The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows interesting magnetic properties evolving with $R$ and metamagnetic transitions under applied magnetic field for some of the compounds. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant x-ray magnetic diffraction experiments are performed on single crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic unit cell matches the chemical cell below the Néel temperatures $T_{N}$ = 22.2 and 33.2 K, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group $Cmmm'$). It features ferromagnetic {\it ac} planes that are stacked in an antiferromagnetic $+-+-$ pattern, with the rare-earth magnetic moments pointing along the $\vec{a}$ direction, which contrasts with the $+--+$ stacking and moment direction along the $\vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign reversal of the coupling constant between second-neighbor $R$ planes as $R$ is varied from Gd and Tb to Yb. The long {\it b} lattice parameter of GdNiSi$_{3}$ and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$, pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of $R$ sets the stage for the magnetic ground state instability observed along this series.
We propose the idea of a spin-lattice liquid, in which spin and lattice degrees of freedom are strongly coupled and remain disordered and fluctuating down to low temperatures. We show that such a state arises naturally from a microscopic analysis of a class of molybdate pyrochlore compounds, and is driven by a giant magnetoelastic effect. Finally, we argue that this could explain some of the experimental features of Y$_2$Mo$_2$O$_7$.
We present first-principles results on the magnetoelastic coupling in $α$-RuCl$_3$ and uncover a striking dependence of the magnetic coupling constants on strain effects. Different magnetic interactions are found to respond very unequally to variations in the lattice, with the Kitaev interaction being the most sensitive. Exact diagonalization results on our magnetoelastic model reproduce recent measurements of the structural Grüneisen parameter and explain the origin of the negative magnetostriction of $α$-RuCl$_3$, disentangling contributions related to different anisotropic interactions and …
Magnetoelastic coupling at the field-induced transition in EuAl$_{12}$O$_{19}$
Charles University（查理大学）；Helmholtz-Zentrum Dresden-Rossendorf (HZDR)（德累斯顿-罗斯多夫亥姆霍兹中心）；B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine（乌克兰国家科学院B.维尔金低温物理与工程研究所）；Max-Planck Institut fur Physik komplexer Systeme（马克斯·普朗克复杂系统物理研究所）
The Kitaev material $α$-RuCl$_3$ is among the most prominent candidates to host a quantum spin-liquid state endowed with fractionalized excitations. Recent experimental and theoretical investigations have separately revealed the importance of both the magnetoelastic coupling and the magnetic anisotropy, in dependence of the applied magnetic field direction. In this combined theoretical and experimental research, we investigate the anisotropic magnetic and magnetoelastic properties for magnetic fields applied along the main crystallographic axes as well as for fields canted out of the honeycomb…
Single crystals of Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl were investigated using high-resolution capacitance dilatometry in magnetic fields up to 15 T. Pronounced magnetoelastic coupling is found upon evolution of long-range antiferromagnetic order at T$_{\mathrm{N}} = 26.4(3)$ K. Grüneisen analysis reveals moderate effects of uniaxial pressure on T$_{\mathrm{N}}$, of $1.8(4)$ K/GPa, $-0.62(15)$ K/GPa and $0.33(10)$ K/GPa for $p \parallel a$, $b$, and $c$, respectively. Below 22 K, Grüneisen scaling fails which implies the presence of competing interactions. The structural phase transition at T$_{\math…
The consequences of the Jahn-Teller (JT) orbital-lattice coupling for magnetism of pseudospin J_{eff}=1/2 and J_{eff}=0 compounds are addressed. In the former case, represented by Sr_2IrO_4, this coupling generates, through the so-called pseudo-JT effect, orthorhombic deformations of a crystal concomitant with magnetic ordering. The orthorhombicity axis is tied to the magnetization and rotates with it under magnetic field. The theory resolves a number of puzzles in Sr_2IrO_4 such as the origin of in-plane magnetic anisotropy and magnon gaps, metamagnetic transition, etc. In J_{eff}=0 systems, …
Magnetoelastic excitations in the pyrochlore spin liquid Tb$_2$Ti$_2$O$_7$
在低温下，Tb $_2$ Ti $_2$ O $_7$进入自旋液体状态，尽管预期磁序和/或结构畸变。利用中子散射，我们已经发现，在这种自旋液体状态的激发晶体场的水平耦合到一个横向声学声子，形成一个混合激发。磁性和声子分支具有相同的色散关系，可以确定，和杂交消失在顺磁状态。我们认为Tb $_2$ Ti $_2$ O $_7$是一种合适的“磁弹性自旋液体”，激发态的杂化抑制了磁有序和结构畸变. Tb $_2$ Ti $_2$ O $_7$的自旋液相现在可以被认为是具有传播玻色子自旋激发的库仑相。
We use a recently developed optical fiber Bragg grating technique, in continuous and pulsed magnetic fields in excess of 90T, to study magnetoelastic correlations in magnetic materials at cryogenic temperatures. Both insulating UO2 and metallic CeRhIn5 present antiferromagnetic ground states, at T_N = 30.3K and T_N = 3.85K respectively. A strong coupling of the magnetism to the crystal lattice degrees of freedom in UO2 is found, revealing piezomagnetism as well as the dynamics of antiferromagnetic domain switching between spin arrangements connected by time reversal. The AFM domains become har…
We present a phenomenological analysis of the magnetoelastic properties of CeCo$_{0.85}$Fe$_{0.15}$Si at temperatures close to the Néel transition temperature $T_N$. Using a Landau functional we provide a qualitative description of the thermal expansion, magnetostriction, magnetization and specific heat data. We show that the available experimental results [Journal of Physics: Condensed Matter 28 346003 (2016)] are consistent with the presence of a structural transition at $T_s\gtrsim T_N$ and a strong magnetoelastic coupling. The magnetoelastic coupling presents a Janus-faced effect: while th…
The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous due to its structural complexity. Magnetometry measurements, and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of Co2V2O7, which consists of two non-equivalent Co sites. Upon cooling below the Neél temperature TN = 6.3 K, we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of long range magnetic order of Co2+ moments. After symmetry analy…
Thermal expansion, magnetostriction and magnetization measurements under magnetic field and hydrostatic pressure were performed on a $\mathrm{UAu_{2}Si_{2}}$ single crystal. They revealed a large anisotropy of magnetoelastic properties manifested by prominent length changes leading to a collapse of the unit-cell volume accompanied by breaking the fourfold symmetry (similar to that in $\mathrm{URu_{2}Si_{2}}$ in the hidden-order state) in the antiferromagnetic state as consequences of strong magnetoelastic coupling. The magnetostriction curves measured at higher temperatures confirm a bulk char…
We report detailed thermodynamic studies on high-quality single crystals of the centrosymmetric skyrmion-hosting intermetallic Gd2PdSi3 by means of high-resolution capacitance dilatometry in fields up to 15 T which are complemented by specific heat and magnetization studies. Our dilatometric measurements show magnetoelastic effects associated with antiferromagnetic order at TN1 = 22.3 K and TN2 = 19.7 K, as well as strong field effects in an applied magnetic field of 15 Tup to 200 K (150 K) for B||c (B||a*, i.e. B perp c). The data allow us to complete the magneticphase diagram, including a ne…
Microscopic spin interactions on a deformed Kagomé lattice of volborthite are investigated through magnetoelastic couplings. A negative longitudinal magnetostriction $ΔL<0$ in the $b$ axis is observed, which depends on the magnetization $M$ with a peculiar relation of $ΔL/L \propto M^{1.3}$. Based on the exchange striction model, it is argued that the negative magnetostriction originates from a pantograph-like lattice change of the Cu-O-Cu chain in the $b$ axis, and that the peculiar dependence arises from the local spin correlation. This idea is supported by DFT+$U$ calculations simulating th…
Effect of magnetoelastic coupling on spin-glass behavior in Heisenberg pyrochlore antiferromagnets with bond disorder
基于阻挫磁性材料中令人困惑的自旋玻璃行为，我们从理论上研究了几何阻挫经典自旋模型中的磁弹性耦合效应。特别是，我们认为键无序海森堡反铁磁体的烧绿石晶格耦合到本地晶格畸变。通过对晶格自由度的积分，我们得到了一个有效的纯自旋模型，即具有键无序的双线性双二次模型，并利用经典的蒙特卡罗模拟对该模型进行了分析。首先，我们讨论了相图以及热力学和磁学性质。我们发现，自旋玻璃转变温度大大提高了自旋-晶格耦合$b$在弱无序制度。这种增强归因于自旋-晶格耦合的存在下形成的半离散简并流形中的热涨落的抑制。我们还发现，随着无序度的增加，在由$b$确定的温度下，体系表现出与键无序度无关的自旋玻璃态和有序度的伴随转变.虽然进一步的邻居交换相互作用起源于合作晶格扭曲的结果在弱无序制度的自旋晶格顺序，伴随的过渡仍然是强大的。我们通过分析磁化率、非线性磁化率和比热的磁滞现象来研究伴随跃迁的性质。此外，我们还讨论了高温顺磁相的线性和非线性磁化率以及顺磁相的单自旋翻转动力学。所有这些结果进行了讨论，与典型的烧绿石磁铁，如Y2 Mo 2 O 7和ZnCr 2 O 4的实验比较。
Time reversal symmetry and magnetoelastic correlations are probed by means of high-resolution volume dilatometry in URu2Si2 at cryogenic temperatures and magnetic fields more than enough to suppress the hidden order state at H_HO(T = 0.66 K) approximately 35 T. We report a significant crystal lattice volume expansion at and above H_HO(T), and even above T_HO, possibly a consequence of field-induced f-electron localization, and hysteresis at some high field phase boundaries that confirm volume involvement. We investigate in detail the magnetostriction and magnetization as the temperature is red…
Magnetoelastic measurements in the piezomagnetic antiferromagnet UO$_{2}$ were performed via the fiber Bragg grating method in magnetic fields up to $150\,\mathrm{T}$ generated by a single-turn coil setup. We show that in short timescales, order of a few micro seconds, pulsed-magnetic fields excite mechanical resonances at temperatures ranging from $10\,\mathrm{K}$ to $300\,\mathrm{K}$, in the paramagnetic as well as within the robust antiferromagnetic state of the material. These resonances, which are barely attenuated within the 100 ms observations, are attributed to the strong magnetoelasti…
We investigate magnetoelectric coupling and low-energy magnetic excitations in multiferroic $α$-Cu$_2$V$_2$O$_7$ by detailed thermal expansion, magnetostriction, specific heat and magnetization measurements in magnetic fields up to 15~T and by high-field/high-frequency electron spin resonance studies. Our data show negative thermal expansion in the temperature range $\leq 200$~K under study. Well-developed anomalies associated with the onset of multiferroic order (canted antiferromagnetism with a significant magnetic moment and ferroelectricity) imply pronounced coupling to the structure. We d…
Ising models on a pyrochlore oxide lattice are usually associated with spin ice materials and "magnetic monopoles". Ever more often effects connecting magnetic and elastic degrees of freedom are reported on these and other related frustrated materials. Here we extend a spin-ice Hamiltonian to include coupling between spins and the O$^{-2}$ ions mediating superexchange; we call it the Magnetoelastic Spin Ice model (MeSI). There has been a long search for a model in which monopoles would spontaneously become the building blocks of new ground-states: the MeSI Hamiltonian is such a model. In spite…
We report high-resolution capacitance dilatometry studies on the uniaxial length changes in a NdB$_4$ single crystal. The evolution of magnetically ordered phases below $T_{\rm N}$= 17.2~K (commensurate antiferromagnetic phase, cAFM), $T_{\rm IT}$= 6.8~K (intermediate incommensurate phase, IT), and $T_{\rm LT}$= 4.8~K (low-temperature phase, LT) is associated with pronounced anomalies in the thermal expansion coefficients. The data imply significant magneto-elastic coupling and evidence of a structural phase transition at $T_{\rm LT}$ . While both cAFM and LT favor structural anisotropy $δ$ be…
We report experimental and theoretical studies on the magnetoelastic interactions in MnPS$_3$. Raman scattering response measured as a function of temperature shows a blue shift of the Raman active modes at 120.2 and 155.1 cm$^{-1}$, when the temperature is raised across the antiferromagnetic-paramagnetic transition. Density functional theory (DFT) calculations have been performed to estimate the effective exchange interactions and calculate the Raman active phonon modes. The calculations lead to the conclusion that the peculiar behavior with temperature of the two low energy phonon modes can …
We report the thermodynamic properties studied by thermal expansion, magnetostriction, magnetisation, and specific heat measurements as well as the low-energy magnetic excitations of \mto\ and investigate how magneto-elastic coupling and magnetic anisotropy affect the evolution of long-range order and the magnetic phase diagram. Specifically, we utilise high-resolution capacitance dilatometry and antiferromagnetic resonance (AFMR) studies by means of high-frequency electron spin resonance (HF-ESR) spectroscopy. The role of anisotropy is reflected by spin-reorientation at $B_{\rm{SF}}$~$\simeq …
High-quality single crystals of CoTiO$_3$ are grown and used to elucidate in detail structural and magnetostructural effects by means of high-resolution capacitance dilatometry studies in fields up to 15 T which are complemented by specific heat and magnetization measurements. In addition, we refine the single-crystal structure of the ilmenite ($R\bar{3}$) phase. At the antiferromagnetic ordering temperature $T_\mathrm{N}$, pronounced $λ$-shaped anomaly in the thermal expansion coefficients signals shrinking of both the $c$ and $b$ axes, indicating strong magnetoelastic coupling with uniaxial …
The Ca$_2$MnReO$_6$ double perovskite is a spin-orbit-assisted Mott insulator with exotic magnetic properties, including a largely non-collinear Mn$^{2+}$ spin arrangement and nearly orthogonal coupling between such spins and the much smaller Re $5d$ magnetic moments. Here, the electron-doped compound Ca$_{1.7}$Y$_{0.3}$MnReO$_6$ is investigated. Neutron and X-ray powder diffraction confirm that nearly full chemical order is maintained at the Mn and Re sites under the Y substitution at the Ca site. X-ray absorption measurements and an analysis of the Mn-O/Re-O bond distances show that the Mn o…
For disordered Heisenberg systems with small single ion anisotropy, two spin glass transitions below the long range ordered phase transition temperature has been predicted theoretically for compositions close to the percolation threshold. Experimental verification of these predictions is still controversial for conventional spin glasses. We show that multiferroic spin glass systems can provide a unique platform for verifying these theoretical predictions via a study of change in magnetoelastic and magnetoelectric couplings, obtained from an analysis of diffraction data, at the spin glass trans…
用光谱法研究了ACr_2 O_4铬尖晶石氧化物磁性半导体在T=10- 335 K宽温区的晶格结构动力学性质。A位离子（A=Mn，Fe，Co，Ni和Cu）的系统变化表明，3d轨道在A位的占据对晶格动力学有很大影响。对于具有轨道简并的化合物（FeCr 2 O 4、NiCr 2 O 4和CuCr 2 O 4），在Jahn-Teller转变和随后的长程磁序开始时，观察到红外活性声子模式的清晰分裂和/或沉默振动模式的激活。虽然MnCr 2 O 4和CoCr 2 O 4显示出多铁性和磁电特性，但在没有轨道简并的尖晶石化合物中没有发现相当大的磁弹性，因为它们即使在其磁性基态也紧密地保持高温立方尖晶石结构。除了晶格振动，还研究了A $^{2+}$离子的原子内3d-3d跃迁，以确定晶体场和Racah参数以及自旋轨道耦合的强度。
Probing the magnetic ground state and magnetoelastic coupling in double perovskite ruthenate: Ca2ScRuO6
Indian Institute of Technology Palakkad（印度理工学院帕拉克卡德分校）；Bhabha Atomic Research Centre（巴哈原子研究中心）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Indian Institute of Technology Kharagpur（印度理工学院卡拉格普尔分校）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）
