Spin freezing and dynamics in Ca_{3}Co_{2-x}Mn_{x}O_{6} (x ~ 0.95) investigated with implanted muons: disorder in the anisotropic next-nearest neighbor Ising model
T. Lancaster, S. J. Blundell, P. J. Baker, H. J. Lewtas, W. Hayes, F. L. Pratt, H. T. Yi, S. -W. Cheong
We present a muon-spin relaxation investigation of the Ising chain magnet Ca_{3}Co_{2-x}Mn_{x}O_{6} (x~0.95). We find dynamic spin fluctuations persisting down to the lowest measured temperature of 1.6 K. The previously observed transition at around T ~18 K is interpreted as a subtle change in dynamics for a minority of the spins coupling to the muon that we interpret as spins locking into clusters. The dynamics of this fraction of spins freeze below a temperature T_{SF}~8 K, while a majority of spins continue to fluctuate. An explanation of the low temperature behavior is suggested in terms of the predictions of the anisotropic next-nearest-neighbor Ising model.
The kagome staircase compounds Ni$_{3}$V$_{2}$O$_{8}$ and Co$_{3}$V$_{2}$O$_{8}$ studied with implanted muons
本文报道了可果美阶梯化合物Ni $_{3}$ V $_{2}$ O $_{8}$和Co $_{3}$ V $_{2}$ O $_{8}$的μ子自旋弛豫（$μ^{+}$ SR）测量结果.这些材料的磁性行为可以用两个不等价的磁性离子位点来描述，称为脊柱位点和交叉结合位点。我们的$μ^{+}$ SR结果使我们能够单独探测这些位置中的每一个，揭示这些位置附近的局部磁场的分布。我们不仅能够确认的基础上提出的散装测量的各个阶段的磁结构，但也给在每个阶段的局部场分布的温度演变的洞察。
We present the results of muon-spin relaxation ($μ^{+}$SR) measurements on antiferromagnetic and ferromagnetic spin chains. In antiferromagnetic CuF$_{2}$(pyz) we identify a transition to long range magnetic order taking place at $T_{\mathrm{N}} = 0.6(1)$ K, allowing us to estimate a ratio with the intrachain exchange of $T_{\mathrm{N}}/|J| \approx 0.1$ and the ratio of interchain to intrachain exchange coupling as $|J'/J| \approx 0.05$. The ferromagnetic chain [Sm(hfac)$_{3}$(boaDTDA)]$_{n}$ undergoes an ordering transition at $T_{\mathrm{c}}=2.8(1)$ K, seen via a broad freezing of dynamic fl…
A new pyrochlore compound, NaCaNi$_2$F$_7$, was recently synthesized and has a single magnetic site with spin-1 Ni$^{2+}$. We present zero field (ZF) and longitudinal field (LF) muon spin rotation ($μ$SR) measurements on this pyrochlore. Density functional theory (DFT) calculations show that the most likely muon site is located between two fluorine ions, but off-centre. A characteristic F-$μ$-F muon spin polarization function is observed at high temperatures where Ni spin fluctuations are sufficiently rapid. The Ni$^{2+}$ spins undergo spin freezing into a disordered ground state below 4~K, wi…
We present the results of x-ray scattering and muon-spin relaxation ($μ^{+}$SR) measurements on the iron-pnictide compound FeCrAs. Polarized non-resonant magnetic x-ray scattering results reveal the 120$^\circ$ periodicity expected from the suggested three-fold symmetric, non-collinear antiferromagnetic structure. $μ^+$SR measurements indicate a magnetically ordered phase throughout the bulk of the material below $T_\mathrm{N}$=105(5) K. There are signs of fluctuating magnetism in a narrow range of temperatures above $T_\mathrm{N}$ involving low-energy excitations, while at temperatures well b…
Origin of magnetic freezing in the pyrochlore Y2Mo2O7
利用核共振和μ子共振以及与场相关的长程X射线和中子散射研究了几何阻挫烧绿石晶格Y $_{2}$ Mo $_{2}$ O $_{7}$中类自旋玻璃相变的性质.长程探针表明Y $_{2}$ Mo $_{2}$ O $_{7}$不发生任何全局对称性变化，即使在$6$ ~T场中也是如此.相比之下，局部信号指示接近临界温度的晶格畸变。核显示至少两个不等价的Y网站，和μ子显示作为力矩大小的函数，在很宽的温度范围内的次线性线加宽。结果表明，即使在高场下，Y $_{2}$ Mo $_{2}$ O $%_{7}$的畸变也发生在晶胞内，而其整体立方对称性保持不变。此外，μ介子的结果清楚地表明磁弹性耦合的存在。
We report results of muon spin relaxation and rotation ($μ$SR) experiments on the spin-liquid candidate~YbMgGaO$_{4}$. No static magnetism $\gtrsim 0.003μ_B$ per Yb ion, ordered or disordered, is observed down to 22~mK, a factor of two lower in temperature than previous measurements. Persistent (temperature-independent) spin dynamics are observed up to 0.20~K and at least 1~kOe, thus extending previous zero-field $μ$SR results over a substantial region of the $H$-$T$ phase diagram. Knight shift measurements in a 10-kOe transverse field reveal two lines with nearly equal amplitudes. Inhomogeneo…
The Kondo insulator SmB6 is purported to develop into a robust topological insulator at low temperature. Yet there are several puzzling and unexplained physical properties of the insulating bulk. It has been proposed that bulk spin excitons may be the source of these anomalies and may also adversely affect the topologically-protected metallic surface states. Here, we report muon spin rotation measurements of SmB6 that show thermally-activated behavior for the temperature dependences of the transverse-field (TF) relaxation rate below 20 K and muon Knight shift below 5-6 K. Our data are consiste…
Spin freezing and magnetic inhomogeneities in bilayer manganites
我们对电子掺杂层状锰氧化物La $_{2-2x}$ Sr $_{1+2x}$ Mn $_2$ O $_7$（0.4< x<1）的多晶样品进行了μ子自旋旋转研究，以研究局域磁结构和自旋动力学。我们的研究结果提供了相分离为A型反铁磁相和电荷有序相的证据（x=0.52）和自旋冻结在低温（T<100K）（0.52<x<0.75）。提出了一个新的相图，其中包括这个自旋冻结区。
The unitary evolution of a quantum system preserves its coherence, but interactions between the system and its environment result in decoherence, a process in which the quantum information stored in the system becomes degraded. A spin-polarized positively-charged muon implanted in a fluoride crystal realises such a coherent quantum system, and the entanglement of muon and nearest-neighbour fluorine nuclear spins gives rise to an oscillatory time-dependence of the muon polarization which can be detected and measured. Here we show that the decohering effect of more distant nuclear spins can be p…
On the "spin-freezing" mechanism in underdoped superconducting cuprates
这封信涉及的自旋冻结过程中观察到的核磁共振-NQR弛豫或μ子自旋旋转欠掺杂铜酸盐超导体。这种现象，有时被称为反铁磁和超导序参数的共存，通常被认为是由随机分布的磁矩与电荷不均匀性（可能是条纹），这表现出他们的波动在T $_c$以下冷却减慢。相反，我们描述的实验结果，由于波动，涡旋-反涡旋，轨道电流状态共存的d波超导状态。一个直接的解释的实验结果，在欠掺杂的Y $_{1-x}$ Ca $_x$ Ba $_2$ Cu $_3$ O $_{6.1}$和La $_{2-x}$ Sr $%_x$ CuO $_4$，从而给出了冻结的轨道电流波动。
The disordered pyrochlore oxide Dy$_{2}$Zr$_{2}$O$_{7}$ shows the signatures of field-induced spin freezing with remnant zero-point spin-ice entropy at 5 kOe magnetic field. We have performed zero-field and longitudinal field Muon spin relaxation ($μ$SR) studies on Dy$_{2}$Zr$_{2}$O$_{7}$. Our zero field studies reveal the absence of both long-range ordering and spin freezing down to 62 mK. The $μ$SR relaxation rate exhibits a temperature-independent plateau below 4 K, indicating a dynamic ground state of fluctuating spins similar to the well-known spin ice system Dy$_{2}$Ti$_{2}$O$_{7}$. The …
Muon spin rotation and resonant soft X-ray scattering experiments on prototype multiferroics RMn2O5 (R = Y, Sm) are used to demonstrate that the local electric displacements are driven by the spin-current (SC) mechanism. Small local electric displacements were evaluated by observing spin polarization at ligand O ions, for which implanted muons served as an extremely sensitive probe. Our results for YMn2O5 provide evidence that the spin polarization of O ions forming a spin cycloid chain with Mn spins increases in proportion to the vector spin chirality (Si x Sj ) of the Mn ions. This relations…
We report a comprehensive muon spectroscopy study of the Zn-barlowite series of $S={\frac{1}{2}}$ kagomé antiferromagnets, Zn$_x$Cu$_{4-x}$(OH)$_{6}$FBr, for $x=0.00$ to $0.99(1)$. By combining muon spin relaxation and rotation measurements with state-of-the-art density-functional theory muon-site calculations, we observe the formation of both $μ$--F and $μ$--OH complexes in Zn-barlowite. From these stopping sites, implanted muon spins reveal the suppression of long-range magnetic order into a possible quantum spin liquid state upon increasing concentration of Zn-substitution. In the parent co…
Combined resistance noise and muon-spin relaxation ($μ$SR) measurements of the ferromagnetic semiconductor HgCr$_2$Se$_4$ suggest a degree of magnetoelectric coupling and provide evidence for the existence of isolated magnetic polarons. These form at elevated temperatures and undergo a percolation transition with a drastic enhancement of the low-frequency 1/$f$-type charge fluctuations at the insulator-to-metal transition at $\sim 95 - 98$ K in the vicinity of the magnetic ordering temperature $T_C \sim 105 - 107$ K. Upon approaching the percolation threshold from above, the strikingly unusual…
The ferromagnetic (FM) nature of Nd2Fe14B has been investigated with muon spin rotation and relaxation (μ^+SR) measurements on an aligned, sintered plate-shaped sample. A clear muon spin precession frequency (f_{FM}) corresponding to the static internal FM field at the muon site showed an order parameter-like temperature dependence and disappeared above around 582 K (~T_C). This indicated that the implanted muons are static in the Nd2Fe14B lattice even at temperatures above around 600 K. Using the predicted muon site and local spin densities predicted by DFT calculations, the ordered Nd moment…
Random singlet physics in the $S = \frac{1}{2}$ pyrochlore antiferromagnet NaCdCu$_2$F$_7$
Charles University（查理大学）；Advanced Science Research Center, Japan Atomic Energy Agency（日本原子力机构先进科学研究中心）；Institute of Physics, Czech Academy of Sciences（捷克科学院物理研究所）；Helmholtz-Zentrum Dresden-Rossendorf (HZDR)（德累斯顿-罗斯多夫亥姆霍兹中心）；ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Science and Technology Facilities Council（英国科学与技术设施委员会卢瑟福阿普尔顿实验室中子与μ子源）
The magnetic ground state of oxynitride pyrochlore Lu$_2$Mo$_2$O$_{5-y}$N$_2$, a candidate compound for the quantum spin liquid ($S=1/2$, Mo$^{5+}$), was studied by muon spin rotation/relaxation experiment. In contrast to Lu$_2$Mo$_2$O$_7$ ($S=1$, Mo$^{4+}$) which exhibits the spin-glass behavior with a freezing temperature $T_g\simeq16$ K, no such spin freezing or long range magnetic order was observed down to 0.3 K. Moreover, two separate magnetic domains were detected below $\sim$13 K, which were characterized by differences in spin dynamics. The first is the "sporadic" spin fluctuation see…
Collective behaviour of electrons, frustration induced quantum fluctuations and entanglement in quantum materials underlie some of the emergent quantum phenomena with exotic quasi-particle excitations that are highly relevant for technological applications. Herein, we present our thermodynamic and muon spin relaxation measurements, complemented by ab initio density functional theory and exact diagonalization results, on the recently synthesized frustrated antiferromagnet Li4CuTeO6, in which Cu2+ ions (S = 1/2) constitute disordered spin chains and ladders along the crystallographic [101] direc…
We report results of magnetization, specific-heat and muon-spin relaxation measurements on single crystals of disorder-free Yb$^{3+}$ triangular lattice Yb(BaBO$_3$)$_3$. The magnetization experiments show anisotropic magnetic properties with Curie-Weiss temperatures $θ_{\perp}=-1.40$~K ($H \perp c$) and $θ_{\parallel}=-1.16$~K ($H \parallel c$) determined from low temperature data. The absence of both long-range antiferromagnetic order and spin freezing is confirmed down to 0.27 K at zero field. A two-level Schottky anomaly due to the opening of the ground-state Kramers doublet is observed fr…
Microscopic magnetic phase evolution in the Weyl semimetal Mn$_3$Sn revealed by $μ^+$SR
KTH Royal Institute of Technology（皇家理工学院）；Uppsala University（乌普萨拉大学）；PSI Center for Neutron and Muon Sciences CNM（瑞士保罗谢勒研究所中子与μ子科学中心）；University of Luxembourg（卢森堡大学）；Forschungszentrum Jülich GmbH（于利希研究中心有限公司）；TRIUMF（特利昂夫实验室）；Institut Laue-Langevin（朗之万-桂良研究所）；RWTH Aachen（亚琛工业大学）
Geometric magnetic frustration (GMF) has attracted substantial interest due to the exotic physics and rich phase diagrams revealed by the cancellation of normally-dominant magnetic interactions, giving impetus for the search for novel frustrated systems, most often based on antiferromagnetic correlations between magnetic ions decorating triangular or tetrahedral lattices. We report here low-temperature magnetic susceptibility and muon spin relaxation results on Li4MgOsO6 and Li3Mg2OsO6, members of the A5BO6 "rock salt ordered" family of frustrated materials. In Li3Mg2OsO6 we find spin freezing…
The nickelate Pr4Ni3O8 features quasi-two-dimensional layers consisting of three stacked square-planar NiO2 planes, in a similar way to the well-known cuprate superconductors. The mixed-valent nature of Ni and its metallic properties makes it a candidate for potentially unconventional superconductivity. We have synthesized Pr4Ni3O8 by topotactic reduction of Pr4Ni3O10 in 10 percent hydrogen gas, and report on measurements of powder-neutron diffraction, magnetization and muon-spin rotation (uSR). We find that Pr4Ni3O8 shows complicated spin-glass behavior with a distinct magnetic memory effect …
Emergent Dynamic Magnetic Ground State in a Mixed 3d/5d Heavy Fermion System CaCu3Ir4O12
ISIS Neutron and Muon Source, STFC, Rutherford Appleton Laboratory（ISIS中子与缪子源，STFC，拉瑟福德阿普尔顿实验室）；Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences（北京凝聚态物理国家实验室，中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Highly Correlated Matter Research Group, Physics Department, University of Johannesburg（约翰内斯堡大学物理系强关联物质研究组）
