Browsing by Author "Din, MFM"

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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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    Effects of Cr substitution on structural and magnetic properties in La0.7Pr0.3Fe11.4Si1.6 compound
    (AIP Scitation, 2014-04-03) Din, MFM; Wang, JL; Studer, AJ; Gu, QF; Zeng, R; Debnath, JC; Shamba, P; Kennedy, SJ; Dou, SX
    In an effort to explore the effect of substitution Fe by Cr in NaZn13-type La0.7Pr0.3Fe11.4−xCrxSi1.6 (x = 0, 0.06, 0.12, 0.26, and 0.34) compounds, the structure and magnetic properties have been investigated by high intensity of x-ray and neutron diffraction, scanning electron microscopy, specific heat, and magnetization measurement. It has been found that a substitution of Cr for Fe in this compounds leads to decrease in the lattice parameter a at room temperature but variation on Curie temperature (TC). While the first order nature of magnetic phase transition around TC does not change with increasing Cr content up to x = 0.34. High intensity x-ray and neutron diffraction study at variable temperatures for highest Cr concentration x = 0.34 confirmed the presence of strong magneto-volume effect around TC and indicated the direct evident of coexistence across magnetic transition as characteristic of first order nature. The values of −ΔSM around TC decrease from 17 J kg−1 K−1 for x = 0 to 12 J kg−1 K−1 for x = 0.06 and then increases with further increasing Cr content up to 17.5 J kg−1 K−1 for x = 0.34 under a change of 0–5 T magnetic field. Similar behavior on relative cooling power which is decrease from 390 J kg−1 for x = 0 to 365 J kg−1 for x = 0.06 at the beginning and then increases up to 400 J kg−1 for x = 0.34. From the point of this view with the highest Cr concentration (x = 0.34) exhibits favourable material candidate for magnetic refrigerator application therefore should inspire further study concerning on higher Cr concentration in this compound. © 2014, AIP Publishing LLC.
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    Effects of Cu substitution on structural and magnetic properties of La0.7Pr0.3Fe11.4Si1.6 compounds
    (Elsevier Ltd., 2013-05-01) Din, MFM; Wang, JL; Zeng, R; Shamba, P; Debnath, JC; Dou, SX
    The structure and magnetic properties of the La0.7Pr0.3Fe11.4−xCuxSi1.6 compounds have been investigated by X-ray diffraction, scanning electron microscopy and magnetisation measurements. Cu substitution for Fe in La0.7Pr0.3Fe11.4−xCuxSi1.6 (x = 0, 0.06, 0.12, 0.23, 0.34) leads to a reduction in hysteresis loss, a decrease in magnetic entropy change but an increase in Curie temperature (TC). The influences of annealing processes at different temperatures on TC, magnetic hysteresis, and the magnetocaloric effect (MCE) of La0.7Pr0.3Fe11.4Si1.6 are investigated in detail. It has been found that a short-time and high temperature annealing process has benefits for the formation of the NaZn13 types as phase compared to a long-time and low temperature annealing process. © 2013, Elsevier Ltd.
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    Magnetic and structural properties of intermetallic NdMn2-xTixSi2 compounds
    (Australian Optical Society, 2012-01-01) Din, MFM; Wang, JL; Zeng, R; Shamba, P; Hutchison, WD; Avdeev, M; Kennedy, SJ; Campbell, SJ
    Giant magnetocalorie effects have been observed in NdMn2-xTixSi2 around the Curie Temperature Tc (with AB = 5-0 T.) The magnetic entropy charge decreases with increasing x from 27 J kg- K- for x=0 to 10 J kg- K- for x =0.3. Neutron investigations indicate that magnetostructural coupling contribution plays a critical role in the large value of magnetic entropy change.
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    Magnetic phase transitions and entropy change in layered NdMn1.7Cr0.3Si2
    (AIP Publishing, 2014-01-27) Din, MFM; Wang, JL; Campbell, SJ; Studer, AJ; Avdeev, M; Kennedy, SJ; Gu, QF; Zeng, R; Dou, SX
    A giant magnetocaloric effect has been observed around the Curie temperature, TC ∼ 42 K, in NdMn1.7Cr0.3Si2 with no discernible thermal and magnetic hysteresis losses. Below 400 K, three magnetic phase transitions take place around 380 K, 320 K and 42 K. Detailed high resolution synchrotron and neutron powder diffraction (10–400 K) confirmed the magnetic transitions and phases as follows: TN intra ∼ 380 K denotes the transition from paramagnetism to intralayer antiferromagnetism (AFl), TN inter ∼ 320 K represents the transition from the AFl structure to the canted antiferromagnetic spin structure (AFmc), while TC ∼ 42 K denotes the first order magnetic transition from AFmc to canted ferromagnetism (Fmc + F(Nd)) due to ordering of the Mn and Nd sub-lattices. The maximum values of the magnetic entropy change and the adiabatic temperature change, around TC for a field change of 5 T are evaluated to be −ΔSM max ∼ 15.9 J kg−1 K−1 and ΔTad max ∼ 5 K, respectively. The first order magnetic transition associated with the low levels of hysteresis losses (thermal <∼0.8 K; magnetic field <∼0.1 T) in NdMn1.7Cr0.3Si2 offers potential as a candidate for magnetic refrigerator applications in the temperature region below 45 K. ©, AIP Publishing LLC.
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    Magnetic properties and magnetocaloric effect in Mn0.9 Ti 0.1 CoGe
    (Australian Institute of Physics, 2013-02-06) Wang, JL; Shamba, P; Hutchison, WD; Din, MFM; Avdeev, M; Kennedy, SJ; Campbell, SJ; Zeng, R; Dou, SX
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    Magnetic properties and magnetocaloric effect of in layered NdMn1.7V0.2Si2
    (Australian Institute of Physics, 2013-02-06) Din, MFM; Wang, JL; Zeng, R; Hutchison, WD; Avdeev, M; Kennedy, SJ; Dou, SX
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    Magnetic properties and magnetocaloric effect of NdMn2-xTixSi2 compounds
    (IOP Publishing Ltd, 2013-10-16) Din, MFM; Wang, JL; Campbell, SJ; Zeng, R; Hutchison, WD; Avdeev, M; Kennedy, SJ; Dou, SX
    The structural and magnetic properties of the intermetallic compounds NdMn 2− x Ti x Si 2 ( x = 0, 0.1, 0.2, and 0.3) have been studied by x-ray and high resolution neutron powder diffraction, specific heat, dc magnetization, and differential scanning calorimetry measurements over the temperature range 3–450 K. The Curie temperature and Néel temperature of NdMn 2 Si 2 decrease from T C = 36 K and T N = 380 K to T C = 14 K and T N = 360 K, respectively, on substitution of Ti ( x = 0.3) for Mn. The magnetocaloric effect at the first order ferromagnetic phase transition at T C , has been investigated in detail. Under a change of magnetic field of 0–5 T, the maximum value of the magnetic entropy change is 27 J kg −1 K −1 at x = 0, reducing to 15.3 J kg −1 K −1 at x = 0.1 and 10 J kg −1 K −1 at x = 0.3; importantly, no thermal or field hysteresis losses occur (eliminated from 0.3 K and 28.5 J kg −1 at x = 0 around T C ) with increase in Ti concentration. Combined with the lack of any hysteresis effects, these findings indicate that NdMn 1.9 Ti 0.1 Si 2 compound offers potential as a candidate for magnetic refrigerator applications in the temperature region below 35 K. © 2013, IOP Publishing LTD.
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    Magnetic properties and magnetocaloric effect of NdMn2−xCuxSi2 compounds
    (AIP Publishing, 2014-02-19) Din, MFM; Wang, JL; Avdeev, M; Gu, QF; Zeng, R; Campbell, SJ; Kennedy, SJ; Dou, SX
    Structural and magnetic properties of NdMn2−x Cu xSi2 compounds (x = 0–1.0) have been investigated by high intensity x-ray and resolution neutron diffraction (3–450 K), specific heat, dc magnetization, and differential scanning calorimetry measurements. Substitution of Cu for Mn leads to an increase in the lattice parameter a but a decrease in c at room temperature. Two magnetic phase transitions have been found for NdMn2−x Cu xSi2 compounds with TN for the antiferromagnetic ordering of Mn-sublatttice and TC for the Nd-sublattice ferromagnetic ordering, respectively. TC increases significantly with increasing Cu content from 36 K at x = 0 to 100 K at x = 1.0. Moreover, it is found that the order of magnetic phase transition around TC also changes from first order at x < 0.6 to second order transition for x ≥ 0.6. The spontaneous magnetization found to decrease with the increase in Cu concentration which can be understood in the term of the dilution effect of Cu for Mn. The values of −ΔSM around TC decrease with increasing x from 27 J kg−1 K−1 for x = 0 to 0.5 J kg−1 K−1 for x = 1.0 under 0–5 T field. Refinement of neutron diffraction patterns for x = 0.2 confirms the magnetic states detected by magnetic study and also indicates that the lattice constants a and c show a distinct variation around TC. © 2014, AIP Publishing LLC.
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    Magnetic transitions and the magnetocaloric effect in the Pr1−xYxMn2Ge2 system
    (Wiley Online Library, 2014-03-26) Wang, JL; Campbell, SJ; Din, MFM
    Layered rare earth compounds in the RMn2X2 series (R = rare-earth; X = Ge, Si) are of interest for potential cooling applications at lower temperatures as they enable the structural and magnetic behavior to be controlled via substitution of R, Mn, and X atoms on the 2a, 4d, and 4e sites respectively. We continue investigations of the Pr1−xYxMn2Ge2 magnetic phase diagram as functions of both composition and Mn–Mn spacing using X-ray and neutron diffraction, magnetization and differential scanning calorimetry measurements. Pr1−xYxMn2Ge2 exhibits an extended region of re-entrant ferromagnetism around x ∼ 0.5 with re-entrant ferromagnetism at inline image for Pr0.5Y0.5Mn2Ge2. The entropy values −ΔSM around the ferromagnetic transition temperatures inline image from the layered antiferromagnetic AFl structure to the canted ferromagnetic structure Fmc (typically inline image) have been derived for Pr1−xYxMn2Ge2 with x = 0.0, 0.2, and 0.5 for ΔB = 0–5 T. The changes in magnetic states due to Y substitution for Pr are discussed in terms of chemical pressure, external pressure, and electronic effects.© 2014, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Magnetism and magnetic structures of PrMn2Ge2-xSix
    (IOP Publishing, 2013-09-25) Wang, JL; Campbell, SJ; Hofmann, M; Kennedy, SJ; Zeng, R; Din, MFM; Dou, SX; Arulraj, A; Stusser, N
    The structural and magnetic properties of seven PrMn2Ge2-xSix compounds with Si concentrations in the range x = 0.0-2.0 have been investigated by x-ray diffraction, magnetic (5-350 K), differential scanning calorimetry (300-500 K) and neutron diffraction (3-480 K) measurements. Replacement of Ge by Si leads to a contraction of the unit cell and significant modifications to the magnetic states-a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Si-rich compounds. The compositional dependence of the room temperature lattice parameters exhibits non-linear behaviour around x = 1.2, reflecting the presence of magnetovolume effects. Re-entrant ferromagnetism has been observed in both PrMn2Ge1.0Si1.0 and PrMn2Ge0.8Si1.2 compounds with co-existence of canted ferromagnetism and canted antiferromagnetism detected, with both compounds exhibiting a larger unit cell volume in the canted Fmc state than in the canted AFmc. Combined with earlier studies of this system, the magnetic phase diagram has been constructed over the full range of PrMn2Ge2-xSix compositions (x = 0.0-2.0) and over the temperature range of interest (T = 3-480 K). In common with other systems in the RMn2X2 series, the overall magnetic behaviour of PrMn2Ge2-xSix compounds is governed by the strong dependence of the magnetic couplings on the Mn-Mn spacing within the ab-plane. Both total manganese moment mu(Mn)(tot) and in-plane manganese moment mu(Mn)(ab) at 5 K are found to decrease with increasing Si content, which can be ascribed to the reduction of Mn-Mn separation distance and stronger Si-Mn hybridization compared with Ge-Mn hybridization. Pr site ferromagnetic ordering occurs for x < 1.6 below T-C(Pr). © 2013, IOP Publishing Ltd.
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    The 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, SJ
    Magnetic 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.
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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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    Neutron diffraction study of MnNiGa2—structural and magnetic behaviour
    (AIP Publishing, 2014-01-07) Wang, JL; Ma, L; Hofmann, M; Avdeev, M; Kennedy, SJ; Campbell, SJ; Din, MFM; Hoelzel, M; Wu, GH; Dou, SX
    MnNiGa2 crystallizes in the L21 (Heusler) structure and has a ferromagnetic ordering temperature TC ∼ 192 K. Rietveld refinement of the neutron diffraction patterns indicates that the Ga atoms occupy the equivalent 8c position, while Mn and Ni share the 4a (0, 0, 0) and 4b (0.5, 0.5, 0.5) sites with a mixed occupancy of Mn and Ni atoms. It is found that that ∼83% of Mn and ∼17% Ni are located at the 4a site while ∼83% of Ni and ∼17% Mn occupy the 4b site. There is no evidence of a magneto-volume effect around TC. In agreement with this finding, our detailed critical exponent analyses of isothermal magnetization curves and the related Arrott plots confirm that the magnetic phase transition at TC is second order. © 2014,AIP Publishing LLC.
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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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    Ti substitution for Mn in MnCoGe - the magnetism of Mn0.9Ti0.1CoGe
    (Elsevier Science, 2013-11-15) Wang, JL; Shamba, P; Hutchison, WD; Din, MFM; Debnath, JC; Avdeev, M; Zeng, R; Kennedy, SJ; Campbell, SJ; Dou, SX
    Bulk magnetization measurements (5–320 K; 0–8 T) reveal that below room temperature Mn0.9Ti0.1CoGe exhibits two magnetic phase transitions at ∼178 K and ∼280 K. Neutron diffraction measurements (3–350 K) confirm that the transition at ∼178 K is due to the structural change from the low-temperature orthorhombic TiNiSi-type structure (space group Pnma) to the higher temperature hexagonal Ni2In-type structure (space group P63/mmc), while the transition at ∼280 K originates from the transition from ferromagnetism to paramagnetism. The magnetocaloric behaviour of Mn0.9Ti0.1CoGe around Tstr ∼ 178 K and TC ∼ 280 K as determined via the magnetic field and temperature dependences of DC magnetisation are given by the maximum values of the magnetic entropy changes −Δ S M max = 6.6 J kg−1 K−1 around Tstr ∼ 178 K, and −Δ S M max = 4.2 J kg−1 K−1 around TC ∼ 280 K for a magnetic field change of ΔB = 0–8 T. Both structural entropy – due to the unit cell expansion of ∼4.04% – and magnetic entropy – due to an increase in the magnetic moment of ∼31% – are found to contribute significantly to the total entropy change around Tstr. Critical analysis of the transition around TC ∼ 280 K leads to exponents similar to values derived from a mean field theory, consistent with long-range ferromagnetic interactions. It was found that the field dependence of −Δ S M max can be expressed as −Δ S M max ∝ Bn with n = 1 for the structural transition around Tstr and n = 2/3 for the ferromagnetic transition around TC, thereby confirming the second order nature of this latter transition.© 2013, Elsevier Ltd.
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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