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15 Jun 2012

Volume 111, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 123510 (2012); http://dx.doi.org/10.1063/1.4729803 (4 pages)

Sz-Chin Steven Lin, Bernhard R. Tittmann, and Tony Jun Huang
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back to top Magnetism and Superconductivity

Josephson comparator with modified dynamic behavior for improved sensitivity

T. Ortlepp, S. Miyajima, H. Toepfer, and A. Fujimaki

J. Appl. Phys. 111, 123901 (2012); http://dx.doi.org/10.1063/1.4729075 (5 pages)

Online Publication Date: 18 June 2012

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The decision of a Josephson comparator is influenced by thermal noise which is limiting the practical sensitivity in many applications of superconductor electronics. We analyzed the Gaussian state distribution theoretically and identified the most effective way to improve the practical sensitivity of a Josephson comparator. We suggest a modified damping concept and demonstrate a gray zone width as low as 840 nA experimentally. This value is about ten times smaller than for conventional Josephson comparators and very close to the theoretical limit at liquid helium temperature.
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74.50.+r Tunneling phenomena; Josephson effects

Magnetic hyperthermia investigation of cobalt ferrite nanoparticles: Comparison between experiment, linear response theory, and dynamic hysteresis simulations

E. L. Verde, G. T. Landi, J. A. Gomes, M. H. Sousa, and A. F. Bakuzis

J. Appl. Phys. 111, 123902 (2012); http://dx.doi.org/10.1063/1.4729271 (8 pages) | Cited 5 times

Online Publication Date: 18 June 2012

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Considerable effort has been made in recent years to optimize materials properties for magnetic hyperthermia applications. However, due to the complexity of the problem, several aspects pertaining to the combined influence of the different parameters involved still remain unclear. In this paper, we discuss in detail the role of the magnetic anisotropy on the specific absorption rate of cobalt-ferrite nanoparticles with diameters ranging from 3 to 14 nm. The structural characterization was carried out using x-ray diffraction and Rietveld analysis and all relevant magnetic parameters were extracted from vibrating sample magnetometry. Hyperthermia investigations were performed at 500 kHz with a sinusoidal magnetic field amplitude of up to 68 Oe. The specific absorption rate was investigated as a function of the coercive field, saturation magnetization, particle size, and magnetic anisotropy. The experimental results were also compared with theoretical predictions from the linear response theory and dynamic hysteresis simulations, where exceptional agreement was found in both cases. Our results show that the specific absorption rate has a narrow and pronounced maxima for intermediate anisotropy values. This not only highlights the importance of this parameter but also shows that in order to obtain optimum efficiency in hyperthermia applications, it is necessary to carefully tailor the materials properties during the synthesis process.
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87.85.Rs Nanotechnologies-applications
75.75.Jn Dynamics of magnetic nanoparticles
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
87.50.ct Therapeutic applications

Enhancement of anisotropic magnetoresistance in MgO/NiFe/MgO trilayers via NiFe nanoparticles in MgO layers

Jiashun Huangfu, Chongjun Zhao, Jingyan Zhang, Baohe Li, and Guanghua Yu

J. Appl. Phys. 111, 123903 (2012); http://dx.doi.org/10.1063/1.4729273 (5 pages)

Online Publication Date: 18 June 2012

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MgO/NiFe/MgO trilayers, the new development in highly sensitive anisotropic magnetoresistance (AMR) sensor film materials, exhibit severely reduced magnetoresistance ratios at small NiFe thicknesses. By inserting ultrathin NiFe(І) layers into the top and bottom MgO layers of MgO/NiFe/MgO trilayers, films with a structure of MgO/NiFe(І)/MgO/NiFe/MgO/NiFe(І)/MgO were designed and synthesized. The AMR value can be significantly enhanced for thin NiFe films due to the improved specular reflections of electrons at both NiFe/MgO interfaces. For a thin NiFe film with the structure of MgO/NiFe(І)(1.5 nm)/MgO/NiFe(5 nm)/MgO/NiFe(І)(1.5 nm)/MgO, the AMR value was greatly enhanced to as high as 2.71%, an increase of 37% over MgO/NiFe(5 nm)/MgO film.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
75.75.-c Magnetic properties of nanostructures
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Spin-torque microwave detector with out-of-plane precessing magnetic moment

O. V. Prokopenko, I. N. Krivorotov, E. Bankowski, T. Meitzler, S. Jaroch, V. S. Tiberkevich, and A. N. Slavin

J. Appl. Phys. 111, 123904 (2012); http://dx.doi.org/10.1063/1.4729301 (6 pages)

Online Publication Date: 19 June 2012

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Operation of a spin-torque microwave detector (STMD) in a weak perpendicular bias magnetic field has been studied theoretically. It is shown that in this geometry a novel dynamical regime of STMD operation, characterized by large-angle out-of-plane magnetization precession, can be realized. The excitation of the large-angle precession has threshold character and is possible only for input microwave currents exceeding a certain frequency-dependent critical value. The output voltage of an STMD increases with the frequency of the input signal but is virtually independent of its power. An STMD working in the regime of large-amplitude out-of-plane precession functions as a non-resonant threshold detector of low frequency microwave signals, due to the large nonlinear shift of its operating frequency. Therefore, it is particularly suitable for applications in microwave energy harvesting.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.40.-x Radiowave and microwave (including millimeter wave) technology

Micromagnetic simulations of sweep-rate dependent coercivity in perpendicular recording media

M. L. Plumer, M. D. Leblanc, J. P. Whitehead, and J. van Ek

J. Appl. Phys. 111, 123905 (2012); http://dx.doi.org/10.1063/1.4729328 (7 pages) | Cited 3 times

Online Publication Date: 19 June 2012

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The results of micromagnetic simulations are presented, which examine the impact of thermal fluctuations on sweep rate dependent coercivities of both single-layer and exchange-coupled-composite (ECC) perpendicular magnetic recording media. M-H loops are calculated at four temperatures and sweep rates spanning five decades with fields applied normal to the plane and at 45°. The impact of interactions between grains is evaluated. The results indicate a significantly weaker sweep-rate dependence for ECC media suggesting more robustness to long-term thermal effects. Fitting the modeled results to Sharrock-like scaling proposed by Feng and Visscher [J. Appl. Phys. 95, 7043 (2004)] is successful only in the case of single-layer media with the field normal to the plane.
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75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.30.Et Exchange and superexchange interactions

Synthesis and characterization of Co2FeAl nanowires

Keshab R. Sapkota, Parshu Gyawali, Andrew Forbes, Ian L. Pegg, and John Philip

J. Appl. Phys. 111, 123906 (2012); http://dx.doi.org/10.1063/1.4729807 (4 pages)

Online Publication Date: 19 June 2012

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We report the growth and characterization of Co2FeAl nanowires. Nanowires are grown using electrospinning method and the diameters range from 50 to 500 nm. These nanowires exhibit cubic crystal structure with a lattice constant of a = 5.639 Å. The nanowires exhibit ferromagnetic behavior with a very high Curie temperature. The temperature dependent magnetization behavior displays an anomaly in the temperature range 600–850 K, which disappears at higher external magnetic fields.
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81.07.Gf Nanowires
75.75.Cd Fabrication of magnetic nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Switching time of a single spin in linearly varying field

Yasutaro Uesaka, Yoshio Suzuki, Osamu Kitakami, Yoshinobu Nakatani, Nobuo Hayashi, and Hiroshi Fukushima

J. Appl. Phys. 111, 123907 (2012); http://dx.doi.org/10.1063/1.4729897 (5 pages)

Online Publication Date: 20 June 2012

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We studied the switching time of a single spin in a field varying linearly in time using a micromagnetics simulation based on the Landau-Lifshitz-Gilbert equation. The applied field larger than the switching field or coercivity is not enough for a spin to switch but some duration of time is also necessary. We found that the value of C1 defined by C1 = ∫ (H−H1)dt was constant when the rate of change in the field was larger than 10 × γHk2, where γ is the gyromagnetic ratio with g value = 2, H is the applied field, H1 is a constant, and Hk is the anisotropy field of the spin. The integration is taken from the time the spin begins switching to the switching time. The equation is a generalized form of the equation, C0 = (H−H0)τsw, in a constant field H. Here, C0 and H0 are constants, and τsw is the switching time. We found that C1 in the region dH/dt>10×γHK2 and C0 in the region H≫HK are the same, but that H1 does not coincide with H0. We found that the head field rise time has a very small effect on the switching field and time of recording media.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials

Magnetoresistance in graphene-based ferromagnetic/ferromagnetic barrier/superconductor junction

Y. Hajati, M. Zargar Shoushtari, and G. Rashedi

J. Appl. Phys. 111, 123908 (2012); http://dx.doi.org/10.1063/1.4729302 (7 pages) | Cited 1 time

Online Publication Date: 20 June 2012

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We study the magnetoresistance (MR) and spin transport in a graphene-based ferromagnetic/ferromagnetic barrier/s-wave superconductor (FFBS) junction for two regimes including retro-Andreev reflection (AR) (EF = 100Δ0) and retroreflection crossing over to specular Andreev reflection (EF = Δ0). We observed that the variation of exchange energy in the ferromagnetic region h1 has a stronger effect on the amplitude of the MR oscillations rather than length, exchange energy, and effective gate potential in the FB region in both regimes. In the EF = 100Δ0 regime, the higher values of exchange energy h1 approach EF, which decrease the amplitude of the MR oscillations with respect to FB length. By increasing the exchange energy up to h1 > EF, a phase shift occurs for the peaks of the MR curves and the amplitude of the MR oscillations reaches its maximum value at the exchange energy hc = 2EF + U0. Furthermore, in the EF = Δ0 regime, at the exchange energy h1 = eV, the amplitude of the MR oscillations approaches its maximum value. At this value of energy of carriers eV + h1 − EF (Dirac point), the sign of the energy will be reversed and a transition from the retroreflection to the specular Andreev reflection occurs. Thus, in this regime (EF = Δ0), by observing the maximum of the MR at specified values of eV and h1, we can measure the Fermi energy of the graphene. While in the EF = 100Δ0 regime, the MR versus bias energy can be tuned from the positive to negative values by varying h1, but in the EF = Δ0 regime, the MR shows only the positive values. In addition, we have investigated the spin conductance in both regimes.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
85.25.-j Superconducting devices
72.25.Dc Spin polarized transport in semiconductors

A study on exchange coupled structures of Fe/NiO and NiO/Fe interfaced with n- and p-silicon substrates

Neelabh Srivastava and P. C. Srivastava

J. Appl. Phys. 111, 123909 (2012); http://dx.doi.org/10.1063/1.4729857 (9 pages)

Online Publication Date: 21 June 2012

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Interfacial structures of ferromagnetic (FM)/antiferromagnetic (AF) (Fe/NiO) and AF/FM (NiO/Fe) on n- and p-Si substrates have been realized by sequential deposition of FM and AF layers on the silicon substrates by electron beam evaporation technique. The structures have been characterized from x-ray diffraction (XRD), atomic force microscopy (AFM), magnetic force microscopy (MFM), and M-H characteristics. It has been found that there is a strong interfacial intermixing to form the various oxide and silicide phases of Fe2O3, β-Fe2O3, β″-Fe2O3, NiSi, Ni3Si, and Fe5Si3. AFM micrographs show the granular morphology of the top layer of the structure, with a large grain size of ∼400 nm, however, the XRD data show the crystallite size of ∼20 to 70 nm. It seems that the crystallites are clustered to form larger grains. MFM features show a large domain size corresponding to AFM grain size for Fe/NiO/Si structure and very small domain of nanometer size for NiO/Fe/Si structure (having NiO as a top layer). M-H characteristics show that the magnetic behavior is only significant for Fe/NiO/nSi structure with a significant coercivity and exchange bias than for all other interfacial structures of Fe/NiO/pSi, NiO/Fe/pSi, and NiO/Fe/nSi. Thus, it has been found that Fe/NiO/nSi structure can be used in magneto-electronic device applications. It seems that the observed result of significant exchange bias and coercivity is due to the microstructural and chemical structure changes in the antiferromagnetic layer along with the roughness (data as obtained from AFM).
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
68.35.Ct Interface structure and roughness

The impact of the lattice symmetry and the inclusion shape on the spectrum of 2D magnonic crystals

J. W. Kłos, M. L. Sokolovskyy, S. Mamica, and M. Krawczyk

J. Appl. Phys. 111, 123910 (2012); http://dx.doi.org/10.1063/1.4729559 (6 pages) | Cited 1 time

Online Publication Date: 21 June 2012

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We investigate spin waves in two-dimensional superlattices in the form of an infinite ferromagnetic slab of finite thickness with periodically embedded ferromagnetic inclusions. One of the reasons of the interest in magnonic superlattices is the possibility of tailoring their spectrum to produce magnonic gaps, crucial for the prospective applications. The objective of this study is to find the optimal values of structural parameters for which low-frequency magnonic gaps will occur and have a maximum width. We provide some guidelines for designing superlattices with a desired spectrum. We focus on the role of the symmetry of the lattice versus other geometrical factors, including the filling fraction and the superlattice constant. We compare the spectra of superlattices with inclusions of circular, hexagonal, and square cross sections.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Microwave heating-induced static magnetic flux penetration in YBa2Cu3O7–δ superconducting thin films

Julien Kermorvant, Jean-Claude Mage, Bruno Marcilhac, Yves Lemaître, Jean-François Bobo, and Cornelis Jacominus van der Beek

J. Appl. Phys. 111, 123911 (2012); http://dx.doi.org/10.1063/1.4730343 (6 pages)

Online Publication Date: 22 June 2012

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The magneto-optical imaging technique is used to visualize the penetration of the magnetic induction in YBa2Cu3O7–δ thin films during surface resistance measurements. The in situ surface resistance measurements were performed at 7 GHz using the dielectric resonator method. When only the microwave magnetic field Hrf is applied to the superconductor, no Hrf-induced vortex penetration is observed, even at high rf power. In contrast, in the presence of a constant magnetic field superimposed on Hrf, we observe a progression of the flux front as Hrf is increased. A local thermometry method based on the measurement of the resonant frequency of the dielectric resonator placed on the YBa2Cu3O7–δ thin film shows that the Hrf–induced flux penetration is due to the increase of the film temperature.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.fc Electric and thermal conductivity
74.25.nn Surface impedance
73.25.+i Surface conductivity and carrier phenomena
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

Interstitial doping induced superconductivity at 15.3 K in Nb5Ge3 compound

A. D. Bortolozo, C. A. M. dos Santos, R. F. Jardim, C. Ritter, A. Devishvili, M. Rotter, F. G. Gandra, and A. J. S. Machado

J. Appl. Phys. 111, 123912 (2012); http://dx.doi.org/10.1063/1.4730611 (6 pages)

Online Publication Date: 25 June 2012

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It is reported superconductivity in Nb5Ge3C0.3, an interstitial carbide compound. The temperature dependence of the electrical resistivity, ac-susceptibility, and heat capacity (HC) indicate that a bulk type-II superconductivity appears at TC = 15.3 K. Magneto-resistance measurements suggest an upper critical field of BC2 ∼ 10.6 T and a coherence length of ξ ∼ 55 Å at zero temperature. Neutron diffraction analyzes locate the carbon atoms at the interstitial 2b site of the Mn5Si3 type-structure. Heat capacity data below TC are well described by BCS theory. The size of the jump at TC is in good agreement with the superconducting volume fraction observed in susceptibility measurements. A Debye temperature and Sommerfeld constant were also extracted from heat capacity data as 343 K and 34 mJ/mol K2, respectively.
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74.25.fc Electric and thermal conductivity
65.40.Ba Heat capacity
74.25.Bt Thermodynamic properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Op Mixed states, critical fields, and surface sheaths
75.30.Cr Saturation moments and magnetic susceptibilities

Charge order suppression, emergence of ferromagnetism and absence of exchange bias effect in Bi0.25Ca0.75MnO3 nanoparticles: Electron paramagnetic resonance and magnetization studies

Geetanjali Singh and S. V. Bhat

J. Appl. Phys. 111, 123913 (2012); http://dx.doi.org/10.1063/1.4730612 (5 pages)

Online Publication Date: 25 June 2012

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We report the results of magnetization and electron paramagnetic resonance (EPR) studies on nanoparticles (average diameter ∼ 30 nm) of Bi0.25Ca0.75MnO3 (BCMO) and compare them with the results on bulk BCMO. The nanoparticles were prepared using the nonaqueous sol-gel technique and characterized by XRD and TEM analysis. Magnetization measurements were carried out with a commercial physical property measurement system (PPMS). While the bulk BCMO exhibits a charge ordering transition at ∼230 K and an antiferromagnetic (AFM) transition at ∼130 K, in the nanoparticles, the CO phase is seen to have disappeared and a transition to a ferromagnetic (FM) state is observed at Tc ∼ 120 K. However, interestingly, the exchange bias effect observed in other nanomanganite ferromagnets is absent in BCMO nanoparticles. EPR measurements were carried out in the X-band between 8 and 300 K. Lineshape fitting to a Lorentzian with two terms (accounting for both the clockwise and anticlockwise rotations of the microwave field) was employed to obtain the relevant EPR parameters as functions of temperature. The results confirm the occurrence of ferromagnetism in the nanoparticles of BCMO.
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75.75.Cd Fabrication of magnetic nanostructures
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Et Exchange and superexchange interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Spin torque switching and scaling in synthetic antiferromagnet free layers with in-plane magnetization

T. Devolder and K. Ito

J. Appl. Phys. 111, 123914 (2012); http://dx.doi.org/10.1063/1.4729776 (8 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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We study the field-induced and the current-induced switching of synthetic antiferromagnet free layers with in-plane magnetization. In practical cases, the energy barrier relevant for the thermal stability depends mainly on the magneto-crystalline anisotropies of the layers. We derive the spin-flop and the direct overwrite fields and their dependence on the asymmetry of the thickness of the two layers of the SyF. This is used to explain why the SyF magnetizations are much more robust to external fields than the anisotropy would tell. We then calculate the spin-torque instability threshold current densities for the acoustical and the optical excitations of the SyF, taking into account that there are spin torques acting on the two layers of the SyF. The acoustical excitation has the lowest instability current. Based on these findings, we finally discuss the scaling of SyF free layers by combining thermal stability requirements and dielectric breakdown avoidance constraints. Scaling can be conducted with either the aim of minimizing the write current or with the aim of minimizing the free layer surface. An absolute minimum of write current can be reached for relatively large cells (166×166 nm2) provided a zero effective magnetization is induced by a proper choice of the free layer thicknesses. Depending on how close the technology can reliably approach to the thickness yielding the easy axis reorientation transition while keeping bulk damping, this current minimum could in principle be as low as 14 μA in the macrospin approximation. If in contrast one aims at small free layer surfaces, then the present CoFeB alloy-based technology cannot reach dimensions below 90×90 nm2.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
77.22.Jp Dielectric breakdown and space-charge effects
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy

Superferromagnetism and coercivity in Co-Al2O3 granular films with perpendicular anisotropy

A. A. Timopheev, I. Bdikin, A. F. Lozenko, O. V. Stognei, A. V. Sitnikov, A. V. Los, and N. A. Sobolev

J. Appl. Phys. 111, 123915 (2012); http://dx.doi.org/10.1063/1.4730397 (7 pages)

Online Publication Date: 26 June 2012

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Magnetic properties of nano-granular Co0.55–(Al2O3)0.45 films have been studied by vibrating sample magnetometry, ferromagnetic resonance, and magnetic force microscopy (MFM). The films possess a growth-induced perpendicular anisotropy related to the shape anisotropy of the granules. Being unpercolated physically, the films demonstrated a clear magnetic percolation behavior in the temperature dependence of the coercivity and MFM scans. The temperature dependence of the coercivity measured along the easy magnetization axis of the granules indicates the presence of a collective long-range magnetic state sustained by a ferromagnetic interparticle interaction. This interaction is supposed to form a homogeneously magnetized superferromagnetic state, however, the perpendicular anisotropy and the competition between the dipole-dipole and ferromagnetic interactions lead to the emergence of an inhomogeneous labyrinth-like magnetic stripe-domain structure with the averaged domain width being about two orders of magnitude larger than the averaged granule size. The temperature evolution of the spontaneous magnetization inside the stripe domains has been measured by the MFM up to the temperature of superferromagnetic ordering (420 K). The formerly developed mean-field-based model of the coercivity of an interacted ensemble has been tested and found to yield adequate quantitative predictions.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Weak ferromagnetism in La-doped BiFeO3 multiferroic thin films

V. V. Lazenka, A. F. Ravinski, I. I. Makoed, J. Vanacken, G. Zhang, and V. V. Moshchalkov

J. Appl. Phys. 111, 123916 (2012); http://dx.doi.org/10.1063/1.4730896 (4 pages) | Cited 4 times

Online Publication Date: 26 June 2012

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Bi1−xLaxFeO3 thin films (x = 0.0, 0.3, 0.5) were grown on glass substrates by thermal physical vapor deposition. The monoclinically distorted crystal structure of the films was revealed by x-ray diffraction at room temperature. Field and temperature (up to 1000 K) dependences of magnetization were studied. Saturation of the room temperature magnetic hysteresis loop has been observed at magnetic field above 0.15 T, demonstrating the weak ferromagnetic nature of the thin films. Our magnetic force microscopy results show clearly the presence of magnetic domains in BFO thin films. These structural and magnetic properties suggest the absence of magnetic spiral spin structure in monoclinically distorted BFO-based thin films.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.aj Insulators
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.-m Intrinsic properties of magnetically ordered materials
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ferromagnetic resonance and magnetooptic study of submicron epitaxial Fe(001) stripes

E. Paz, F. Cebollada, F. J. Palomares, J. M. González, J. S. Martins, N. M. Santos, and N. A. Sobolev

J. Appl. Phys. 111, 123917 (2012); http://dx.doi.org/10.1063/1.4730136 (10 pages)

Online Publication Date: 27 June 2012

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We present a combined magnetooptic and ferromagnetic resonance study of a series of arrays of single-crystalline Fe stripes fabricated by electron beam lithography on epitaxial Au(001)/Fe(001)/MgO(001) films grown by pulsed laser deposition. The analysis of the films revealed a clear four-fold magnetocrystalline anisotropy, with no significant presence of other anisotropy sources. The use of a large series of arrays, with stripe widths between 140 and 1000 nm and separation between them of either 200 nm or 500 nm, allowed studying their magnetization processes and resonance modes as well as the effects of the dipolar interactions on both. The magnetization processes of the stripes were interpreted in terms of a macrospin approximation, with a good agreement between experiments and calculations and negligible influence of the dipolar interactions. The ferromagnetic resonance spectra evidenced two types of resonances linked to bulk oscillation modes, essentially insensitive to the dipolar interactions, and a third one associated with edge-localized oscillations, whose resonance field is strongly dependent on the dipolar interactions. The ability to produce a high quality, controlled series of stripes provided a good opportunity to achieve an agreement between the experiments and calculations, carried out by taking into account just the Fe intrinsic properties and the morphology of the arrays, thus evidencing the relatively small role of other extrinsic factors.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
81.16.Nd Micro- and nanolithography
75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy

Uniaxial magnetic anisotropy in Pd/Fe bilayers on Al2O3 (0001) induced by oblique deposition

Chiao-Sung Chi, Bo-Yao Wang, Way-Faung Pong, Tsung-Ying Ho, Cheng-Jui Tsai, Fang-Yuh Lo, Ming-Yau Chern, and Wen-Chin Lin

J. Appl. Phys. 111, 123918 (2012); http://dx.doi.org/10.1063/1.4730632 (7 pages) | Cited 2 times

Online Publication Date: 27 June 2012

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This study reports the preparation of self-organized 1-dimensional magnetic structures of Fe on Al2O3 (0001) by oblique deposition. The x-ray diffraction (XRD) results in this study show the preferred (110) texture of the Fe films. XRD and extended x-ray adsorption fine structure measurements indicate larger oblique deposition angle (65°) leads to more disorder in the Fe crystalline structure. After capping with a Pd overlayer, the Pd/Fe/Al2O3 (0001) still exhibits uniaxial magnetic anisotropy induced by the underlying 1-dimensional Fe nanostructure. This uniaxial magnetic anisotropy changes with the variation in Fe thickness and oblique deposition angle. These results clearly indicate the feasibility of manipulating uniaxial magnetic anisotropy and crystalline order through the oblique deposition of magnetic materials.
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81.16.-c Methods of micro- and nanofabrication and processing
61.66.Bi Elemental solids
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra

Changes in magnetic properties of Co/Pd multilayers induced by hydrogen absorption

Kineshma Munbodh, Felio A. Perez, and David Lederman

J. Appl. Phys. 111, 123919 (2012); http://dx.doi.org/10.1063/1.4729797 (6 pages) | Cited 2 times

Online Publication Date: 28 June 2012

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The saturation magnetization (MS) and perpendicular anisotropy energy (KP) of Co/Pd multilayers were studied when the samples were exposed to 1 atm of H2 at room temperature. The samples had fixed Co nominal thicknesses of 2.5 Å and 4.5 Å and Pd thickness values ranging from 0 Å to 25 Å. The interface structure was determined from the x-ray scattering length density (SLD) profile. When the Pd thickness was less than 10 Å, there was a large amount of interface disorder which resulted in no change in MS and KP. As the Pd thickness increased, the SLD contrast between the Co and Pd layers also increased, leading to a decrease in MS and KP after H2 absorption. This can be explained by a decrease in H2 solubility as interface alloying became more dominant for thinner layers, which resulted from a smaller hydrogen electron transfer to the Pd 4d band. The changes in MS and KP in the less interdiffused samples also resulted from this electron transfer. Magnetic changes were reversible with characteristic absorption and desorption times of approximately 40 s for 1 atm of H2.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
78.70.Ck X-ray scattering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
66.30.Ny Chemical interdiffusion; diffusion barriers
64.75.Bc Solubility
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