Ni Magnetic Moment Research Articles

Revelation of Ni magnetic moment in GdNi single crystal by soft X-ray magnetic circular dichroism

Magnetic moment of Ni in GdNi single crystal was studied through the soft X-ray absorption spectra (XAS) and the magnetic circular dichroism (MCD) at the Ni L 2,3-edges and the Gd M 4,5-edges. Our experiment revealed for the first time that the Ni 3d band is not filled completely even at the content of 50 at.% of Gd and the Ni does retain a total magnetic moment coupling antiparallel to that of Gd. This result implied that the Ni in GdNi holds an intrinsic magnetic moment even at 50 at.% of Gd and contradicts the well-known charge transfer model. Further by employing the magneto-optical sum rule, the spin and orbital angular magnetic moment were evaluated and discussed.

Ni intercalation of titanium diselenide: effect on the lattice, specific heat and magnetic properties

Intercalated NixTiSe2 compounds with Ni concentration up to x = 0.5 have been investigated using x-ray diffraction, magnetic susceptibility and specific heat measurements. A set of peculiarities caused by the intercalation, such as a significant decrease of the gap between Se–Ti–Se trilayers and depletion of the low-frequency phonons due to the stiffening of the lattice as well as an enhancement of the density of electronic states at low Ni content (x < 0.33), is attributed to hybridization of the Ni 3d states with TiSe2 bands and formation of covalent-like links between Se–Ti–Se trilayers via the inserted Ni ions. NixTiSe2 compounds with intercalant content up to x = 0.5 show a paramagnetic behaviour unlike MxTiSe2 compounds intercalated by other 3d metals (M = Cr, Mn, Fe, Co). The Ni magnetic moment in NixTiSe2 is suggested to be of an itinerant nature. A pronounced correlation between the change of the lattice parameter c0 and the value of the effective magnetic moment, which is observed in NixTiSe2 as well in MxTiSe2 systems intercalated by other 3d metals, indicates that the magnetic moment on the inserted atom is controlled by the hybridization degree of M 3d states with TiSe2 bands.

Nanogranular Phase Formation During Devitrification of Fe(NiCo)ZrB Amorphous Alloys

A comprehensive review of our recent experimental and theoretical developments in the processing of nanocrystalline soft magnetic materials made by crystallization of amorphous precursors and containing new nanocrystalline phases is given. The relationship between the structures of the metastable and equilibrium phases and their transformations are discussed. Nickel-rich amorphous precursors with stoichiometry Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat-treated at temperatures ranged from 420 °C to 600 °C for one hour to form nanostructured alloy. The transformation from the amorphous state into the nanocrystalline state was investigated by the differential scanning calorimetry (DSC), the x-ray diffraction (XRD), the vibrating sample magnetometry (VSM) and Mossbauer techniques. The annealing favours the emergence of cubic FexNi23-xB6 crystalline grains (10-25 nm in diameter). Magnetic measurements made at 4.2-1100 K reveal rather high value of saturation magnetization (nearly 60 and 40 Am2/kg at 4.2 K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300 K 57Fe Mossbauer results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital (TB-LMTO) method. However, anomalous high magnetic moments of Fe and Co atoms were found in some inequivalent positions in the crystal structure.

Nanogranular FexNi23−xB6 phase formation during devitrificationof nickel-rich Ni64Fe16Zr7B12Au1 amorphous alloy

Nickel-rich amorphous precursors with chemical composition of Ni64Fe16Zr7B12Au1 were produced by melt-spinning technique and then heat treated at temperatures ranging from 435to600°C for 1h to form a nanostructure. Properties of the amorphous and the nanocrystalline samples were investigated by the differential scanning calorimetry, the x-ray diffraction (XRD), the vibrating sample magnetometry, and Mössbauer techniques. The annealing favors the emergence of cubic FexNi23−xB6 crystalline grains (10–25nm in diameter). Magnetic measurements made at 4.2–1100K reveal rather high value of saturation magnetization (nearly 60 and 40Am2∕kg at 4.2K and room temperature, respectively) in amorphous as well as in nanocrystalline states. These facts are consistent with 300K Fe57 Mössbauer effect results which are well supported by the calculations of Ni and Fe magnetic moments in Ni23B6 and Fe23B6 phases, using the spin polarized tight binding linear muffin-tin orbital method. However, anomalous high magnetic moments of Fe atoms were found in some inequivalent positions in the crystal structure.

Element-specific hysteresis loops and the anisotropy of the orbital moment of Pt in Ni/Pt multilayers

Angular- and field-dependent X-ray magnetic circular dichroism measurements at Pt and Ni L 3,2 edges of a Ni 2/Pt 2 multilayer with considerable perpendicular magnetic anisotropy are reported. The anisotropy of the orbital moment which is the microscopic origin of magnetic anisotropy energy is found, within the experimental accuracy, to be the same for Ni and Pt. Element-specific hysteresis loops show that Ni and Pt magnetic moments follow the same path during magnetization reversal. Both results suggest that the induced magnetic moment of Pt closely follows the behavior of the magnetic moment of Ni.

Synthesis, Crystal and Magnetic Structure of the Double Perovskites A2NiMoO6 (A = Sr, Ba): A Neutron Diffraction Study

AbstractA2NiMoO6 (A = Sr, Ba) perovskites have been prepared in polycrystalline form by thermal treatment, in air, of previously decomposed citrate precursors. These materials have been studied by X‐ray (XRD) and neutron powder diffraction (NPD) data. At room temperature, the crystal structure is tetragonal, space group I4/m, for Sr2NiMoO6 and for Ba2NiMoO6 the crystal structure is cubic, space group Fm$\bar 3$ m. Both perovskites contain divalent Ni cations. The low temperature antiferromagnetic ordering has been followed from sequential neutron diffraction data. Peaks of magnetic origin appear in the NPD patterns below temperatures of TN = 81.2 K and TN = 64.3 K for the Sr and Ba compounds, respectively. The magnetic structures are defined by a propagation vector k = (1/2,0,1/2) for Sr2NiMoO6 and k = (1/2,1/2,1/2) for Ba2NiMoO6. The refined magnitude of the Ni magnetic moments also suggests a divalent oxidation state with S = 1. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)

Exchange coupling in Fe/NiO/Co film studied by soft x-ray resonant magnetic reflectivity

A 10 nm Fe/5 nm NiO/10 nm Co polycrystalline trilayer prepared by magnetron sputtering has been investigated by resonant magnetic reflectivity of linearly polarized soft x rays (transversal magneto-optical Kerr effect geometry) at the L 3 edges of Fe, Ni, and Co. The exchange coupling in the trilayer, introduced during synthesis, has been altered by cooling through the Neel temperature T N of NiO at three different cooling fields H F C . We show that the chemical structure at the interfaces, the grain size and the magnetic properties of the trilayer are governed by factors such as successive heat treatment, magnetic field applied during synthesis and cooling through T N of NiO. Clear evidence for oxidation of Fe and Co states has been obtained, suggestive for the formation of mixed oxides at the Fe/NiO and NiO/Co interfaces. Oxidized Fe and Co are found to carry a net magnetic moment, which couples to the moments of the metallic states. We find that the coupling between oxidized and metallic Co spins is ferromagnetic, whereas the coupling between oxidized and metallic Fe spins is antiferromagnetic. We observe the presence of two types of excess Ni spins. A rigid excess Ni magnetic moment is induced at the interface during synthesis as follows from the strong asymmetry of the x-ray Kerr loops of the oxidized Co spins at H F C = 0 Oe and metallic Co spins at H F C =240 Oe. Heat treatment leads to appearence of a soft excess Ni magnetic moment, which is ferromagnetically coupled to the metallic Fe and Co spins and exhibits a conventional hysteresis loop. Competing interactions lead to frustrated magnetization at the NiO/Fe interface and cause a tilt of the Fe spins away from the direction of applied magnetic field. This manifests itself in the presence of characteristic humps in the Fe Kerr loops.

THE FERMI SURFACE IN A MAGNETIC METAL–INSULATOR INTERFACE

Nickel (111) and the interface of hexagonal boron nitride on Ni(111) serve as model systems for an itinerant ferromagnet that is truncated with vacuum or a single layer insulator. These systems are investigated with angle-scanned He I and He II photoemission. Upon formation of the h-BN/Ni(111) interface the work function drops by 1.8 eV and the minority Ni Λ3d-band shifts by 0.13 eV to higher binding energy. This indicates that the Ni magnetic moment decreases in the interface. Spin-polarized band structure calculations from bulk nickel identify the observed minority and majority bands. The experimental Fermi surface maps show that h-BN distorts a minority d-band in a way which is consistent with the decreasing magnetic moment. It can be seen that h-BN affects the scattering of the electrons. Effects in the photoemission final and initial state are recognized.

Magnetic properties and shape memory of Fe-doped Ni52Mn24Ga24 single crystals

Single crystals of a pseudoquaternary Heusler alloy, Ni52Mn16Fe8Ga24, have now been synthesized. The substitution of Fe for Mn strengthens the magnetic exchange interactions, increasing the Curie temperature to 381 K. The Fe also increases the Ni magnetic moment to 0.41 μB relative to that in the stoichiometric Heusler composition. The strain accompanying the martensitic transformation is 2.4% in zero field and can be enhanced to 4.2% by a field of 1.2 T. A field-induced strain of 1.15% has been induced along [001] in unstressed crystals with magnetic fields of 1.2 T applied at 291 K.

Caging of Ni clusters by benzene molecules and its effect on the magnetism of Ni clusters

Global optimization of the geometry of small Ni clusters interacting with benzene molecules yields equilibrium structures where the Ni atoms find themselves caged between the benzene molecules. This leads to quenching of the Ni magnetic moment in most of the complexes even though the structure of the caged Ni clusters remain relatively unchanged from their otherwise free gas phase geometry. The accuracy of these predictions, based on density functional theory with generalized gradient approximation for exchange and correlation, is established by the good agreement achieved between the calculated and available experimental dissociation energies and ionization potentials.

Charge and Spin Order in RNiO3(R=Nd, Y) by LSDA+U Method

Electronic structures of NdNiO 3 and YNiO 3 are calculated by using the LSDA+U method with rotational invariance. No orbital order on Ni sites is observed in the calculations for the two systems. Different types of charge ordering are found in the two systems. In a small distorted system NdNiO 3 , all nickel ions are trivalent, while oxygen sites show charge ordering and spin density polarization in the energy range of Ni e g σ * band. In a large distorted system YNiO 3 , charge disproportionation occurs. Therefore, the charge ordering stabilizes the asymmetry of the arrangement of Ni magnetic moments in both systems.

Magnetic properties of Ni-dopedSr2CuO3

We report the effects of doping Ni $(S=1)$ in place of Cu $(S=\frac{1}{2})$ in the quasi-one-dimensional Heisenberg antiferromagnetic (1DHAF) chain compound ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}.$ For the low doping levels considered here, ${\mathrm{Sr}}_{2}{\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{O}}_{3}$ $(0&lt;~x&lt;~0.03),$ the lattice parameters do not change significantly upon doping. The magnetic susceptibility $\ensuremath{\chi}$ (ratio of the magnetization M to the applied field $H)$ is found to have a Curie-like dependence at low temperatures. While the Curie constant ${C}_{M}$ is found to increase with Ni doping, its magnitude is considerably smaller than expected from isolated $S=1$ Ni magnetic moments. This would seem to arise from the unusual nature of the ground state of the $S=\frac{1}{2}$ 1DHAF compound ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}.$

Electronic structures and magnetism of LaNi5–xFex compounds

A systematic study of the magnetic moments and hyperfine interactions of the LaNi5–xFex compounds was performed using the spin-polarized tight-binding-linear-muffin-tin-orbital methods (TBLMTO). The calculated results were compared with neutron diffraction and Mössbauer experimental data and found to be in good agreement. Fe atoms exhibit more localized magnetic moments in LaNi5–xFex when the Fe content x is lower than 1.0. The calculated magnetic moments of the Fe atoms approach values as large as 2.5μB due to the dilution effect. The strong s–d hybridization between the Ni and La atoms and the neighboring Fe in the Fe-substituted samples results in a large transferred valence contribution to the total hyperfine field. It is found that the Fe and Ni magnetic moments decrease abruptly at a unit cell volume which is 5% smaller than the observed volume in LaNi4Fe due to the instability of the Fe magnetic moment. LaNi5 becomes ferromagnetic when the unit cell volume is larger than its original volume.

Effect of the Cu capping thickness on the magnetic properties of thin Ni/Cu(0 0 1) films

We have studied the effect of the Cu capping thickness (in the range 20⩽ t Cu ⩽180 Å) on the magnetic and structural properties of ultrathin FCC 40 Å Ni/Cu(0 0 1) films by means of magneto-optic Kerr effect (MOKE) magnetometry, polarised neutron reflection (PNR) and grazing incidence X-ray surface diffraction (GID) measurements. MOKE measurements show that perpendicular magnetic anisotropy (PMA) is observed for the whole of the Cu thickness range studied, while an increase of the coercive field with t Cu is found. The variation of the in-plane strain in the Ni film is shown to increase monotonously between 20 and 90 Å Cu capping thickness from −1.60±0.03% to −1.86±0.07% as revealed by GID, while PNR measurements show a marked decrease in the Ni magnetic moment per atom with increasing Cu capping layer thickness, from 0.54±0.03 μ B for t Cu=50 Å to 0.45±0.03 μ B for t Cu=180 Å. These results clearly show that a strain-induced reduction in the Ni magnetic moment per atom occurs. The increase in the coercive field is also attributed to the increase in the strain of the Ni film.

X-ray magnetic circular dichroic magnetometry on Ni/Pt multilayers

X-ray magnetic circular dichroism measurements have been performed on Ni/Pt multilayers at a temperature of 10 K. The element specificity and shell selectivity of the technique allows us to probe Ni and Pt magnetic moments and to separate them into their constituent spin (μS) and orbital (μL) magnetic moments. The Ni magnetic moment at the interface is found to be reduced. However, magnetically “dead” Ni layers are unambiguously ruled out. Induced Pt magnetic moments up to about 0.3 μB/atom are reported. The results are compared to ab initio calculations and to previous experiments performed on NiPt alloys. The role of intermixing in the reduction of the Ni magnetic moments is also discussed.

Magnetic interactions studies of Co and Ni-doped manganites using soft XMCD

An investigation of the electronic structure and magnetic moments of Co2+ and Ni2+ cations in doped CMR manganites Pr0.5Ca0.5(Mn1−xBx)O3 (B=Co with x=0.05 and B=Ni with x=0.04) was realized using soft X-ray Absorption Spectroscopy (sXAS) and soft X-ray Magnetic Circular Dichroism (sXMCD) at Co, Ni and Mn L2,3-edges. Compared to similar XAS experiments in Cr doped manganites, a smaller charge transfer character from Co or Ni 3d band to the oxygen 2p band is evidenced at low doping rate which suggest that Co and Ni ions would not participate directly in the double exchange phenomena contrary to Cr3+ ions.sXMCD showed that Co and Ni magnetic moments align parallel to the Mn magnetic moments, contrary to the Cr magnetic moment which was shown to align antiparallel to the Mn sublattice in Cr doped samples. A simple phenomelogical model, based on electronic phase segregations, is proposed to understand the nature of the magnetic interactions in the doped manganites. It shows that the physical properties induced by Co and Ni doping in manganites are not controlled by the same mechanism as in Cr doped manganites.

Contesting results for magnetic moments in nickel thin films

We report on Korringa-Kohn-Rostoker Green's function calculations for the ground-state moments of ultrathin Ni films on Cu(001) and on four monolayers (ML) Co/Cu(001). The calculations for Ni/Cu(001) show a slight enhancement of the Ni magnetic moment at the surface but a large reduction of the Ni magnetic moment at the Cu interface. The number of d holes at the surface and interface shows a small reduction. However, for Co/Cu(001) the calculation gave only a slightly decreased interface magnetic moment. For Ni on a ferromagnetic substrate, such as 4 ML Co/Cu(001), no reduction of the magnetic moment occurs, so that Ni at the interface retains its bulk value. These results are in contradiction with recent experimental results obtained using x-ray magnetic circular dichroism on ferromagnetic Ni films grown epitaxially on ultrathin films of Co. For decreasing film thickness, the number of holes and the magnetic moment show a gradual decrease.

Induced and cooperative order of Nd ions in NdNiO3

Low-temperature specific heat measurements on NdNiO3 evidence the onset of Nd cooperative ordering at TN2=0.77 K. Because of the particular arrangement of the Ni magnetic moments, half of the Nd ions have an antiferromagnetically compensated environment while the other half have a noncompensated one. We show that both types of Nd ions are affected by a different but non-negligible Nd–Ni exchange field, in contrast with the current model used in literature.

X-ray magnetic-circular-dichroism study of Ni/Fe (001) multilayers

The structure and magnetic properties of Fe/Ni(001) multilayers are studied using x-ray diffraction, magneto-optical Kerr effect magnetometry, and x-ray magnetic circular dichroism. Multilayers are deposited with constant Fe layers (12 \AA{}) and wedged Ni layers (0--30 \AA{}), repeated 20 times, to explore the magnetic moment and the structure dependence upon thickness of Ni ${(t}_{\mathrm{Ni}}).$ Up to ${t}_{\mathrm{Ni}}\ensuremath{\approx}16$ \AA{} (11 ML), both the Fe and the Ni have a bct structure, similar to the bulk structure of bcc Fe. The magnetic moments of Ni in the bct region are nearly constant at 0.85${\ensuremath{\mu}}_{B}$ for a Ni thickness ${t}_{\mathrm{Ni}}$ in the range 3 \AA{}$&lt;{t}_{\mathrm{Ni}}&lt;16$ \AA{}. This represents a significant enhancement over the moment in bulk fcc Ni (0.59$\ensuremath{\mu}B).$ The Fe/Ni multilayer undergoes a crystalline phase transition between 16 \AA{}$&lt;{t}_{\mathrm{Ni}}&lt;23$ \AA{}, beyond which both the Fe and Ni have an fct structure. In the fct region, the Ni magnetic moment is close to its bulk value and the Fe magnetic moment drops to 1.5${\ensuremath{\mu}}_{B},$ which is $\ensuremath{\sim}70%$ of its bulk value. The crystalline phase transition is also accompanied by a rotation of the magnetic easy axis by 45$\ifmmode^\circ\else\textdegree\fi{}$ in the plane of the film.

Magnetic and crystallographic properties of LaNi/sub (5-x)/Fe/sub x/

The magnetic and crystallographic properties of LaNi/sub (5-x)/Fe/sub x/ samples (1/spl les/x/spl les/1.4) have been studied by X-ray diffraction, neutron diffraction, SQUID and Mossbauer spectroscopy. Samples with x/spl ges/1.2 display typical ferromagnetic behavior. The substitution of iron for nickel in LaNi/sub 5/ increases the unit cell volume and Curie temperature. The majority (>90%) of the Fe atoms appear to occupy the 3g site. Induced Ni magnetic moments at 30 K have been calculated using the bulk magnetization data and iron magnetic moments.