Magnetic Compton Profiles Research Articles

Detection of Ni magnetic moment inGdNi2 compound by magnetic Compton profile (MCP) method

The Ni magnetic moment in theGdNi2 Laves phase compound is studied in detail by the use of the magnetic Comptonprofile (MCP) method. Analysis of the MCP, measured at 30 K, reveals thatthe spin component of Ni 3d electrons coupled antiparallel to that of Gd 4felectrons, and it was confirmed that the Ni retains a spin magnetic moment of0.16 ± 0.08 μB.Furthermore, the total magnetic moment, including the angular momentum component, is found tobe 0.23 ± 0.11 μB and this value that is obtained is in accord with that derived from direct measurement ofthe bulk magnetization. Our finding of the existence of the Ni magnetic momentcontradicts the well-known fact that Ni loses its magnetic moment in the Laves phase ofrare-earth (RE)–Ni compounds. In addition, the magnetic moment originating from theelectrons with s- and p-character, which are donated by the Gd and Ni atoms, is alsoobserved and quantified.

Magnetic Compton profiles of Fe by effective potentials

Many studies of the ferromagnetic metal Fe have been reported and discussed,such as spin-polarized band calculations, photoemissions, dHvA (de Haas–vanAlphen) experiments and Compton profiles experiments. However, theoreticalmagnetic Compton profiles (MCPs) of bcc Fe are not in good agreement withexperimental results, especially in the low momentum region. It is said that thisdiscrepancy is caused in the local spin density approximation (LSDA). Kubo et al calculated the MCPs of bcc Fe with full-potential linearized augmented plane wave(FLAPW) method and lowering the centre of gravity of the p-states. Their resultsare in good agreement with the experimental one. Recently, we suggested a newLSDA +U method which is effective for metals. For nonmagnetic state bcc V andbcc Cr, the shape of the Fermi surfaces and the population of thed ϵ orbital are improved. In this paper, we show that ourLSDA +U method improves the size of the N-centred hole pocket and MCPs forferromagnetic Fe. We used a modified WIEN97 package by adding two kinds ofLSDA +U versions, LSDA +UDFT and LSDA +U1.0. In the self-consistent field (SCF) calculation, the fixed-spin-moment scheme isapplied.

Fully relativistic description of magnetic Compton profiles with an application toUFe2

Fully relativistic description of magnetic Compton profiles with an application to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">U</mml:mi><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Spin-polarized electron momentum density in [formula omitted

The spin-polarized electron momentum density (EMD) of single-crystal ferromagnetic GdRh 3 B 2 has been probed by the magnetic Compton scattering technique. The spin moment is determined to be 6.83 ± 0.43 μ B per formula unit and the one-dimensional projection of the spin-polarized EMD (magnetic Compton profile) is obtained along the [ 1 0 1 ¯ 0 ] direction. These results are in good agreement with those predicted by a first-principles band structure computation with the spin–orbit interactions.

A magnetic Compton scattering study of [formula omitted

We have performed the first magnetic Compton scattering study of a transuranium compound, NpNiGa 5 . We have measured magnetic Compton profiles in two magnetic ordered phases of this compound. The magnetic Compton profiles in both ordered phases indicate that ferromagnetic components exist in the ordered phases. The signs of the magnetic effects suggest that the contribution of the 5f electrons of Np atoms is dominant to the total spin moments in the ordered phases.

A new approach to measuring high-resolution magnetic Compton profiles

It is demonstrated that long-term stability in the polarization of incident photons delivered from an insertion device makes it possible to measure magnetic Compton profiles with a momentum resolution of 0.15 atomic units or better, without employing a solid-state detector and the traditional method of reversing the external magnetic field or the handedness of the polarization of incident photons in an asynchronous cycle with a short period of tens to hundreds of seconds.

Anisotropies of magnetic Compton profiles in Co∕Pd multilayer system

Anisotropies of spin-projected wave functions are measured on a Pd∕Co multilayer system by measuring magnetic Compton profiles. The anisotropies of the wave functions are decomposed into the contributions of Co 3d states and Pd 4d states using an atomic model by a Hartree-Fock calculation assuming uniaxial (cylindrical) symmetry. Perpendicular anisotropy in Pd∕Co multilayers is dominated by the anisotropy of Co 3d states; states with both magnetic quantum number ∣m∣=2 and ∣m∣=1 contribute.

Magnetic Compton Scattering Study on Metamagnetism in Itinerant Uranium Compounds

We have investigated the itinerant uranium compound UCoAl using the magnetic Compton scattering technique. We have measured magnetic Compton profiles at 5 K with an applied magnetic fields of 1 and 3 T, both above the metamagnetic transition. We found that the magnetic effect in magnetic Compton scattering is negative at 1 T, which demonstrates that the spin moments of uranium 5f electrons dominate the total spin moments in this compound. It is also observed that the absolute value of the magnetic effect decreases as the magnetic field increases. This suggests that the cobalt spin moment is induced or increased by increasing magnetic field.

Orbital-Wise Decomposition of Magnetic Compton Profiles in Ferromagnetic Uranium Compound

It is demonstrated that the magnetic Compton profile of ferromagnetic UGe 2 is decomposed into partial profiles which are calculated from U 5f atomic wavefunctions with different magnetic quantum numbers, m 's. This decomposition shows that the m = -3 and m = -2 states dominate the total spin moment of this ferromagnetic compound, and the magnetic properties estimated from the decomposition results are favorably compared with theoretical predictions and other experimental observations.

Hole concentration dependence of Mn eg orbital state in bilayer manganites studied by magnetic Compton profile measurement

Abstract Magnetic Compton profiles (MCP) have been measured in the [100], [110] and [001] directions on the single crystals of La 2−2 x Sr 1+2 x Mn 2 O 7 ( x =0.30, 0.35 and 0.42) at 10 K. The occupation numbers in t 2g and two e g type orbitals ( x 2 − y 2 and 3 z 2 − r 2 ) of Mn-3 d state are evaluated from the line-shape analysis of MCP's in the [001] direction by using theoretical profiles derived from the ab initio calculations for (MnO 6 ) 8− cluster. It has been found that the e g state is dominated by the x 2 − y 2 type orbital at every hole concentration, x , and the 3 z 2 − r 2 type orbital population decreases with increasing x . From the result, the connections of e g orbital state with the electron correlation effect, exchange interactions, lattice distortion and electronic inhomogeneity are discussed.

Extracting d-orbital occupancy from magnetic Compton scattering in bilayer manganites

Abstract We consider the shape of the magnetic Compton profile (MCP), J mag ( p z ), in La 1.2 Sr 1.8 Mn 2 O 7 for momentum transfer p z along the [110] direction and the associated reciprocal form factor B ( r ) defined by taking the one-dimensional Fourier transform of J mag ( p z ). B ( r ) is shown to contain a prominent dip at r ≈1 A, where the minimum value B min of B ( r ) can be related to the occupancies of the e g orbitals of d x 2 − y 2 and d 3 z 2 − r 2 symmetry in the system. We illustrate our procedure in detail by analyzing the measured MCP at 5 K and the MCP computed within the framework of the local spin density approximation (LSDA) and comment on the differences between the measured and computed e g occupancies as a reflection of the limitations of the LSDA in treating electron correlation effects.

High-resolution magnetic Compton profile of iron

High-resolution magnetic Compton profile of iron

Orbital-wise decomposition of magnetic Compton profiles and spin moments in UGe2

Orbital-wise decomposition of magnetic Compton profiles and spin moments in UGe2

Magnetic Compton Scattering Studies of Electrochemically Hydrogenated Nickel

The influence of hydrogen absorption on the electronic and magnetic states of nickel was investigated by using the magnetic Compton scattering method, associated with band structure calculation. Hydrogen-free, hydrogen-charged and hydrogen-discharging nickel foils were prepared in an electrochemical cell, then their magnetic Compton profiles (MCPs) were measured with circularly polarized 173 keV X-rays in magnetic fields of ±2.5 T at room temperature in situ. The MCP of the hydrogen-charged nickel was separated into the respective profiles of α-phase NiH0.03 and β-phase NiH0.7. The MCP of the β-phase NiH0.7 indicates that this hydride is weakly ferromagnetic with a small spin moment µ<0.1 µB/Ni where the positive d-like component is nearly cancelled out by the negative s,p-like component. The band structure calculation yields such a small moment in the hydrogen-ordered NiH0.75, but smaller absolute values of the d-like and the sp-like components than the observed ones.

Experimental Study on Interlayer Magnetic Coupling in Sputtered Al/Fe/Al/Gd Magnetic Multilayer Films. I

Interlayer magnetic coupling (IMC) between Fe and Gd layers through Al spacer has been experimentally studied on [Al( R A)/Gd(40 A)/Al( R A)/Fe(20 A)]× N /Al(5 A) magnetic multilayers, where R =0, 5, 10, and 20 as nominal figures. Magnetization curves and the temperature dependence of magnetization are reported. Magnetic Compton-profile technique has been used to determine the amounts and the signs of spin magnetizations of Fe and Gd layers for R =5 and 20. A line-shape analysis of the magnetic Compton profile on the multilayer of R =5 has verified that the IMC is antiferromagnetic, and the negative small amount of magnetization of Gd layer exists even at room temperature under 1 kOe, despite the absence of ferromagnetic magnetization of a Al(5 A)/Gd(40 A) multilayer at room temperature. The antiferromagnetic IMC has been confirmed in the case of R =0, 5 and 10, but the IMC is not observed in the case of R =20.

Molecular orbital cluster calculation study of electron correlation and local lattice instability inLa2−2xSr1+2xMn2O7

In order to examine covalence and polaron effects in the bilayer manganite ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$, we have performed molecular orbital cluster calculations. Two types of ${({\mathrm{Mn}}_{2}{\mathrm{O}}_{11})}^{15\ensuremath{-}}$ clusters, one with the manganese aligned in the $a$ direction and the other in the $c$ direction, were embedded in a point charge environment that mimicked the crystal environment of the bilayer manganite at $x=0.40$, and their electronic states were calculated by the unrestricted Hartree-Fock (UHF) and the complete active-space self-consistent field (CASSCF) methods. The CASSCF result for the cluster along the $a$ direction exhibits double-well potential energy surfaces for symmetry-breaking deformations. This indicates small polaron formation in this system. On the other hand, the UHF calculation did not give double-well potential surfaces, showing the importance of the electron correlation for the polaron formation. Significantly large wells are obtained for the in-plane antiphase breathing and in-plane antiphase $\mathrm{O}\mathrm{Mn}\mathrm{O}$ stretching deformations. The double-well barrier for the former is $68\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ and that for the latter is $92\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, where the former is close to the experimentally obtained polaron hopping activation energy above ${T}_{\mathrm{c}}$. A similar calculation for the cluster along the $c$ direction exhibits a negligibly small double well, indicating that the polaron effect is very small in the carrier hopping in the $c$ direction within a bilayer. Electronic structures have been investigated using natural orbitals. At a double-well minimum, a localized polaron orbital is seen. In the ground state, a small but significant hole population is found in $p$ orbitals of the bridging oxygen, and a slight electron population is found in the ${e}_{g}$ orbital above the localized polaron orbital. For the cluster along the $a$ direction and without deformation, the first excited state is an electron-transfer state where an electron is moved from the bridging oxygen ${p}_{z}$ to a manganese ${e}_{g}$ orbital. This excited state couples with the ground state by the pseudo-Jahn-Teller effect, thus, the polaron is the ``pseudo-Jahn-Teller polaron.'' Using the natural orbitals, we have calculated magnetic Compton profiles and compared with experiment. Comparison between the experimental and theoretical results suggests the presence of polarons below ${T}_{\mathrm{c}}$. We briefly discuss the implication of this result in relation to the colossal magnetoresistance effect.

A magnetic Compton scattering study of double perovskiteSr2FeMoO6

The spin-polarized electron momentum distribution (magnetic Compton profile: MCP) of ferromagneticSr2FeMoO6 has been measured using the magnetic Compton scattering technique at room temperature.The experimental MCP is in good agreement with that obtained by a first-principlesband-structure calculation. The experiment and calculation reveal a hollow aroundpz = 0, which support the conclusion that there exists a negatively spin-polarized Fe 3d–Mo 4dmixed state.

Temperature-Dependent Orbital Degree of Freedom of a Bilayer Manganite by Magnetic Compton Scattering

We have measured temperature-dependent magnetic Compton profiles (MCPs) from a single crystal of La1.2Sr1.8Mn2O7. The MCPs, which involved the scattering of circularly polarized x rays, are in general related to the momentum density of all the unpaired spins in the system. Nevertheless, we show that when the x-ray scattering vector lies along the [110] direction, the number of magnetic electrons of a specific symmetry, i.e., d electrons of x(2)-y(2) symmetry, yield a distinct signature in the MCP, allowing us to monitor substantial changes in the occupancy of the dx(2)(-y(2)) states over the investigated temperature range of 5-200 K. This study indicates that magnetic Compton scattering can provide a powerful window on the properties of specific magnetic electrons in complex materials.

Development of measuring magnetic Compton profiles by grazing incidence geometry

A novel technique of measuring a magnetic Compton profile using the grazing angle geometry against a sample surface (Grazing Incidence Magnetic Compton Profile) has been successively developed. Measurements of a magnetic moment and a magnetic Compton profile are possible for a Fe 200 nm film on a thick glass substrate. The estimated thinnest limit for measurements is 100 nm for a Fe film.

Magnetic Compton profiles of Fe thin film and anisotropy of Co/Pd multilayer

The magnetic Compton profiles (MCPs) of Fe thin film with 1 μm thickness have been successfully measured, using polyethylene terephtalate (PET) substrates with 4 μm thickness to reduce scattering photons from substrate. We have succeeded for the first time to observe the anisotropy of MCPs in the Co/Pd multilayer. The magnetic out-of-plane anisotropy of the current Co (0.8 nm)/Pd (1.6 nm) multilayer sample can be explained by the model of a large number of the | m|=1 states of 3d-bands.