Browsing by Author "Cheng, ZX"

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    A comparative study of magnetic behaviors in TbNi2, TbMn2 and TbNi2Mn
    (AIP Publishing LLC., 2014-01-01) Wang, JL; Din, MFM; Kennedy, SJ; Hong, F; Campbell, SJ; Studer, AJ; Wu, GH; Cheng, ZX; Dou, SX
    All TbNi2, TbMn2, and TbNi2Mn compounds exhibit the cubic Laves phase with AB2-type structure in spite of the fact that the ratio of the Tb to transition-metal components in TbNi2Mn is 1:3. Rietveld refinement indicates that in TbNi2Mn the Mn atoms are distributed on both the A (8a) and B (16d) sites. The values of the lattice constants were measured to be a¼14.348A ° (space group F-43 m), 7.618A ° , and 7.158A ° (space group Fd-3 m) for TbNi2, TbMn2, and TbNi2Mn, respectively. The magnetic transition temperatures TC were found to be TC¼38K and TC¼148K for TbNi2 and TbNi2Mn, respectively, while two magnetic phase transitions are detected for TbMn2 at T1¼20K and T2¼49 K. Clear magnetic history effects in a low magnetic field are observed in TbMn2 and TbNi2Mn. The magnetic entropy changes have been obtained. © 2014 AIP Publishing LLC.
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    Driving magnetostructural transitions in layered intermetallic compounds
    (American Physical Society, 2013-05-23) Wang, JL; Caron, L; Campbell, SJ; Kennedy, SJ; Hofmann, M; Cheng, ZX; Din, MFM; Studer, AJ; Brück, E; Dou, SX
    We report the dramatic effect of applied pressure and magnetic field on the layered intermetallic compound Pr0.5Y0.5Mn2Ge2. In the absence of pressure or magnetic field this compound displays interplanar ferromagnetism at room temperature and undergoes an isostructural first order magnetic transition (FOMT) to an antiferromagnetic state below 158 K, followed by another FOMT at 50 K due to the reemergence of ferromagnetism as praseodymium orders (T-C(Pr)). The application of a magnetic field drives these two transitions towards each other, whereas the application of pressure drives them apart. Pressure also produces a giant magnetocaloric effect such that a threefold increase of the entropy change associated with the lower FOMT (at T-C(Pr)) is seen under a pressure of 7.5 kbar. First principles calculations, using density functional theory, show that this remarkable magnetic behavior derives from the strong magnetoelastic coupling of the manganese layers in this compound. © 2013, American Physical Society.
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    Large magnetoelectric coupling in magnetically short-range ordered Bi5Ti3FeO15 film
    (Nature Research, 2014-06-11) Zhao, HY; Kimura, H; Cheng, ZX; Osada, M; Wang, JL; Wang, XL; Dou, SX; Liu, Y; Yu, JD; Matsumoto, T; Tohei, T; Shibata, N; Ikuhara, Y
    Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi5Ti3FeO15 with high ferroelectric Curie temperature of ~1000 K. Bi5Ti3FeO15 thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi5Ti3FeO15 with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe·cm even at room temperature. © 2020 Springer Nature Limited
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    Magnetic structure and magnetocaloric properties of LaMn2Ge2
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Wang, JL; Cheng, ZX; Wang, WQ; Wang, CW; Hutchison, WD; Campbell, SJ
    The extensive set of ternary intermetallic RMn2X2 compounds (R = rare earth, T = transitional metal, X = Ge or Si) have been investigated extensively in the past few decades due to their interesting range of physical properties [e.g. 1-3]. Recently, significant attention has been paid to the magnetocaloric effect (MCE) of RMn2X2 compounds for their potential application in magnetic refrigeration. Their MCE properties are important as RMn2X2 compounds enable a wide range of structural and magnetic behaviours and related transitions to be controlled via substitution of R, Mn, and X atoms on the 2a, 4d, and 4e sites respectively [e.g. 4-7]. We have carried out a detailed investigation of the LaMn2Ge2 compound using neutron diffraction and magnetic measurements, focusing on the magnetic behaviour of the Mn-sublattice. With decreasing temperature, the magnetic state changes from paramagnetism to incommensurate canted antiferromagnetism AFfs at TN~ 360 K and then gives way to incommensurate canted ferromagnetism Fmi below TC ~ 323 K. No obvious magnetoelastic coupling were detected from refinement of the variable neutron diffraction patterns (5 K - 450K) while detailed analyses of magnetic data indicate that the magnetic phase transition is second order. Under magnetic field changes of 2 T and 8 T, the maximum values of the magnetic entropy change (-DELTASM max) around TC reach 1.65 J/kg K and 4.42 J/kg K, respectively.
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    The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction
    (American Institute of Physics, 2012-10-22) Cortie, DL; Stampfl, APJ; Klose, F; Du, Y; Wang, XL; Zhao, HY; Kimura, H; Cheng, ZX
    High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120K with a (1/2 1/2 1/2) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites. © 2012, American Institute of Physics.
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    The magnetocaloric effect and critical behaviour of the Mn0.94Ti0.06CoGe alloy
    (IOP Publishing Ltd., 2013-02-06) Shamba, P; Wang, JL; Debnath, JC; Kennedy, SJ; Zeng, R; Din, MFM; Hong, F; Cheng, ZX; Studer, AJ; Dou, SX
    Structural, magnetic and magnetocaloric properties of the Mn(0.94)Ti(0.06)CoGe alloy have been investigated using x-ray diffraction, DC magnetization and neutron diffraction measurements. Two phase transitions have been detected, at T(str) = 235 K and T(C) = 270 K. A giant magnetocaloric effect has been obtained at around Tstr associated with a structural phase transition from the low temperature orthorhombic TiNiSi-type structure to the high temperature hexagonal Ni(2)In-type structure, which is confirmed by neutron study. In the vicinity of the structural transition, at T(str), the magnetic entropy change, -Delta S(M) reached a maximum value of 14.8 J kg(-1) K(-1) under a magnetic field of 5 T, which is much higher than that previously reported for the parent compound MnCoGe. To investigate the nature of the magnetic phase transition around T(C) = 270 K from the ferromagnetic to the paramagnetic state, we performed a detailed critical exponent study. The critical components gamma, beta and delta determined using the Kouvel-Fisher method, the modified Arrott plot and the critical isotherm analysis agree well. The values deduced for the critical exponents are close to the theoretical prediction from the mean-field model, indicating that the magnetic interactions are long range. On the basis of these critical exponents, the magnetization, field and temperature data around T(C) collapse onto two curves obeying the single scaling equation M(H, epsilon) = epsilon(beta)f +/- (H/epsilon(beta+gamma)). © 2013 IOP Publishing LTD
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    On the crystal structure and magnetic properties of the Mn0.94Ti0.06CoGe alloy
    (American Institute of Physics., 2013-05-07) Shamba, P; Wang, JL; Debnath, JC; Zeng, R; Hong, F; Cheng, ZX; Studer, AJ; Kennedy, SJ; Dou, SX
    Structural and magnetic properties of Mn0.94Ti0.06CoGe have been studied by a combination of bulk magnetisation and neutron diffraction measurements over the temperature range of 5 K-350 K. The crystal structural transition occurs at T-str (similar to 235 K) with a change in symmetry from the low temperature orthorhombic TiNiSi-type structure (space group Pnma) to the high temperature hexagonal Ni2In-type structure (space group P63/mmc) and the magnetic phase transition takes place around T-C = 270 K. It is found that the structural transition around T-str is incomplete and there is a co-existence of the orthorhombic and hexagonal structures between T-str and T-C (similar to 270 K). These results are discussed in connection with the magnetic and magnetocaloric behaviours in Mn0.94Ti0.06CoGe. © 2013, American Institute of Physics.
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    Spin reorientation transition and negative magnetoresistance in ferromagnetic NdCrSb3 single crystals
    (MDPI, 2023-02-20) Chen, L; Zhao, WY; Wang, ZC; Tang, F; Fang, Y; Zeng, Z; Xia, ZC; Cheng, ZX; Cortie, DL; Rule, KC; Wang, XL; Zheng, RK
    High-quality NdCrSb3 single crystals are grown using a Sn-flux method, for electronic transport and magnetic structure study. Ferromagnetic ordering of the Nd3+ and Cr3+ magnetic sublattices are observed at different temperatures and along different crystallographic axes. Due to the Dzyaloshinskii–Moriya interaction between the two magnetic sublattices, the Cr moments rotate from the b axis to the a axis upon cooling, resulting in a spin reorientation (SR) transition. The SR transition is reflected by the temperature-dependent magnetization curves, e.g., the Cr moments rotate from the b axis to the a axis with cooling from 20 to 9 K, leading to a decrease in the b-axis magnetization f and an increase in the a-axis magnetization. Our elastic neutron scattering along the a axis shows decreasing intensity of magnetic (300) peak upon cooling from 20 K, supporting the SR transition. Although the magnetization of two magnetic sublattices favours different crystallographic axes and shows significant anisotropy in magnetic and transport behaviours, their moments are all aligned to the field direction at sufficiently large fields (30 T). Moreover, the magnetic structure within the SR transition region is relatively fragile, which results in negative magnetoresistance by applying magnetic fields along either a or b axis. The metallic NdCrSb3 single crystal with two ferromagnetic sublattices is an ideal system to study the magnetic interactions, as well as their influences on the electronic transport properties. © 2023 The Authors, Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
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    Spin-cycloid instability as the origin of weak ferromagnetism in the disordered perovskite Bi0.8La0.2Fe0.5Mn0.5O3
    (American Physical Society, 2014-04-23) Bertinshaw, J; Cortie, DL; Cheng, ZX; Avdeev, M; Studer, AJ; Klose, F; Ulrich, C; Wang, XL
    Powder neutron diffraction and magnetometry studies have been conducted to investigate the crystallographic and magnetic structure of Bi0.8La0.2Fe0.5Mn0.5O3. The compound stabilizes in the Imma orthorhombic crystal symmetry in the measured temperature range of 5 to 380 K, with a transition to antiferromagnetic order at TN≈240 K. The spin cycloid present for BiFeO3 is found to be absent with 50% Mn3+ cation substitution, leading to G-type antiferromagnetic order with an enhanced out-of-plane canted ferromagnetic component, evident from measurable weak-ferromagnetic hysteresis. Structural modifications do not solely explain this behavior, indicating that modified electron exchange interactions must be taken into account. A classical spin simulation was developed to investigate the effect of random substitution in a disordered pseudocubic perovskite. The calculations took into account the nearest-neighbor, next-nearest-neighbor, and Dzyaloshinskii-Moriya interactions, along with the local spin anisotropy. Using this framework to extend the established Hamiltonian model for BiFeO3, we show that only certain types of perturbations at a magnetic defect and the surrounding molecular fields trigger a simultaneous collapse of cycloidal order and the emergence of the long-range weak-ferromagnetic component. By adopting values for the Mn molecular fields appropriate for REMnO3 (RE= rare earth), simulations of BiMn0.5Fe0.5O3 exhibit the key magnetic properties of our experimental observations.© 2014, American Physical Society.
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    Structural and magnetic properties of RTiNO2 (R=Ce, Pr, Nd) perovskite nitride oxides
    (Elsevier, 2015-03-01) Porter, SH; Huang, ZG; Cheng, ZX; Avdeev, M; Chen, ZX; Dou, SX; Woodward, PM
    Neutron powder diffraction indicates that CeTiNO2 and PrTiNO2 crystallize with orthorhombic Pnma symmetry (Ce: a=5.5580(5), b=7.8369(7), and c=5.5830(4) Å; Pr: a=5.5468(5), b=7.8142(5), and c=5.5514(5) Å) as a result of a–b+a– tilting of the titanium-centered octahedra. Careful examination of the NPD data, confirms the absence of long range anion order in both compounds, while apparent superstructure reflections seen in electron diffraction patterns provide evidence for short range anion order. Inverse magnetic susceptibility plots reveal that the RTiNO2 (R=Ce, Pr, Nd) compounds are paramagnetic with Weiss constants that vary from −28 to −42 K. Effective magnetic moments for RTiNO2 (R=Ce, Pr, Nd) are 2.43 μB, 3.63 μB, and 3.47 μB, respectively, in line with values expected for free rare-earth ions. Deviations from Curie–Weiss behavior that occur below 150 K for CeTiNO2 and below 30 K for NdTiNO2 are driven by magnetic anisotropy, spin–orbit coupling, and crystal field effects. © 2015 Elsevier Inc.
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    Substitution of Y for Pr in PrMn2Ge2-the magnetism of Pr0.8Y0.2Mn2Ge2
    (American Institute of Physics, 2013-05-07) Wang, JL; Campbell, SJ; Hofmann, M; Kennedy, SJ; Avdeev, M; Din, MFM; Zeng, R; Cheng, ZX; Dou, SX
    Pr0.8Y0.2Mn2Ge2 is found to exhibit four magnetic transitions on decreasing the temperature from the paramagnetic region: (i) paramagnetism to intralayer antiferromagnetism (AFl) at T-N(intra); (ii) AFl to canted ferromagnetism (Fmc) at T-C(inter); (iii) Fmc to conical magnetic ordering of the Mn sublattice (Fmi) at T-cc; and (iv) Fmi(Mn) to Fmi(Mn) + F(Pr) at T-C(Pr). These changes in magnetic structure are discussed in terms of changes in the Mn-Mn separation distances caused by the unit cell contraction and by electronic effects due to replacement of 20% of Pr with Y. © 2013 American Institute of Physics.
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    Suppression of the spin spiral in an antiferromagnetic BiFe 0.5 Mn 0.5 O3 thin film and powder
    (Australian Institute of Physics, 2012-02-02) Cortie, DL; Du, Y; Cheng, ZX; Klose, F; Wang, XL
    Since the advent of the spintronics paradigm [1], there has been a resurgence of interest in materials that simultaneously possess magnetic and ferroelectric ordering [2]. Such materials provide the realistic prospect of manipulating magnet elements using electric fields at room temperature. While electric field control has recently been demonstrated using the interfacial coupling between a multiferroic oxide and a metallic thin film [3], there is still a search to find a suitable single phase ferromagnetic multiferroic [4,5]. Previous work reported that a metastable phase of BiMnO3 was ferromagnetic with a Curie temperature of 99K [5] whereas BiFeO3 . is a canted anti-ferromagnetic below 640K with ferroelectric order [2]. We explored the effect on magnetic structure of including high percentages of Mn into a BiFeO3 host in a La0.2BiFe 0.5 Mn 0.5 O3 compound. Neutron diffraction was performed on an epitaxial nanoscale film using the instrumentation at ANSTO to obtain the magnetic structure at low temperature, and the results were compared with powders and magnetometry data. The neutron data for the film and powders both indicate a single magnetic transition to a highly collinear G-type antiferromagnetic order where the incommensurate spin spiral present for BiFeO3 appears to be suppressed by the addition of Mn . The Neél temperature is shifted to 225 K. The c/a ratio of the unit cell is found to differ between thin film and the powder suggesting that the epitaxial lattice matching to the SrTiO3 substrate strains the film in the ab plane but preserves the overall unit cell volume leading to a lattice expansion in the c direction and a further reduction in Neel temperature to 130 K. The magnetic properties of the film and powder appear to be dramatically different from the properties of nanoparticles reported for the same compound which showed multiple magnetic transitions to higher temperatures [4].
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    Topological insulator VxBi1.08-x Sn0.02Sb0.9Te2S as a promising n-type thermoelectric material
    (Elsevier, 2022-10) Chen, L; Zhao, WY; Li, M; Yang, G; Guo, L; Bake, A; Liu, P; Cortie, DL; Zheng, RK; Cheng, ZX; Wang, XL
    As one of the most important n-type thermoelectric (TE) materials, Bi2Te3 has been studied for decades, with efforts to enhance the thermoelectric performance based on element doping, band engineering, etc. In this study, we report a novel bulk-insulating topological material system as a replacement for n-type Bi2Te3 materials: V doped Bi1.08Sn0.02Sb0.9Te2S (V:BSSTS). The V:BSSTS is a bulk insulator with robust metallic topological surface states. Furthermore, the bulk band gap can be tuned by the doping level of V, which is verified by magnetotransport measurements. Large linear magnetoresistance is observed in all samples. Excellent thermoelectric performance is obtained in the V:BSSTS samples, e.g., the highest figure of merit ZT of ~ 0.8 is achieved in the 2% V doped sample (denoted as V0.02) at 530 K. The high thermoelectric performance of V:BSSTS can be attributed to two synergistic effects: (1) the low conductive secondary phases Sb2S3, and V2S3 are believed to be important scattering centers for phonons, leading to lower lattice thermal conductivity; and (2) the electrical conductivity is increased due to the high-mobility topological surface states at the boundaries. In addition, by replacing one third of costly tellurium with abundant, low-cost, and less-toxic sulfur element, the newly produced BSSTS material is inexpensive but still has comparable TE performance to the traditional Bi2Te3-based materials, which offers a cheaper plan for the electronics and thermoelectric industries. Our results demonstrate that topological materials with unique band structures can provide a new platform in the search for new high performance TE materials. © 2022 Elsevier B.V.
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    Tuneable magnetic phase transitions in layered CeMn2Ge2-xSix compounds
    (Springer Nature, 2015-06-19) Din, MFM; Wang, JL; Cheng, ZX; Dou, SX; Kennedy, SJ; Avdeev, M; Campbell, SJ
    The structural and magnetic properties of seven CeMn2Ge2-xSix compounds with x = 0.0–2.0 have been investigated in detail. Substitution of Ge with Si leads to a monotonic decrease of both a and c along with concomitant contraction of the unit cell volume and significant modifications of the magnetic states - a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Si-rich compounds. The magnetic phase diagram has been constructed over the full range of CeMn2Ge2-xSix compositions and co-existence of ferromagnetism and antiferromagnetism has been observed in CeMn2Ge1.2Si0.8, CeMn2Ge1.0Si1.0 and CeMn2Ge0.8Si1.2 with novel insight provided by high resolution neutron and X-ray synchrotron radiation studies. CeMn2Ge2-xSix compounds (x = 0, 0.4 and 0.8) exhibit moderate isothermal magnetic entropy accompanied with a second-order phase transition around room temperature. Analysis of critical behaviour in the vicinity of TCinter for CeMn2Ge2 compound indicates behaviour consistent with three-dimensional Heisenberg model predictions. © 2021 Springer Nature Limited