigated, and ferromagnetic interactions within the arrays have been found. From heat capacity measurements, we have found that this compound exhibits a three-dimensional ferromagnetic phase transition at TC = 1.54 K, and the specific heat just above TC shows a Schottky anomaly which originates from an energy gap caused by uniaxial magnetic anisotropy. These results suggest that [Co3(SBA)2(OH)2(H2O)2]n consists of weakly coupled 1D ferromagnetic Ising arrays.

EuCo2Ge2 with the tetragonal structure is a Eu-divalent antiferromagnet with the Neel temperature T N = 23 K. The magnetic easy-axis corresponds to the [100] direction (a-axis), while the [001] direction (c-axis) is a hard-axis. The magnetization for H ∥ [ 100 ] indicates a metamagnetic transition at 25 kOe and saturates above 75 kOe. On the other hand, the hard-axis magnetization increases approximately linearly and saturates above 110 kOe. The magnetic phase diagram was constructed. A characteristic feature in EuCo2Ge2 is known as a valence transition under pressure, from Eu 2 + δ to Eu 3 − δ ′ ( δ , δ ′ 1 ). We also clarified the valence transition by measuring the electrical resistivity under pressure. The valence transition occurs at 3 GPa, with a hysteresis, and terminates at about 4.5 GPa. Further increasing pressure, the electronic state is changed into a moderate heavy fermion state and approaches the nearly trivalent electronic state.

α-Co hydroxide nanosheets have been synthesized and their magnetic properties were investigated. By using a soft chemical exfoliation technique, exfoliated α-Co hydroxide nanosheets, typically with lateral dimensions of few 100 nm, were obtained in a colloidal suspension. The magnetic responses of a sample consisting of a colloidal suspension of the nanosheets indicates a ferromagnetic phase transition occurs at TC=37.8 K. The magnetization possesses a linear temperature dependence at low temperatures below TC. In addition to this observation, the magnetization is proportional to (1-T/TC)β with β=0.8±0.1 near TC, which imply that the surface magnetism dominates in the exfoliated α-Co hydroxide nanosheets.

We report on a simple method to fabricate a nitrogen N-containing nano-graphite with magnetic moments. By using chlorinated phthalonitrile as the building block and potassium K as the coupling reagent, a paramagnetic N-containing nano-graphite has been successfully prepared. From transmission electron microscopy images, X-ray photoelectron spectroscopy, and X-ray diffraction experiments, it is evident that the reaction product consists of randomly connected flakes of nano-graphite that contains large amount of N-decorated vacancy and edges. Interestingly, this N-containing nano-graphite shows a Curie-like paramagnetism that originates isolated magnetic moments on N-decorated vacancies and edges. These results make the N-containing nano-graphite a promising candidate for versatile applications in the fields of magnetics and spintronics.

We succeeded in growing single crystals of SrTGe 3 (T: transition metal) by the In-flux method and measured the electrical resistivity, specific heat, and de Haas–van Alphen (dHvA) effect. We confirmed superconductivity in SrPdGe 3 and SrPtGe 3 , which was previously observed using polycrystal samples, and also found superconductivity for SrRhGe 3 , SrIrGe 3 , and SrNiGe 3 . Furthermore, from the results of dHvA experiments and energy band calculations, Fermi surfaces of SrIrGe 3 are found to split into two similar Fermi surfaces, reflecting the Rashba-type non-centrosymmetric tetragonal structure. We also grew single crystals of EuTGe 3 by the same In-flux method and studied magnetic properties, especially focusing on magnetism of EuIrGe 3 with a Neel temperature T N =12.2 K and a successive magnetic transition T ' N =7.3 K. The magnetic phase diagram of EuIrGe 3 is found to consist of three antiferromagnetic phases named AF1, AF2, and AF3. A critical field H c reaching a saturated moment of 7 μ B /Eu is determined as H c ≃ 160 kOe from a high-field magnetization curve. We proposed a simple helical magnetic structure based on the Dzyaloshinskii-Moriya interaction.

We report the discovery of a large-magnetoresistance (LMR) phenomenon in a family of ${\mathrm{BaMn}}_{2}{Pn}_{2}$ antiferromagnets ($Pn$ = P, As, Sb, and Bi) with parity-time symmetry. The resistivities of these materials are reduced by 60 times in magnetic fields $\mathbf{H}$, thus yielding a LMR of about $\ensuremath{-}98%$. The LMR changes systematically along with the $Pn$ elements, hinting that its origin is the spin-orbit coupling and/or $d\ensuremath{-}p$ orbital hybridization. A positive MR component emerging on top of the negative LMR at low temperatures suggests an orbital-sensitive magnetotransport as $\mathbf{H}$ suppresses the conduction of the electronlike carriers in the $d$-like band but enhances that of holelike ones in the $d\ensuremath{-}p$ hybridized band. The anisotropy of the LMR reveals that the electrical conductivity is extremely sensitive to the minute changes in the direction of the antiferromagnetic moments induced by the parity-time symmetry-breaking $\mathbf{H}$, which is perpendicular to the antiferromagnetic spin-ordered direction. We attribute the observed LMR to the nontrivial low-energy bands of ${\mathrm{BaMn}}_{2}{Pn}_{2}$ antiferromagnets, which are governed by the parity-time symmetry.

We successfully synthesized a verdazyl-based charge-transfer salt $[o\text{\ensuremath{-}}\mathrm{MePy}\text{\ensuremath{-}}\mathrm{V}\text{\ensuremath{-}}{(p\text{\ensuremath{-}}\mathrm{Br})}_{2}]{\mathrm{FeCl}}_{4}$, which has ${S}_{\mathrm{V}}=1/2$ on the radical $o\text{\ensuremath{-}}\mathrm{MePy}\text{\ensuremath{-}}\mathrm{V}\text{\ensuremath{-}}{(p\text{\ensuremath{-}}\mathrm{Br})}_{2}$ and ${S}_{\mathrm{Fe}}=5/2$ on the ${\mathrm{FeCl}}_{4}$ anion. Ab initio molecular orbital calculations indicate the formation of an ${S}_{\mathrm{V}}=1/2$ honeycomb lattice composed of three types of exchange interaction with two types of inequivalent sites. Further, the ${S}_{\mathrm{V}}=1/2$ at one site is sandwiched by ${S}_{\mathrm{Fe}}=5/2$ spins through antiferromagnetic (AF) interactions. The magnetic properties indicate that the dominant AF interactions between the ${S}_{\mathrm{V}}=1/2$ spins form a gapped singlet state, and the remaining ${S}_{\mathrm{Fe}}=5/2$ spins cause an AF order. The magnetization curve exhibits a linear increase up to approximately 7 T, and an unconventional 5/6 magnetization plateau appears between 7 and 40 T. We discuss the differences between the effective interactions associated with the magnetic properties of the present compound and ($o$-MePy-V)${\mathrm{FeCl}}_{4}$. We explain the low-field linear magnetization curve through a mean-field approximation of an ${S}_{\mathrm{Fe}}=5/2$ spin model. At higher field regions, the 5/6 magnetization plateau and subsequent nonlinear increase are reproduced by the ${S}_{\mathrm{V}}=1/2$ AF dimer, in which a particular internal field is applied to one of the spin sites. The ESR signals in the low-temperature and low-field regime are explained by conventional two-sublattice AF resonance modes with easy-axis anisotropy. These results demonstrate that exchange interactions between ${S}_{\mathrm{V}}=1/2$ and ${S}_{\mathrm{Fe}}=5/2$ spins in $[o\text{\ensuremath{-}}\mathrm{MePy}\text{\ensuremath{-}}\mathrm{V}\text{\ensuremath{-}}{(p\text{\ensuremath{-}}\mathrm{Br})}_{2}]{\mathrm{FeCl}}_{4}$ realize unconventional magnetic properties with low-field classical behavior and field-induced quantum behavior.

The high-field multifrequency electron spin resonance (ESR), the magnetization, and the specific heat of single crystals of BaCo2V2O8 (a quasi-one-dimensional Ising-like antiferromagnet with S = 1/...

The magnetic properties of the S = 1/2 distorted kagome antiferromagnet CdCu3(OH)6Cl2 have been studied by magnetic susceptibility, heat capacity, and high-field magnetization measurements. The mag...

We grew single crystals of EuCo2P2 and EuT2Ge2 (T: Co, Rh, Ir, Ni, and Pd) by the Bridgman method and Sn- and In-flux methods, and studied their magnetic properties by measuring the specific heat, ...

We have determined the crystal structures of new Co(II) polynuclear complex Co(sba)(H2O)2·H2O (sba ​= ​4-sulfobenzoate) (1) by X-ray crystallography. The crystal structure of 1 shows Co(II) uniform chains in which octahedral Co(II) centers are connected through double μ-OH2 single syn-syn μ-carboxylato bridging ligands, and these uniform chains are well separated by the sba ligands. Magnetization and magnetic susceptibility data of a single crystal of 1 taken along the different crystallographic axes suggest a large uniaxial magnetic anisotropy, the so-called Ising anisotropy, possessing large c∗-axis magnetic moments. Magnetic susceptibility data of 1 is explained by an 1D Ising ferromagnet with intra-chain exchange interaction of Jz/kB ​= ​39.6 ​K.

We report on the pressure–magnetic field–temperature (p–B–T) phase diagram of BaVS3 that was constructed by measuring the magnetic susceptibility and the high-field magnetization under pressure. Th...

We grew single crystals of EuCu2Si2 by the Bridgman and In-flux methods, and studied their crystallographic and magnetic properties precisely to clarify the ground state at low temperatures. The Br...

We present a new model compound with the $S=1/2$ frustrated square lattice composed of the charge-transfer salt ($o$-MePy-V)${\mathrm{PF}}_{6}$. $Ab\phantom{\rule{4pt}{0ex}}initio$ calculations indicate the formation of an $S=1/2$ square lattice, in which six types of nearest-neighbor ferromagnetic and antiferromagnetic interactions cause frustration. By applying a magnetic field, we observe an unusually gradual increase of magnetization and a subsequent 1/2-plateau-like behavior. A numerical analysis using the tensor network method qualitatively demonstrates such behaviors and suggests a collinear ordered state and a field-enhanced quantum fluctuation. Furthermore, the local magnetization and ${T}_{1}^{\ensuremath{-}1}$ probed by nuclear magnetic resonance measurements support these findings.

We report a simple method to fabricate Mn-doped poly(triazine imide) (PTI) by using melamine and cyanuric chloride as the building blocks, and Mn as the coupling agent. This material forms a two-dimensional imide-bridged triazine (C6N9H3) network, with an ordered arrangement of 24-atom voids. The synthesized PTI exhibits a large magnetization due to the localized d-electrons of Mn2+ ions, which suggests that PTI contains a large number of Mn2+ ions in the 24-atom voids. In addition, on being treated with HNO3, PTI absorbs NO3− ions in the 24-atom voids, which replace the Mn2+ ions present there, and forms a structurally well-ordered host-guest conjugated sheet, PTI·NO3. X-ray diffraction measurements of PTI·NO3 indicate that it crystallizes in the hexagonal space group P63cm, with lattice parameters a = 8.43 A and c = 6.52 A. The remaining Mn2+ ions are intercalated within the interlayer 24-atom void center sites to maintain charge balance, and constitute an Mn–NO3 column along the c-axis. The Mn2+-intercalated PTI·NO3 structure exhibits Curie paramagnetism, with a negative Weiss temperature. The present study reports the bulk synthesis of a well-characterized, crystalline, graphitic carbon nitride containing magnetic transition metal (TM) ions, that has potential applications in carbon-based magnetic materials and catalysis.

We present a model compound for the $S=2$ antiferromagnetic (AF) spin chain composed of the salt ($o$-MePy-$\mathrm{V}){\mathrm{FeCl}}_{4}$. Ab initio molecular-orbital calculations indicate the formation of a partially stacked two-dimensional (2D) spin model comprising five types of exchange interactions between $S=1/2$ and $S=5/2$ spins, which locate on verdazyl radical and Fe ion, respectively. The magnetic properties of the synthesized crystals indicate that the dominant interaction between the $S=1/2$ and $S=5/2$ spins stabilizes an $S=2$ spin in the low-temperature region, and an effective $S=2$ AF chain is formed for $T\ensuremath{\ll}10$ K and $Hl4$ T. We explain the magnetization curve and electron-spin-resonance modes quantitatively based on the $S=2$ AF chain. At higher fields above quantitatively 4 T, the magnetization curve assumes two-thirds of the full saturation value for fields between 4 and 20 T, and approaches saturation at $\ensuremath{\sim}40$ T. The spin model in the high-field region can be considered as a quasi-2D $S=1/2$ honeycomb lattice under an effective internal field caused by the fully polarized $S=5/2$ spin.

We report on the experimental results of magnetic susceptibility, specific heat, electron spin resonance (ESR), and high-field magnetization measurements on a polycrystalline sample of the spin-$1/2$ distorted honeycomb-lattice antiferromagnet Cu$_2$(pymca)$_3$(ClO$_4$). Magnetic susceptibility shows a broad peak at about 25~K, which is typical of a low dimensional antiferromagnet, and no long range magnetic order is observed down to 0.6~K in the specific heat measurements. Magnetization curve up to 70~T at 1.4~K shows triple stepwise jumps. Assuming three different exchange bonds $J_{\rm A}$, $J_{\rm B}$ and $J_{\rm C}$ from the structure, the calculated magnetization curve reproduces the observed one when $J_{\rm A}/k_{\rm B} = 43.7~{\rm K}$, $J_{\rm B}/J_{\rm A} = 1$ and $J_{\rm C}/J_{\rm A} = 0.2$ except the magnetization near 70~T, where the observed magnetization indicates another step while the calculated magnetization becomes saturated. The relationship between magnetization plateaus and exchange bonds is discussed based on the numerical calculations., Comment: 5 pages, 5 figures

Exotic spin-multipolar ordering in spin transition metal insulators has so far eluded unambiguous experimental observation. A less studied, but perhaps more feasible fingerprint of multipole character emerges in the excitation spectrum in the form of quadrupolar transitions. Such multipolar excitations are desirable as they can be manipulated with the use of light or electric field and can be captured by means of conventional experimental techniques. Here we study single crystals of multiferroic ${\mathrm{Sr}}_{2}{\mathrm{CoGe}}_{2}{\mathrm{O}}_{7}$ and observe a two-magnon spin excitation appearing above the saturation magnetic field in electron spin resonance (ESR) spectra. Our analysis of the selection rules reveals that this spin excitation mode does not couple to the magnetic component of the light, but it is excited by the electric field only, in full agreement with the theoretical calculations. Due to the nearly isotropic nature of ${\mathrm{Sr}}_{2}{\mathrm{CoGe}}_{2}{\mathrm{O}}_{7}$, we identify this excitation as a purely spin-quadrupolar two-magnon mode.

We have performed electron spin resonance (ESR) measurements in the low temperature magnetic-ordered state of polycrystalline samples of CdYb2S4. This material is one of the rare-earth spinel compounds in which Yb3+ ions form the pyrochlore lattice, and consequently, CdYb2S4 possesses anomalous properties caused by geometrical frustration and anisotropic terms. Some ESR signals have been detected, and their resonance fields are well-fitted by linear lines in the frequency vs. magnetic-field plane. One of the ESR modes appears to intersect the origin of this plane, suggesting a nearly gapless feature in the magnetically ordered state of this material. Two additional ESR modes appear above H c = 2.6 T, indicating that there is a field-induced phase transition at H c. Given the nearly gapless feature of CdYb2S4, we expect that the ground state of CdYb2S4 must be either the Palmer–Chalker state or the ψ 2 state.

Recent theories have revealed topological differences between one-dimensional (1D) Heisenberg antiferromagnets (HAFs) with odd and even integer spins ( S ). With this renewed interest, we have investigated the low-field magnetic susceptibility, specific heat, and high-field magnetization of single-crystal samples of MnCl 3 (bpy), bpy=2,2t-bipyridine, which is regarded as an S = 2 quasi-1D HAF. With the magnetic field oriented along the a*, b and c directions, the magnetic susceptibilities possess broad maxima around 100K. When the magnetic field is parallel to the b -axis, a sharp peak at 11K is observed in the magnetic susceptibility, while a smaller feature is detected in the specific heat, indicating a transition to long-range antiferromagnetic order. At 1.7K, the high-field magnetization curve along the c -axis shows a spin-flop transition, while the responses in the other directions show monotonic increases. These experimental findings confirm that MnCl 3 (bpy) is not an ideal model system to study the S =2 Haldane phase.

We investigate the magnetic torque and magnetoresistance (MR) responses in oblique magnetic fields in micrometer-sized specimens of the hexagonal chiral magnetic crystal ${\mathrm{CrNb}}_{3}{\mathrm{S}}_{6}$. The results exhibit hysteresis over a wide range of applied field angles, while reversible behavior appears only when the magnetic field is closely aligned to the helical axis of the crystal. Stepwise changes of the magnetic torque and MR detected in the hysteresis region indicate the existence of chiral solitons in the oblique magnetic fields. A magnetic phase diagram is derived from the experimental results, and the stability of the chiral magnetic phases, such as the chiral soliton lattice and chiral conical phase, and the nature of the phase transition between them are discussed.

We observe a disappearance of the 1/3 magnetization plateau and a striking change of the magnetic configuration under a moderate doping of the model triangular antiferromagnet RbFe(MoO4)2. The reason is an effective lifting of degeneracy of mean-field ground states by a random potential of impurities, which compensates, in the low-temperature limit, the fluctuation contribution to free energy. These results provide a direct experimental confirmation of the fluctuation origin of the ground state in a real frustrated system. The change of the ground state to a least collinear configuration reveals an effective positive biquadratic exchange provided by the structural disorder. On heating, doped samples regain the structure of a pure compound, thus allowing for an investigation of the remarkable competition between thermal and structural disorder.