arXiv subjects

Z. M. Tian

Publications and source records attributed to Z. M. Tian.

6 recordsLinked to original sources

arXiv2022

Incommensurate magnetic order in Sm$_3$BWO$_9$ with the distorted kagome lattice

We investigate the magnetic ground state of Sm$_3$BWO$_9$ with the distorted kagome lattice. A magnetic phase transition is identified at $T_N=0.75$ K from the temperature dependence of specific heat. From $^{11}$B nuclear magnetic resonance (NMR) measurements, an incommensurate magnetic order is shown by the double-horn type spectra under a $c$-axis magnetic field. While, absence of line splitting is observed for field oriented within the $ab$-plane, indicating the incommensurate modulation of the internal field strictly along $c$-axis. From the spin dynamics, the critical slowing down behavior is observed in the temperature dependence of $1/T_1$ with $μ_0H\perp c$-axis, which is completely absent in that with $μ_0H||c$-axis. Based on the local symmetry of $^{11}$B sites, we analyze the hyperfine coupling tensors and propose two constraints on the possible magnetic structure. The single ion anisotropy should play an important role in the determination of the contrasting ground states of Sm$_3$BWO$_9$ and Pr$_3$BWO$_9$.

cond-mat.str-el↗

arXiv2022

Spin excitations in the quantum dipolar magnet Yb(BaBO$_3$)$_3$

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 from the low-temperature specific-heat measurements when the applied magnetic fields $μ_0H >0.7$~T. At zero field, the increase of both $C_{\rm mag}/T$ and the muon spin relaxation rate $λ$ below 1~K is due to the electronic spin excitations, which often exist in quantum magnets where dipole-dipole interaction creates an anisotropy of magnetic properties. The spin excitation is also supported by the unusual maximum of field dependence of $λ$ due to the field-induced increase of the density of excitations. We argue that dipolar interaction is dominant and induces the spin dynamics in the quantum magnet Yb(BaBO$_3$)$_3$.

cond-mat.str-el↗

arXiv2021

Local evidence for collective spin excitations in the distorted kagome antiferromagnet Pr$_3$BWO$_9$

We report the local probe investigation of a frustrated antiferromagnet Pr$_3$BWO$_9$ with the distorted kagome lattice. Absence of magnetic order or spin freezing is indicated by the spectral analysis down to 0.3 K and specific heat measurements down to 0.09 K. The Knight shifts show an upturn behavior with the sample cooling down, which is further suppressed by external field. For the spin dynamics, gapped spin excitation is observed from the temperature dependence of spin-lattice relaxation rates, with the gap size proportional to the applied magnetic field intensity. Comparatively, an unexpected sharp peak is observed in the nuclear spin-spin relaxation rate data at $T^*\sim 4-5$ K. These results indicate an unconventional persistent fluctuating paramagnetic ground state with antiferromagnetic collective spin excitations in the strongly frustrated spin system.

cond-mat.str-el↗

arXiv2020

NMR study of the spin correlations in the $S=1$ armchair chain Ni$_2$NbBO$_6$

We report our nuclear magnetic resonance (NMR) study on the structurally spin chain compound Ni$_2$NbBO$_6$ with complex magnetic coupling. The antiferromagnetic transition is monitored by the line splitting resulting from the staggered internal hyperfine field. The magnetic coupling configuration proposed by the first-principle density functional theory (DFT) is supported by our NMR spectral analysis. For the spin dynamics, a prominent peak at $T\sim35$ K well above the Néel temperature ($T_N\sim20$ K at $μ_0H=10$ T) is observed from the spin-lattice relaxation data. As compared with the dc-susceptibility, this behavior indicates a antiferromagnetic coupling with the typical energy scale of $\sim3$ meV. Thus, the Ni$_2$NbBO$_6$ compound can be viewed as strongly ferromagnetically coupled armchair spin chains along the crystalline $b$-axis. These facts place strong constraints to the theoretical model for this compound.

cond-mat.str-el↗

arXiv2020

NMR study of the spin excitations in the frustrated antiferromagnet Yb(BaBO$_3$)$_3$ with a triangular lattice

In this paper, we study the spin excitation properties of the frustrated triangular-lattice antiferromagnet Yb(BaBO$_3$)$_3$ with nuclear magnetic resonance. From the spectral analysis, neither magnetic ordering nor spin freezing is observed with temperature down to $T=0.26$ K, far below its Curie-Weiss temperature $|θ_w|\sim2.3$ K. From the nuclear relaxation measurement, precise temperature-independent spin-lattice relaxation rates are observed at low temperatures under a weak magnetic field, indicating the gapless spin excitations. Further increasing the field intensity, we observe a spin excitation gap with the gap size proportional to the field intensity. These phenomena suggest a very unusual strongly correlated quantum disordered phase, and the implications for the quantum spin liquid state are further discussed.

cond-mat.str-el↗

arXiv2018

Ultralow-temperature thermal conductivity of Pr2Ir2O7: a metallic spin-liquid candidate with quantum criticality

The frustrated pyrochlore iridate Pr$_2$Ir$_2$O$_7$ was proposed as a metallic quantum spin liquid located at a zero-field quantum critical point. Here we present the ultralow-temperature thermal conductivity measurements on the Pr$_2$Ir$_2$O$_7$ single crystals to detect possible exotic excitations. In zero field, the thermal conductivity shows a dramatic suppression above a characteristic temperature $T_s \approx$ 0.12 K. With increasing field, $T_s$ increases and the thermal conductivity tends to saturate above $H$ = 5 T. The Wiedemann-Franz law is verified at high fields and inferred at zero field. It suggests the normal behavior of electrons at the quantum critical point, and the absence of mobile fermionic magnetic excitations. The strong suppression of thermal conductivity is attributed to the scattering of phonons by the spin system, likely the fluctuating spins. These results shed new light on the microscopic description on this novel compound.

cond-mat.str-el↗