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15 Aug 2010

Volume 108, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 041901 (2010); http://dx.doi.org/10.1063/1.3474648 (2 pages)

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin
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back to top Magnetism and Superconductivity

Fabrication and characterization of highly textured Nd–Fe–B thin film with a nanosized columnar grain structure

C. Y. You, Y. K. Takahashi, and K. Hono

J. Appl. Phys. 108, 043901 (2010); http://dx.doi.org/10.1063/1.3474990 (4 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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We have fabricated a highly textured Nd–Fe–B thin film with a hard magnetic performance: Mr = 1.39 T, Hc = 827 kA/m, and (BH)max = 358 kJ/m3. The microstructure of the film was characterized in detail by cross-sectional and plane-view transmission electron microscopy observations. The film consisted of nanosized columnar grains with an average size of 40 nm and included a strong diffraction contrast along the grain boundary. A high resolution energy filtered image indicated that Nd was enriched discontinuously along the grain boundary, causing an unsuitable decoupling among the Nd2Fe14B grains, which is in agreement with the pinninglike feature of the initial magnetization curve.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries
75.50.Ww Permanent magnets
75.50.Vv High coercivity materials

Spin dependent Compton scattering study of magnetic transitions in Ir doped CeFe2

B. L. Ahuja, B. K. Sharma, V. Purvia, S. Tiwari, A. Koizumi, T. Nagao, Y. Sakurai, and N. Sakai

J. Appl. Phys. 108, 043902 (2010); http://dx.doi.org/10.1063/1.3475311 (5 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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First and second order magnetic transitions in Ce(Fe0.97Ir0.3)2 are studied using the magnetic Compton scattering technique. The measurements on polycrystalline sample were carried out at SPring8, Japan for different temperatures and magnetizing fields using 175 keV elliptically polarized synchrotron radiation. The temperature dependent magnetic effects (ratio between magnetic scattering intensity and charge scattering intensity) show the magnetic transitions from antiferromagnetic→ferromagnetic→paramagnetic phases which are consistent with the magnetization data. The temperature and field dependent spin-polarized momentum densities have been analyzed mainly in terms of contribution from Fe(3d) and Ce(4f) sites to determine their role in the formation of total spin moments and thereby magnetic transitions.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.-g Interactions of particles and radiation with matter
75.50.Bb Fe and its alloys

The solid solution Gd2NixCu2−xMg: Large reversible magnetocaloric effect and a drastic change of the magnetism by substitution

Stefan Linsinger, Wilfried Hermes, Matthias Eul, and Rainer Pöttgen

J. Appl. Phys. 108, 043903 (2010); http://dx.doi.org/10.1063/1.3466775 (8 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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Various samples of the solid solution Gd2NixCu2−xMg were synthesized from the elements in sealed tantalum ampoules in an induction furnace. All members crystallize with the tetragonal Mo2FeB2 type structure, space group P4/mbm, and they were characterized on the basis of Guinier powder patterns and energy dispersive X-rays analyses. The lattice parameters decrease with increasing nickel content in a Vegard-like manner. The Gd2NixCu2−xMg samples show Curie–Weiss behavior with slightly higher magnetic moment values than the theoretical one for a free Gd3+ ion. The substitution of copper by nickel has a drastic influence on the magnetism and magnetic ordering temperature. For Gd2Ni0.5Cu1.5Mg a temperature induced FM→AFM order-to-order transition was observed, whereas Gd2Ni1.0Cu1.0Mg is a metamagnet with HCr of about 8 kOe at 5 K. For both compounds, a large reversible magnetocaloric effect (MCE) near their ordering temperatures occurs. The values of the maximum magnetic entropy change −ΔSMmax reach 9.5 and 11.4 J kg−1 K−1 for the field change of 5 T with no obvious hysteresis loss around 65 K for Gd2Ni0.5Cu1.5Mg and Gd2Ni1.0Cu1.0Mg, respectively. The corresponding relative cooling power with 688 and 630 J kg−1 is relatively high as compared to other MCE materials in that temperature range. These results indicate that Gd2NixCu2−xMg could be a promising system for magnetic refrigeration at temperatures below liquid N2.
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75.30.Sg Magnetocaloric effect, magnetic cooling
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
75.30.Cr Saturation moments and magnetic susceptibilities
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic properties of α′ martensite in austenitic stainless steel studied by a minor-loop scaling law

Satoru Kobayashi, Nobuhiro Kikuchi, Seiki Takahashi, Yasuhiro Kamada, and Hiroaki Kikuchi

J. Appl. Phys. 108, 043904 (2010); http://dx.doi.org/10.1063/1.3475651 (8 pages) | Cited 2 times

Online Publication Date: 16 August 2010

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We study the scaling behavior of magnetic minor hysteresis loops in strain-induced ferromagnetic α′ martensites in an austenitic 316-type stainless steel. A scaling relationship between the hysteresis loss and the remanence, with a power law exponent of approximately 1.35, was found irrespective of the volume fraction of the α′ martensites as well as temperature. The coefficient of the power law largely decreases with volume fraction, whereas it increases with a decrease in temperature and exhibits a kink at around 40 K, close to the Néel temperature of an austenitic γ′ phase. The behavior of the coefficient was interpreted from the viewpoint of the morphology and exchange interaction of α′ martensites.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Magnetization reversal behavior in high coercivity Zr doped α-Fe/Nd2Fe14B nanocomposite alloys

P. Y. Zhang, R. Hiergeist, J. Lüdke, M. Albrecht, and H. L. Ge

J. Appl. Phys. 108, 043905 (2010); http://dx.doi.org/10.1063/1.3457105 (6 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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The magnetization reversal behavior for rapidly solidified Zr-doped α-Fe/Nd2Fe14B alloys with high coercivity has been investigated by analyzing hysteresis curves and recoil loops of demagnetization curves. A drastic increase in the coercivity Hc from 620 to 855 kA/m at room temperature by an addition of 1 at. % Zr in α-Fe/Nd2Fe14B alloys has been observed. The maximum value of the integrated recoil loop area for Zr-doped samples of 3.05 kJ/m3 is much lower than that of the Zr-free sample. This result can be explained by a larger recoverable portion of the magnetization remaining in the Zr-free sample as long as the applied reversal field is below the coercivity Hc, i.e., it is an effect of an increased exchange-coupling in the Zr-free sample. The coercivity mechanism of the α-Fe/Nd2Fe14B nanocomposite magnets was analyzed in terms of the Kondorsky model and the plot of Hc(T)/Ms(T) versus HNmin(T)/Ms(T) (Kronmüller plot), respectively.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions

Design and characterization of a field-switchable nanomagnetic atom mirror

T. J. Hayward, A. D. West, K. J. Weatherill, P. J. Curran, P. W. Fry, P. M. Fundi, M. R. J. Gibbs, T. Schrefl, C. S. Adams, I. G. Hughes, S. J. Bending, and D. A. Allwood

J. Appl. Phys. 108, 043906 (2010); http://dx.doi.org/10.1063/1.3466995 (9 pages) | Cited 4 times

Online Publication Date: 18 August 2010

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We present a design for a switchable nanomagnetic atom mirror formed by an array of 180° domain walls confined within Ni80Fe20 planar nanowires. A simple analytical model is developed which allows the magnetic field produced by the domain wall array to be calculated. This model is then used to optimize the geometry of the nanowires so as to maximize the reflectivity of the atom mirror. We then describe the fabrication of a nanowire array and characterize its magnetic behavior using magneto-optic Kerr effect magnetometry, scanning Hall probe microscopy, and micromagnetic simulations, demonstrating how the mobility of the domain walls allow the atom mirror to be switched “on” and “off” in a manner which would be impossible for conventional designs. Finally, we model the reflection of 87Rb atoms from the atom mirror’s surface, showing that our design is well suited for investigating interactions between domain walls and cold atoms.
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78.20.Ls Magneto-optical effects
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
37.10.-x Atom, molecule, and ion cooling methods
42.79.Bh Lenses, prisms and mirrors

Transport dynamics with alternate Cooper-pair and quasiparticle tunnelings in one-dimensional charge Josephson arrays

I. L. Ho, M. C. Lin, K. Aravind, C. S. Wu, and C. D. Chen

J. Appl. Phys. 108, 043907 (2010); http://dx.doi.org/10.1063/1.3462444 (7 pages) | Cited 2 times

Online Publication Date: 18 August 2010

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For a single weak-coupled Josephson junction, stochastic Cooper-pair tunnelings drive the superconducting current on low voltage biases, while quasiparticle tunnelings stimulate the normal current on high biases above the superconducting gap voltage. Considering these interactive dynamics simultaneously in one-dimensional weak-coupled Josephson arrays in electrodynamic environments, the theoretical work by rate equations is structured herein, and the charge transport associated with short-range (Cooper pair and quasiparticle) and long-range (Cooper-pair soliton and quasiparticle soliton) behaviors is analyzed.
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74.50.+r Tunneling phenomena; Josephson effects
74.81.Fa Josephson junction arrays and wire networks

Anisotropic magnetostriction in a 〈110〉 oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 after coaxial field annealing

Changsheng Zhang, Tianyu Ma, Ruilei Qi, and Mi Yan

J. Appl. Phys. 108, 043908 (2010); http://dx.doi.org/10.1063/1.3467785 (5 pages) | Cited 4 times

Online Publication Date: 18 August 2010

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Axial magnetostriction of Terfenol-D oriented crystals is highly anisotropic when changing the magnetization direction. Magnetostrictions of a 〈110〉 oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 were investigated under magnetic fields with a series of angles θ to its axis. Totally different anisotropic magnetostrictive behaviors are observed after annealing under a coaxial field of 240 kA/m. The magnetostriction for the field annealed specimen seems unsaturated even under 640 kA/m for angles θ in the range from 0° to 55°. At these angles, magnetostriction “ascending” is observed during the final magnetization process, while magnetostriction “dropping” occurs at angles above 35° for the untreated crystal. With the increase in angle θ, the corresponding field where magnetostriction starts dropping decreases for the untreated crystal, while the field at which magnetostriction starts ascending increases for the field annealed one. A simplified model based on moment “jump” and “rotation” is proposed to explain such anisotropic behaviors.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects

A simple bilayered magnetoelectric random access memory cell based on electric-field controllable domain structure

Jia-Mian Hu, Zheng Li, Jing Wang, Jing Ma, Y. H. Lin, and C. W. Nan

J. Appl. Phys. 108, 043909 (2010); http://dx.doi.org/10.1063/1.3463408 (6 pages) | Cited 9 times

Online Publication Date: 18 August 2010

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By considering the domain wall scattering in ferromagnetic striped-domain structure, we present a simple bilayered magnetoelectric random access memory cell with a ferromagnetic thin film grown on a ferroelectric layer. The calculations show that the striped-domain structure in the ferromagnetic film can change into a single-domain structure upon applying an electric field to the ferroelectric layer. As a result, the presence (absence) of the domain walls in response to the striped-domain (single-domain) state can cause an abrupt change in the film resistivity, which could be employed for memory applications accordingly.
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84.30.Sk Pulse and digital circuits

Influence of quenching rate on the magnetic and martensitic properties of Ni–Fe–Ga melt-spun ribbons

H. Okumura and K. Uemura

J. Appl. Phys. 108, 043910 (2010); http://dx.doi.org/10.1063/1.3465613 (4 pages) | Cited 1 time

Online Publication Date: 19 August 2010

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We have fabricated Ni–Fe–Ga β single phase alloy ribbons with Ga content less than 25 at. %. Higher spinning rate of melt-spinning technique can produce β single phase alloys without precipitation of γ particles, whereas lower spinning rate results in the β+γ two phase structure. This higher quenching rate is found to be able to fully suppress the formation of γ phase during fabrication. The martensitic and magnetic transition temperatures of β phase ribbons are both above room temperature, and the ribbon show saturation magnetization as high as 56.5 emu/g at room temperature. These features are attractive for practical applications. The effects of quenching rate on microstructure, martensitic transformation, and magnetic properties are discussed.
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81.05.Bx Metals, semimetals, and alloys
81.20.-n Methods of materials synthesis and materials processing
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.30.Kf Martensitic transformations

Electric-field control of ferromagnetic resonance in monolithic BaFe12O19–Ba0.5Sr0.5TiO3 heterostructures

Jaydip Das, Young-Yeal Song, and Mingzhong Wu

J. Appl. Phys. 108, 043911 (2010); http://dx.doi.org/10.1063/1.3467777 (5 pages) | Cited 2 times

Online Publication Date: 19 August 2010

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This paper demonstrates an electric-field tuning of the ferromagnetic resonance (FMR) responses at millimeter wave frequencies for a monolithic magneto-electric heterostructure. The layered stack is comprised of c-axis oriented and low loss barium hexaferrite (BaM) and (111) oriented ferroelectric barium strontium titanate (BSTO) layers along with embedded platinum electrode layers, all fabricated by pulsed laser deposition technique. A tunability of the FMR frequency as large as 3.5 MHz/V has been observed at 60 GHz due to application of bias voltages in the range of several volts. The realization of such a large tunability relies on the quasi-lattice-to-lattice contact between the BaM and BSTO layers as well as the high quality of those layers.
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75.85.+t Magnetoelectric effects, multiferroics
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity
75.50.Gg Ferrimagnetics

Magnetization reversal of two-dimensional superlattices of Mn3O4 nanocubes and their collective dipolar interaction effects

Weimeng Chen, Chinping Chen, and Lin Guo

J. Appl. Phys. 108, 043912 (2010); http://dx.doi.org/10.1063/1.3466983 (8 pages) | Cited 1 time

Online Publication Date: 20 August 2010

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Magnetic properties of two-dimensional (2D) paddy-field like superlattices of Mn3O4 cubic nanoparticles have been investigated by magnetization measurements. The 2D ordered structure extends over several microns in size. Each nanocube is of single-crystal about 6 nm in size. The magnetic properties are investigated with the powders dispersed in nonmagnetic n-eicosane to “dilute” the dipolar interaction. By accounting for the temperature variation effect of the magnetocrystalline anisotropy, Kmag(T), the temperature dependent coercivity, HC(T), can be well described by the equation, HC(T) = H0kmag(T)/mS(T){1−[kBT ln(t/t0)/E0kmag(T)]3/4}, in which kmag(T) = Kmag(T)/Kmag(0) is the reduced temperature dependent magnetocrystalline anisotropy and mS(T) = MS(T)/MS(0) is the reduced saturation magnetization. The effects of collective dipolar interaction on the magnetic properties are also studied with the as-prepared powder sample. The apparent magnetic anisotropy is seriously reduced with the presence of dipolar interaction. The switching volume is determined by the analysis on the magnetic measurements both with and without the dipolar interaction effect. There is a discrepancy in the value of switching volume determined by the two different analysis methods. Possible reasons are discussed.
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75.60.Jk Magnetization reversal mechanisms
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures

Effect of Ni/Mn ratio on phase transformation and magnetic properties in Ni–Mn–In alloys

N. V. Rama Rao, V. Chandrasekaran, and K. G. Suresh

J. Appl. Phys. 108, 043913 (2010); http://dx.doi.org/10.1063/1.3467966 (7 pages) | Cited 5 times

Online Publication Date: 20 August 2010

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The effect of variation in Ni/Mn ratio on structure, phase transformation, and magnetic properties was investigated in the Ni50−xMn37+xIn13 alloys. Small change in the Ni/Mn ratio drives the structure from martensite of tetragonal L10 to austenite of cubic L21 at room temperature. With decrease in Ni/Mn ratio or increase in Mn content the martensitic transformation temperature was found to decrease and the alloys do not undergo phase transformation below a critical value (7.86) of valence electron concentration (e/a). Temperature and field dependence of magnetization data reveals the complex magnetic nature arising from the coexistence of ferromagnetic and antiferromagnetic interactions in the system. It was found that the effect of Ni/Mn and Mn/In ratios on phase transformation and magnetic properties in Ni–Mn–In alloys is similar if the e/a value of the alloy system remains unchanged.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
61.66.Dk Alloys
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Hysteresis effects in the magnetic-field-induced reverse martensitic transition in magnetic shape-memory alloys

Thorsten Krenke, Seda Aksoy, Eyüp Duman, Mehmet Acet, Xavier Moya, Lluís Mañosa, and Antoni Planes

J. Appl. Phys. 108, 043914 (2010); http://dx.doi.org/10.1063/1.3466770 (4 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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We study the mechanism of magnetic-field-induced reverse martensitic transformations by considering the field-induced temperature-shifts in the thermal hysteresis loop of the magnetization and critical fields determined from magnetization isotherms. We consider first the temperature-shifts in a symmetric thermal hysteresis loop and extend the discussion to the case of the Heusler-based Ni50Mn34In16 magnetically superelastic alloy having a nonsymmetric thermal hysteresis loop. We obtain two different temperature-behaviors for the critical field depending on whether the initial measurement temperature lies on the forward or on the reverse transformation path of the thermal hysteresis.
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81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
Author Select

Magnetic states of a rf superconducting quantum interference device containing a double-barrier Josephson junction

R. De Luca

J. Appl. Phys. 108, 043915 (2010); http://dx.doi.org/10.1063/1.3478743 (5 pages) | Cited 1 time

Online Publication Date: 26 August 2010

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The magnetic properties of a rf superconducting quantum interference device containing one overdamped double-barrier junction are studied. The effective nonsinusoidal expression for the current-phase relation with an additional half harmonic term is used for the double-barrier junction. Devices with inhomogeneous double-barrier junctions show a characteristic feature: for fixed and not too high superconducting loop inductance values, transition from irreversible to reversible magnetic behavior can be induced by increasing the difference in the Josephson coupling of the two junctions.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)

Bulk and surface physical properties of a CrO2 thin film prepared from a Cr8O21 precursor

K. Iwai, Y. Muraoka, T. Wakita, M. Hirai, T. Yokoya, Y. Kato, T. Muro, and Y. Tamenori

J. Appl. Phys. 108, 043916 (2010); http://dx.doi.org/10.1063/1.3471811 (4 pages)

Online Publication Date: 26 August 2010

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We have prepared a CrO2 thin film by chemical vapor deposition from a Cr8O21 precursor and studied the bulk and surface physical properties. The CrO2 thin film is grown on a TiO2 (100) substrate by heating of a Cr8O21 precursor and TiO2 (100) substrate together in a sealed quartz tube. The prepared film is found from x-ray diffraction analysis to be an (100)-oriented single phase. The magnetization and resistivity measurements indicate that the film is a ferromagnetic metal with a Curie temperature of about 400 K. Cr 3s core-level and valence band photoelectron spectroscopy spectra reveal the presence of a metallic CrO2 in the surface region of the film. Our work indicates that preparation from a Cr8O21 precursor is promising for obtaining a CrO2 thin film with the metallic surface.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.aj Insulators
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

First-principles prediction of the negatively-charged nitrogen-silicon-vacancy center in cubic silicon carbide

Fengchun Pan, Mingwen Zhao, and Liangmo Mei

J. Appl. Phys. 108, 043917 (2010); http://dx.doi.org/10.1063/1.3471813 (4 pages) | Cited 2 times

Online Publication Date: 26 August 2010

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We performed density-functional theory calculations to study the energetic stability and the electronic structures of negatively-charged nitrogen-silicon-vacancy center (N-VSi)− in cubic silicon carbide (3C–SiC). We show that the (N-VSi)− center is energetically preferable in n-type 3C–SiC and possesses a stable 3A2 ground state and doubly degenerated 3E excited states. The (N-VSi)− centers prefer to couple weakly in an antiferromagnetic way, triggered by superexchange between them. Our work indicates that 3C–SiC may be an economical candidate material to achieve a solid state qubit operation beyond diamond.
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71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.-m Methods of electronic structure calculations
75.50.Ee Antiferromagnetics
61.72.jd Vacancies

Surface spin-glass and exchange bias in Sr2FeMoO6 nanoparticle

Srimanta Middey, Somnath Jana, and Sugata Ray

J. Appl. Phys. 108, 043918 (2010); http://dx.doi.org/10.1063/1.3478750 (5 pages) | Cited 8 times

Online Publication Date: 27 August 2010

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Tunneling magnetoresistance in polycrystalline double perovskite Sr2FeMoO6 exhibits many unusual features, which can be efficiently probed by manipulating the tunnel barriers/grain surfaces. Accordingly, many experimental reports appeared on nanosized particles of Sr2FeMoO6 with largely enhanced grain boundary contributions. However, for the first time we report the existence of a spin-glasslike component, along with conventional ferromagnetism, in well-characterized Sr2FeMoO6 nanoparticles, which has been critically confirmed by the perceptible exchange bias effect, observed in these nanoparticles. Our results suggest that the spin-glass component is likely to reside on the surface of each particle, which probably provides useful clues about the unusual tunneling magnetoresistance responses, always exhibited by nanocrystalline Sr2FeMoO6.
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81.16.-c Methods of micro- and nanofabrication and processing
75.50.Lk Spin glasses and other random magnets
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Et Exchange and superexchange interactions
61.72.Mm Grain and twin boundaries
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Crossover from reversible to irreversible magnetic exchange-spring processes in antiferromagnetically exchange-coupled soft/hard bilayer structures

Guang-hua Guo, Guang-fu Zhang, and Xi-guang Wang

J. Appl. Phys. 108, 043919 (2010); http://dx.doi.org/10.1063/1.3478752 (5 pages)

Online Publication Date: 27 August 2010

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The demagnetization processes of antiferromagnetically exchange-coupled soft/hard bilayer structures have been studied using a one-dimensional atomic chain model, taking into account the anisotropies of both soft and hard layers. It is found that for bilayer structures with strong interfacial exchange coupling, the demagnetization process exhibits typical reversible magnetic exchange-spring behavior. However, as the strength of the interfacial exchange coupling is decreased, there is a crossover point Ashc, after which the process becomes irreversible. The phase diagram of reversible and irreversible exchange-spring processes is mapped in Ash and Ns plane, where Ash and Ns are the interfacial exchange coupling and soft layer thickness, respectively. The thickness dependence of the bending field, which characterizes the onset of the exchange spring in the soft layer, is numerically examined and compared with analytical models.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Wx Spin crossover
75.78.Cd Micromagnetic simulations

Spatial sensitivity mapping of Hall crosses using patterned magnetic nanostructures

M. Alexandrou, P. W. Nutter, M. Delalande, J. de Vries, E. W. Hill, F. Schedin, L. Abelmann, and T. Thomson

J. Appl. Phys. 108, 043920 (2010); http://dx.doi.org/10.1063/1.3475485 (5 pages) | Cited 4 times

Online Publication Date: 31 August 2010

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Obtaining an accurate profile of the spatial sensitivity of Hall cross structures is crucial if such devices are to be used to analyze the switching behavior of magnetic nanostructures and determine the switching field distribution of bit patterned media. Here, we have used the anomalous Hall effect to investigate the switching of patterned Co/Pt multilayer magnetic nanoislands, where the Hall cross has been integrated into the Pt seed layer. Using the anomalous Hall output voltage we have observed the magnetic switching of individual islands, allowing the spatial sensitivity across a Hall cross structure to be determined. The experimental results agree well with numerical simulation studies, using a three-dimensional finite element model, and with existing theoretical studies, where the spatial sensitivity of two-dimensional Hall cross structures have been found numerically.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
73.63.-b Electronic transport in nanoscale materials and structures
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ss Magnetic recording materials

Interpretation of hysteresis loops of GaMnAs in the framework of the Stoner–Wohlfarth model

A. Winter, H. Pascher, H. Krenn, X. Liu, and J. K. Furdyna

J. Appl. Phys. 108, 043921 (2010); http://dx.doi.org/10.1063/1.3466771 (6 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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We have used the magnetooptical Kerr effect to investigate the shape of the hysteresis loops of thin GaMnAs films grown on substrates with different buffer layers. Depending on whether the easy axis of magnetization is in the plane of the thin film or out of the plane, and depending on the orientation of the external magnetic field with respect to the crystallographic axes, a great variety of hysteresis loops is observed. Because magnetooptical effects depend linearly on specific components of the magnetization, it has been possible to determine the orientation of the magnetization with varying magnetic field. The experimental findings are very well described by the Stoner–Wohlfarth model of coherent magnetization rotation, yielding precise values for the anisotropy constants. We present this model and its use in the context of magnetooptical measurements as a relatively simple and straightforward method for establishing magnetization parameters of ferromagnetic semiconductors in thin film form.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Pp Magnetic semiconductors

Magnetic phase separation in Nd0.5(Ca,Sr)0.5MnO3

T. Geetha Kumary, J. G. Lin, and M. C. Valsakumar

J. Appl. Phys. 108, 043922 (2010); http://dx.doi.org/10.1063/1.3475503 (4 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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The phase separation of Nd0.5Ca0.5−ySryMnO3, for 0 ≤ y ≤ 0.5, is studied via electron spin resonance (ESR) in the temperature range 80–400 K. Two types of magnetic phases are found to coexist in the samples with y>0 below a phase separation temperature T∗. The ESR line width exhibits a minimum near the charge order transition temperature TCO for samples with y<0.25, and near T∗ for y ≥ 0.25. A systematic decrease in line width is observed as y increases from 0 to 0.5. The g factors increase slightly and the ESR intensities increase exponentially when the temperature decreases in the paramagnetic region. Our results demonstrate presence of two local magnetic structures due to the intrinsic phase separation.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
75.20.Ck Nonmetals
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
76.30.-v Electron paramagnetic resonance and relaxation

Consequences of the magnetocaloric effect on magnetometry measurements

B. R. Hansen, C. R. H. Bahl, L. Theil Kuhn, A. Smith, K. A. Gschneidner, Jr., and V. K. Pecharsky

J. Appl. Phys. 108, 043923 (2010); http://dx.doi.org/10.1063/1.3466977 (5 pages) | Cited 2 times

Online Publication Date: 31 August 2010

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Magnetization curves recorded at high sweep-rates on magnetic materials near a phase transition temperature can be affected by temperature changes in the material due to the magnetocaloric effect. This change in the sample temperature is a result of the quasiadiabatic conditions that can occur under such conditions and we demonstrate its effects on magnetization curves of two magnetocaloric materials, La(Fe0.945Co0.055)11.9Si1.1 and Gd5Si2Ge2. We show how a quantity calculated from isothermal magnetization curves, the magnetic entropy change, ΔSM, is affected by the erroneous data. As ΔSM is a measure of the magnetocaloric effect, the discrepancies demonstrated here are more severe close to a peak in ΔSM, which is precisely the quantity that is of interest and reported on in the literature from possibly erroneous magnetization data. We also demonstrate how, through simple measurements and without a direct measurement of the sample temperature, one can determine an appropriate sweep-rate of the magnetic field.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Monitoring magnetization reversal and perpendicular anisotropy by the extraordinary Hall effect and anisotropic magnetoresistance.

D. P. Rosenblatt, M. Karpovski, and A. Gerber

J. Appl. Phys. 108, 043924 (2010); http://dx.doi.org/10.1063/1.3475690 (5 pages) | Cited 4 times

Online Publication Date: 31 August 2010

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Simultaneous magnetotransport measurements of the extraordinary Hall effect and anisotropic magnetoresistance were used to monitor the normal and in-plane projections of magnetization in thin Co/Pd multilayers with perpendicular anisotropy. By reconstructing the magnitude and orientation of the magnetization vector we were able to track the reversal of magnetization and distinguish among the processes of coherent rotation and domain nucleation. The Stoner–Wohlfarth model was used to extract anisotropy constants from data collected during the coherent rotation. We show that magnetization reversal occurs coherently over a major part of the cycle under a canted magnetic field when the field's inclination exceeds a certain sample-dependent angle. The applicability range of the Stoner–Wohlfarth model and thus reliability of the calculated anisotropy constants is significantly improved when measurements are performed under canted fields.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.47.Np Metals and alloys
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