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R Nirmala
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R Nirmala
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R Nirmala
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Nirmala, R.
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11 results
Now showing 1 - 10 of 11
- PublicationThe isothermal section of Gd-Ni-Si system at 1070 K(01-03-2016)
;Morozkin, A. V. ;Knotko, A. V. ;Yapaskurt, V. O. ;Manfrinetti, P. ;Pani, M. ;Provino, A.; ;Quezado, S.Malik, S. K.The Gd-Ni-Si system has been investigated at 1070 K by X-ray and microprobe analyses. The existence of the known compounds, i.e.: GdNi10Si2, GdNi8Si3, GdNi5Si3, GdNi7Si6, GdNi6Si6, GdNi4Si, GdNi2Si2, GdNiSi3, Gd3Ni6Si2, GdNiSi, GdNiSi2, GdNi0.4Si1.6, Gd2Ni2.35Si0.65, Gd3NiSi2, Gd3NiSi3 and Gd6Ni1.67Si3, has been confirmed. Moreover, five new phases have been identified in this system. The crystal structure for four of them has been determined: Gd2Ni16-12.8Si1-4.2 (Th2Zn17-type), GdNi6.6Si6 (GdNi7Si6-type), Gd3Ni8Si (Y3Co8Si-type) and Gd3Ni11.5Si4.2 (Gd3Ru4Ga12-type). The compound with composition ~Gd2Ni4Si3 still remains with unknown structure. Quasi-binary phases, solid solutions, were detected at 1070 K to be formed by the binaries GdNi5, GdNi3, GdNi2, GdNi, GdSi2 and GdSi1.67; while no appreciable solubility was observed for the other binary compounds of the Gd-Ni-Si system. Magnetic properties of the GdNi6Si6, GdNi6.6Si6 and Gd3Ni11.5Si4.2 compounds have also been investigated and are here reported. - PublicationRNi8Si3 (R=Gd,Tb): Novel ternary ordered derivatives of the BaCd11 type(01-01-2016)
;Pani, M. ;Morozkin, A. V. ;Yapaskurt, V. O. ;Provino, A. ;Manfrinetti, P.; Malik, S. K.The title compounds have been synthesized and characterized both from the structural and magnetic point of view. Both crystallize in a new monoclinic structure strictly related to the tetragonal BaCd11 type. The structure was solved by means of X-ray single-crystal techniques for GdNi8Si3 and confirmed for TbNi8Si3 on powder data; the corresponding lattice parameters (obtained from Guinier powder patterns) are a=6.3259(2), b=13.7245(5), c=7.4949(3) Å, β=113.522(3)°, Vcell=596.64(3) Å3 and a=6.3200(2), b=13.6987(4), c=7.4923(2) Å, β=113.494(2)°, Vcell=594.88(2) Å3. The symmetry relationship between the tI48-I41/amd BaCd11 aristotype and the new ordered mS48-C2/c GdNi8Si3 derivative is described via the Bärnighausen formalism within the group theory. The large Gd-Gd (Tb-Tb) distances, mediated via Ni-Si network, likely lead to weak magnetic interactions. Low-field magnetization vs temperature measurements indicate weak and field-sensitive antiferromagnetic ground state, with ordering temperatures of 3 K in GdNi8Si3 and about 2-3 K in TbNi8Si3. On the other hand, the isothermal field-dependent magnetization data show the presence of competing interactions in both compounds, with a field-induced ferromagnetic behavior for GdNi8Si3 and a ferrimagnetic-like behavior in TbNi8Si3 at the ordering temperature TC/N of about (or slightly higher than) 3K. The magnetocaloric effect, quantified in terms of isothermal magnetic entropy change ΔSm, has the maximum values of -19.8 J(kg K)-1 (at 4 K for 140 kOe field change) and -12.1 J(kg K)-1 (at 12 K for 140 kOe field change) in GdNi8Si3 and TbNi8Si3, respectively. - PublicationMo2NiB2-type {Gd, Tb, Dy)2Ni2.35Si0.65 and La2Ni3-type {Dy, Ho}2Ni2.5Si0.5 compounds: Crystal structure and magnetic properties(01-01-2015)
;Morozkin, A. V. ;Isnard, O.; Malik, S. K.The crystal structure of new Mo2NiB2-type {Gd, Tb, Dy}2Ni2.35Si0.65 (Immm, No. 71, oI10) and La2Ni3-type {Dy, Ho}2Ni2.5Si0.5 (Cmce No. 64, oC20) compounds has been established using powder X-ray diffraction studies. Magnetization measurements show that the Mo2NiB2-type Gd2Ni2.35Si0.65 undergoes a ferromagnetic transition at ∼66 K, whereas isostructural Tb2Ni2.35Si0.65 shows an antiferromagnetic transition at ∼52 K and a field-induced metamagnetic transition at low temperatures. Neutron diffraction study shows that, in zero applied field, Tb2Ni2.35Si0.65 exhibits c-axis antiferromagnetic order with propagation vector K=[1/2, 0, 1/2] below its magnetic ordering temperature and Tb magnetic moment reaches a value of 8.32(5) μB at 2 K. The La2Ni3-type Dy2Ni2.5Si0.5 exhibits ferromagnetic like transition at ∼42 K with coexisting antiferromagnetic interactions and field induced metamagnetic transition below ∼17 K. The magnetocaloric effect of Gd2Ni2.35Si0.65, Tb2Ni2.35Si0.65 and Dy2Ni2.5Si0.5 is calculated in terms of isothermal magnetic entropy change and it reaches a maximum value of -14.3 J/kg K, -5.3 J/kg K and -10.3 J/kg K for a field change of 50 kOe near 66 K, 52 K and 42 K, respectively. Low temperature magnetic ordering with enhanced anisotropic effects in Tb2Ni2.35Si0.65 and Dy2Ni2.35Si0.65 is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +12.8 J/kg K and ∼+9.9 J/kg K, respectively at 7 K for a field change of 50 kOe. - PublicationCeNi3-type rare earth compounds: crystal structure of R3Co7Al2 (R=Y, Gd–Tm) and magnetic properties of {Gd–Er}3Co7Al2, {Tb, Dy}3Ni8Si and Dy3Co7.68Si1.32(15-03-2017)
;Morozkin, A. V. ;Yapaskurt, V. O.; ;Quezado, S.Malik, S. K.The crystal structure of new CeNi3-type {Y, Gd–Tm}3Co7Al2 (P63/mmc. N 194, hP24) compounds has been established using powder X-ray diffraction studies. The magnetism of Tb3Ni8Si and Dy3Ni8Si is dominated by rare earth sublattice and the magnetic properties of R3Co7Al2 (R =Gd–Er) and Dy3Co7.68Si1.32 are determined by both rare earth and cobalt sublattices. Magnetization data indicate ferromagnetic ordering of {Tb, Dy}3Ni8Si at 32 K and 21 K, respectively. Gd3Co7Al2 and Tb3Co7Al2 exhibit ferromagnetic ordering at 309 K and 209 K, respectively, whereas Dy3Co7Al2, Ho3Co7Al2, Er3Co7Al2 and Dy3Co7.68Si1.32 show a field dependent ferromagnetic-like ordering at 166 K, 124 K, 84 K and 226 K, respectively followed by a low temperature transition at 34 K for Dy3Co7Al2, 18 K for Ho3Co7Al2, 56 K for Er3Co7Al2, 155 K and 42 K for Dy3Co7.68Si1.32. Among these compounds, Dy3Ni8Si shows largest magnetocaloric effect (isothermal magnetic entropy change) of −11.6 J/kg·K at 18 K in field change of 50 kOe, whereas Tb3Co7Al2, Dy3Co7Al2 and Dy3Co7.68Si1.32 exhibit best permanent magnet properties in the temperature range of 2–5 K with remanent magnetization of 11.95 μB/fu, 12.86 μB/fu and 14.4 μB/fu, respectively and coercive field of 3.0 kOe, 1.9 kOe and 4.4 kOe, respectively. - PublicationMagnetic ordering of Mo2NiB2-type {Gd, Tb, Dy)2Co2Al compounds by magnetization and neutron diffraction study(15-11-2017)
;Morozkin, A. V. ;Genchel, V. K. ;Garshev, A. V. ;Yapaskurt, V. O. ;Isnard, O. ;Yao, Jinlei; ;Quezado, S.Malik, S. K.The magnetic ordering of Mo2NiB2-type {Gd, Tb, Dy}2Co2Al (Immm, No. 71, oI10) compounds has been established using bulk magnetic measurements and neutron diffraction study. Polycrystalline Gd2Co2Al, Tb2Co2Al and Dy2Co2Al undergo ferrimagnetic transitions (TC) at 78 K, 98 K and 58 K, respectively, and low-temperature field induced transition (Tm) around 15 K, 20 K and 15 K, respectively. Between Tm and TC Gd2Co2Al, Tb2Co2Al and Dy2Co2Al are soft ferrimagnets. Below Tm Gd2Co2Al is soft ferrimagnet, whereas Tb2Co2Al and Dy2Co2Al exhibit permanent magnet properties with residual magnetization per rare earth of 4.95 B and 4.8 B, respectively, and large coercive field of 72 kOe and 22 kOe, respectively, at 2 K. The magnetocaloric effects of Gd2Co2Al, Tb2Co2Al and Dy2Co2Al were calculated in terms of isothermal magnetic entropy change and they reach maximum values of −10.4 J/kg K, −7.6 J/kg K and −6.6 J/kg K for a field change of 50 kOe near 75 K, 98 K and 58 K, respectively. Low-temperature transition of Gd2Co2Al is followed by the magnetic entropy change of −2.9 J/kg K in a field change of 50 kOe at 15 K. Low temperature magnetic ordering with enhanced anisotropic effects in Tb2Co2Al and Dy2Co2Al is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +19.9 J/kg K at 20 K (field change 0–50 kOe) and +2.7 J/kg K at 15 K (field change 0–10 kOe), respectively. Neutron diffraction study shows that, in zero applied field, Tb2Co2Al exhibits c-axis ferrimagnetic ordering with magnetic space group Immm′ and propagation vector K0 = [0, 0, 0] below TCND ∼ 111 K with MTb = 8.86(15) B and MCo = 0.26(2) B at 2 K. - PublicationMgZn2-type {Ho, Er, Tm}FeGa rare earth compounds: Crystal structure and magnetic properties(01-09-2017)
;Morozkin, A. V. ;Genchel, V. K. ;Garshev, A. V. ;Yapaskurt, V. O.; ;Quezado, S.Malik, S. K.The crystal structure of new hexagonal MgZn2-type {Ho, Tm}FeGa compounds (space group P63/mmc, N 194, hP12) has been established using powder X-ray diffraction studies. The magnetic properties of polycrystalline MgZn2-type ErFeGa compound have been studied using bulk magnetization data. ErFeGa exhibits ferromagnetic ordering at TC = 77 K and field sensitive antiferromagnetic-like ordering at Tm ~ 58 K in field of 100 Oe and Tm ~ 10 K in field of 5 kOe. The paramagnetic susceptibility follows Curie-Weiss law with effective paramagnetic moment per formula unit (Meff/fu) of 9.59 μB and paramagnetic Weiss temperature (ΘP) of 27 K. At 2 K, ErFeGa exhibits hard magnetic properties with remanent magnetization per formula unit (Mres/fu) of 3.7 μB, coercive field (Hcoer) of 8.2 kOe and critical field (Hcrit) of ~9.6 kOe. The magnetocaloric effect of ErFeGa has been calculated in terms of isothermal magnetic entropy change (ΔSm) and maximum ΔSm values are −5.5 J/kg K for a field change of 0–50 kOe (relative cooling power RCP50 kOe ~ 410 J/kg), −13.0 J/kg K for a field change of 0–140 kOe (RCP140 kOe ~ 1230 J/kg) at 70 K and +1.7 J/kg K for a field change of 0–10 kOe at 10 K (RCP10 kOe ~ 34 J/kg). - PublicationThe Gd-Co-Al system at 870/1070 K as a representative of the rare earth-Co-Al family and new rare-earth cobalt aluminides: Crystal structure and magnetic properties(01-05-2018)
;Morozkin, A. V. ;Garshev, A. V. ;Knotko, A. V. ;Yapaskurt, V. O. ;Mozharivskyj, Y. ;Yuan, Fang ;Yao, Jinlei; ;Quezado, S.Malik, S. K.The Gd-Co-Al system has been investigated at 870/1070 K by X-ray and elemental EDS analyses. The existence of the known compounds Gd2Co3Al9 (Y2Co3Ga9-type), Gd3Co4.5Al11.5 (Gd3Co4.6Al11) (Gd3Ru4Al12-type), Gd3Co6–7.4Al3–1.6 (CeNi3-type), GdCo1.15–0.65Al0.85–1.35 (MgZn2-type), Gd2Co2Al (Mo2NiB2-type) and Gd3Co3.5–3.25Al0.5–0.75 (W3CoB3-type) has been confirmed at 870/1070 K. Structure types have been determined for Gd2Co6Al19 (U2Co6Al19-type), Gd7Co6Al7 (Pr7Co6Al7-type), Gd6Co2–2.21Al1–0.79 (Ho6Co2Ga-type) and Gd14Co3.2Al2.8 (Gd14Co2.58Al3.42 at 970 K) (Lu14Co3In3-type). The structures of Gd6Co2Al, Gd6Co2.21Al0.79 and Gd14Co2.58Al3.42 flux-grown at 970 K have been refined from the single crystal X-ray diffraction data. Additionally, new ternary compounds Gd2Co5.7–5.3Al1.3–1.7 (Er2Co7-type) and ~Gd58Co20Al22 (unknown type structure) have been identified. Quasi-binary solid solutions were detected for Gd2Co17, GdCo5, Gd2Co7, GdCo3, GdCo2 and GdAl2 at 870/1070 K, while no appreciable solubility was observed for the other binary compounds in the Gd-Co-Al system. Magnetic properties of the Gd2Co3Al9, Gd3Co4.6Al11, Gd7Co6Al7, Gd6Co2.2Al0.8 and Gd14Co2.58Al3.42 compounds have been studied and are presented in this work. Gd6Co2.2Al0.8, Gd3Co4.6Al11, Gd7Co6Al7 and Gd14Co2.58Al3.42 order ferromagnetically, while Gd2Co3Al9 displays antiferromagnetic transition. Additionally, {Y, Sm, Tb - Tm}2Co6Al19 (U2Co6Al19-type), Yb2Co3Al9 (Y2Co3Ga9-type), {Y, Sm, Tm, Yb}3Co4.6Al11 (Gd3Ru4Al12-type) and Tb7Co6Al7 (Pr7Co6Al7-type) compounds have been synthesized and investigated. - PublicationMagnetic ordering in Sc2CoSi2-type R2FeSi2 (R=Gd, Tb) and R2CoSi2 (R=Y, Gd-Er) compounds(01-09-2016)
;Morozkin, A. V. ;Knotko, A. V. ;Yapaskurt, V. O. ;Pani, M.; ;Quezado, S.Malik, S. K.Magnetic and magnetocaloric properties of Sc2CoSi2-type R2TSi2 (R=Gd-Er, T=Fe, Co) compounds have been studied using magnetization data. These indicate the presence of mixed ferromagnetic and antiferromagnetic interactions in these compounds. One observes a ferromagnetic transition followed by an antiferromagnetic order and a further possible spin-reorientation transition at low temperatures. Compared to Gd2{Fe, Co}Si2, the Tb2FeSi2 and {Tb-Er}2CoSi2 compounds exhibit remarkable hysteresis (for e.g. Tb2FeSi2 shows residual magnetization Mres/Tb=2.45 μB, coercive field Hcoer=14.9 kOe, and critical field Hcrit∼5 kOe at 5 K) possibly due to the magnetocrystalline anisotropy of the rare earth. The R2{Fe, Co}Si2 show relatively small magnetocaloric effect (i.e. isothermal magnetic entropy change, ΔSm) around the magnetic transition temperature: the maximal value of MCE is demonstrated by Ho2CoSi2 (ΔSm=-8.1 J/kg K at 72 K and ΔSm=-9.4 J/kg K at 23 K in field change of 50 kOe) and Er2CoSi2 (ΔSm=-13.6 J/kg K at 32 K and ΔSm=-8.4 J/kg K at 12 K in field change of 50 kOe). - PublicationTwo-layer compounds in rare earth-{Fe, Co, Ni, Rh, Pd, Pt}-Te systems: crystal structure and magnetic properties(01-03-2021)
;Yao, Jinlei ;Malik, S. K. ;Quezado, S.; ;Morozkin, A. V. ;Garshev, A. V. ;Knotko, A. V.Yapaskurt, V. O.The partial isothermal sections of {Gd, Ho}-Ni-Te and Gd-Co-Te systems (~40–100 at. % of rare earth) have been investigated at 1070 K by X-ray and electron microprobe analysis. The Y5Ni2Te2-type {Tb, Dy, Ho}5Fe2Te2 and {Gd, Tb, Dy, Ho}5{Co, Ni}2Te2 (space group Cmcm, No. 63, oC36), Er7Ni2Te2-type Er7Co2Te2, {Y, Dy, Ho}7Ni2Te2, Ho7{Rh, Pd}2Te2 and {Y, Gd}7Pt2Te2 (space group Imm2, No. 44, oI22), Fe2P-type Ho6NiTe2 (space group P-62m, No. 189, hP9) and Sc6PdTe2-type Ho6{Rh, Pd}Te2 and {Y, Gd}6PtTe2 (space group Pnma, No. 62, oP36) compounds have been established using powder X-ray diffraction studies. Magnetization measurements show that the Y5Ni2Te2-type {Tb, Dy, Ho}5Fe2Te2, {Gd, Tb, Dy}5Co2Te2 and {Tb, Ho}5Ni2Te2 compounds exhibit a high-temperature ferromagnetic ordering with low-temperature spin-reorientation transition for Tb-, Dy- and Ho-containing compounds. Below Curie temperature, Tb5Fe2Te2, Tb5Co2Te2 and Ho5Ni2Te2 are soft ferromagnets, while they show hard magnetic properties below spin-reorientation transition. At 2 K, Tb5Co2Te2 and Tb5Fe2Te2 exhibit a coercive field of 35 kOe and ~30 kOe and the residual magnetization of 17.2 μB and 22.9 μB per formula unit, leading to theoretical maximum energy product of ~620 kJ/m3 and ~700 kJ/m3, respectively. Ho5Ni2Te2 reaches a maximum magnetic entropy change of −10.0 J/kg⋅K and −9.4 J/kg⋅K for a magnetic field change of 0–50 kOe at 45 K and 20 K, respectively. - PublicationNew orthorhombic derivative of CaCu5-type structure: RNi 4Si compounds (R=Y, La, Ce, Sm, Gd-Ho), crystal structure and some magnetic properties(16-10-2013)
;Morozkin, A. V. ;Knotko, A. V. ;Yapaskurt, V. O. ;Yuan, Fang ;Mozharivskyj, Y.The crystal structure of new YNi4Si-type RNi4Si (R=Y, La, Ce, Sm, Gd-Ho) compounds has been established using powder X-ray diffraction. The YNi4Si structure is a new structure type, which is orthorhombic derivative of CaCu5-type structure (space group Cmmm N 65, oC12). GdNi4Si and DyNi4Si compounds order ferromagnetically at 25 and 19 K, respectively whereas YNi4Si shows antiferromagnetic nature. At 15 K, DyNi4Si shows second antiferromagnetic-like transition. The magnetic moment of GdNi4Si at 5 K in 50 kOe field is ~7.2 μB/f.u. suggesting a completely ordered ferromagnetic state. The magnetocaloric effect of GdNi4Si is calculated in terms of isothermal magnetic entropy change and it reaches the maximum value of -12.8 J/kg K for a field change of 50 kOe near TC ~25 K. © 2013 Elsevier Inc.