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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Effects of step decoration by oxygen on ultrathin film magnetic anisotropy; p(1×1)Fe on vicinal W(100)

Hector C. Mireles and J. L. Erskine

J. Appl. Phys. 93, 7139 (2003); http://dx.doi.org/10.1063/1.1556198 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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The mechanisms responsible for surface-step-induced magnetic anisotropy in ultrathin films on vicinal surfaces were explored by studying the effects resulting from surface oxygen adsorption. Magnetic hysteresis loops produced by ultrathin (1–4 ML) Fe films on a variable-step-density W(100) surface were measured using the magneto-optic Kerr effect. Auger electron spectroscopy was used to determine surface oxygen coverage. Significant reductions of the switching fields that characterize the uniaxial surface-step-induced anisotropy were observed. The oxygen-coverage dependencies were found to be consistent with step decoration (preferential chemisorption at steps) and support the highly localized nature of magnetic anisotropy energies associated with the Néel pair-bonding model of surface-step-induced magnetic anisotropy. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Rf Surface magnetism
68.43.Mn Adsorption kinetics
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
68.47.De Metallic surfaces

Scanning tunneling microscopy studies of the Fe3O4(001) surface using antiferromagnetic probes

G. Mariotto, S. F. Ceballos, S. Murphy, and I. V. Shvets

J. Appl. Phys. 93, 7142 (2003); http://dx.doi.org/10.1063/1.1556199 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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We have studied the (001) surface of a Fe3O4 single crystal using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). The STM measurements were performed using a novel tip of antiferromagnetic MnNi alloy. Atomically resolved STM images provide evidence of a surface terminated at the octahedral plane, with rows of Fe cations running along the 〈110〉 crystallographic axes. Two different kinds of Fe cations with a separation of 6 Å were imaged, while the periodicity between Fe cations of the same kind is about 12 Å. We propose an interpretation of the anomalous corrugation observed in terms of a spin polarized effect, resulting in magnetic contrast between Fe2+ and Fe3+ ions in octahedral coordination. © 2003 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Dv Composition, segregation; defects and impurities
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
07.79.Cz Scanning tunneling microscopes
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
75.70.Rf Surface magnetism

Electronic structure calculations of hexagonal and cubic phases of Co3Pt

S. D. Willoughby, R. A. Stern, R. Duplessis, J. M. MacLaren, M. E. McHenry, and D. E. Laughlin

J. Appl. Phys. 93, 7145 (2003); http://dx.doi.org/10.1063/1.1556200 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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Using first principles electronic structure calculations we investigated structural and magnetic properties of three distinct phases of Co3Pt. Relaxed lattice constants, total energies, magnetocrystalline anisotropies, and density of states were calculated for each phase at their equilibrium lattice constants, as well as under expansion and contraction stresses. These computations may help clarify the results of some recent but ambiguous experiments on Co3Pt. © 2003 American Institute of Physics.
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71.20.Be Transition metals and alloys
61.66.Dk Alloys
75.30.Gw Magnetic anisotropy
71.15.Nc Total energy and cohesive energy calculations
75.50.Cc Other ferromagnetic metals and alloys

Electronic susceptibility and Curie temperature of the double-exchange model within dynamical mean-field theory

R. S. Fishman and M. Jarrell

J. Appl. Phys. 93, 7148 (2003); http://dx.doi.org/10.1063/1.1556201 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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Due to its applications to the manganites, the double-exchange (DE) model has been intensively studied over the past ten years. An especially promising approach to investigate the DE model is dynamical mean-field theory (DMFT), which becomes exact in infinite dimension but accurately describes local quantum fluctuations in three dimensions. In this article, we use DMFT to solve the Bethe–Salpeter equation for the electronic susceptibility above TC. Assuming a semicircular density-of-states, we obtain an analytic relation for TC in the limit of large Hund’s coupling from the condition that the inverse electronic susceptibility vanishes. Our expression for TC agrees with an earlier result based on the local-moment susceptibility and corrects a mistake in a result based on the self-consistent equation for the magnetization below TC. © 2003 American Institute of Physics.
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75.30.Et Exchange and superexchange interactions
75.10.Lp Band and itinerant models
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities

Magnetic structures of CrPt3 by first-principles calculations

Youngsoo Kwon, T. H. Rho, Sangsoo Lee, and Soon C. Hong

J. Appl. Phys. 93, 7151 (2003); http://dx.doi.org/10.1063/1.1558609 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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In order to investigate systematically the magnetic structures of CrPt3, four different magnetic structures of ferrimagnetism (FIM), A-, C-, and G-type antiferromagnetism (AFM) for L12 structure and two different ones of FIM and A-type AFM for D022 structure were calculated. The full-potential linearized augmented plane wave (FLAPW) method was employed to solve Kohn–Sham equation self-consistently, using general gradient approximation for exchange-correlation potential. We found that L12 FIM is most stable among all of the aforementioned states. For D022, AFM is more stable than FIM by a significant energy difference (102 meV/Cr–atom). For D022 AFM the coupling between Cr and Pt atoms is ferromagnetic unlike FIM. The calculated magnetic moments are calculated to 2.78, 2.81, 2.81, and 2.88 μB for FIM, A-, C-, and G-type AFM in L12, and 2.36, 2.59 μB for FIM and AFM in D022, respectively. The magnetism is proven to be very sensitive to a crystal structure. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics
71.15.-m Methods of electronic structure calculations
31.15.xr Self-consistent-field methods
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Local spin-density waves in Cr–V alloys: Dependence on temperature and applied magnetic field

L. M. de Oliveira, W. A. Ortiz, and A. J. A. de Oliveira

J. Appl. Phys. 93, 7154 (2003); http://dx.doi.org/10.1063/1.1556202 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The appearance of Curie–Weiss behavior in itinerant antiferromagnetic systems is an important subject of research in the case of Cr alloys. The nature of the phenomenon is associated to stabilization of a short-range order, which allows formation of local spin-density waves below a certain temperature, TLOC. In this work we present results of magnetic susceptibility of Cr–x at. %V alloys (x=0, 0.1, 0.2, and 0.4) where, TLOC is observed. Our results show that not only does a dependence of TLOC with V concentration exist, but it also presents a linear dependence on the applied magnetic field. The effective magnetic moment estimated from Curie–Weiss fittings also show a decreasing dependence with the applied magnetic field. © 2003 American Institute of Physics.
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75.30.Ds Spin waves
75.50.Ee Antiferromagnetics
75.30.Hx Magnetic impurity interactions
75.30.Cr Saturation moments and magnetic susceptibilities

Role of domain and interface spin structure on exchange bias in CoNi/Gd/CoNi trilayers

B. Altuncevahir, S. Demirtaş, and A. R. Koymen

J. Appl. Phys. 93, 7157 (2003); http://dx.doi.org/10.1063/1.1556203 (3 pages)

Online Publication Date: 9 May 2003

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In this study, dc remanence measurements were performed on a sputter deposited CoNi(top)/Gd/CoNi trilayers. The remanence state of the CoNi(top)/Gd bilayer, which is the hard layer, determines the exchange bias field strength. If the sample is cooled from room temperature at the remanence state corresponding to the hard layer coercive field, the exchange bias becomes zero. Domains form in the hard layer at this remanence state. The angular dependence of the coercive field does not indicate magnetization reversal by domain wall motion. The bottom soft CoNi layer exchange couples to each domain in the hard layer at the interface. This causes the exchange bias field to become zero on the average. If the trilayer is cooled at its full remanence state, the formation of Hb anisotropy is observed in the angular dependence of coercivity. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
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