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1 May 2010

Volume 107, Issue 9, Articles (09xxxx)

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back to top Micromagnetics, Magnetization Processes, Wall Dynamics, and Imaging

Magnetic properties of FeCo alloys measured by energy-loss magnetic chiral dichroism

B. Warot-Fonrose, C. Gatel, L. Calmels, V. Serin, E. Snoeck, and S. Cherifi

J. Appl. Phys. 107, 09D301 (2010); http://dx.doi.org/10.1063/1.3358217 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2010

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The energy loss magnetic chiral dichroism (EMCD) in a transmission electron microscope to study magnetic devices of reduced dimensions is a young and very promising technique. It relies on the study of electron energy loss spectra acquired in specific locations of the diffraction pattern. The sensitivity of the method to the magnetic properties is investigated on a series of FexCo1−x alloys. The spectra can reflect modifications of magnetic or structural properties and the iron-cobalt alloys present the advantage of having a crystal structure which remains body centered cubic on a wide composition range. A significant variation of the EMCD signal as a function of the composition of the alloy has been detected and attributed to changes in the magnetic moment.
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75.30.Cr Saturation moments and magnetic susceptibilities
61.66.Dk Alloys
78.20.Fm Birefringence
79.20.Uv Electron energy loss spectroscopy

Magnetic vortex dynamics on a picoseconds timescale in a hexagonal Permalloy pattern

Je-Ho Shim, Dong-Hyun Kim, Brooke Mesler, Jung-Hwan Moon, Kyung-Jin Lee, Erik Anderson, and Peter Fischer

J. Appl. Phys. 107, 09D302 (2010); http://dx.doi.org/10.1063/1.3358223 (3 pages) | Cited 1 time

Online Publication Date: 20 April 2010

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We observed a motion of magnetic vortex core in a hexagonal Permalloy pattern by means of soft x-ray microscopy. Pump-probe stroboscopic observation on a picosecond timescale has been carried out after exciting a ground state vortex structure by an external field pulse of 1 ns duration. Vortex core is excited off from the center position of the hexagonal pattern but the analysis of the core trajectory reveals that the motion is nongyrotropic.
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75.78.Jp Ultrafast magnetization dynamics and switching
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Bb Fe and its alloys

Magnetic antiphase domains in Co/Ru/Co trilayers

Zhen Li, Ralph Skomski, Steven Michalski, Lanping Yue, and Roger D. Kirby

J. Appl. Phys. 107, 09D303 (2010); http://dx.doi.org/10.1063/1.3367966 (3 pages) | Cited 1 time

Online Publication Date: 21 April 2010

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Ultrathin Co/Ru/Co trilayers are investigated experimentally by magnetization curves and magnetic-force microscopy (MFM). Emphasis is on the domain-wall fine structure of antiphase domain walls in the films. The trilayers are produced by sputtering and consist of two Co layers of equal thickness (5 nm), exchange-coupled through a Ru layer of variable thickness. The sign and magnitude of the interlayer exchange are tuned by the thickness of the Ru interlayer. The exchange and its distribution are investigated by measurements of the static magnetization curves. For a Ru thickness of 0.4 nm, the exchange is predominantly antiferromagnetic and the MFM images show fairly immobile domain walls. Micromagnetic model calculations yield immobile antiphase domain walls whose thickness decreases with increasing magnetic field but is typically of the order of 100 nm in agreement with experiment.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.78.Fg Dynamics of domain structures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Ee Antiferromagnetics

Magneto-optical imaging and coercivity mapping of GdFe spin-valve structures

Takayuki Ishibashi, Terumasa Kosaka, Masayuki Naganuma, Tatsutoshi Shioda, Ken-ichi Aoshima, Nobuhiko Funabashi, Kenji Machida, Kiyoshi Kuga, and Naoki Shimidzu

J. Appl. Phys. 107, 09D304 (2010); http://dx.doi.org/10.1063/1.3367980 (3 pages)

Online Publication Date: 21 April 2010

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GdFe spin-valve structures, Si/bottom electrode/TbFeCo/CoFe (1 nm)/Cu (6 nm)/GdFe (10 nm)/Ru, with dimensions of 20×20 μm2 were investigated by a magneto-optical imaging technique. In a parallel configuration, i.e., a configuration in which the magnetization directions of GdFe and TbFeCo layers are parallel, the coercivity (Hc) decreases when nucleation centers are present in the patterns. In the antiparallel configuration, although few nucleation centers are present the deviation in Hc is greater than that in the parallel configuration.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Measuring the effects of low energy ion milling on the magnetization of Co/Pd multilayers using scanning electron microscopy with polarization analysis

B. J. McMorran, A. C. Cochran, R. K. Dumas, Kai Liu, P. Morrow, D. T. Pierce, and J. Unguris

J. Appl. Phys. 107, 09D305 (2010); http://dx.doi.org/10.1063/1.3358218 (3 pages) | Cited 5 times

Online Publication Date: 30 April 2010

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The dependence of the magnetization profile of Co/Pd multilayer films with very thin individual layers, Co(0.4 nm)/Pd(0.6 nm), on the energy of ion milling is investigated using scanning electron microscopy with polarization analysis (SEMPA). The effect of Ar ion milling on the Co/Pd magnetization angle distribution is compared for ion milling at 50 eV, 1 keV, and 2 keV. We find that 1 and 2 keV Ar ion milling causes a measurable change in the out-of-plane magnetization angle distribution as material is removed, but ion milling with 50 eV Ar ions does not significantly alter the magnetization. This enables quantitative imaging of all three vector components of the surface magnetization of the Co/Pd multilayer films with 20 nm lateral spatial resolution using SEMPA.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.20.Wk Machining, milling
75.70.Rf Surface magnetism
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Lorentz transmission electron microscopy observation of magnetic domains in La0.825Sr0.175(Mn,Al)O3

S. Mori, K. Yoshidome, Y. Nagamine, Y. Togawa, K. Yoshii, and K. Takenaka

J. Appl. Phys. 107, 09D306 (2010); http://dx.doi.org/10.1063/1.3358225 (3 pages)

Online Publication Date: 3 May 2010

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Nonmagnetic Al substitution effect on the stability of a ferromagnetic (FM) metallic state in double-exchange manganite, La0.825Sr0.175MnO3, was investigated by Lorentz transmission electron microscopy (TEM), in combination with magnetic measurements. Both FM transition temperature (Tc) and the rhombohedral-to-orthorhombic (R-to-O) transition temperature (Ts) decreased by a few percent of Al substitution. An in situ Lorentz TEM observation revealed that drastic change of the FM domain structure took place through the R-to-O structural transition. The magnetization decreased slightly at Ts and characteristic spin-glass state is realized in the low-temperature region below Ts.
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75.60.Ch Domain walls and domain structure
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Lk Spin glasses and other random magnets
75.30.Et Exchange and superexchange interactions
64.70.K- Solid-solid transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Effects of vortex chirality and shape anisotropy on magnetization reversal of Co nanorings (invited)

Kai He, David J. Smith, and Martha R. McCartney

J. Appl. Phys. 107, 09D307 (2010); http://dx.doi.org/10.1063/1.3358233 (6 pages) | Cited 6 times

Online Publication Date: 3 May 2010

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The effects of vortex chirality and shape anisotropy on the magnetization reversal of thin Co nanorings with and without slots have been investigated using off-axis electron holography and micromagnetic simulations. Stepped hysteresis loops were determined and typical well-defined states, including onion states, vortex states, flux-closure (FC) states, and omega (Ω) states were identified during reversal for different element shapes. The chirality of the vortex (vortices) formed after the onion states determined the switching mechanism. The Co nanorings and slotted rings with applied field parallel to the slots showed multistep switching via onion-FC-onion mode, also involving the formation and annihilation of vortex (vortices), whereas slotted rings with applied field perpendicular to the slots exhibited simple one-step switching by abrupt chirality reversal of the FC states. The influence of shape anisotropy on switching fields is also discussed in terms of demagnetization energy.
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75.60.Jk Magnetization reversal mechanisms
75.78.Cd Micromagnetic simulations
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Visualizing the propagation of volume magnetization in bulk ferromagnetic materials by neutron grating interferometry (invited)

C. Grünzweig, C. David, O. Bunk, J. Kohlbrecher, E. Lehmann, Y. W. Lai, R. Schäfer, S. Roth, P. Lejcek, J. Kopecek, and F. Pfeiffer

J. Appl. Phys. 107, 09D308 (2010); http://dx.doi.org/10.1063/1.3365373 (6 pages)

Online Publication Date: 5 May 2010

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In this article we report on a neutron interferometry technique based on diffraction gratings which was used to visualize the geometry-dependent magnetization processes in bulk ferromagnetic materials. The contrast origin is based on the refraction of unpolarized neutrons at magnetic domain walls and the obtained image is termed neutron dark-field image (DFI). The magnetization process is imaged by measuring the spatially resolved domain wall density distribution of the sample. The sample under investigation was a polycrystalline steel plate where the magnetization process was imaged for different sample orientations. The DFI results of the magnetization processes were verified on the one hand by complementary neutron small angle scattering (SANS) experiments and on the other hand by finite element method (FEM) simulations. The obtained SANS and FEM results verify the same magnetization process behavior as observed in the DFI results.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
02.70.Dh Finite-element and Galerkin methods
75.60.Ch Domain walls and domain structure

High frequency magnetic field imaging by frequency modulated magnetic force microscopy

Hitoshi Saito, Wei Lu, Kodai Hatakeyama, Genta Egawa, and Satoru Yoshimura

J. Appl. Phys. 107, 09D309 (2010); http://dx.doi.org/10.1063/1.3368706 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2010

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High frequency ac magnetic field from magnetic recording head was successfully imaged by using our newly developed frequency-modulated magnetic force microscopy (FM-MFM), which uses the frequency modulation of cantilever oscillation caused by applying ac magnetic field to a mechanically oscillated cantilever. The FM-MFM has been demonstrated and the experimental results show good agreement with our proposed models for FM-MFM. The amplitude and phase images of an ac magnetic field can be obtained separately by using the FM-MFM technique with a lock-in amplifier. By taking advantage of this technique, the present FM-MFM method opens a possibility to evaluate the magnetic field characteristics of magnetic recording head with high spatial resolution.
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07.79.Pk Magnetic force microscopes
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Electron holography study of the local magnetic switching process in magnetic tunnel junctions

E. Javon, C. Gatel, A. Masseboeuf, and E. Snoeck

J. Appl. Phys. 107, 09D310 (2010); http://dx.doi.org/10.1063/1.3358219 (2 pages) | Cited 2 times

Online Publication Date: 12 May 2010

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We present an electron holography experiment enabling the local and quantitative study of magnetic properties in magnetic tunnel junction. The junction was fully characterized during the switching process and each possible magnetic configuration was highlighted with magnetic induction maps. No magnetic coupling was found between the two layers. We plot a local hysteresis loop that was compared with magnetometry measurement at the macroscopic scale confirming the validity of the local method.
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42.40.-i Holography
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.78.Jp Ultrafast magnetization dynamics and switching

Circular dichroism in the electron microscope: Progress and applications (invited)

P. Schattschneider, I. Ennen, S. Löffler, M. Stöger-Pollach, and J. Verbeeck

J. Appl. Phys. 107, 09D311 (2010); http://dx.doi.org/10.1063/1.3365517 (6 pages) | Cited 6 times

Online Publication Date: 12 May 2010

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According to theory, x-ray magnetic circular dichroism in a synchrotron is equivalent to energy loss magnetic chiral dichroism (EMCD) in a transmission electron microscope (TEM). After a synopsis of the development of EMCD, the theoretical background is reviewed and recent results are presented, focusing on the study of magnetic nanoparticles for ferrofluids and Heusler alloys for spintronic devices. Simulated maps of the dichroic strength as a function of atom position in the crystal allow evaluating the influence of specimen thickness and sample tilt on the experimental EMCD signal. Finally, the possibility of direct observation of chiral electronic transitions with atomic resolution in a TEM is discussed.
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78.20.Ls Magneto-optical effects
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures

Magnetostriction and magnetic structure in annealed recrystallization of strain-forged ferromagnetic shape memory Fe–Pd–Rh alloys

Yin-Chih Lin and Hwa-Teng Lee

J. Appl. Phys. 107, 09D312 (2010); http://dx.doi.org/10.1063/1.3367979 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2010

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Bulk ferromagnetic shape memory Fe68–Pd30–Rh2 and Fe66–Pd30–Rh4 (at. %) alloys were strain-forged to produce a 35%–40% reduction in thickness. The reduced alloys were thermally annealed at 950–1050 °C for various times to induce recrystallization. The magnetostriction test demonstrated that the grain size reduction of recrystallization had a direct influence on the magnetic properties of the materials. The magnetostrictive strain measurements revealed that the strain-forged metal treated with thermal recrystallization to induce the fine-grained structure had a higher magnetostriction as well as a higher magnetostrictive susceptibility (Δλ∥s/ΔH). It was also found that at room temperature, the saturation magnetostriction (λs = 77×10−6) of the fine-grained Fe–Pd–Rh alloys strain-forged with thermal recrystallization was higher than that of those without grain size reduction (λs = 50–56×10−6), where λs is (2/3)[λ∥s−λ⊥s]. In addition, with the magnetic field applied perpendicular to the sample’s longitude, the fine-grained Fe–Pd–Rh material contracted by as much as λ⊥s = −36×10−6. This value is about three times higher than that of alloys without grain size reduction. Microstructure investigation indicated that a magnetic applied field normal to the sample’s longitude caused high contraction (λ⊥s) of the fine-grained Fe–Pd–Rh alloys, which could be ascribed mainly to the grain refinement as well as deformation twins or microtwins (transformation and transverse twins). The study demonstrates that the magnetostrictive strains of Fe–Pd–Rh alloys induced in the L10 martensite by the magnetic field can be attributed to the reorientation of the L10 martensite twin structures.
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75.80.+q Magnetomechanical effects, magnetostriction
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
81.40.Lm Deformation, plasticity, and creep
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Cr Saturation moments and magnetic susceptibilities
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