Short-range Magnetic Correlations Research Articles

Canted antiferromagnetic phases in the candidate layered Weyl material EuMnSb2

${\mathrm{EuMnSb}}_{2}$ is a candidate topological material which can be tuned towards a Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM) phases. The coupling of bands dominated by pure Sb layers hosting topological fermions to Mn and Eu magnetic states provides a potential path to tune the topological properties. Here we present single-crystal neutron diffraction, magnetization, and heat-capacity data as well as polycrystalline $^{151}\mathrm{Eu}$ M\"ossbauer data which show that three AFM phases exist as a function of temperature, and we present a detailed analysis of the magnetic structure in each phase. The Mn magnetic sublattice orders into a C-type AFM structure below ${T}_{{\text{N}}_{\text{Mn}}}=323(1)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ with the ordered Mn magnetic moment ${\mathbf{\ensuremath{\mu}}}_{\mathbit{\text{Mn}}}$ lying perpendicular to the layers. AFM ordering of the Eu sublattice occurs below ${T}_{{\text{N}}_{\text{Eu1}}}=23(1)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ with the ordered Eu magnetic moment ${\mathbit{\ensuremath{\mu}}}_{\text{Eu}}$ canted away from the layer normal and ${\mathbf{\ensuremath{\mu}}}_{\mathbit{\text{Mn}}}$ retaining its higher temperature order. ${\mathbit{\ensuremath{\mu}}}_{\text{Eu}}$ is ferromagnetically aligned within each Eu layer but exhibits a complicated AFM layer stacking. Both of these higher-temperature phases are described by magnetic space group (MSG) $P{n}^{\ensuremath{'}}{m}^{\ensuremath{'}}{a}^{\ensuremath{'}}$ with the chemical and magnetic unit cells having the same dimensions. Cooling below ${T}_{{\text{N}}_{\text{Eu2}}}=9(1)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ reveals a third AFM phase where ${\mathbf{\ensuremath{\mu}}}_{\mathbit{\text{Mn}}}$ remains unchanged but ${\mathbit{\ensuremath{\mu}}}_{\text{Eu}}$ develops an additional substantial in-plane canting. This phase has MSG $P11\frac{{2}_{1}}{{a}^{\ensuremath{'}}}$. We also find some evidence of short-range magnetic correlations associated with the Eu between $12\phantom{\rule{4pt}{0ex}}\text{K}\ensuremath{\lesssim}T\ensuremath{\lesssim}30\phantom{\rule{4pt}{0ex}}\text{K}$. Using the determined magnetic structures, we postulate the signs of nearest-neighbor intralayer and interlayer exchange constants and the magnetic anisotropy within a general Heisenberg model. We then discuss implications of the various AFM states in ${\mathrm{EuMnSb}}_{2}$ and their potential for tuning topological properties.

Short range spin-spin correlation, spin-phonon coupling and isostructural phase transition in hetero-tri-spin 3d-5d-4f double perovskite Sm2CoIrO6

The low temperature vibrational properties of Ir-based double perovskite Sm2CoIrO6 (SMCO) has been investigated by Raman scattering to gain an insight into the mechanism of the isostructural phase transition present at ​∼ ​104 ​K under ambient atmospheric pressure. The temperature dependent Raman study also reveals the development of short range magnetic correlation above the long range magnetic ordering. From the comprehensive temperature dependent study, it is found that the system before entering the state of long range ferrimagnetic ordering, undergoes from a state of conventional paramagantism to a state of correlated paramagnetism. The interaction of the phonons with the underlying magnetic degrees of freedom has been studied for the most prominent mode in terms of Fano asymmetric parameter. The strong spin-phonon coupling below the global ordering temperature results in a significant softening of the phonon modes involving stretching and/or vibration of the (Co/Ir)O6 octahedra.

Relaxor ferroelectric nature and magnetoelectric coupling of the one dimensional frustrated Ca3CoMnO6

The typical ↑↑↓↓ spin order of the one-dimensional frustrated Ca 3 CoMnO 6 breaks the inversion symmetry and results in the ferroelectricity. But the previous calculations predict a much larger ferroelectric polarization than the experimental observation. To comprehend the divergence, Ca 3 CoMnO 6 ceramics were prepared and the magnetic, dielectric properties were studied. In accordance with the formation of short range magnetic correlation, around the antiferromagnetic transition temperature T N the Ca 3 CoMnO 6 ceramics present weak relaxor ferroelectric nature. It implies the existence of polar nanoregions. Thus, the destruction of long range ferroelectric order and the formed polar nanoregions should be responsible for the suppressed macroscopic ferroelectric polarization. The activation energy and static freezing temperature of Ca 3 CoMnO 6 are also calculated. The obtained values are E a = 6.31 × 10 −3 eV and T f = 1.5 K, respectively. Both of them are lower about two orders of magnitude than the conventional relaxor ferroelectrics. Magnetic field dependent dielectric permittivity manifests the large magnetodielectric coupling of Ca 3 CoMnO 6 . Under the application of field of 7 T, the dielectric permittivity reduces by about 10%. • Around the antiferromagnetic transition temperature T N the Ca 3 CoMnO 6 ceramics present weak relaxor ferroelectric nature. • The Ca 3 CoMnO 6 ceramicspresent weak relaxor ferroelectric nature. • Magnetic field dependent dielectric permittivity manifests the largemagnetodielectric coupling.

Frustration, strain and phase co-existence in the mixed valent hexagonal iridate Ba3NaIr2O9

Using detailed synchrotron diffraction, magnetization, thermodynamic and transport measurements, we investigate the relationship between the mixed valence of Ir, lattice strain and the resultant structural and magnetic ground states in the geometrically frustrated triple perovskite iridate Ba3NaIr2O9. We observe a complex interplay between lattice strain and structural phase co-existence, which is typically not observed in this family of compounds. The low temperature magnetic ground state is characterized by the absence of long-range magnetic order, and points towards the condensation of a cluster glass state from an extended regime of short range magnetic correlations.

Magnetic correlations in infinite-layer nickelates: An experimental and theoretical multimethod study

We report a comprehensive study of magnetic correlations in ${\mathrm{LaNiO}}_{2}$, a parent compound of the recently discovered family of infinite-layer (IL) nickelate superconductors, using multiple experimental and theoretical methods. Our specific heat, muon-spin rotation ($\ensuremath{\mu}\mathrm{SR}$), and magnetic susceptibility measurements on polycrystalline ${\mathrm{LaNiO}}_{2}$ show that long-range magnetic order remains absent down to 2 K. Nevertheless, we detect residual entropy in the low-temperature specific heat, which is compatible with a model fit that includes paramagnon excitations. The $\ensuremath{\mu}\mathrm{SR}$ and low-field static and dynamic magnetic susceptibility measurements indicate the presence of short-range magnetic correlations and glassy spin dynamics, which we attribute to local oxygen nonstoichiometry in the average infinite-layer crystal structure. This glassy behavior can be suppressed in strong external fields, allowing us to extract the intrinsic paramagnetic susceptibility. Remarkably, we find that the intrinsic susceptibility shows non-Curie-Weiss behavior at high temperatures, in analogy to doped cuprates that possess robust nonlocal spin fluctuations. The distinct temperature dependence of the intrinsic susceptibility of ${\mathrm{LaNiO}}_{2}$ can be theoretically understood by a multimethod study of the single-band Hubbard model in which we apply complementary cutting-edge quantum many-body techniques (dynamical mean-field theory, cellular dynamical mean-field theory, and the dynamical vertex approximation) to investigate the influence of both short- and long-ranged correlations. Our results suggest a profound analogy between the magnetic correlations in parent (undoped) IL nickelates and doped cuprates.

Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the N\'eel temperature $T_{\mathrm{N}}$ = 307 K. The magnetic correlation length in the paramagnetic state is significantly longer along the crystallographic $c$ axis than within the $ab$ plane, pointing to anisotropic magnetic interactions. Ab initio calculations of the spin-spin correlations using density functional theory in the disordered local moment approach reproduce this result with quantitative accuracy. These findings constitute the first real-space picture of short-range spin correlations in a magnetically enhanced thermoelectric and inform future efforts to optimize thermoelectric performance by magnetic means.

Magnetic terahertz resonances above the Néel temperature in the frustrated kagome antiferromagnet averievite

Time-domain magneto-THz spectroscopy is utilized to study the frustrated magnet averievite ${\mathrm{Cu}}_{5\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{V}}_{2}{\mathrm{O}}_{10}$(CsCl). Pronounced THz resonances are observed in unsubstituted samples ($x=0$) when cooling below the onset of short-range magnetic correlations. The influence of external magnetic effects confirms the magnetic origin of these resonances. Increasing Zn substitution suppresses the resonances, as frustration effects dominate, reflecting the nonmagnetic phases for $x>0.25$ compounds. The temperature evolution of the THz spectra is complemented with electron spin resonance spectroscopy. This comparison allows a direct probe of the different contributions from magnetic order, frustration, and structural properties in the phase diagram of averievite. Our results illustrate the effect of magnetic interactions in THz spectra of frustrated magnets.

Synthesis and Physical Properties of Iridium-Based Sulfide Ca1−xIr4S6(S2) [x = 0.23–0.33

We present the synthesis and characterization of the iridium-based sulfide Ca1−xIr4S6(S2). Quality and phase analysis were conducted by means of energy-dispersive X-ray spectroscopy (EDXS) and powder X-ray diffraction (XRD) techniques. Structure analysis reveals a monoclinic symmetry with the space group C 1 2/m 1 (No. 12), with the lattice constants a = 15.030 (3) Å, b = 3.5747 (5) Å and c = 10.4572 (18) Å. Both X-ray diffraction and EDXS suggest an off-stoichiometry of calcium, leading to the empirical composition Ca1−xIr4.0S6(S2) [x = 0.23–0.33]. Transport measurements show metallic behavior of the compound in the whole range of measured temperatures. Magnetic measurements down to 1.8 K show no long range order, and Curie–Weiss analysis yields θCW = −31.4 K, suggesting that the compound undergoes a magnetic state with short range magnetic correlations. We supplement our study with calculations of the band structure in the framework of the density functional theory.

Singular magnetic dilution behavior in a quasicrystal approximant

We report the effect of magnetic dilution on the physical properties of $({\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}){\mathrm{Cd}}_{6}$ approximant crystals (ACs), close siblings of their corresponding quasicrystal (QC). Compared to the pure system ${\mathrm{GdCd}}_{6}$, we observe remarkable changes in the thermodynamic and magnetic bulk properties near and below the static-ordering temperatures from diluting the magnetic Gd atoms with nonmagnetic Y atoms by only 1--3% $(x=0.01--0.03)$. On the other hand, the corresponding QC system exhibits a monotonic change in its spin-glass behavior upon the magnetic dilution. We discuss the origin of the magnetic-dilution behavior in the present AC system in terms of possible magnetic frustration and short-range magnetic correlation that can be linked to its peculiar structure.

Chemical tuning of magnetic anisotropy and correlations in Ni1−xFexPS3

We report the temperature and composition dependence of static magnetic susceptibility and Raman spectroscopic measurements on van der Waals antiferromagnets ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PS}}_{3}$. The end members ${\mathrm{NiPS}}_{3}$ and ${\mathrm{FePS}}_{3}$ feature $XY$- and Ising-like magnetism, respectively, enabling chemical tuning of magnetic anisotropy and spin correlations. ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{PS}}_{3}$ shows a turnover from the $XY$ to Ising anisotropy through $x\ensuremath{\approx}0.1$. Although the $XY$ anisotropy is rapidly suppressed on introducing Fe content, two-magnon scattering evidences the slow repression of short-range magnetic correlations deep inside the Fe-rich side. Counterintuitively, the two-magnon signal undergoes less renormalization of its energy with increasing $x$ despite the larger spin number and enhanced classical magnetism. The disparate static and dynamic magnetic behaviors indicate the emergence of an exotic spin state in alloy van der Waals magnets.

Investigation of spin-phonon coupling and local magnetic properties in magnetoelectric Fe2TeO6

Spin-phonon coupling originated from spin-lattice correlation depends upon different exchange interactions in transition metal oxides containing 3d magnetic ions. Spin-lattice coupling can influence the coupling mechanism in magnetoelectric material. To understand the spin–lattice correlation in inverse trirutile Fe2TeO6 (FTO), magnetic properties and phonon spectra are studied. Signature of short-range magnetic correlation induced by 5/2–5/2 dimeric interaction and magnetic anomaly at 150 K is observed apart from the familiar sharp transition (TN ∼ 210 K) corresponding to long-range order by magnetization and heat capacity measurements. The magnetic transitions and the spin dynamics are further locally probed by muon spin resonance (μSR) measurement in both zero fields (ZF) and longitudinal field (LF) mode. Three dynamically distinct temperature regimes; (i) T > TN, (ii) TN > T > 150 K, and (iii) T < 150 K, are observed. A change in the spin dynamics is realized at 150 K by μSR, though previous studies suggest long-range antiferromagnetic order. The renormalization of phonon frequencies observed in Raman spectra below 210 K suggests the existence of spin-phonon coupling in the material. The coupling strength is quantified as in the range 0.1–1.2 cm−1 following the mean-field and two-spin cluster approximations. We propose that the spin-phonon coupling mediated by the Fe-O2-Fe interbilayer exchange play a significant role in magnetoelectric ME coupling observed in the material.

Magnetic correlations in the triangular antiferromagnet FeGa2S4

The crystal structure and magnetic correlations in triangular antiferromagnet FeGa$_2$S$_4$ are studied by x-ray diffraction, magnetic susceptibility, neutron diffraction and neutron inelastic scattering. We report significant mixing at the cation sites and disentangle magnetic properties dominated by major and minor magnetic sites. The magnetic short-range correlations at 0.77 \AA$^{-1}$ correspond to the major sites and being static at base temperature they evolve into dynamic correlations around 30 - 50 K. The minor sites contribute to the magnetic peak at 0.6 \AA$^{-1}$, which vanishes at 5.5 K. Our analytical studies of triangular lattice models with bilinear and biquadratic terms provide the ratios between exchanges for the proposed ordering vectors. The modelling of the inelastic neutron spectrum within linear spin wave theory results in the set of exchange couplings $J_1=1.7$\,meV, $J_2=0.9$\,meV, $J_3=0.8$\,meV for the bilinear Heisenberg Hamiltonian. However, not all features of the excitation spectrum are explained with this model.

Understanding the short-range magnetic correlations in MnTe through magnetic pair distribution function analysis

Understanding the short-range magnetic correlations in MnTe through magnetic pair distribution function analysis

Absence of long-range magnetic order in lithium-containing honeycombs in the Li–Cr–Sb(Te)–O phases

Li3((LiCr)(Te/Sb))O6 compounds where Cr atoms along with Li and Te or Sb are part of a honeycomb and are studied using magnetic susceptibility, specific heat, x-ray photoelectron spectroscopy and neutron diffraction. The oxides stoichiometries as determined from the neutron diffraction studies are Li4.47Cr0.53TeO6 and Li3.88Cr1.12SbO6 with a stable oxidation state of +3 for Cr. Both the compounds crystallize in space group C2/m with intermixing of cations at the 4g sites leaving the 2a sites preferentially for Te or Sb. Again, the Li+ ions alone predominantly occur in the interlayer sites. Both the compounds show a broad anomaly in specific heat at 8 K, which is robust against 8 T. A corresponding anomaly is absent in the magnetic susceptibility but recovers from its derivative, dχ(T)/dT. We ascertain the magnetic anomaly temperatures (T a ) of Li4.47Cr0.53TeO6 and Li3.88Cr1.12SbO6 as 5.9 K and 6.7 K respectively from specific heat. Although the physical properties indicated a low temperature anomaly, neutron diffraction data did not reveal a magnetic signal or a structural anomaly down to 1.5 K. This rules out a conventional long-range ordered magnetic ground state in either compounds. Combining the results from specific heat, neutron diffraction and electron paramagnetic resonance, we put forth a scenario of depleted honeycomb lattice of Cr3+ with predominant short-range magnetic correlations as the magnetic ground states of the title compounds.

Probing the interplay between lattice dynamics and short-range magnetic correlations in CuGeO3 with femtosecond RIXS

Investigations of magnetically ordered phases on the femtosecond timescale have provided significant insights into the influence of charge and lattice degrees of freedom on the magnetic sub-system. However, short-range magnetic correlations occurring in the absence of long-range order, for example in spin-frustrated systems, are inaccessible to many ultrafast techniques. Here, we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is capable of probing such short-ranged magnetic dynamics in a charge-transfer insulator through the detection of a Zhang–Rice singlet exciton. Utilizing trRIXS measurements at the O K-edge, and in combination with model calculations, we probe the short-range spin correlations in the frustrated spin chain material CuGeO3 following photo-excitation, revealing a strong coupling between the local lattice and spin sub-systems.

Regulation of Cr3+ doping on the defect characteristics and magnetic order in the CuFe1-xCrxO2 ceramics

ABSTRACT The defect characteristic and magnetic properties of CuFe1-x Cr x O2 (x = 0.0–0.4) compounds have been investigated in detail. The results demonstrate that Cr3+ ions enter into the CuFeO2 lattice sites and induce local lattice contraction but do not change the valance state of Cu+ and Fe3+ ions. We calculate the positron annihilation lifetime in the bulk and vacancy defect trapping states by the atomic superposition method in 3 × 3 × 1 CuFeO2 super-cell. Combined with theoretical calculation results, the positron annihilation results indicate that the positrons are mainly annihilated in vacancy clusters in CuFe1-x Cr x O2. The substitution of Cr3+ for Fe3+ ions decreases the open volume and increases the concentration of vacancy defects but does not change the integral defect surroundings at annihilation sites. Magnetization measurements manifest that doping with Cr3+ reduces the antiferromagnetic transition temperature and promotes the formation of short-range magnetic correlation. Meanwhile, the enhanced short-range magnetic correlation in Cr3+-doped CuFeO2 is more readily driven by thermal activation energy and a faster dynamic behavior can be seen in time windows.

Optical magnons with dominant bond-directional exchange interactions in the honeycomb lattice iridate α−Li2IrO3

We have used resonant inelastic x-ray scattering to reveal optical magnons in a honeycomb lattice iridate $\alpha$-Li$_{2}$IrO$_{3}$. The spectrum in the energy region 20-25 meV exhibits momentum dependence, of which energy is highest at the location of the magnetic Bragg peak, ($\textit{h}, \textit{k}$) = ($\pm$0.32, 0), and lowered toward (0, 0) and ($\pm$1, 0). We compare our data with a linear spin-wave theory based on a generic nearest-neighbor spin model. We find that a dominant bond-directional Kitaev interaction of order 20 meV is required to explain the energy scale observed in our study. The observed excitations are understood as stemming from optical magnon modes whose intensity is modulated by a structure factor, resulting in the apparent momentum dependence. We also observed diffuse magnetic scattering arising from the short-range magnetic correlation well above $\textit{T}_{N}$. In contrast to Na$_{2}$IrO$_{3}$, this diffuse scattering lacks the $C_3$ rotational symmetry of the honeycomb lattice, suggesting that the bond anisotropy is far from negligible in $\alpha$-Li$_{2}$IrO$_{3}$.

Successive magnetic ordering in two CoII-ladder metal-organic frameworks

Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds. Here, we report two metal-organic frameworks [CoII(ox)(bphy)•0.1(DMF)•0.1(MeOH)] n ( 1 ) and [CoII3(ox)3(bphy)2(DMF)2] n ( 2 ) comprised of zigzag and necklace CoII-ladders, respectively. Together with a previously reported compound [CoII(ox)(bphy)•0.2(DMF)] n ( 3 ) consisting of spiraling zigzag CoII-ladders, these three compounds provide a good system for comparative structural and magnetic studies. Comprehensive magnetic analysis reveals that the three compounds undergo long-range magnetic ordering at ~2.6 K but exhibit vastly different short-range magnetic correlations: compound 1 shows short-range spin-canted antiferromagnetism ordering at ~14.0 K; compound 2 demonstrates successive short-range antiferromagnetism ordering at ~15.5 and ~12.6 K; compound 3 shows slow magnetic relaxation with T b≈ 4.6 K. These results demonstrate long-range magnetic ordering is readily accessible in the frameworks of ox2− bridging CoII-ladders linked by bphy, where short-range magnetic correlations can be systematicly tuned by the CoII-ladder structures.

Metastable and localized Ising magnetism in α−CoV2O6 magnetization plateaus

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

Existence of short-range magnetic correlation and observation of large magnetocaloric effect in BiGdO3 compound

In the present study, we have investigated the detailed magnetic and magnetocaloric properties of the rare-earth-based polycrystalline BiGdO3 compound, synthesized by the solid-state reaction method. Detailed magnetic measurements show the absence of long-range magnetic ordering down-to 2 K. Zero-field heat capacity study also supports this result. However, all these magnetic and heat capacity measurements reveal the possibility of having a weak short-range antiferromagnetic correlation in this system below 40 K. Detailed analysis of the magnetic isotherms (using modified Langevin function) and field-dependent magnetic entropy change (using mean-field theory) nicely represent the existence of short-range antiferromagnetic correlation in this system. The prepared material also exhibits a large magnetic entropy change of about 25 J kg−1 K−1 at 2.6 K and a large adiabatic temperature change of 14.8 K at 12 K for the magnetic field change of 0–70 kOe. This observed large magnetocaloric effect at this low temperature region is possibly a consequence of the absence of long-range magnetic ordering and the presence of field-induced ferromagnetic behaviour in this BiGdO3 compound.