Now showing 1 - 10 of 70
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    Electrical and magnetotransport properties of canted antiferromagnet Dy5Si2Ge2
    (01-01-2002) ; ; ;
    Morozkin, A. V.
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    Chu, Z.
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    Yelon, W. B.
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    Malik, S. K.
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    Prasad, V.
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    Subramanyam, S. V.
    Since the giant magnetocaloric effect is encountered in a ferromagnetic Gd5Si2Ge2 alloy near room temperature it is considered as a suitable material for magnetic refrigerator applications. Also a commensurate structural transition occurs at the magnetic transition temperature and there is a good correlation between the crystal structure and magnetic properties. Such observations have triggered numerous experimental studies on similar rare earth alloys and compounds. We have synthesized its Dy- analogue, namely, Dy5Si2Ge2 and have characterized it by means of room temperature X-ray diffraction, ac magnetic susceptibility (15 K-300 K), electrical resistivity (at zero field and at 6 T), thermoelectric power (15 K-300 K) and neutron diffraction (at 300 K and 9.2 K) experiments.
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    Magnetocaloric effect in textured rare earth intermetallic compound ErNi
    (01-05-2018)
    Sankar, Aparna
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    Chelvane, J. Arout
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    Morozkin, A. V.
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    Nigam, A. K.
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    Quezado, S.
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    Malik, S. K.
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    Melt-spun ErNi crystallizes in orthorhombic FeB-type structure (Space group Pnma, no. 62) similar to the arc-melted ErNi compound. Room temperature X-ray diffraction (XRD) experiments reveal the presence of texture and preferred crystal orientation in the melt-spun ErNi. The XRD data obtained from the free surface of the melt-spun ErNi show large intensity enhancement for (1 0 2) Bragg reflection. The scanning electron microscopy image of the free surface depicts a granular microstructure with grains of ∼1 μm size. The arc-melted and the melt-spun ErNi compounds order ferromagnetically at 11 K and 10 K (TC) respectively. Field dependent magnetization (M-H) at 2 K shows saturation behaviour and the saturation magnetization value is 7.2 μB/f.u. for the arc-melted ErNi and 7.4 μB/f.u. for the melt-spun ErNi. The isothermal magnetic entropy change (ΔSm) close to TC has been calculated from the M-H data. The maximum isothermal magnetic entropy change, -ΔSmmax, is ∼27 Jkg-1K-1 and ∼24 Jkg-1K-1 for the arc-melted and melt-spun ErNi for 50 kOe field change, near TC. The corresponding relative cooling power values are ∼440 J/kg and ∼432 J/kg respectively. Although a part of ΔSm is lost to crystalline electric field (CEF) effects, the magnetocaloric effect is substantially large at 10 K, thus rendering melt-spun ErNi to be useful in low temperature magnetic refrigeration applications such as helium gas liquefaction.
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    The isothermal section of Gd-Ni-Si system at 1070 K
    (01-03-2016)
    Morozkin, A. V.
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    Knotko, A. V.
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    Yapaskurt, V. O.
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    Manfrinetti, P.
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    Pani, M.
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    Provino, A.
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    Quezado, S.
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    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.
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    Magnetism and electronic transport in R2Mn3Si5 (R = Dy, Ho and Er) compounds
    (26-07-2001) ; ; ;
    Morozkin, A. V.
    Magnetic susceptibility, electrical resistivity and thermoelectric power measurements on new rare earth ternary intermetallic R2Mn3Si5 (R = Dy, Ho and Er) compounds crystallizing in the Sc2Fe3Si5-type tetragonal crystal structure were carried out in the temperature range 15-300 K. Dy- and Ho-based alloys show two successive magnetic transitions (Dy2Mn3Si5 at 76 and 32 K; Ho2Mn3Si5 at 67 and 19 K) and the Er-based compound undergoes a magnetic transition around 55 K. The electrical resistivity is ferromagnetic metal-like, displaying typical low temperature T2 dependence and a high temperature spin-disorder contribution. Thermoelectric power is negative at room temperature, crosses zero and has a broadened peak feature centered around 50 K indicating a phonon drag effect at low temperatures and it does not have the signature of magnetic ordering. The successive magnetic transitions are suggestive of the presence of competing magnetic interactions in these systems. © 2001 Elsevier Science B.V.
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    Magnetization and neutron diffraction studies on Dy 5Si 2Ge 2
    (15-05-2005) ; ; ;
    Morozkin, A. V.
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    Cai, Q.
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    Chu, Z.
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    Yang, J. B.
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    Yelon, W. B.
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    Malik, S. K.
    The compound Dy5 Si2 Ge2 crystallizes in an orthorhombic structure (Sm5 Ge4 type, space group Pnma). Magnetization measurements performed in the temperature range of 2-300 K in applied fields up to 7 T reveal that this compound orders antiferromagnetically at 56 K (TN) but with a positive paramagnetic Curie temperature θP. Magnetization-field isotherms, obtained at 5 K and 20 K, display a field-induced antiferromagnetic to ferromagnetic transition. The magnetization approaches saturation in a field of 6 T with a moment value of ~8 μB Dy3+. Neutron diffraction measurements, carried out at 9.2 K, suggest that Dy moments arrange spirally along the a axis giving rise to a canted antiferromagnetic structure. The analysis of neutron diffraction data yields an ordered state magnetic moment of 7.63 μB per Dy3+ ion. © 2005 American Institute of Physics.
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    Magnetic properties of CaCu5-type RNi3TSi (R=Gd and Tb, T=Mn, Fe, Co and Cu) compounds
    (01-12-2015)
    Morozkin, A. V.
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    Knotko, A. V.
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    Yapaskurt, V. O.
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    Yao, Jinlei
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    Yuan, Fang
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    Mozharivskyj, Y.
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    Quezado, S.
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    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.
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    Magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds
    (15-02-2017)
    Morozkin, A. V.
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    Yapaskurt, V. O.
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    Quezado, S.
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    Malik, S. K.
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    Mozharivskyj, Y.
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    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.
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    RNi8Si3 (R=Gd,Tb): Novel ternary ordered derivatives of the BaCd11 type
    (01-01-2016)
    Pani, M.
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    Morozkin, A. V.
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    Yapaskurt, V. O.
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    Provino, A.
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    Manfrinetti, P.
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    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.
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    Large 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.
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    Arout Chelvane, J.
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    Morozkin, A. V.
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    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.
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    Effect of co-site dilution on the magnetism of RCo5 (R =Gd, Y) compounds
    (01-03-2018)
    Nikitin, S. A.
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    Bogdanov, A. E.
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    Morozkin, A. V.
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    Knotko, A. V.
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    Yapaskurt, V. O.
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    Ovchenkova, I. A.
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    Smirnov, A. V.
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    Quezado, S.
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    Malik, S. K.
    The magnetic and magnetocaloric properties of the RCo5-xGax (R =Gd, Y; x =1, 1.5, 1.6, 1.7) compounds have been studied. X-ray and electron microprobe analysis show that the samples are single phase and crystallize in the hexagonal CaCu5 - type structure (space group P6/mmm, N 191, hP6). The magnetic properties have been studied from 2 to 400 K under magnetic fields in the region of 1 to 140 kOe. With increasing Ga amount the magnetic ordering temperature decreases rapidly. The increase in Ga concentration leads to the reduction of the magnetic moment of Co sublattice and the Curie temperature. It has been found that the paramagnetic susceptibility follows the Néel-type law for GdCo5-xGax (x =1.5, 1.6, 1.7) and the Curie-Weiss law for YCo3.3Ga1.7. The molecular field coefficients and sublattice magnetizations were determined on a basis of the Néel theory and experimental data. The magnetocaloric effect and refrigerant capacity have been estimated over a wide temperature range of 10-350 K.