Spin-polarised relativistic electronic structure calculations

Krutzen, B. C. H.; Springelkamp, F.

doi:10.1088/0953-8984/1/44/009

Cited by 63 publications

(30 citation statements)

References 36 publications

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“…3. The general behavior of the exchange-split A2 states is in reasonably good agreement with our self-consistent relativistic augmented plane-wave calculations and with other recent calculations [1]. How-ever, the measured bandwidths are narrower (by ~50%) and the measured binding energies are about 0.25 eV closer to the Fermi level than predicted.…”

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confidence: 91%

Temperature-dependent conduction-band exchange splitting in ferromagnetic hcp gadolinium: Theoretical predictions and photoemission experiments

et al. 1992

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Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along V-A of the three-dimensional Brillouin zone. The A2 band exchange splitting (0.85 eV) and dispersion (0.5 eV) are in reasonably good agreement with self-consistent local spindensity approximation calculations. The conduction-band magnetic exchange splitting vanishes at the Curie temperature following a conventional power law with a Heisenberg critical exponent. This "Stoner modeP' collapse of the exchange splitting is in striking contrast to corresponding results observed in transition-metal ferromagnets.PACS numbers: 75.10.Lp, 75.50.Cc, 79.60.Cn Gadolinium is a prototype Heisenberg ferromagnet in which the magnetic moments of atomiclike 4/ states are coupled via exchange with the conduction electrons-the well-known RKKY interaction. Hund's rule applied to the half-filled 4/ shell of Gd accounts for the S'^'^ state having no orbital angular momentum (L=0) and maximum spin (y =L-l-iS'= J ). The conduction band (and valence structure of Gd atoms) is a stable trivalent {5d6s^) configuration, and the measured saturated magnetic moment per atom for Gd metal (7.63^fi/atom) reveals a significant contribution (0.63/ifi/atom) to the total moment arising from conduction-band spin polarization. Gadolinium has also been considered an important prototype material for testing local-spin-density approximation (LSDA) calculations in rare-earth metals where exchange and relativistic (spin-orbit) effects play important roles [1]. In spite of the recent theoretical progress, important questions remain concerning the accuracy with which the standard LSDA formalism deals with 4/conduction-electron exchange effects. Experimental progress in understanding the electronic and magnetic properties of Gd and other rare-earth metals has been primarily achieved via neutron scattering [2] and de Haas-van Alphen [3] measurements. Photoemission studies [4-11] have achieved some success in eluci-dating novel electronic and magnetic behavior of rareearth metals, but the progress has been limited primarily by the difficulty of achieving impurity-free well-ordered crystal surfaces.One of the first attempts [4] to measure electronic structure of a bulk single-crystal rare-earth metal (Gd) using angle-resolved photoemission met with limited success. The photoemission spectra were found not to exhibit the systematic variation of peak positions (bindingenergy changes) as a function of photon energy that are understood as manifestations of direct transitions between bulk band states. The absence of bulk band behavior in the photoemission spectra was attributed to strong momentum broadening associated with short electron

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confidence: 91%

Temperature-dependent conduction-band exchange splitting in ferromagnetic hcp gadolinium: Theoretical predictions and photoemission experiments

et al. 1992

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“…Photoemission studies report the energy separations between the G 4 2 2 G 1 1 points [9] and G 4 2 2 A 1 points [8] to be by about a factor of 2 smaller than that predicted by the state-of-the-art calculations [10,11] [shown in Fig. 1(a) for the ferromagnetic ground state [12] ].…”

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Electronic Band Structure of Gd: A Consistent Description

Maiti

Malagoli²,

Magnano³

et al. 2001

Phys. Rev. Lett.

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The dispersion of the Gd ͑5d6s͒-valence bands has been investigated by means of spin-and angleresolved photoemission. The spin analysis of various spectral features shows that their weak dispersion and unusual broadening is due to the photoelectron lifetime rather than to correlation induced band narrowing as previously proposed. These results resolve a long-standing discrepancy between theoretical and experimental descriptions of the rare earth band structure. DOI: 10.1103/PhysRevLett.86.2846 The unique electronic and magnetic properties of lanthanides result from the coexistence of both highly localized and delocalized levels in the valence region. While the 4f electrons maintain an atomic character in these metals, the (5d6s) states form the metallic bonding and mediate the indirect exchange interaction among the 4f moments.Photoemission spectroscopy gives direct access to the excited-and ground-state configurations of the 4f shell that are indeed well understood for the lanthanide metals [1]. On the contrary, no satisfactory picture of the (5d6s) states exists so far. Even fundamental questions such as the accuracy of the band structure methods for the ground-state description or the influence of many-body effects on the excitation spectra have not yet found an answer. In fact, band structure calculations based on the local spin density approximations (LSDA) predict a large bandwidth for the (5d6s) states in rare earths similar to that of the preceding elements (alkali and alkaline earth metals) in the Periodic Table. These latter cases [2-5] exhibit strongly dispersive photoemission features that are reasonably well interpreted within the paradigms based on effective single-particle approximations, although a quantitative description requires detailed consideration of many-body effects. In sharp contrast, angle-resolved photoemission from lanthanides does not display the expected dispersive behavior of the (5d6s)-bulk states. Various observations [6][7][8] seem to indicate a failure of the effective singleparticle descriptions to the (5d6s) photoemission and suggest the importance of correlation effects.The situation is well illustrated by the case of Gd, which is the most extensively studied lanthanide element for its importance as a prototypical Heisenberg ferromagnet (T C 293 K). Photoemission studies report the energy separations between the G 4 2 2 G 1 1 points [9] and G 4 2 2 A 1 points [8] to be by about a factor of 2 smaller than that predicted by the state-of-the-art calculations [10,11] [shown in Fig. 1(a) for the ferromagnetic ground state [12] ]. Correspondingly, only a significantly weak energy dispersion of the D 2 band is observed by varying the photon energy [8,9]. While this latter observation, separately taken, could possibly be explained by momentum broadening [2], the concomitant discrepancy between the experimental and theoretical bandwidth leads to attribute [8] both the effects to strong electron-electron interactions. Notably, such band narrowing in Gd appears to be much larger than ...

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“…Gadolinium has been considered an important prototype material for testing local-spin-density approximation (LSDA) calculations on rare-earth metals where localized 4f electrons, exchange, and relativistic (spin-orbit) eA'ects play important roles [1][2][3][4][5][6]. In the rare earths, the LSDA appears to overestimate the itineracy of 4f levels leading to predictions of structural, electronic, and magnetic properties often in relatively poor agreement with experiment, a few exceptions being La and Lu which have either an empty or filled 4f shell.…”

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confidence: 99%

Surface magnetism of Gd(0001): Evidence of ferromagnetic coupling to bulk

1992

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Previous polarized electron experiments and recent ab initio calculations suggest that the surface layer magnetic moments of Gd(0001) are antiferromagnetieally coupled to the bulk magnetic moments.Spin-polarized photoemission data are presented which show that the spin polarization of the magnetic surface state and the surface 4f states of Gd(OOOI ) are coupled ferromagnetically to the bulk magnetic moment.PACS numbers: 75. 10.Lp, 75.50.Cc, 79.60.Cn Gadolinium has been considered an important prototype material for testing local-spin-density approximation (LSDA) calculations on rare-earth metals where localized 4f electrons, exchange, and relativistic (spin-orbit) eA'ects play important roles [1][2][3][4][5][6]. In the rare earths, the LSDA appears to overestimate the itineracy of 4f levels leading to predictions of structural, electronic, and magnetic properties often in relatively poor agreement with experiment, a few exceptions being La and Lu which have either an empty or filled 4f shell. Calculations for bulk Gd typically yield lattice constants which vary by a factor of 2 beyond limits considered appropriate for systems where the LSDA is judged accurate. LSDA calculations of band structure and magnetic properties are often in reasonable agreement with experiment. Recent self-consistent calculations for bulk Gd have yielded a conduction-band magnetic moment per atom (-0. 57pti) in good agreement with measurements (-0.63), and an average 5d-band exchange splitting (-0.6 eV) in reasonable agreement with recent angle-resolved photoemission measurements [7] of the A2 band dispersion and exchange splitting. However, the binding energies and dispersion of the h2 bands obtained from existing LSDA calculations do not agree with experimental results (-50% discrepancies), suggesting either inaccuracies in the calculations, inliuence of surface eA'ects due to short electron mean free paths [8], or strong many-body eITects [9] in the photoemission similar to those apparent in Ni. Surface properties of Gd(0001) are of intrinsic interest and also provide an additional means of testing LSDA calculations. Previous surface-sensitive probes of magnetism applied to Gd(0001) have established novel behavior. Spin-polarized low-energy electron-diA'raction (SPLEED) and magneto-optic Kerr eAect (MOKE) measurements [10] of single-crystal Gd(0001) surfaces [11] prepared on W(110) confirmed the existence of enhanced surface ferromagnetic order at temperatures up to 310 K ( -20 K above the bulk Curie temperature Tcb =293 K). These results, along with spin-polarized photoemission experiments [10] that probed bulk and surface 4f excitations, were interpreted as indicating antiferromagnetic coupling between the surface 4f spins and those of the underlying ferromagnetic bulk. Recent ab initio calculations [12] have examined the structural, electronic, and magnetic properties of Gd (0001), taking into account the total system energy.Several important results were obtained that can be directly compared with experimental results: First, th...

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Spin-polarised relativistic electronic structure calculations

Cited by 63 publications

References 36 publications

Temperature-dependent conduction-band exchange splitting in ferromagnetic hcp gadolinium: Theoretical predictions and photoemission experiments

Temperature-dependent conduction-band exchange splitting in ferromagnetic hcp gadolinium: Theoretical predictions and photoemission experiments

Electronic Band Structure of Gd: A Consistent Description

Surface magnetism of Gd(0001): Evidence of ferromagnetic coupling to bulk

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