Browsing by Author "Ren, QY"
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- ItemThe effect of Fe and Ni substitution in magnetocaloric MnCoGe(Australian Institute of Physics, 2013-02-05) Ren, QY; Hutchinson, WD; Wang, JL; Kemp, W; Cobas, R; Cadogan, JM; Campbell, SJThe MnCoGe family of compounds shows potential as a rare-earth free material for magnetocaloric applications around room temperature. We present initial findings on the effects of the substitution of Fe and Ni for Mn in a series of Mn1-xTxCoGe compounds (T = Fe, Ni; x = 0.04 - 0.10). Investigations include x-ray diffraction, differential scanning calorimetry(200 - 670 K) and magnetisation (5 - 350 K) measurements in magnetic fields up to 8 T. The influence of the Fe and Ni substitutions on the transformation temperature between the hexagonal and orthorhombic structures, the resultant phase fractions and their magnetic phase transitions are reported.
- ItemESR studies of magnetocaloric PrMn2-xFexGe2(Australian Institute of Physics, 2014-02-05) Ren, QY; Hutchison, WD; Campbell, SJ; Wang, JLIn a recent paper, we investigated the magnetic structures, phase transitions and magnetocaloric entropy of PrMn1.6Fe0.4Ge2 by a combination of bulk magnetometry, 57Fe Mössbauer spectroscopy and electron spin resonance (ESR) over the temperature range 5-300 K. This work followed on from a broader study of the PrMn2-xFexGe2 family of compounds, in which it was found that with decreasing temperature from the paramagnetic region, three magnetic phase transitions have been detected for PrMn1.6Fe0.4Ge2. The transition temperatures and related magnetic structures (using the notation of [3]) the magnetic structures are: (i) paramagnetism to intralayer antiferromagnetism (AFl) at TN intra=370 K; (ii) AFl to canted ferromagnetism (Fmc) at TC inter∼230 K, and (iii) a third transition around TC Pr∼30 K with ferromagnetic ordering of the Pr sublattice resulting in the combined magnetic region (Fmc+F(Pr)). Here the ESR, focusing on the Pr3+ 4f magnetic moment and undertaken in the vicinity of the lowest transition temperature, is the subject of further analysis in order to correlate the observed resonant line/s and changes in g-factors with the phases mentioned above. In particular an aim is to link the increase in g factor of the Pr3+ ion (from g = 0.85 in the region above TC Pr∼30 K to g ~ 2.5 at 8 K) with the bulk moments measured via DC magnetisation.
- ItemMagnetic and structural transitions in magnetocaloric Mn(Co1-xNix)Ge alloys(Australian Institute of Physics, 2017-02-01) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Cadogan, JM; Campbell, SJThe magnetocaloric effect (MCE) - a significant temperature change due to the entropy change around magnetic transitions in materials driven by magnetisation or demagnetisation - has emerged as an increasingly important topic in condensed matter physics in the past two decades. A direct (positive) MCE occurs around a magnetic transition from ferromagnetism (FM) to paramagnetism (PM), while an inverse (negative) MCE is obtained around a magnetic transition from antiferromagnetism (AFM) to FM. If such magnetic transitions couple with a structural transition, a first-order magneto-structural transition can form and hence strengthen the MCE. In this work, the magnetic and structural transitions have been tuned by substitution of Ni for Co in MnCoGe. The Mn(Co1-xNix)Ge samples (x = 0.14 - 1.00) were studied by magnetisation, x-ray and neutron powder diffraction measurements over the temperature range 5 - 450 K. Mn(Co1-xNix)Ge alloys have an orthorhombic (Orth) TiNiSi-type structure (Pnma) at low temperature with transformation to a hexagonal (Hex) Ni2In-type structure (P63/mmc) at the martensitic transformation temperature TM. The increase of the Ni content changes the orthorhombic phase from FM (x < 0.55) to spiral-AFM (x ≥ 0.55). In addition, the transformation temperature TM for the reverse martensitic transformation - from orthorhombic to hexagonal - decreases with Ni content x when x < 0.55 and then increases when x ≥ 0.55. The adjustment of TM leads to the occurrences of first-order FM-Orth/PM-Hex magneto-structural transitions and large values of the direct MCE in the samples with ~0.20 < x < ~0.60. Moreover, the spiral-AFM/FM magnetic transitions in the orthorhombic phase for samples with ~0.55 < x < ~0.75 result in an inverse MCE.
- ItemThe magnetic properties and magnetocaloric effect in (Mn1-xNix)CoGe(Australian Institute of Physics, 2016-02-02) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Campbell, SJMagnetic refrigeration based on magnetocaloric effect is considered as a potential alternative to the conventional gas-compression based refrigeration [1], because the former can improve energy efficiency and reduce emission of environment-harmful chemicals. Materials with firstorder magneto-structural transitions are of great interest for large magnetocaloric effect, e.g. Gd5(Si,Ge)4 and Heusler alloys [3]. Magneto-structural transition and large magnetocaloric effect were also observed in MnCoGe-based alloys. For MnCoGe-based alloys, there are two stable crystallographic structures: nominally low temperature TiNiSi-type orthorhombic structure (Pnma, martensitic phase) and the high temperature Ni2In-type hexagonal structure (P63/mmc, austenitic phase), with a martensitic transformation around TM ~650 K [4]. Both phase present as ferromagnetic state at low temperature with Curie temperature of ~345 K and ~275 K, for the martensitic and austenitic phases, respectively. When the martensitic transition temperature TM is moved into the temperature range of the two Curie temperatures, e.g. Fe doping (Mn1−xFex)CoGe [5], coupling of magnetic and lattice structures is obtained and hence present a magneto-structural transition from the ferromagnetic martensite to the paramagnetic austenite. In this work, Ni was used as substitute for Mn to drive the martensitic transformation temperature. The crystallographic structures and magnetic properties of annealed (Mn1-xNix)CoGe (x = 0.02, 0.03, 0.04, 0.05, 0.06 and 0.07) were studied via X-ray diffraction (T = 20-310 K) and magnetisation (T = 5-340 K) measurements. Then the magneto-structural transition were confirmed by neutron diffraction experiments (T = 5-320 K), and the influence of magnetic field on the magnetostructural transition were investigated using magnetic-field neutron diffraction (B = 0-9 T). The magnetic entropy changes have been derived in the conventional way from a series of isothermal magnetisation experiments, e.g. –Sm ~ 8.8 J kg−1 K−1 for a magnetic field change of B = 0-5 T in (Mn0.95Ni0.05)CoGe.
- ItemThe magnetic properties and magnetocaloric effect in Mn1-xNixCoGe(Australian Institute of Physics, 2015-02-03) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Campbell, SJMnCoGe-based compounds reveal promise for magnetic refrigeration and as such have been extensively investigated over the last decade [1]. Refrigeration based on magnetic cooling via the magnetocaloric effect offers potential as an alternative to conventional gas-compression systems. MoCoGe-based compounds have two crystallographic structures: nominally low temperature TiNiSi-type orthorhombic structure (Pnma) and the high temperature Ni2In-type hexagonal structure (P63/mmc). When the structural transition temperature between these two structures is ‘tuned’ between the respective Curie temperatures of the phases (~345 K for the orthorhombic phase and ~275 K for the hexagonal phase [1]), a magneto-structural transition can be obtained. Such a transition allows a direct change from the ferromagnetic orthorhombic phase to the paramagnetic hexagonal phase [1]. For a magneto-structural transition, the lattice and magnetic entropy changes occur simultaneously, thereby providing scope for observation of a large magnetocaloric effect [2]. The crystallographic structures and magnetic properties of annealed Mn1-xNixCoGe (x = 0.02, 0.03, 0.04, 0.05, 0.06 and 0.07) have been investigated using variable temperature X-ray diffraction and neutron diffraction (T = 5 - 320 K) with neutron diffraction measurements carried out both with and without applied magnetic fields for Mn0.95Ni0.05CoGe (B = 0 - 8 T). Such experiments allow separation of the structural and magnetic contributions to the total entropy change at a magneto-structural transition [3]. The magnetic entropy changes have been derived in the conventional way from a series of isothermal magnetisation experiments, e.g. –ΔSm ~8.8 J kg-1 K-1 for a magnetic field change of ΔB = 0 - 5 T in Mn0.95Ni0.05CoGe.
- ItemMagnetic structures of magnetocaloric (Mn1-xNix)CoGe and Mn(Co1-xNix)Ge alloys(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Lee, WT; Cadogan, JM; Campbell, SJThe magnetocaloric effect (MCE) - a significant temperature change around the magnetic transitions in materials driven by magnetisation or demagnetisation - has emerged as an increasingly important topic in condensed matter physics in the past two decades. This development is due primarily to potential applications in refrigeration as an alternative to gas-based compression-expansion refrigeration [1]. A large MCE occurs generally around a magnetic transition, especially when the magnetic transition coincides with a structural transition (magneto-structural transition) [1]. MnCoGe-based compounds offer particular scope for MCE applications, particularly for cooling around room temperature with previous studies having shown that it is relatively straightforward to engineer the structural transition temperature and thereby produce a magneto-structural transition [2]. In the present work, a series of (Mn1-xNix)CoGe (x = 0.0-0.07) and Mn(Co1-xNix)Ge (x = 0.14-1.00) samples have been prepared in order to investigate the effects of doping the Mn and Co sites of MnCoGe with Ni. The crystal structures and magnetisation were measured using XRD (20-310 K) and PPMS (5-320 K) with the magneto-structural transitions studied using neutron powder diffraction and polarised neutron diffraction (5-450 K; WOMBAT, OPAL). Magneto-structural transitions from ferromagnetic-orthorhombic (FM-Orth) structure to paramagnetic-hexagonal (PM-Hex) structure were obtained in both (Mn1-xNix)CoGe and Mn(Co1-xNix)Ge around room temperature. A spiral antiferromagnetic (SP-AFM) structure was also observed in the orthorhombic structure of Mn(Co1-xNix)Ge (x ≥ 0.55) at low temperature, following by a magnetic transition from SP-AFM to FM at higher temperature. In addition, the influence of magnetic field on the FM-Orth/PM-Hex magneto-structural transition was studied using field dependent neutron diffraction (5-320 K; 0-9 T). Our investigations show that normal (inverse) MCE are obtained around the FM-Orth/PM-Hex (SP-AFM/FM) transitions in (Mn1-xNix)CoGe and Mn(Co1-xNix)Ge.
- ItemMagnetism and magnetocaloric effect of Mn0.98Fe0.02CoGe(Wiley Online Library, 2014-03-26) Ren, QY; Hutchison, WD; Wang, JL; Muñoz-Pérez, S; Cadogan, JM; Campbell, SJThe crystallographic and magnetic properties of Mn0.98Fe0.02CoGe have been investigated by X-ray diffraction, dc magnetization and neutron diffraction over the temperature range 20–450 K. The temperature dependence of the phase fractions of the orthorhombic and hexagonal phases is described well by a Gaussian distribution. The Mn0.98Fe0.02CoGe sample exhibits a first-order magneto-structural transition centred at TMS ∼ 297 K of FWHM ∼37 K with a magnetic entropy change of −ΔSM = 24(1) J kg−1 K−1 for ΔB = 0–5 T. Neutron diffraction indicates a ferromagnetic orthorhombic structure below TMS with only the Mn carrying magnetic moment (3.98(6) µB) at 20 K. The sample is paramagnetic in the hexagonal phase above TMS.© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- ItemThe magneto-structural transition in magnetocaloric Mn1-xFexCoGe(Australian Institute of Physics, 2015-02-03) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Din, MFM; Muñoz-Pérez, S; Cadogan, JM; Campbell, SJMagnetic refrigeration techniques based on the magnetocaloric effect are considered an increasingly viable alternative to conventional gas-compression refrigerant, particularly with energy-saving and environmental aspects in mind. Following the discovery of a large magnetocaloric effect in Gd5Si2Ge2, researchers have shifted their attention to investigation of materials exhibiting magneto-structural transitions where large magnetic entropy changes are expected. MnCoGe-based compounds are promising materials for the exploration of large magnetocaloric effects. They are relatively cheap (no rare earth elements) and, importantly, allow an appropriate temperature window (275 – 345 K) around room temperature in which the magneto-structural transition may be positioned. It has been established that Fe is a suitable substitute for Mn to ‘tune’ the structural transition temperature and hence obtain a magneto-structural transition. Here we present the results of a detailed investigation of the structural and magnetic properties and magnetocaloric effect for a range of as-prepared Mn1-xFexCoGe alloys (x = 0.01, 0.02, 0.03 and 0.04) using temperature variable x-ray diffraction (20 – 310 K), neutron diffraction (5 – 450 K) and physical properties measurement system (PPMS, 5 – 300 K). Particular attention will focus on analysis of neutron diffraction data for Mn0.98Fe0.02CoGe and the nature of the magnetic phase transition in Mn0.98Fe0.02CoGe.
- ItemMagnetocaloric Mn(Co1-xNix)Ge - structural and magnetic transitions(Australian Institute of Physics, 2018-01-30) Ren, QY; Hutchinson, WD; Wang, JL; Studer, AJ; Campbell, SJThe structural and magnetic properties of MnCoGe-based alloys have been studied extensively in recent years due to their potential application as magnetic cooling materials based on the magnetocaloric effect (MCE). The Mn(Co1-xNix)Ge series is of particular interest as magnetic transitions in the range 275 K to 345 K generally coincide with a martensitic structural transition TM, with such an overlap then allowing scope for the formation of magneto-structural transitions (ferromagnetic orthorhombic to paramagnetic hexagonal) and hence an associated large MCE [e.g. 1]. Neutron diffraction, magnetisation and x-ray experiments on Mn(Co1-xNix)Ge compounds (x = 0.12 to 1.00) have demonstrated magnetic structures ranging from ferromagnetic for x < 0.50 to non-collinear spiral antiferromagnetic for x > 0.55 at low temperature (e.g. 5 K). TM is found to decrease initially with increasing Ni content and then increase. First-order magneto-structural transitions are observed in Mn(Co1-xNix)Ge samples for ~0.20 < x < ~0.65 with the presence of ferro-/antiferro-magnetic structures in Mn(Co1-xNix)Ge allowing investigation of both direct and inverse magnetocaloric effects. Our results (including the magnetic phase diagram for Mn(Co1-xNix)Ge) are discussed in terms of the increase of valence electron concentration on substitution of Ni (3d84s2) for Co (3d74s2) in the orthorhombic phase, leading to expansion of the unit cell and redistribution of the valence electrons [2].
- ItemNegative thermal expansion of Ni-doped MnCoGe around room temperature - magnetic tuning(Australian Institute of Physics, 2019-02-05) Ren, QY; Hutchinson, WD; Wang, JL; Studer, AJ; Wang, G; Zhou, H; Ma, J; Campbell, SJSeveral materials have been shown to exhibit abnormal contraction with increasing temperature; the phenomenon of negative thermal expansion (NTE). Given this special property, NTE materials fulfill important functions in many modern technologies, such as electrodes of fuel cell, organic light-emitting diode (OLED), optical fibre, as well as high precision electronics and optical mirrors. In general, Nate properties are associated with local structural distortions or phase transitions, such as transverse phonon vibration in rigid unit modes, exile network of metal-organic framework, charge transfer, magneto-volume effect, ferroelectric transition, as well as displacive phase transition. Control or manipulation of Nate properties have become topics of increasing importance over the past two decades. Effective methods to produce materials with Nate properties include chemical doping, nanostructuralization, hydration and applied pressure. Recently, MoCoGe-based compounds were considered as a group of materials that exhibit giant NTE, with this behaviour attributed to the displacive martensitic phase transformation. In this investigation, we reported a new method to manipulate the NTE properties using applied magnetic fields. It is found that doping of 5% Ni on the Mn site could bring about a magneto-structural (MS) coupling in MnCoGe-based compounds. Magnetic-field-dependent neutron diffraction measurements demonstrated that an 8 T magnetic field could suppress the NTE by 31% at 295 K through this MS coupling.
- ItemThermal batteries based on inverse barocaloric effects(Science Advances, 2023-02) Zhang, Z; Li, K; Lin, SC; Song, R; Yu, DH; Wang, Y; Wang, JF; Kawaguchi, S; Zhang, Z; Yu, CY; Li, XD; Chen, J; He, LH; Mole, RA; Yuan, B; Ren, QY; Qian, K; Cai, ZL; Yu, JG; Wang, MC; Zhao, CY; Tong, X; Zhang, ZD; Li, BTo harvest and reuse low-temperature waste heat, we propose and realize an emergent concept-barocaloric thermal batteries based on the large inverse barocaloric effect of ammonium thiocyanate (NH4SCN). Thermal charging is initialized upon pressurization through an order-to-disorder phase transition, and the discharging of 43 J g-1 takes place at depressurization, which is 11 times more than the input mechanical energy. The thermodynamic equilibrium nature of the pressure-restrained heat-carrying phase guarantees stable long-duration storage. The barocaloric thermal batteries reinforced by their solid microscopic mechanism are expected to substantially advance the ability to take advantage of waste heat. Copyright © 2023 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).