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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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36 results
Now showing 1 - 10 of 36
- PublicationPreservation of large low temperature magnetocaloric effect in metamagnetic intermetallic compounds RCu2 (R = Gd, Tb, Dy, Ho and Er) upon rapid solidification(30-01-2020)
;Rajivgandhi, R. ;Chelvane, J. Arout ;Nigam, A. K. ;Malik, S. K.In this work, magnetic and magnetocaloric properties of melt-spun RCu2 (R = Gd, Tb, Dy, Ho and Er) compounds have been studied. The melt-spun samples have formed in the same orthorhombic crystal structure (space group Imma, no. 74) as that of the arc-melted samples but with a development of crystallographic texture and micron-size grains. The melt-spun ribbons of RCu2 (R = Gd, Tb, Dy, Ho and Er) order antiferromagnetically at 43 K, 51 K, 28 K, 10 K and 11 K (TN) respectively. The ordering temperatures are almost the same as that of the arc-melted samples. The RCu2 compounds show one or more field induced transitions below TN. Therefore, a normal magnetocaloric effect is observed in these compounds when the magnetic field change is larger than the metamagnetic critical field and inverse magnetocaloric effect is observed for smaller field changes. The microgranularity does not seem to smear out the metamagnetic transition. The maximum of isothermal magnetic entropy change, ΔSmmax, is about −2.1 Jkg−1K−1, -5.5 Jkg−1K−1, -5.2 Jkg−1K−1, -17.2 Jkg−1K−1 and -11.7 Jkg−1K−1 respectively for the melt-spun RCu2 (R = Gd, Tb, Dy, Ho and Er) samples for 50 kOe field change. The refrigeration capacity is found to be 40 Jkg-1, 160 Jkg-1, 166 Jkg-1, 230 Jkg-1 and 207 Jkg-1 respectively, for the above samples. These values are nearly the same as that of the arc-melted counterparts. Thus the large magnetocaloric effect in the temperature range of 10 K–70 K make these melt-spun RCu2 samples potential materials for low temperature refrigeration applications. The results also ascertain melt-spinning process as an alternate technique for the production of magnetocaloric alloys and intermetallics. - PublicationMagnetic properties of CaCu5-type RNi3TSi (R=Gd and Tb, T=Mn, Fe, Co and Cu) compounds(01-12-2015)
;Morozkin, A. V. ;Knotko, A. V. ;Yapaskurt, V. O. ;Yao, Jinlei ;Yuan, Fang ;Mozharivskyj, Y.; ;Quezado, S.Malik, S. K.Magnetic properties and magnetocaloric effect of CaCu5-type RNi3TSi (R=Gd and Tb, T=Mn, Fe, Co and Cu) compounds have been investigated. Magnetic measurements of RNi3TSi display the increasing of Curie temperature and the decreasing of magnetocaloric effect and saturated magnetic moment in the row of 'RNi3CuSi-RNi3NiSi-RNi3CoSi-RNi3MnSi-RNi3FeSi'. In contrast to GdNi3{Mn, Fe, Co}Si, TbNi3{Mn, Fe, Co}Si exhibit significant magnetic hysteresis. The coercive field increases from TbNi4Si (~0.5 kOe) to TbNi3CoSi (4 kOe), TbNi3MnSi (13 kOe) and TbNi3FeSi (16 kOe) in field of 50 kOe at 5 K, whereas TbNi3CuSi exhibits a negligible coercive field. - PublicationMagnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds(15-02-2017)
;Morozkin, A. V. ;Yapaskurt, V. O.; ;Quezado, S. ;Malik, S. K. ;Mozharivskyj, Y.Isnard, O.The magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds (space group Cmcm, oC32) was investigated via magnetization measurements and neutron diffraction study in a zero-applied field. {Sm, Tb, Er}3Co2Ge3 and Ho3Ni2Ge3 exhibit field sensitive complex antiferromagnetic orderings with TN=51 K, Tm=10 K for Sm3Co2Ge3, TN=34 K, Tm=13 K for Tb3Co2Ge3, TN=7 K for Er3Co2Ge3 and TN=11 K for Ho3Ni2Ge3. At 2 K and above the critical field of ~5 kOe, 20 kOe, 4 kOe and 7 kOe for Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3, respectively, saturation magnetizations per rare-earth atom are 6.5 μB for Tb3Co2Ge3, 7.0 μB for Er3Co2Ge3 and 8.0 μB for Ho3Ni2Ge3 in the field of 140 kOe, whereas magnetization of Sm3Co2Ge3 has an antiferromagnetic behaviour. The isothermal magnetic entropy change, ΔSm, indicates a field-induced ferromagnetic ordering in Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3 with a maximal ΔSm value of −10.9 J/kg K for Ho3Ni2Ge3 at 11 K for a field change of 50 kOe. In a zero-applied magnetic field, below TN=33 K and down to TmND=15 K Tb3Ni2Ge3 shows an ac-antiferromagnetic ordering with the C2′/c magnetic space group, a K0=[0, 0, 0] propagation vector and a aTb3Ni2Ge3×bTb3Ni2Ge3×cTb3Ni2Ge3 magnetic unit cell. Below TmND=15 K, its magnetic structure is a sum of the ac-antiferromagnetic component with the C2′/c magnetic space group of the K0 vector and a sine-modulated a-antiferromagnetic component of the K1=[0, 0, ±1/3] propagation vector (the magnetic unit cell is aTb3Ni2Ge3×bTb3Ni2Ge3×3cTb3Ni2Ge3). The magnetic structure is made from the ‘Tb2 - 2Tb1′ clusters of the Tb1 8f and Tb2 4c sublattices with a dominant role of the Tb2 sublattices in the magnetic ordering of Tb3Ni2Ge3. - PublicationLarge low field magnetocaloric effect in multicomponent Laves phase intermetallic compounds Gd<sub>0.33</sub>Dy<sub>0.33</sub>Ho<sub>0.33</sub>Al<sub>2</sub>, Tb<sub>0.33</sub>Ho<sub>0.33</sub>Er<sub>0.33</sub>Al<sub>2</sub> and Dy<sub>0.33</sub>Ho<sub>0.33</sub>Er<sub>0.33</sub>Al<sub>2</sub>(01-01-2023)
;Jesla, P. K. ;Arout Chelvane, J. ;Morozkin, A. V.Multicomponent Laves phase intermetallic compounds Gd0.33Dy0.33Ho0.33Al2, Tb0.33Ho0.33Er0.33Al2 and Dy0.33Ho0.33Er0.33Al2 have been synthesized by arc-melting. The samples crystallize in cubic (MgCu2-type, Space group Fd-3m) structure. Temperature dependent magnetization measurements reveal ferromagnetic order in the Gd0.33Dy0.33Ho0.33Al2, Tb0.33Ho0.33Er0.33Al2 and Dy0.33Ho0.33Er0.33Al2 compounds at 84 K, 45 K and 33 K (TC) respectively. Magnetization vs magnetic field data at 5 K suggest soft ferromagnetism. Magnetocaloric effect is estimated in terms of isothermal magnetic entropy change and adiabatic temperature change in magnetic fields up to 15 kOe and it is quite large. Therefore, these multicomponent Laves phase compounds could be useful for realizing magnetic refrigeration-based hydrogen liquefaction. - 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 and magnetocaloric properties of Ho6Co2Ga-type Dy6Co2.5Sn0.5 compound(15-03-2015)
;Morozkin, A. V.; Malik, S. K.DC magnetization studies on Dy6Co2.5Sn0.5 compound (orthorhombic, Ho6Co2Ga-type, space group Immm, No. 71) have been carried out in the temperature range of 2-300 K and in magnetic fields up to 140 kOe. A field induced metamagnetic transition is observed below its Néel point of 42 K (at 2 K the critical field Hc is 37 kOe). Magnetization-field isotherms have been measured for this compound near magnetic transition temperatures from which isothermal magnetic entropy change, ΔSm, has been computed. The maximum ΔSm values of -5.2 J/kg K (for a field change of 80 kOe) and +6.5 J/kg K (for a field change of 50 kOe) are observed at 52 K and 13 K, 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. - PublicationMagnetic order of Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 as a representative of the family of compounds with orthorhombic distortion of rare earth lattice(17-04-2015)
;Morozkin, A. V. ;Isnard, O.; Malik, S. K.Magnetic measurements indicate that the rare earth intermetallic compounds Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 (Dy3Co2.2Si1.8-type) exhibit ferromagnetic transition at 132 K and 74 K and a spin-reorientation transition around 42 K and 35 K, respectively. Below Curie temperature, both compounds are soft ferromagnets, whereas below the spin reorientation transition they are permanent magnets with antiferromagnetic component: the values of critical field Hc=30 kOe, coercive field Hcoer=17 kOe and residual magnetization Mres=4.1 μB/Tb for Tb3Co2.2Si1.8 and Hc=14 kOe, Hcoer=21.5 kOe and Mres=3.7 μB/Dy for Dy3Co2.2Si1.8 at 2 K. The magnetocaloric effect of Dy3Co2.2Si1.8 is calculated in terms of isothermal magnetic entropy change (ΔSm) and it reaches a values of -16.5 J/kg K at 75 K for a field change of 140 kOe (-8.1 J/kg K at 70 K, for 0-50 kOe change) and -6.0 J/kg K for a field change of 140 kOe (-1.4 J/kg K, for 0-50 kOe change) around 40 K. Neutron diffraction study in zero applied field shows mixed ferro-antiferromagnetic ordering of Tb3Co2.2Si1.8 below ~127 K with wave vectors K0=[0, 0, 0] and K1=[±Kx, 0, 0] (Kx≥3/10). Between ~127 K and 53 K the magnetic structure of Tb3Co2.2Si1.8 is set of canted ferromagnetic cones with a resulting b-axis ferromagnetic component, whereas below 43 K its magnetic structure is set of canted ferromagnetic cones with a resulting c-axis ferromagnetic component. Between 53 K and 43 K the high-temperature magnetic order of Tb3Co2.2Si1.8 transforms to the low-temperature order via an intermediate state. The level of orthorhombic distortion of the Tb-sublattice determines the magnetic ordering of Tb3Co2.2Si1.8 in the Tb→Tb3Co2.2Si1.8→Tb3Co2Ge3→TbGe sequence. - PublicationMagnetic properties of Fe2P-type R6CoTe2 compounds (R=Gd-Er)(01-06-2010)
;Morozkin, A. V. ;Mozharivskyj, Yu ;Svitlyk, V.; ;Isnard, O. ;Manfrinetti, P. ;Provino, A.Ritter, C.The magnetic structure of the Fe2P-type R6CoTe2 phases (R=Gd-Er, space group P6-2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: TC=220 K and TCN=180 K for Gd6CoTe2, TC=174 K and TCN=52 K for Tb6CoTe2, TC=125 K and TCN=26 K for Dy6CoTe2, TCN=60 K and TN=22 K for Ho6CoTe2 and TCN∼30 K and TN∼14 K for Er6CoTe2. Between 174 and 52 K Tb6CoTe2 has a collinear magnetic structure with K0=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52 K it adopts a non-collinear ferromagnetic one. Below 60 K the magnetic structure of Ho6CoTe2 is that of a non-collinear ferromagnet. The holmium magnetic components with a K0=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K1=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K0 vector from the collinear to the non-collinear state. Below 30 K Er6CoTe2 shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K0=[0, 0, 0] and K1=[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the MErK0 and MErK1 magnetic components. In these phases, no local moment was detected on the cobalt site. The magnetic entropy of Gd6CoTe2 increases from ΔSmag=-4.5 J/kg K at 220 K up to ΔSmag=-6.5 J/kg K at 180 K for the field change Δμ0H=0-5 T. © 2010 Elsevier Inc. All rights reserved.