Sm Moments Research Articles

Electronic structure along Sm[formula omitted]Co[formula omitted]Ge[formula omitted] twin boundaries

Ln2Co3Ge5 (Ln = lanthanide) intermetallics possess intriguing electronic and magnetic properties. The compound Sm2Co3Ge5 exhibits antiferromagnetic ordering coupled with a magnetic moment that exceeds the theoretical moment of trivalent Sm suggesting a magnetic contribution from Co. Twinning is observed in Sn flux-grown monoclinic Sm2Co3Ge5 along (100) planes. While the influence of twin boundaries on superconducting oxides and 2D-materials is well-studied, its effects on bulk lanthanide-based intermetallics are rarely explored. Using monochromated electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (TEM), we investigate the impact of twin domains on the local strain and electronic structure of Sm2Co3Ge5. The boundaries between twinned domains primarily exhibit shear strain and have a constant oxidation state, but fine structure emerges in the Co L2,3 edges at twin boundaries, indicative of 3d-electron hybridization and occupation of states not present in bulk grain spectra. These findings provide insights into tuning the bulk properties of lanthanide-transition metal systems with complex magnetism.

Magnetic properties versus interface density in rigid-exchange-coupled amorphous multilayers with induced uniaxial anisotropy

We demonstrate the possibility to tune the saturation magnetization, coercivity, and uniaxial in-plane anisotropy constant in amorphous bilayers and multilayers of Co85(Al70Zr30)15 and Sm11Co82Ti7 through the interface density. From magnetometry and x-ray circular dichroism (XMCD) measurements, we conclude that the easy-axis coercivity μ0Hc increases four times when the number of bilayer repetitions, N, increases from 1 to 10 within a constant total sample thickness of 20 nm. At the same time, the anisotropy constant Ku also increases by a factor four, whereas the saturation magnetization Ms decreases slightly. The Co spin and orbital moments, ms and ml, are found to be approximately constant within the sample series. The average total Co moment is only 0.8–0.9 μB/atom, but the ml/ms ratio is strongly enhanced compared to pure Co. Magnetization curves extracted from XMCD measurements show that the Co and Sm moments are ferromagnetically coupled for all samples.

Magnetotransport as a probe for the interplay between Sm and Fe magnetism in SmFeAsO

The complex magnetic ordering of parent compounds of most unconventional superconductors is crucial for the understanding of high-temperature superconductivity (SC). Within this framework, we have performed temperature-dependent magnetotransport experiments on a single crystal of SmFeAsO, a parent compound of iron pnictide superconductors. We observe multiple features in the measured transport properties at temperatures below the antiferromagnetic (AFM) ordering of Sm, , which evolve with in-plane magnetic field, suggesting a rich variety of metamagnetic transitions never before observed in this compound. Considering that transport mainly involves Fe d orbitals at the Fermi level, these findings suggest that the features originate from magnetic transitions of the Fe moments sublattice, which in turn may be induced by magnetic transitions of the Sm moments sublattice via the interaction between Fe and Sm moments. We outline a possible scenario in which the Fe moments, strongly affected by the Sm ordering below T NSm, reorder to an in-plane canted AFM structure, which is washed out by the application of an in-plane magnetic field up to 9 T. Our work shows that transport properties are a valuable tool for investigating magnetic ordering in iron pnictide parent compounds, where the interplay of magnetism and SC is believed to be the origin of high-temperature SC.

Multimodal analysis of Zr substitution effects on magnetic and crystallographic properties in (Sm1−xZrx)(Fe0.8Co0.2)12 compounds with ThMn12 structure

SmFe12-based compounds containing Zr atoms have been recognized as candidates for novel high-performance permanent magnet materials with a high saturation magnetization. Partial substitution of Sm with Zr in (Sm1−xZrx)(Fe0.8Co0.2)12 has been known to enhance the magnetization of the compound. This study focused on (Sm1−xZrx)(Fe0.8Co0.2)12 single-crystalline films to evaluate the effects of Zr substitution for Sm on their structural and magnetic properties via systematic multimodal analysis. X-ray absorption fine structure (XAFS) and scanning transmission electron microscopy indicated a selective occupation of the Sm site by Zr atoms without disturbing the Fe sublattices. The chemical shift in the Zr-K edge XAFS spectra suggested electron transfer from Zr to the Fe band. Soft X-ray magnetic circular dichroism analysis proved that the magnetic moment of Sm was two orders of magnitude smaller than the magnetic moments of Fe and Co, and its contribution to the total magnetization was negligible. The partial substitution of Sm with Zr resulted in a volumetric expansion and c-axis length elongation despite Zr having a smaller atomic radius, which is unique to (Sm1−xZrx)(Fe0.8Co0.2)12 without structure-stabilizing elements such as Ti, V, and Si. This anisotropic expansion is explained by an increase in the magnetic moment and magnetic interactions in the Fe8f site, which is induced by the electron transfer from Zr to Fe8f atoms. Thus, we conclude that the electron transfer from Zr to the Fe8f atoms principally drives magnetization enhancement in (Sm1−xZrx)(Fe0.8Co0.2)12 single-crystalline films.

Magnetic order and magnetic properties of the oxygen deficient SmBaMn2O5 layered perovskite

Magnetism in SmBaMn2O5 was investigated on a single crystal by magnetic and neutron diffraction measurements. This is an oxygen deficient perovskite with a layered ordering of Sm and Ba cations. Mn atoms are coordinated with five oxygens forming a square pyramid and they are ordered in a checkerboard pattern of expanded-compressed pyramids in the ab-plane. The neutron diffraction study revealed a ferrimagnetic ordering of Mn moments below TN=134 K. Macroscopic measurements reveal a very anisotropic behavior. Measurements with the external magnetic field parallel (M||c) and perpendicular (M⊥c) to the c-axis confirm that this is the easy axis above 10 K. Below this temperature, the Sm sublattice begins to polarize and the magnetization M||c decreases while M⊥c experiences a huge increase. This indicates that Sm moments begin to order around 10 K in the ab-plane with a minor component on the c-axis that opposes the overall magnetization from Mn sublattices.

Multiple magnetization reversal and field induced orbital moment switching in intermetallic SmMnSi compound

We report anomalous magnetic reversal (MR)/negative magnetization (NM) state associated with the field induced switching of orbital moment (μLSm) of the Sm atom. This material shows an antiferromagnetic transition at Néel temperature (TN∼240 K) followed by a NM state in between compensation temperatures (T∗ and T∗∗). The MR/NM state vanishes above 12.5 kOe, while T∗ and T∗∗ follow opposite magnetic field dependency in field cooled cooling (FCC) magnetization. In the high field (H>20 kOe), the thermo-magnetization [M(T)] curve produces a mirror like inversion in magnetization within (T∗−T∗∗) with respect to its low field FCC counterpart. Within the NM region, the exchange bias field (HEB) changes its sign across compensation temperatures for suitable field cooling (FC). We estimated a large FC inverse and conventional HEB of 8 and −4.8 kOe at T=130 K. Furthermore, the magnetic entropy change (ΔSm) and adiabatic temperature change (ΔTad) calculated from the specific heat [Cp(T,H)] measurements also show sign reversal at T∗∗. These unusual behaviors are explained in terms of field induced switching of μLSm, which is oppositely coupled to the spin moment of Sm (μSSm), Mn–Mn/Sm exchange interactions, and polarized conduction electron moment (μSCEP). Additionally, Cp(T,H) exhibit Schottky anomaly around 3 K due to Zeeman splitting of Sm energy levels.

Experimental Observation of Monoclinic Distortion in the Insulating Regime of SmNiO3 by Synchrotron X-ray Diffraction.

RNiO3 (R = rare-earth element) perovskite materials are well-known to exhibit characteristic metal-insulator transitions. The structural distortion increases as the R member becomes smaller along the series. For SmNiO3, a high-hydrostatic-pressure preparation procedure, yielding samples with much enhanced crystalline quality, combined with the extremely high angular resolution of synchrotron X-ray diffraction (XRD) allowed us to identify a monoclinic phase in the insulating regime (below the metal-insulator transition temperature (TMI) of 127 °C), defined in the space group P21/n. This monoclinic symmetry had not been demonstrated directly using nonresonant XRD or neutron diffraction. This has important repercussions on the electronic nature of this material since the monoclinic structure contains two inequivalent Ni positions, implying a charge disproportionation phenomenon. In the metallic regime (above TMI), the standard orthorhombic Pbnm structure is observed. Therefore, there is a coupled structural and electronic transition, as happens for the very small rare-earth compounds of the RNiO3 perovskite series. Across TMI there is a dramatic rearrangement of the lattice parameters, degree of tilting, and distortion of the NiO6 octahedra, showing the convergence of the Ni-O bond lengths upon entering the metallic phase. Brown's valence analysis of the different elements agrees with other reported values in the literature, matching with bond and charge disproportionation models. By magnetization measurements a Néel temperature (TN) corresponding to the antiferromagnetic ordering of the Ni moments is identified at TN= 220 K, whereas Sm moments experience long-range ordering below 36 K.

Probing magnetic order and disorder in the one-dimensional molecular spin chains CuF2(pyz) and [Ln(hfac)3(boaDTDA)]n (Ln = Sm, La) using implanted muons

We present the results of muon-spin relaxation (SR) measurements on antiferromagnetic and ferromagnetic spin chains. In antiferromagnetic CuF2(pyz) we identify a transition to long range magnetic order taking place at K, allowing us to estimate a ratio with the intrachain exchange of and the ratio of interchain to intrachain exchange coupling as . The ferromagnetic chain [Sm(hfac)3(boaDTDA)]n undergoes an ordering transition at K, seen via a broad freezing of dynamic fluctuations on the muon (microsecond) timescale and implying . The ordered radical moment continues to fluctuate on this timescale down to 0.3 K, while the Sm moments remain disordered. In contrast, the radical spins in [La(hfac)3(boaDTDA)]n remain magnetically disordered down to T = 0.1 K suggesting .

Nanogranular, Melt-Spun Intermetallic Compound SmNi: Magnetocaloric Effect and Large Coercivity

Rare earth intermetallic compound SmNi has been synthesized by melt spinning under argon atmosphere. This sample crystallizes in orthorhombic structure (CrB-type, Space group Cmcm, No. 63) and exhibits texture and nanograin formation. The average crystallite size calculated from powder X-ray diffraction data is ~17 nm. Melt-spun SmNi orders ferromagnetically at ~47 K ( $T_{C}$ ) and this is close to $T_{C}$ of the arc-melted sample. The saturation magnetization value at 10 K is only ~0.24 $\mu _{B}$ /f.u., whereas a large coercivity of ~24 kOe is observed. Isothermal magnetic entropy change, $\Delta S_{m}$ , shows a maximum at $T_{C}$ , of ~−1 J/kg $\cdot$ K, for 50 kOe field change with a relative cooling power value of ~10 J/kg. Small moment of Sm, strong magnetocrystalline anisotropy, complex magnetic structure, and nanograin size all influence the magnetism of melt-spun SmNi.

Magnetic structures and magnetic phase transitions in RMn2Si2

Magnetic properties of the LaMn2Si2 and La0.6R0.4Mn2Si2 (R = Sm, Tb, Gd) compounds with layered ThCr2Si2-type structure have been studied using quasi-single-crystalline and polycrystalline samples. Substitution of the R atoms for La decreases the interatomic distances and changes the ordering of the Mn sublattice from ferromagnetic to antiferromagnetic. Magnetic structure of the substituted compounds has been found to depend on the anisotropy of R ions. The Sm moments are oriented in the basal plane and weakly coupled with the Mn sublattice. For R = Tb, frustrations prevent the formation of long-range magnetic ordering in Tb sublattice. For the system with Gd, the antiferromagnetic Mn-Mn and Gd-Mn interactions lead to a change of magnetic anisotropy from the easy-axis to the easy-plane type.

Ferromagnetic quantum criticality in Sm1−xLaxNiC2 ( x=0.85 , 0.92, and 0.96)

We report $\ensuremath{\mu}\mathrm{SR}$ experiments on the ternary compounds ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{NiC}}_{2}$ ($x=0.85$, 0.92, and 0.96), crossing from a ferromagnetic to a superconducting phase. Zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements of the ferromagnetic sample ($x=0.85$) unveil a glassylike character of the ferromagnetically ordered state. At the putative quantum critical compound ($x$ = 0.92), fluctuations of the Sm moments slow down below 2 K and remain dynamic down to 30 mK, showing persisting spin dynamics. Moreover, we find a time-field scaling ($t/{H}^{\ensuremath{\gamma}}$) of the $\ensuremath{\mu}\mathrm{SR}$ asymmetry function, evidencing quantum critical fluctuations. As to the superconducting material ($x$ = 0.96), the muon spin-relaxation rate displays a $\ensuremath{\lambda}$-like peak at $T=250$ mK, indicating the coexistence of weak magnetism and filamentary superconductivity. Our results demonstrate that ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{NiC}}_{2}$ constitutes a model system for studying a ferromagnetic quantum critical point tuned by chemical pressure.

Exploring the Magnetic Susceptibility of a Haldane Compound Sm $$_{2}$$ 2 BaNiO $$_{5}$$ 5 : Optical Spectroscopy of Sm $$^{3+}$$ 3 + Kramers Doublets

An optical spectroscopic study of quasi-Haldane chain nickelate Sm\(_{2}\)BaNiO\(_{5}\) is presented. A temperature-dependent splitting of the ground-state Kramers doublet of the Sm\(^{3+}\) ion due to an antiferromagnetic ordering at \(T_{N}\) = 55 K has been obtained experimentally and used to calculate the Schottky-type anomaly in magnetic susceptibility. The value of the magnetic moment of Sm\(^{3+}\) ion at zero temperature has been estimated within the model of the ground doublet. One-dimensional magnetic behavior of the nickel subsystem is emphasized.

Robust ferromagnetism in the compressed permanent magnetSm2Co17

The compound ${\mathrm{Sm}}_{2}{\mathrm{Co}}_{17}$ displays magnetic properties amenable to permanent magnet applications owing to both the $3d$ electrons of Co and the $4f$ electrons of Sm. The long-standing description of the magnetic interactions between the Sm and Co ions implies a truly ferromagnetic configuration, but some recent calculations challenge this axiom, suggesting at least a propensity for ferrimagnetic behavior. We have used high-pressure synchrotron x-ray techniques to characterize the magnetic and structural properties of ${\mathrm{Sm}}_{2}{\mathrm{Co}}_{17}$ to reveal a robust ferromagnetic state. The local Sm moment is at most weakly affected by compression, and the ordered moments show a surprising resilience to volumetric compressions of nearly 20%. Density functional theory calculations echo the magnetic robustness of ${\mathrm{Sm}}_{2}{\mathrm{Co}}_{17}$.

Order Having Disorder in a New Samarium Compound

An atypical magnetic order was discovered in single crystals of the new Sm compound SmPt2Si2. The bulk measurements indicate that the majority of the Sm moments remains disordered in the magnetically ordered phase.

Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution LaxSm1–xCrO3

A new mixed rare-earth orthochromite series, LaxSm1-xCrO3, prepared through single-step hydrothermal synthesis is reported. Solid solutions (x = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal treatment of amorphous mixed-metal hydroxides at 370 °C for 48 h. Transmission electron microscopy (TEM) reveals the formation of highly crystalline particles with dendritic-like morphologies. Rietveld refinements against high-resolution powder X-ray diffraction (PXRD) data show that the distorted perovskite structures are described by the orthorhombic space group Pnma over the full composition range. Unit cell volumes and Cr-O-Cr bond angles decrease monotonically with increasing samarium content, consistent with the presence of the smaller lanthanide in the structure. Raman spectroscopy confirms the formation of solid solutions, the degree of their structural distortion. With the aid of shell-model calculations the complex mixing of Raman modes below 250 cm(-1) is clarified. Magnetometry as a function of temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr(3+) spins with weak ferromagnetic component at Néel temperatures (TN) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr(3+) and Sm(3+) ions are examined with enhanced susceptibilities below TN due to polarization of Sm(3+) moments. At low temperatures the Cr(3+) sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility.

The influence of substitution of Mn by Fe and Co on magnetocaloric effect and magnetoresistance properties of SmMn2Ge2

Magnetocaloric and magnetoresistance properties of SmMn2−xFexGe2 (x=0.05 and 0.10) and SmMn2−xCoxGe2 (x=0.05 and 0.15) compounds have been studied by magnetic and resistance measurements in the temperature range between 30 and 350K. All compounds exhibit metamagnetic transition from antiferromagnetism to ferromagnetism around the Sm moments ferromagnetic ordering temperature-TSm and Mn moments antiferromagnetic ordering temperature-TN1. The magnetic entropy changes of these compounds are estimated from the Maxwell equation, Maxwell Clausius Clapeyron equation, Landau theory and mean-field theory. The maximum magnetic entropy change values of SmMn1.90Fe0.10Ge2 and SmMn1.85Co0.15Ge2 compounds are −8.1Jkg−1K−1 and −5.1Jkg−1K−1 in a magnetic field change of 5T, respectively. These compounds show negative magnetoresistance around the magnetic phase transition temperatures. The magnetoresistance value of SmMn1.95Fe0.05Ge2 is −23% at TSm which is bigger than the magnetoresistance value of SmMn2Ge2 (−15%).

Strong coupling of Sm and Fe magnetism in SmFeAsO as revealed by magnetic x-ray scattering

The magnetic structures adopted by the Fe and Sm sublattices in SmFeAsO have been investigated using element specific x-ray resonant and non-resonant magnetic scattering techniques. Between 110 and 5 K, the Sm and Fe moments are aligned along the c and a directions, respectively according to the same magnetic representation $\Gamma_{5}$ and the same propagation vector (1, 0, 0.5). Below 5 K, magnetic order of both sublattices change to a different magnetic structure and the Sm moments reorder in a magnetic unit cell equal to the chemical unit cell. Modeling of the temperature dependence for the Sm sublattice as well as a change in the magnetic structure below 5 K provide a clear evidence of a surprisingly strong coupling between the two sublattices, and indicate the need to include anisotropic exchange interactions in models of SmFeAsO and related compounds.

Structure and magnetic property of CoFe 2− xSm xO 4 ( x = 0–0.2) nanofibers prepared by sol–gel route

CoFe 2− x Sm x O 4 ( x = 0–0.2) nanofibers with diameters about 100–300 nm have been prepared using the organic gel-thermal decomposition method. The composition, structure and magnetic properties of the CoFe 2− x Sm x O 4 nanofibers were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, inductive coupling plasma mass analyzer and vibrating sample magnetometer. The CoFe 2− x Sm x O 4 ( x = 0–0.2) nanofibers obtained at 500–700 °C are of a single spinel structure. But, at 800 °C with a relatively high Sm content of 0.15–0.2 the spinel CoFe 2− x Sm x O 4 ferrite is unstable and the second phase of perovskite SmFeO 3 occurs. The crystalline grain sizes of the CoFe 2− x Sm x O 4 nanofibers decrease with Sm contents, while increase with the calcination temperature. This grain reduction effect of the Sm 3+ ions doping is largely owing to the lattice strain and stress induced by the substitution of Fe 3+ ions with larger Sm 3+ ions in the ferrite. The saturation magnetization and coercivity increase with the crystallite size in the range of 8.8–57.3 nm, while decrease with the Sm content from 0 to 0.2 owing to a smaller magnetic moment of Sm 3+ ions. The perovskite SmFeO 3 in the composite nanofibers may contribute to a high coercivity due to the interface pinning, lattice distortion and stress in the ferrite grain boundary fixing and hindering the domain wall motion.

Magnetocapacitive effects in the NéelN-type ferrimagnetSmMnO3

Magnetocapacitive effects were investigated for N\'eel's $N$-type ferrimagnetic ${\text{SmMnO}}_{3}$, which shows temperature-induced magnetization reversal at the compensation temperature $({T}_{\text{comp}}=9.4\text{ }\text{K})$ in a low magnetic field $B$ $(l\ensuremath{\sim}1\text{ }\text{T})$. When higher $B$ is applied, remarkable anomalies were observed in the temperature profiles of magnetization, dielectric constant, and dielectric relaxation time around ${T}_{\text{comp}}$. These coupled field-induced anomalies give rise to striking magnetocapacitance and could be attributed to simultaneous reversals of ferrimagnetically coupled Sm and Mn moments. In addition, peculiar cooling-field dependent asymmetric magnetocapacitance was observed at ${T}_{\text{comp}}$.

Coexistence of magnetism and superconductivity in the hole doped FeAs-based superconducting compound

Abstract The magnetic and superconducting properties of the Sm-doped FeAs-based superconducting compound were investigated under wide ranges of temperature and magnetic field. After the systematical magnetic ion substitution, the superconducting transition temperature decreases with increasing magnetic moment. The hysteresis loop of the La 0.87− x Sm x Sr 0.13 FeAsO sample shows a superconducting hysteresis and a paramagnetic background signal. The paramagnetic signal is mainly attributed to the Sm moments. The experiment demonstrates that the coexistence of magnetism and superconductivity in the hole doped FeAs-based superconducting compounds is possible. Unlike the electron doped FeAs-based superconducting compounds SmFeAsOF, the hole doped superconductivity is degraded by the substitution of La by Sm. The hole-doped and electron-doped sides are not symmetric.