arXiv subjects

H. D. Yang

Publications and source records attributed to H. D. Yang.

At least 19 recordsLinked to original sources

arXiv2025

Successive magnetic transitions and multiferroicity in layered honeycomb BiCrTeO$_{6}$

Low-dimensional magnetic systems based on honeycomb lattices provide a promising platform for exploring exotic quantum phenomena that emerge from the intricate interplay of competing spin, orbital, lattice, and dipolar degrees of freedom. Here, we present a comprehensive study of the layered honeycomb lattice antiferromagnet BiCrTeO$_6$ using magnetization, specific heat, muon spin--relaxation ($\mu$SR) spectroscopy, dielectric, pyrocurrent, and high-resolution synchrotron X-ray diffraction (SXRD) measurements. Our results reveal an array of intriguing and strongly correlated phenomena, including two successive antiferromagnetic transitions at $T_{\rm N1}\approx16$ K and $T_{\rm N2}\approx11$ K, a pronounced magnetodielectric coupling effect, and ferroelectric order at $T_{\rm N2}$. Consequently, this compound emerges as a new spin-driven multiferroic system. The SXRD analysis reveals a magnetoelastic-coupling-induced structural phase transition at $T_{\rm N2}$, characterized by a symmetry lowering from P$\bar{3}$1c (163) to P31c (159), which likely triggers the onset of ferroelectricity. In addition to its low-temperature multiferroic behavior, the system exhibits dielectric relaxor characteristics at higher temperatures within the paramagnetic region ($T<50$ K), which is intrinsically linked to the antisite disorder of Cr and Te atoms.

cond-mat.str-el↗

arXiv2025

Highly Entangled Magnetodielectric and Magnetostriction effects, and Spin-Phonon coupling in the Antiferromagnetic Ni$_2$ScSbO$_6$

Magnetic systems with noncentrosymmetric crystal structures are renowned for their complex magnetic ordering and diverse and fascinating physical properties. In this report, we provide a comprehensive study of the chiral magnetic system Ni$_2$ScSbO$_6$, which exhibits a robust incommensurate long-range antiferromagnetic spin ordering at a temperature of $T_N = 62$~K, as revealed by bulk magnetization, specific heat, and neutron diffraction studies. This magnetic ordering triggers a series of intriguing phenomena, including prominent magnetodielectric coupling manifested by a dielectric peak at $T_N$, significant spin-phonon coupling resulting in strong phonon renormalization characterized by anomalous softening of various Raman modes, and a remarkable volume magnetostriction effect probed by high-resolution synchrotron X-ray diffraction. These phenomena are intricately interlinked, positioning the present system as a rare and interesting material.

cond-mat.mtrl-sci↗

arXiv2025

Coexistence of magnetic and dielectric glassy states in alternating kagome and triangular lattice LuBaCo$_4$O$_7$ cobaltite

To date, the alternating kagome and triangular lattice cobaltites, RBaCo$_4$O$_7$ (R = Ca, Y, and rare earth elements), have been well studied for their large structural distortions, anisotropic exchange interactions, chiral spin liquid states, and giant multiferroic properties. Here, we report the co-existence of magnetic and dielectric glassy states in LuBaCo$_4$O$_7$ below 50 K. AC magnetization studies show an absence of conventional spin-freezing behavior. The cooling and heating in unequal fields (CHUF), thermal cycling, and time-dependent magnetization measurements at low temperature ($T$) show the presence of magnetic glassy state. The $T$-dependent dielectric constant $\epsilon'$ measurements exhibit a strong frequency-independent response at the first-order structural phase transition $T = 160$ K (trigonal $P31c$ to monoclinic $Cc$) and also significant features at the $T = 110$ K (monoclinic $Cc$ to orthorhombic $Pbn2_1$) phase transition. Further, $\epsilon'$ shows a frequency-independent peak at 43 K ($Pbn2_1$) and also dipolar glassy features below 20 K ($Cc$). The non-equilibrium magnetic glassy dynamics and dipolar glassy state at low-$T$ arises from the kinetic arrest of $Cc$ and $Pbn2_1$ phases. From the dielectric probe, we are able to clearly distinguish the kinetically arrested phases at low-$T$ , whereas the bulk magnetization studies are unable to do so as the arrested phases have low magnetic moments.

cond-mat.str-el↗

arXiv2025

Susceptibility anisotropy and absence of ferroelectric order in the Kitaev spin liquid candidate Na$_2$Co$_2$TeO$_6$

We report the magnetic, magnetodielectric, and electric polarization properties of single crystals of the Co-based Kitaev Spin Liquid (KSL) candidate Na$_2$Co$_2$TeO$_6$ (NCTO). The sample shows magnetic transitions at 26 K, 16 K, and 5 K, consistent with the literature. The magnetic measurements along and perpendicular to the Co-honeycomb planes show a strong anisotropy in susceptibility and in Curie-Weiss (C-W) temperatures. The experimental anisotropic C-W temperatures of NCTO qualitatively match with the theoretical C-W temperatures, calculated using the HKTF model [C. Kim \textit{et al.}, J. Phys.: Condens. Matter \textbf{34}, 045802 (2021)]. We find from our temperature- and field-dependent dielectric and pyroelectric ($I_p$) current studies ($H\parallel ab$ and $E\perp ab$) that our single crystal NCTO samples do not have a finite electric polarization below 100 K. These $I_p$ studies confirm the absence of a magnetoelectric coupling and electric polarization properties in the title compound and suggest that the zig-zag AFM structure is more favorable than the triple-$Q$ structure with AFM Kitaev interactions.

cond-mat.str-el↗

arXiv2019

Magnetic glassy state at low spin state of Co3+ in EuBaCo2O5+δ (δ = 0.47) cobaltite

The magnetic glassy state is a fascinating phenomenon, which results from the kinetic arrest of the first order magnetic phase transition. Interesting properties, such as metastable magnetization and nonequilibrium magnetic phases, are naturally developed in the magnetic glassy state. Here, we report magnetic glass property in the low spin state of Co3+ in EuBaCo2O5+δ (δ = 0.47) cobaltite at low temperature (T < 60 K). The measurements of magnetization under the cooling and heating in unequal fields, magnetization relaxation and thermal cycling of magnetization show the kinetic arrest of low magnetization state below 60 K. The kinetically arrested low temperature magnetic phase is further supported through the study of isothermal magnetic entropy, which shows the significant entropy change. The present results will open a new window to search the microscopic relation between the spin state transitions and the kinetic arrest induced magnetic glassy phenomena in complex materials.

cond-mat.mtrl-sci↗

arXiv2019

Increasing the skyrmion stability in Cu$_2$OSeO$_3$ by chemical substitution

The cubic chiral helimagnets with the $P2_13$ space group represent a group of compounds in which the stable skyrmion-lattice state is experimentally observed. The key parameter that controls the energy landscape of such systems and determines the emergence of a topologically nontrivial magnetic structures is the Dzyaloshinskii-Moriya interaction (DMI). Chemical substitution is recognized as a convenient instrument to tune the DMI in real materials and has been successfully utilized in studies of a number of chiral magnets, such as MnSi, FeGe, MnGe, and others. In our study, we applied small-angle neutron scattering to investigate how chemical substitution influences the skyrmionic properties of an insulating helimagnet Cu$_2$OSeO$_3$ when Cu ions are replaced by either Zn or Ni. Our results demonstrate that the DMI is enhanced in the Ni-substituted compounds (Cu,Ni)$_2$OSeO$_3$, but weakened in (Cu,Zn)$_2$OSeO$_3$. The observed changes in the DMI strength are reflected in the magnitude of the spin-spiral propagation vector and the temperature stability of the skyrmion phase.

cond-mat.str-el↗

arXiv2017

Extremely large non-saturating magnetoresistance and ultrahigh mobility due to topological surface states in metallic Bi2Te3 topological insulator

Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been investigated at high and low bulk charge carrier concentrations. At low charge carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. At high charge carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. WAL due to topological surface states shows no dependence on the nature (electrons or holes) of the bulk charge carriers. The observations of an extremely large, non-saturating magnetoresistance, and ultrahigh mobility in the samples with lower carrier density further support the presence of surface states. The physical parameters characterizing the WAL effects are calculated using the Hikami-Larkin-Nagaoka formula. At high charge carrier concentrations, there is a greater number of conduction channels and a decrease in the phase coherence length compared to low charge carrier concentrations. The extremely large magnetoresistance and high mobility of topological insulators have great technological value and can be exploited in magneto-electric sensors and memory devices.

cond-mat.str-el↗

arXiv2015

Antisite disorder driven spontaneous exchange bias effect in La2-xSrxCoMnO6 (0<x<1)

Doping at the rare-earth site by divalent alkaline-earth ions in perovskite lattice has witnessed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report an antisite disorder driven spontaneous exchange bias effect as a result of hole carrier (Sr2+) doping in La2-xSrxCoMnO6 (0 < x < 1) double perovskites. X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder with the increase of Sr content up to x = 0.5 and thereby decreases from x = 0.5 to 1. X-ray absorption spectroscopy has revealed that only Co is present in mixed valent Co2+ and Co3+ states with Sr doping to compensate the charge neutrality. Magnetotransport is strongly correlated with the increase of antisite disorder. The antisite disorder at the B-site interrupts the long-range ferromagnetic order by introducing various magnetic interactions and instigates reentrant glassy dynamics, phase separation and canted type antiferromagnetic behavior with the decrease of temperature. This leads to novel magnetic microstructure with unidirectional anisotropy that causes spontaneous exchange bias effect that can be tuned with the amount of antisite disorder.

cond-mat.str-el↗

arXiv2014

Metamagnetic behavior and effect of field cooling on sharp magnetization jumps in multiferroic Y2CoMnO6

We present sharp magnetization jumps and field induced irreversibility in magnetization in multiferroic Y2CoMnO6. Appearance of magnetic relaxation and field sweep rate dependence of magnetization jumps resemble the martensite like scenario and suggests the coexistence of E*-type antiferromagnetic and ferromagnetic phases at low temperatures. In Y2CoMnO6, the critical field required for the sharp jump can be increased or decreased depening on the magnitude and direction of the cooling field; this is remarkably different from manganites or other metamagnetic materials where the critical field increases irrespective of the direction of the field cooling. The cooling field dependence on the sharp magnetization jumps has been described by considering exchange pinning mechanism at the interface, like in exchange bias model.

cond-mat.str-el↗

arXiv2013

THz Generation and Detection on Dirac Fermions in Topological Insulators

This study shows that a terahertz (THz) wave can be generated from the (001) surface of cleaved Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ and Cu-doped Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ single crystals using 800 nm femtosecond pulses. The generated THz power is strongly dependent on the carrier concentration of the crystals. An examination of the dependence reveals the two-channel free carrier absorption to which Dirac fermions are indispensable. Dirac fermions in Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ are significantly better absorbers of THz radiation than bulk carriers at room temperature. Moreover, the characteristics of THz emission confirm the existence of a recently proposed surface phonon branch that is normalized by Dirac fermions.

cond-mat.mes-hall↗

arXiv2011

Coexistence of isotropic s-wave and extended s-wave order parameters in FeSe as revealed by the low-temperature specific heat

The comprehensive low-temperature specific heat C(T) data identify both an isotropic s-wave and an extended s-wave order parameters coexisting in a superconducting single crystal FeSe with Tc=8.11 K. The isotropic gap Δ0=1.33 meV on the hole Fermi sheets and the extended s-wave gap Δ=Δe(1+α*cos2_theta) with Δe=1.13 meV and α=0.78 on the electron Fermi sheets. The extended s-wave is rather anisotropic but the low energy quasiparticle excitations demonstrate no sign of the accidental nodes. The coefficient γ(H) manifesting the quasiparticle contribution to C is a non-linear function of the applied magnetic field H in the mixed state in accord with the anisotropic multi-order parameters.

cond-mat.supr-con↗

arXiv2010

Colossal Electroresistance and Colossal Magnetoresistance in Spinel Multiferroic CdCr2S4

Colossal magnetoresistance (CMR) and electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition (MIT) in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive (CMC), colossal electrocapacitive (CEC), CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.

cond-mat.str-el↗

arXiv2010

Anomalous pressure effect on the magnetic ordering in multiferroic BiMnO3

We report the magnetic field dependent dc magnetization and the pressure-dependent (pmax ~ 16 kbar) ac susceptibilities Xp(T) on both powder and bulk multiferroic BiMnO3 samples, synthesized in different batches under high pressure. A clear ferromagnetic (FM) transition is observed at TC ~ 100 K, and increases with magnetic field. The magnetic hysteresis behavior is similar to that of a soft ferromagnet. Ac susceptibility data indicate that both the FM peak and its temperature (TC) decrease simultaneously with increasing pressure. Interestingly, above a certain pressure (9 ~ 11 kbar), another peak appears at Tp ~ 93 K, which also decreases with increasing pressure, with both these peaks persisting over some intermediate pressure range (9 ~ 13 kbar). The FM peak disappears with further application of pressure; however, the second peak survives until present pressure limit (pmax ~ 16 kbar). These features are considered to originate from the complex interplay of the magnetic and orbital structure of BiMnO3 being affected by pressure.

cond-mat.str-el↗

arXiv2010

Multiple magnetic transitions in multiferroic BiMnO3

The magnetic phase variations under hydrostatic pressure on multiferroic BiMnO3 have been examined by the dc magnetization [Mg(T)], magnetic hysteresis [Ueff(H)], and ac susceptibility [X'g(T)]. Three magnetic transitions, manifested as kinks I, II, and III on the Mg(T)], curves, were identified at 8.7 and 9.4 kbar. With increasing pressure, transition temperatures of kink I and kink II TkI and TkII tend to decrease, but the temperature of kink III TkIII showed more complex variation. Under increasing magnetic field, TkI and TkII increase; however, TkIII decreases. Combining [Mg(T)] curves with Ueff(H) and X'g(T), more detailed properties of these three kinks would be shown as follows. Kink I is a long-range soft ferromagnetic transition which occurs at TkI 100 K under ambient pressure but is suppressed completely at 11.9 kbar. Kink II emerges at 8.7 kbar along with TkII 93 K which is also long-range soft ferromagnetic but canted in nature. Kink III, a canted antiferromagnetic transition, appears at TkIII 72.5 K along with kink II also at 8.7 kbar. The proposed phase diagrams at ambient pressure, 9.4 and 11.9 kbar show the different magnetic features of BiMnO3. These findings are believed to result from the variations in crystal structure influenced by the external pressure. These results also indicate the common complicated

cond-mat.str-el↗

arXiv2009

High-field magnetization of a two dimensional spin frustration system Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br and Cl)

High-field magnetization, M($H$), on Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br and Cl) were measured by using a pulse magnet. These compounds have a two dimensional crystal structure and a distorted kagome spin frustrated system which is builded by the Ni$^{2+}$ ions ($\textbf{S}$ = 1). The Néel transition temperatures are $T_{N} \sim$ 28 and 23 K for X = Br and Cl, respectively. When $T < T_{N}$, we observed a step-like transition at $H_{c} \sim$ 11 and 10 T for X = Br and Cl, respectively. On the other hand, at $T > T_{N}$, the field-dependent magnetization curves behaved like a monotonically increasing straight line up to 55 T. The $H_{c}$ value is close to those obtained by previous spin resonance studies in which a model of spin-flop scenario was proposed to explain the field-dependent resonance spectra. Their model predicts a further transition at around 23 T, however, our observations did not show any plateau behaviors, saturation or other anomalies up to 55 T, suggesting that the further transition possibly exists at a much higher field region.

cond-mat.str-el↗

arXiv2007

Experimental evidence for a two-gap structure of superconducting NbSe_2: a specific heat study in external magnetic fields

To resolve the discrepancies of the superconducting order parameter in quasi-two-dimensional NbSe_2, comprehensive specific-heat measurements have been carried out. By analyzing both the zero-field and mixed-state data with magnetic fields perpendicular to and parallel to the c axis of the crystal and using the two-gap model, we conclude that (1) more than one energy scale of the order parameter is required for superconducting NbSe_2 due to the thermodynamic consistency; (2)delta_L=1.26 meV and delta_S=0.73 meV are obtained; (3) N_S(0)/N(0)=11%~20%; (4) The observation of the kink in gamma(H) curve suggests that the two-gap scenario is more favorable than the anisotropic s-wave model to describe the gap structure of NbSe_2; and (5)delta_S is more isotropic and has a three-dimensional-like feature and is located either on the Se or the bonding Nb Fermi sheets.

cond-mat.supr-con↗

arXiv2007

A Low-Temperature Specific Heat Study of the Giant Dielectric Constant Materials

Low-temperature specific-heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the specific heat data at very low-temperature range, 0.6 to 1.5 K, and moderately low-temperature range, 1.5 to 5 K, in addition to the expected Debye terms, we noticed significant contributions originated from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurred at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behaviors at both low and high frequency regions.

cond-mat.mtrl-sci↗

arXiv2006

Possible coexistence of s-wave and unconventional pairing in Na_xCoO_2-yH2O:a new insight from impurity effects

To shed light on the symmetry of the superconducting order parameter in Na_xCoO_2-yH_2O, the Mn doping effects are studied. X-ray absorption spectroscopy verifies that the doped Mn impurities occupy the Co sites and are with a valance close to +4. Impurity scattering by Mn is in the unitary limit that, however, does not lead to strong Tc suppression. This absence of the strong impurity effects on T_c is not consistent with the simple picture of a sign-changing order parameter. Coexistence of the s-wave and unconventional order parameters is proposed to reconcile all existing experiments and has been directly observed by the specific heat experiments.

cond-mat.supr-con↗