[Show abstract][Hide abstract] ABSTRACT: The anomalous Hall effect (AHE) in the "dirty region" (sigma(xx) < 10(4) S/cm) is studied in amorphous Co40Fe40B20 (CoFeB) thin films. Ostensively the conventionally adopted scaling (sigma(AH) proportional to sigma(1.6)(xx)) appears to be valid, but we find that the results can be better explained by the proper scaling [sigma(AH) = -(alpha sigma(-1)(xx0) + beta sigma(-2)(xx0))sigma(2)(xx) - b]. This implies that the AHE in the dirty region can also be well described by the standard skew scattering, side jump, and the intrinsic mechanisms.
Full-text · Article · Dec 2014 · Physical Review B
[Show abstract][Hide abstract] ABSTRACT: The longitudinal spin Seebeck effect (LSSE) and the anomalous Nernst
effect (ANE) are investigated in various metal/insulator junction
systems and a clear separation of the LSSE from the ANE induced by
static magnetic proximity is demonstrated. This separation is realized
by comparing transverse thermoelectric voltage in in-plane magnetized
(IM) and perpendicularly magnetized (PM) configurations, where the LSSE
appears only in the IM configuration while the ANE appears both in the
IM and PM configurations. We show that, in
Pt/Y3Fe5O12 samples, the LSSE voltage
in the IM configuration is three orders of magnitude greater than the
proximity-ANE contamination estimated from the data in the PM
configuration. This quantitative voltage comparison between the IM and
PM configurations is corroborated by systematic voltage measurements in
Au/Gd3Ga5O12 samples and by our
phenomenological model calculation. The LSSE measurements in high
magnetic field regions further confirm that the observed voltage in the
Au/Y3Fe5O12 samples is of magnon
origin. We apply this voltage comparison method also to a
sample and show that both the LSSE and ANE exist in this sample.
Full-text · Article · Dec 2013 · Physical Review B
[Show abstract][Hide abstract] ABSTRACT: Magneto-transport properties have been investigated for epitaxial thin films
of B20-type MnSi grown on Si(111) substrates. Both Lorentz transmission
electron microscopy (TEM) images and topological Hall effect (THE) clearly
point to the robust formation of skyrmions over a wide temperature-magnetic
field region. New features distinct from those of bulk MnSi are observed for
epitaxial MnSi films: a shorter (nearly half) period of the spin helix and
skyrmions, and an opposite sign of THE. These observations suggest versatile
features of skyrmion-induced THE beyond the current understanding.
[Show abstract][Hide abstract] ABSTRACT: We report a large and nonvolatile bipolar-electric-field-controlled magnetization at room temperature in a Co(40)Fe(40)B(20)/Pb(Mg(1/3)Nb(2/3))(0.7)Ti(0.3)O(3) structure, which exhibits an electric-field-controlled looplike magnetization. Investigations on the ferroelectric domains and crystal structures with in situ electric fields reveal that the effect is related to the combined action of 109° ferroelastic domain switching and the absence of magnetocrystalline anisotropy in Co(40)Fe(40)B(20). This work provides a route to realize large and nonvolatile magnetoelectric coupling at room temperature and is significant for applications.
Full-text · Article · Mar 2012 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: We report a large and nonvolatile bipolar-electric-field-controlled magnetization at room temperature in a Co40Fe40B20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 structure, which exhibits an electric-field-controlled looplike magnetization. Investigations on the ferroelectric domains and crystal structures with in situ electric fields reveal that the effect is related to the combined action of 109° ferroelastic domain switching and the absence of magnetocrystalline anisotropy in Co40Fe40B20. This work provides a route to realize large and nonvolatile magnetoelectric coupling at room temperature and is significant for applications.
Full-text · Article · Mar 2012 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: Protruding nanostructure is produced in the single layer of CuxAu1 − x surface alloy grown on Cu(001) due to the mismatch strain which has been utilized as a template to tune the magnetic anisotropy of overlays recently. The protrusion network was investigated by in situ scanning tunneling microscopy (STM) combined with low energy electron diffraction (LEED) as a function of the stoichiometry. The measurement revealed the structure of the protrusion and its correlation with the composition. Interestingly, we observed a twin-domain phase of the protrusion when the film approaches the fully hetero-epitaxial range.
No preview · Article · Sep 2010 · Journal of Physics Condensed Matter
[Show abstract][Hide abstract] ABSTRACT: Magnetoelectroluminescence (MEL) of organic semiconductor has been
experimentally tuned by adopting blended emitting layer consisting of both hole
and electron transporting materials. A theoretical model considering
intermolecular quantum correlation is proposed to demonstrate two fundamental
issues: (1) two mechanisms, spin scattering and spin mixing, dominate the two
different steps respectively in the process of the magnetic field modulated
generation of exciton; (2) the hopping rate of carriers determines the
intensity of MEL. Calculation successfully predicts the increase of singlet
excitons in low field with little change of triplet exciton population.
[Show abstract][Hide abstract] ABSTRACT: With continuous variable composition, an artificial pseudomorphic template of 1 ML Cu(1-x)Au(x) was achieved by epitaxial growth on Cu(001), in which the magnetic anisotropy and the spin reorientation transition of Ni films were investigated in situ. The result clearly indicates that the strain induced protruding nanostructures at the interface dominates in tuning the magnetic anisotropy. while the interface chemistry plays a minor role. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3263717]
Full-text · Article · Nov 2009 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: The magnetic anisotropy and interlayer coupling of epitaxially grown Ni/Cu/Co sandwich on Cu(100) have been studied in situ as a function of Cu and Ni thicknesses by magneto-optic Kerr effect. Oscillatory magnetic anisotropy of Ni layer is observed and attributed to the oscillatory interlayer coupling between the Ni and Co layers.
[Show abstract][Hide abstract] ABSTRACT: We report electric detection of ferromagnetic resonance (FMR) in epitaxially grown single crystal iron film through microwave photovoltage generation technique. The experimental results agree well with the established theory about FMR in iron films, showing excellent extendability of such a technique onto different ferromagnets as an effective way to study magnetocrystalline anisotropy and spin excitations. Furthermore, the information about the phase of magnetization precession is implicated in the lineshape of photovoltage, which makes it possible to probe in details into magnetic phase dynamics that is of significance for devising spintronic devices.
Full-text · Article · Jan 2009 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: FexPd1-x films were epitaxially grown on Au(001). The structure changes from face-centered-cubic (fcc) to face-centered-tetragonal (fct) at x˜0.6, then to body-centered-cubic (bcc) at x˜0.85. Ferromagnetism shows up at 300 K when x is 0.06. The cubic magnetocrystalline anisotropy constant K switches from negative to positive as x increases to 0.34.
No preview · Article · Mar 2008 · Physics Letters A
[Show abstract][Hide abstract] ABSTRACT: Co/NiO/Fe trilayers are grown on Ag(001) substrate using Molecular Beam Epitaxy (MBE). Element-specific magnetic domain images on both ferromagnetic (FM) Co and Fe layers and antiferromagnetic NiO layer are obtained using X-ray Magnetic Circular Dichrism (XMCD) and X-ray Linear Dichrism (XMLD), respectively. By comparing these magnetic domain images, we find that the Co-Fe interlayer coupling across the NiO spacer layer exhibits a transition from a 90^o-coupling to a collinear coupling as the NiO film thickness increases. This observation is shown to be directly related to the NiO magnetic structure and its interaction at the Co/NiO and NiO/Fe interfaces.
[Show abstract][Hide abstract] ABSTRACT: The finite-temperature magnetism of Ni and permalloy in body-centered-cubic (bcc) and face-centered-cubic (fcc) phases is studied theoretically using ab initio supercell calculations and Green's function methods. The results confirm and explain the general experimental trend that the fcc phases have higher Curie temperatures than the bcc counterparts. In addition, the spin-wave stiffness constants of bcc-Ni and bcc-permalloy are predicted.
Full-text · Article · Feb 2008 · Physical Review B
[Show abstract][Hide abstract] ABSTRACT: Molecular beam epitaxially grown Fe on GaAs(001) capped by Au overlayer with variable thickness had been investigated in situ by magneto-optical Kerr effect (MOKE). It is observed that the MOKE intensity as a function of Au film thickness decays much faster than that derived from the well-known Zak's theory. This can be explained by different optical parameters of ultrathin films from bulk values. It is also found that a minimum thickness of 1.4 nm Au is needed to effectively prevent the oxidation of Fe film at 300 K in atmosphere.
No preview · Article · Jun 2007 · Thin Solid Films
[Show abstract][Hide abstract] ABSTRACT: Permalloy with a body-centered-cubic structure has been grown on GaAs(001) by molecular beam epitaxy. Its magnetism, Curie temperature, and magnetic anisotropy are determined experimentally and compared to those of conventional face-centered-cubic Permalloy. Unexpectedly the vanishing magnetic cubic anisotropy in Permalloy is found to be independent of its atomic structure but depends only upon the stoichiometry of Fe and Ni in the FexNi1-x alloy. This observation is further investigated and confirmed by first-principles electronic band calculations, which help to understand the long-standing issue of why Permalloy should be a soft magnet.
[Show abstract][Hide abstract] ABSTRACT: Magnetic stripe domains in Fe∕Ni∕Cu(001) were imaged and studied using photoemission electron microscopy. The stripe domain width decreases exponentially as the system approaches the spin reorientation transition (SRT) point. A reduction of the Curie temperature (TC) is observed within a narrow gap of the SRT region. For film with fixed thickness, the stripe domains below TC represent only part of the stripe phase due to a higher SRT temperature than TC.
No preview · Article · Jun 2005 · Physical Review B
[Show abstract][Hide abstract] ABSTRACT: The first normal emission experiment result on bcc Ni ultrathin film is presented in comparison with the one on fcc Ni. Its agreement with band structure calculation, by supplementing our former results on the magnetic properties of bcc Ni, verifies from the electronic viewpoint the successful epitaxy of this metastable phase of Ni which doesn't exist in nature.
[Show abstract][Hide abstract] ABSTRACT: The body-centered-cubic (bcc) phase of Ni, which does not exist in nature, has been achieved as a thin film on GaAs(001) at 170 K via molecular beam epitaxy. The bcc Ni is ferromagnetic with a Curie temperature of 456 K and possesses a magnetic moment of 0.52+/-0.08 micro(B)/atom. The cubic magnetocrystalline anisotropy of bcc Ni is determined to be +4.0x10(5) ergs x cm(-3), as opposed to -5.7x10(4) ergs x cm(-3) for the naturally occurring face-centered-cubic (fcc) Ni. This sharp contrast in the magnetic anisotropy is attributed to the different electronic band structures between bcc Ni and fcc Ni, which are determined using angle-resolved photoemission with synchrotron radiation.
Full-text · Article · May 2005 · Physical Review Letters