arXiv subjects

X. G. Liu

Publications and source records attributed to X. G. Liu.

At least 19 recordsLinked to original sources

arXiv2019

Magnetism study on a frustration-free spatially anisotropic $S$ = 1 square lattice antiferromagnet Ni[SC(NH$_2$)$_2$]$_6$Br$_2$

Magnetism of the $S$ = 1 Heisenberg antiferromagnets on the spatially anisotropic square lattice has been scarcely explored. Here we report a study of the magnetism, specific heat, and thermal conductivity on Ni[SC(NH$_2$)$_2$]$_6$Br$_2$ (DHN) single crystals. Ni$^{2+}$ ions feature an $S$ = 1 rectangular lattice in the $bc$ plane, which can be viewed as an unfrustrated spatially anisotropic square lattice. A long-range antiferromagnetic order is developed at $T \rm_N =$ 2.23 K. Below $T\rm_N$, an upturn is observed in the $b$-axis magnetic susceptibility and the resultant minimum might be an indication for the $XY$ anisotropy in the ordered state. A gapped spin-wave dispersion is confirmed from the temperature dependence of the magnetic specific heat. Anisotropic temperature-field phase diagrams are mapped out and possible magnetic structures are proposed.

cond-mat.mtrl-sci↗

arXiv2017

Magnetization, specific heat, and thermal conductivity of hexagonal ErMnO$_3$ single crystals

We report a study of magnetism and magnetic transitions of hexagonal ErMnO$_3$ single crystals by magnetization, specific heat and heat transport measurements. Magnetization data show that the $c$-axis magnetic field induces three magnetic transitions at 0.8, 12 and 28 T. The specific heat shows a peak at 2.2 K, which is due to a magnetic transition of Er$^{3+}$ moments. For low-$T$ thermal conductivity ($κ$), a clear dip-like feature appears in $κ(H)$ isotherm at 1--1.25 T for $H \parallel ab$; while in the case of $H \parallel c$, a step-like increase is observed at 0.5--0.8 T. The transition fields in $κ(H)$ are in good agreement with those obtained from magnetization, and the anomaly of $κ$ can be understood by a spin-phonon scattering scenario. The natures of magnetic structures and corresponding field-induced transitions at low temperatures are discussed.

cond-mat.mtrl-sci↗

arXiv2017

Ferroelectricity of structural origin in spin-chain compounds Ca$_3$Co$_{2-x}$Mn$_x$O$_6$

We report a systematic study of the structure, electric and magnetic properties of Ca$_3$Co$_{2-x}$Mn$_x$O$_6$ single crystals with $x =$ 0.72 and 0.26. The DC and AC magnetic susceptibilities display anomalies with characteristic of the spin freezing. The crystals show ferroelectric transition at 40 K and 35 K ($T_{FE}$) for $x =$ 0.72 and 0.26, respectively, with a large value of 1400 $μ$C/m$^2$ at 8 K for electric polarization ($P_c$) along the spin-chain ($c$-axis) direction. Interestingly, the electric polarization perpendicular to the chain direction ($P_{ab}$) can also be detected and has value of 450 and 500 $μ$C/m$^2$ at 8 K for the $x =$ 0.72 and 0.26 samples, respectively. The specific heat and magnetic susceptibility show no anomaly around $T_{FE}$, which means that the electric polarization of these samples has no direct relationship with the magnetism. The X-ray diffraction and the Raman spectroscopy indicate that these samples may undergo Jahn-Teller distortions that could be the reason of electric polarization.

cond-mat.mtrl-sci↗

arXiv2017

Low-temperature heat transport of CuFe$_{1-x}$Ga$_x$O$_2$ ($x =$ 0--0.12) single crystals

We report a study on the thermal conductivity of CuFe$_{1-x}$Ga$_x$O$_2$ ($x =$ 0--0.12) single crystals at temperatures down to 0.3 K and in magnetic fields up to 14 T. CuFeO$_2$ is a well-known geometrically frustrated triangular lattice antiferromagnet and can be made to display multiferroicity either by applying magnetic field along the $c$ axis or by doping nonmagnetic impurities, accompanied with rich behaviors of magnetic phase transitions. The main experimental findings of this work are: (i) the thermal conductivities ($κ_a$ and $κ_c$) show drastic anomalies at temperature- or field-induced magnetic transitions; (ii) the low-$T$ $κ(H)$ isotherms exhibit irreversibility in a broad region of magnetic fields; (iii) there are phonon scattering effect caused by magnetic fluctuations at very low temperatures. These results demonstrate strong spin-phonon coupling in this material and reveal the non-negligible magnetic fluctuations in the "ground state" of pure and Ga-doped samples.

cond-mat.str-el↗

arXiv2016

Heat switch effect in an antiferromagnetic insulator Co$_3$V$_2$O$_8$

We report a heat switch effect in single crystals of an antiferromagnet Co$_3$V$_2$O$_8$, that is, the thermal conductivity ($κ$) can be changed with magnetic field in an extremely large scale. Due to successive magnetic phase transitions at 12--6 K, the zero-field $κ(T)$ displays a deep minimum at 6.7 K and rather small magnitude at low temperatures. Both the temperature and field dependencies of $κ$ demonstrate that the phonons are strongly scattered at the regime of magnetic phase transitions. Magnetic field can suppress magnetic scattering effect and significantly recover the phonon thermal conductivity. In particular, a 14 T field along the $a$ axis increases the $κ$ at 7.5 K up to 100 times. For $H \parallel c$, the magnitude of $κ$ can be suppressed down to $\sim$ 8% at some field-induced transition and can be enhanced up to 20 times at 14 T. The present results demonstrate that it is possible to design a kind of heat switch in the family of magnetic materials.

cond-mat.str-el↗

arXiv2015

Thermal conductivity of the diamond-chain compound Cu_3(CO_3)_2(OH)_2

Thermal conductivity (κ) of a distorted spin diamond-chain system, Cu_3(CO_3)_2(OH)_2, is studied at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the κ(T) curve with heat current along the chain direction has very small magnitudes and shows a pronounced three-peak structure. The magnetic fields along and perpendicular to the chains change the κstrongly in a way having good correspondence to the changes of magnetic specific heat in fields. The data analysis based on the Debye model for phononic thermal conductivity indicates that the heat transport is due to phonons and the three-peak structure is caused by two resonant scattering processes by the magnetic excitations. In particular, the spin excitations of the chain subsystem are strongly scattering phonons rather than transporting heat.

cond-mat.str-el↗

arXiv2015

Thermal conductivity of IPA-CuCl_3: Evidences of ballistic magnon transport and limited applicability of the Bose-Einstein condensation model

The heat transport of the spin-gapped material (CH_3)_2CHNH_3CuCl_3 (IPA-CuCl_3), a candidate quantum magnet with Bose-Einstein condensation (BEC), is studied at ultra-low temperatures and in high magnetic fields. Due to the presence of the spin gap, the zero-field thermal conductivity (κ) is purely phononic and shows a ballistic behavior at T < 1 K. When the gap is closed by magnetic field at H = H_{c1}, where a long-range antiferromanetic (AF) order of Cu^{2+} moments is developed, the magnons contribute significantly to heat transport and exhibit a ballistic T^3 behavior at T < 600 mK. In addition, the low-T κ(H) isotherms show sharp peaks at H_{c1}, which indicates a gap re-opening in the AF state (H > H_{c1}) and demonstrates limited applicability of the BEC model to IPA-CuCl_3.

cond-mat.str-el↗

arXiv2014

Low-temperature heat transport of the geometrically frustrated antiferromagnets R_2Ti_2O_7 (R = Gd and Er)

We report a systematic study on the low-temperature thermal conductivity (κ) of R_2Ti_2O_7 (R = Gd and Er) single crystals with different directions of magnetic field and heat current. It is found that the magnetic excitations mainly act as phonon scatterers rather than heat carriers, although these two materials have long-range magnetic orders at low temperatures. The low-T κ(H) isotherms of both compounds show rather complicated behaviors and have good correspondences with the magnetic transitions, where the κ(H) curves show drastic dip- or step-like changes. In comparison, the field dependencies of κare more complicated in Gd_2Ti_2O_7, due to the complexity of its low-T phase diagram and field-induced magnetic transitions. These results demonstrate the significant coupling between spins and phonons in these materials and the ability of heat-transport properties probing the magnetic transitions.

cond-mat.str-el↗

arXiv2013

Growth of (CH$_3$)$_2$NH$_2$CuCl$_3$ single crystals using evaporation method with different temperatures and solvents

The bulk single crystals of of low-dimensional magnet (CH$_3$)$_2$NH$_2$CuCl$_3$ (DMACuCl$_3$ or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 $^{\circ}$C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of x-ray diffraction, specific heat and magnetic susceptibility.

cond-mat.str-el↗

arXiv2013

Crystal growth and characterization of Haldane chain compound Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$

The bulk single crystals of $S = 1$ chain compound Ni(C$_3$H$_{10}$N$_2$)$_2$NO$_2$ClO$_4$ are grown by using a slow evaporation method at a constant temperature and a slow cooling method. It is found that the optimum condition of growing large crystals is via slow evaporation at 25 $^\circ$C using 0.015 mol Ni(ClO$_4$)$_2$$\cdot$6H$_2$O, 0.015 mol NaNO$_2$, and 0.03 mol 1,3-propanediamine liquid dissolved into 30 ml aqueous solvent. High-quality crystals with size up to $18 \times 7.5 \times 5$ mm$^3$ are obtained. The single crystals are characterized by measurements of x-ray diffraction, magnetic susceptibility, specific heat and thermal conductivity. The susceptibilities along three crystallographic axes are found to exhibit broad peaks at $\sim 55$ K, and then decrease abruptly to zero at lower temperatures, which is characteristic of a Haldane chain system. The specific heat and the thermal conductivity along the $c$ axis can be attributed to the simple phononic contribution and are analyzed using the Debye approximation.

cond-mat.str-el↗

arXiv2012

Large magnetic heat transport in a Haldane chain material Ni(C$_3H_{10}N_2)_2NO_2ClO_4

We report a study on the heat transport of an S = 1 Haldane chain compound Ni(C_3H_{10}N_2)_2NO_2ClO_4 at low temperatures and in magnetic fields. The zero-field thermal conductivities show a remarkable anisotropy for the heat current along the spin-chain direction (κ_b) and the vertical direction (κ_c), implying a magnetic contribution to the heat transport along the spin-chain direction. The magnetic-field-induced change of the spin spectrum has obviously opposite impacts on κ_b and κ_c. In particular, κ_b(H) and κ_c(H) curves show peak-like increases and dip-like decreases, respectively, at \sim 9 T, which is the critical field that minimizes the spin gap. These results indicate a large magnetic thermal transport in this material.

cond-mat.str-el↗

arXiv2012

Low-temperature heat transport and magnetic-structure transition of the hexagonal TmMnO_3 single crystals

We study the low-temperature heat transport, as well as the magnetization and the specific heat, of TmMnO_3 single crystals to probe the transitions of magnetic structure induced by magnetic field. It is found that the low-T thermal conductivity (κ) shows strong magnetic-field dependence and the overall behaviors can be understood in the scenario of magnetic scattering on phonons. In addition, a strong "dip"-like feature shows up in κ(H) isotherms at 3.5--4 T for H \parallel c, which is related to a known spin re-orientation of Mn^{3+} moments. The absence of this phenomenon for H \parallel a indicates that the magnetic-structure transition of TmMnO_3 cannot be driven by the in-plane field. In comparison, the magnetothermal conductivity of TmMnO_3 is much larger than that of YMnO_3 but smaller than that of HoMnO_3, indicating that the magnetisms of rare-earth ions are playing the key role in the spin-phonon coupling of the hexagonal manganites.

cond-mat.str-el↗

arXiv2012

Paramagnetic ground state with field-induced partial order in Nd_3Ga_5SiO_{14} probed by low-temperature heat transport

We study the low-temperature heat transport of Nd_3Ga_5SiO_{14}, which is a spin-liquid candidate, to probe the nature of ground state and the effect of magnetic field on the magnetic properties. The thermal conductivity (κ) shows a purely phononic transport in zero field. The external magnetic field along the c axis induces a dip-like behavior of κ(H), which can be attributed to a simple paramagnetic scattering on phonons. However, the magnetic field along the ab plane induces another step-like decrease of κ. This kind of κ(H) behavior is discussed to be related to a field-induced partial order, which yields low-energy magnetic excitations that significantly scatter phonons. These results point to a paramagnetic ground state that partial magnetic order can be induced by magnetic field along the ab plane, which is also signified by the low-T specific heat data.

cond-mat.str-el↗

arXiv2012

Heat transport of quasi-one-dimensional Ising-like antiferromagnet BaCo_2V_2O_8 in the longitudinal and transverse fields

The very-low-temperature thermal conductivity (κ) is studied for BaCo_2V_2O_8, a quasi-one-dimensional Ising-like antiferromagnet exhibiting an unusual magnetic-field-induced order-to-disorder transition. The nearly isotropic transport in the longitudinal field indicates that the magnetic excitations scatter phonons rather than conduct heat. The field dependence of κshows a sudden drop at \sim 4 T, where the system unndergoes the transition from the Néel order to the incommensurate state. Another dip at lower field of \sim 3 T indicates an unknown magnetic transition, which is likely due to the spin-flop transition. Moreover, the κ(H) in the transverse field shows a very deep valley-like feature, which moves slightly to higher field and becomes sharper upon lowering the temperature. This indicates a magnetic transition induced by the transverse field, which however is not predicted by the present theories for this low-dimensional spin system.

cond-mat.str-el↗

arXiv2011

Heat transport of the quasi-one-dimensional alternating spin chain material (CH_{3})_{2}NH_{2}CuCl_{3}

We report a study of the low-temperature heat transport in the quasi-one-dimensional S = 1/2 alternating antiferromagnetic-ferromagnetic chain compound (CH_{3})_{2}NH_{2}CuCl_{3}. Both the temperature and magnetic-field dependencies of thermal conductivity are very complicated, pointing to the important role of spin excitations. It is found that magnetic excitations act mainly as the phonon scatterers in a broad temperature region from 0.3 to 30 K. In magnetic fields, the thermal conductivity show drastic changes, particularly at the field-induced transitions from the low-field Néel state to the spin-gapped state, the field-induced magnetic ordered state, and the spin polarized state. In high fields, the phonon conductivity is significantly enhanced because of the weakening of spin fluctuations.

cond-mat.str-el↗

arXiv2011

Low-temperature heat transport of the layered spin-dimer compound Ba_3Mn_2O_8

We report the study on the low-temperature heat transport of Ba_3Mn_2O_8 single crystal, a layered spin-dimer compound exhibiting the magnetic-field-induced magnetic order or the magnon Bose-Einstein condensation. The thermal conductivities (κ) along both the ab plane and the c axis show nearly isotropic dependence on magnetic field, that is, κis strongly suppressed with increasing field, particularly at the critical fields of magnetic phase transitions. These results indicate that the magnetic excitations play a role of scattering phonons and the scattering effect is enhanced when the magnetic field closes the gap in the spin spectrum. In addition, the magnons in the BEC state of this materials do not show notable ability of carrying heat.

cond-mat.str-el↗

arXiv2011

Thermal conductivity of pure and Zn-doped LiCu_2O_2 single crystals

We report a study of the low-temperature thermal conductivity (κ) of pure and Zn-doped LiCu_2O_2 single crystals. The κ(T) of pure LiCu_2O_2 single crystal shows a double-peak behavior, with two peaks locating at 48 K and 14 K, respectively. The different dependences of the peaks on the Zn concentration indicate that the high-T peak is likely due to the phonon transport while the low-T one is attributed to the magnon transport in the spin spiral ordering state. In addition, the magnetic field can gradually suppress the low-T peak but does not affect the high-T one; this further confirms that the low-T peak is originated from the magnon heat transport.

cond-mat.str-el↗

arXiv2010

Magnetic phase transitions and magnetoelectric coupling of GdFeO_3 single crystals probed by low-temperature heat transport

The low-temperature thermal conductivity (κ) of GdFeO_3 single crystals is found to be strongly dependent on magnetic field. The low-field κ(H) curves show two "dips" for H \parallel a and only one "dip" for H \parallel c, with the characteristic fields having good correspondence with the spin-flop and the spin-polarization transitions. A remarkable phenomenon is that the subKelvin thermal conductivity shows hysteretic behaviors on the history of applying magnetic field, that is, the κ(H) isotherms measured with field increasing are larger than those with field decreasing. Intriguingly, the broad region of magnetic field (\sim 0--3 T) showing the irreversibility of heat transport coincides with that presenting the ferroelectricity. It is discussed that the irreversible κ(H) behaviors are due to the phonon scattering by ferroelectric domain walls. This result shows an experimental feature that points to the capability of controlling the ferroelectric domain structures by magnetic field in multiferroic materials.

cond-mat.str-el↗