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14 Feb 2013

Volume 113, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 064301 (2013); http://dx.doi.org/10.1063/1.4789897 (11 pages)

Y. G. Marinov, G. B. Hadjichristov, A. G. Petrov, S. Marino, C. Versace, and N. Scaramuzza
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back to top Magnetism and Superconductivity

The role of octahedral tilting in the structural phase transition and magnetic anisotropy in SrRuO3 thin film

Wenlai Lu, Wen Dong Song, Kaihua He, Jianwei Chai, Cheng-Jun Sun, Gan-Moog Chow, and Jing-Sheng Chen

J. Appl. Phys. 113, 063901 (2013); http://dx.doi.org/10.1063/1.4790699 (7 pages) | Cited 1 time

Online Publication Date: 8 February 2013

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We present a stoichiometry-dependent structural phase transition in SrRuO3 film on SrTiO3 substrate. The oxygen stoichiometry in the films was varied by changing the oxygen partial pressure P(O2) during the deposition process. For SrRuO3 films with P(O2) ≥ 60 mTorr, they exhibited a pseudo-orthorhombic structure with in-plane uniaxial magnetic anisotropy. On the other hand for films with P(O2) ≤ 45 mTorr, the tetragonal SrRuO3 phase with a perpendicular uniaxial magnetic anisotropy was stabilized at room temperature. The big difference in the magnetic anisotropy of these two SrRuO3 phases was shown to be closely linked to their respective RuO6 octahedral rotation patterns: the RuO6 octahedra rotate differently along the two orthogonal in-plane directions in the pseudo-orthorhombic phase, whereas in the tetragonal phase only octahedral rotations around z-axis are present and the octahedral tilts along the in-plane axes are diminished. First-principles calculations show that such a suppression of the RuO6 octahedra tilting in the tetragonal phase arises from the oxygen vacancies at the octahedral apex (along z-axis). This work demonstrates that the stoichiometry plays an important role in determining the octahedral rotations and tilts in the perovskite materials, which may induce new phases with distinctively different structural symmetry and physical property.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.72.jd Vacancies
64.70.K- Solid-solid transitions
75.30.Gw Magnetic anisotropy

Search for long-range ferromagnetism: Charge-spin co-doped Ba1−x−yLax+yTi1−xMxO3 (M = Cr, Fe, and Co)

D. F. Shao, J. Yang, H. B. Jian, X. B. Zhu, and Y. P. Sun

J. Appl. Phys. 113, 063902 (2013); http://dx.doi.org/10.1063/1.4790869 (7 pages)

Online Publication Date: 8 February 2013

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We investigate the structural, magnetic, and electrical properties of charge-spin co-doped Ba1−x−yLax+yTi1−xMxO3 (M = Cr, Fe, and Co). For Ba1−x−yLax+yTi1−xCrxO3, carrier doping induces short-range ferromagnetism, and we find a large negative magnetoresistance in these compounds. However, for Ba1−x−yLax+yTi1−xMxO3 (M = Fe and Co), the magnetism does not seem to couple with the charge carriers. The transport properties of Ba1−x−yLax+yTi1−xCrxO3 can be described by a three-dimensional variable-range-hopping model that implies itinerant charge carriers, whereas almost all the samples of Ba1−x−yLax+yTi1−xMxO3 (M = Fe and Co) exhibit high resistivity. It is known that only the itinerant charge carriers can enhance the coupling of two isolated magnetic ions. Therefore, there is almost no long-range ferromagnetism in the studied system.
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61.66.Fn Inorganic compounds
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.up Other materials

Planar Hall resistance ring sensor based on NiFe/Cu/IrMn trilayer structure

Brajalal Sinha, Tran Quang Hung, Torati Sri Ramulu, Sunjong Oh, Kunwoo Kim, Dong-Young Kim, Ferial Terki, and CheolGi Kim

J. Appl. Phys. 113, 063903 (2013); http://dx.doi.org/10.1063/1.4790139 (5 pages)

Online Publication Date: 8 February 2013

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We have investigated the sensitivity of a planar Hall resistance sensor as a function of the ring radius in the trilayer structure Ta(3)/IrMn(10)/Cu(0.2)/NiFe(10)/Ta(3) (nm). The diagonal components of magnetoresistivity tensor in rectangular prism corresponding to anisotropic magnetoresistance are few ten times larger than that of off-diagonal component corresponding to planar Hall resistance. However, it is noteworthy that the resultant contribution is governed by the off-diagonal components due to the cancellation of diagonal components in the self-balanced bridge configuration. Both the experimental and theoretical results show that the sensitivity varies linearly with the ring radius. In multi-ring architecture, the circumference can be increased to a limit, which consequently enhances sensitivity. We found the sensitivity of the investigated 7-rings planar Hall to be more than 600 μV/Oe.
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85.75.Ss Magnetic field sensors using spin polarized transport
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.-w Magnetic instruments and components

Increasing Curie temperature in tetragonal Mn2RhSn Heusler compound through substitution of Rh by Co and Mn by Rh

Vajiheh Alijani, Olga Meshcheriakova, Juergen Winterlik, Guido Kreiner, Gerhard H. Fecher, and Claudia Felser

J. Appl. Phys. 113, 063904 (2013); http://dx.doi.org/10.1063/1.4791564 (4 pages)

Online Publication Date: 11 February 2013

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The tetragonal Mn2RhSn Heusler compound shows better lattice match with MgO than do Mn3−xGa and tetragonal Mn3−xCoxGa Heusler compounds and hence is better suited for spin transfer torque applications. Beside the improved lattice match, this compound shows a low saturation magnetic moment reduces the current to switch which makes it more relevant for application in spin transfer torque devices. This compound shows a low Curie temperature; introducing Co into this system and increasing the Rh content leads to an increase in the Curie temperature. Doping with Co retains the tetragonal structure, with improved lattice match with MgO and low magnetic moment, intact up to x = 0.6, although doping with Rh changes the structure from tetragonal to cubic.
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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
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.72.up Other materials
64.70.kd Metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Origin of the different multiferroism in BiFeO3 and GaFeO3

S. G. Bahoosh and J. M. Wesselinowa

J. Appl. Phys. 113, 063905 (2013); http://dx.doi.org/10.1063/1.4791586 (6 pages)

Online Publication Date: 11 February 2013

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We have proposed microscopic models for describing the multiferroic properties of BiFeO3 and GaFeO3. It is shown that the mechanisms of the multiferroism are different. In BiFeO3, the magnetoelectric coupling is biquadratic, whereas in GaFeO3 it is linear. The site disorder between Ga and Fe is a primary source of the net magnetic moment in GaFeO3. The temperature and magnetic field dependence of the polarization is calculated in order to show that the proposed models for these two multiferroics are correct. Near the magnetic phase transition temperature TN we obtain a kink in the electric properties.
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75.85.+t Magnetoelectric effects, multiferroics
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

Crystal asymmetry and low-angle grain boundary governed persistent photoinduced magnetization in small bandwidth manganites

S. Majumdar, T. Elovaara, H. Huhtinen, S. Granroth, and P. Paturi

J. Appl. Phys. 113, 063906 (2013); http://dx.doi.org/10.1063/1.4789596 (9 pages)

Online Publication Date: 11 February 2013

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Persistent photo-induced magnetization (PPM) in low bandwidth manganite Pr1−xCaxMnO3 (PCMO) thin film is reported in the low hole doped regime (x = 0.1). X-ray diffraction, x-ray photoelectron spectroscopy, and magnetic measurements in dark and under illumination on the as-grown, vacuum, and oxygen annealed thin films of PCMO showed that the PPM effect is strongly dependent on the crystal symmetry, low angle grain boundaries, and the Mn valence states in the material. Compared with the as-grown and vacuum annealed film, the oxygen annealed film shows much less low-angle grain boundaries, higher crystal symmetry, and long range ferromagnetic (FM) ordering and in this sample PPM is not significant. These results clearly indicate that in this large band gap material PCMO, photo-induced FM interaction mainly arises due to improved domain-wall movement of the short range FM clusters. Significant PPM can be obtained for films with higher amount of grain boundaries, oxygen vacancies, and strain related defects.
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61.72.Mm Grain and twin boundaries
81.40.Gh Other heat and thermomechanical treatments
73.20.At Surface states, band structure, electron density of states
79.60.Dp Adsorbed layers and thin films
71.20.Ps Other inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Stable thrust on a finite-sized magnet above a Meissner superconducting torus

Jose-Luis Perez-Diaz, Efren Diez-Jimenez, Ignacio Valiente-Blanco, and Javier Herrero-de-Vicente

J. Appl. Phys. 113, 063907 (2013); http://dx.doi.org/10.1063/1.4792037 (4 pages)

Online Publication Date: 12 February 2013

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Forces and torques exerted by a superconducting torus on a permanent magnet have been mapped. It is demonstrated that stable orbits exist. Moreover, provided that the magnet remains in any of these orbits, the first critical field in the superconductor is never overpassed and the superconductor remains in the Meissner state. The consequent absence of hysteresis makes these kinds of device perfect candidates for non-frictional bearings or gyroscopes.
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84.71.Ba Superconducting magnets; magnetic levitation devices

Effect of excess Mg and nano-additives on the superconducting properties of weakly connected bulk MgB2

P. P. S. Bhadauria, Anurag Gupta, Hari Kishan, and A. V. Narlikar

J. Appl. Phys. 113, 063908 (2013); http://dx.doi.org/10.1063/1.4790802 (7 pages)

Online Publication Date: 12 February 2013

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Series of ex-situ polycrystalline MgB2 bulk samples, by adding different additives like more of excess Mg (5 wt. %), nanoparticles of Ag (3 wt. %), and SiC (10 wt. %) to a previously optimized composition MgB2 + Mg (5 wt. %), were prepared by solid state synthesis route. Detailed investigations were carried out by XRD, SEM, and thermoelectric power S(T), resistivity ρ(T), and magnetization M(B) at temperatures T = 4.2–300 K and applied fields B = 0–8 T. All the samples typically show low connectivity (i.e., normal state current carrying cross section ∼0.9%–3%). The effect of different additives was different on the critical current density (Jc) of the samples. The Jc, for instance at T = 4.2 K and B = 1 T, varied between 4.8 × 107 and 2.8 × 108 A/m2 for various samples. In comparison to the previously optimized values, the Jc was enhanced by further addition of 5 wt. % Mg and degraded both by nano-SiC and nano-Ag addition. However, many of the other properties of the samples were not much affected. For instance, the samples did not show any change in the superconducting onsets, S(T) and the parallel upper critical field (Bc2|| (T) ∼ 11–13 T at 20 K and 20–21 T at 4.2 K). The Jc(B) dependence also shows similar behavior in all the samples, where the Jc is found to scale as B−1 up to a sample independent crossover field Bcr ∼ 2 T and 1.3 T at T = 4.2 and 20 K, respectively. At higher fields B > Bcr, the Jc(B) curves branch out and decrease rapidly towards zero at a sample dependent characteristic field. We try to understand these results quantitatively in terms of changes in connectivity, pinning, and anisotropy driven percolation. However, all our results and analysis point out that the intra-particle regions stay unaffected and mainly the inter-particle regions get affected by the additives leading to the Jc variation in the weakly connected samples.
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74.62.Dh Effects of crystal defects, doping and substitution
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.fg Thermoelectric effects
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Oxygen stoichiometry and magnetic properties of LuFe2O4+δ

Fan Wang, Jungho Kim, G. D. Gu, Yongjae Lee, Saebyok Bae, and Young-June Kim

J. Appl. Phys. 113, 063909 (2013); http://dx.doi.org/10.1063/1.4792036 (7 pages) | Cited 1 time

Online Publication Date: 12 February 2013

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We report a comprehensive investigation of the magnetic properties of LuFe2O4 (LFO) samples with different oxygen stoichiometries. Samples with excess oxygen exhibit spin glass behavior without long-range magnetic order, while three-dimensional ferrimagnetic order exists in a stoichiometric sample. Dissimilar experimental observations reported in several papers can be understood consistently when oxygen stoichiometry is taken into account. The stoichiometric sample orders magnetically below TN = 243 K, and a monoclinic lattice distortion sets in below TL = 175 K. This structural change is sensitive to the applied magnetic field, indicating strong spin-lattice coupling in this material. Unusual low-field thermal magnetization behavior was observed near TL, and its origin is discussed.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Bi Elemental solids
61.66.Dk Alloys
75.10.Nr Spin-glass and other random models
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Gg Ferrimagnetics
75.50.Lk Spin glasses and other random magnets

The influence of a Pb surfactant on the magnetism of dilute Si1–xMnx films

S. Kahwaji, W. Bowman, M. D. Robertson, and T. L. Monchesky

J. Appl. Phys. 113, 063910 (2013); http://dx.doi.org/10.1063/1.4792219 (6 pages)

Online Publication Date: 13 February 2013

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We investigated the effect of Pb surfactant on the growth mode and magnetism of dilute Si1−xMnx thin films grown by molecular beam epitaxy. We find that the nanocolumns that form in Pb-free samples are paramagnetic with a small saturation moment that drops with increasing Mn concentration. On the contrary, samples grown with 2 monolayers of Pb contain MnSi1.7 nanorods that lie in the plane of the films. Although the saturation moment of these samples also drops rapidly with increasing Mn concentration, it is as high as 0.65 μB/Mn. At the lowest Mn concentration (x = 0.5%), the samples grown with a Pb surfactant exhibit two ferromagnetic transitions at the Curie temperatures TC1 ≈ 40 K and TC2>400 K. While the transition at TC1 is consistent with the Curie temperature of bulk MnSi1.7 crystals, TC2 is possibly due to a second phase resulting from Mn in the Si matrix.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
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
68.55.A- Nucleation and growth

Exchange bias in manganite/SrRuO3 superlattices

M. Ziese, F. Bern, and I. Vrejoiu

J. Appl. Phys. 113, 063911 (2013); http://dx.doi.org/10.1063/1.4790877 (6 pages)

Online Publication Date: 13 February 2013

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The magnetization processes in Pr0.7Ca0.3MnO3/SrRuO3 and La0.7Sr0.3MnO3/SrRuO3 superlattices were studied. In both superlattices the ferromagnetic layers are antiferromagnetically coupled across the interfaces. Whereas superlattice La0.7Sr0.3MnO3/SrRuO3 showed a three-step magnetization reversal mechanism for all temperatures, superlattice Pr0.7Ca0.3MnO3/SrRuO3 had a compensation point with a two-step below and a three-step reversal mechanism above the compensation temperature. Exchange-bias and coercive fields, the vertical magnetization shift as well as the minor loop opening were measured as a function of the cooling field. Main findings were a change of the exchange-bias field from negative to positive values for increasing cooling fields in the two-step reversal regime and from negative values to zero for increasing cooling fields in the three-step reversal regime. Exchange-bias training occurs mostly within the first magnetization cycle. The data are consistent with the formation of interfacial domain walls.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms

Novel microwave near-field sensors for material characterization, biology, and nanotechnology

R. Joffe, E. O. Kamenetskii, and R. Shavit

J. Appl. Phys. 113, 063912 (2013); http://dx.doi.org/10.1063/1.4791713 (10 pages)

Online Publication Date: 13 February 2013

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The wide range of interesting electromagnetic behavior of contemporary materials requires that experimentalists working in this field master many diverse measurement techniques and have a broad understanding of condensed matter physics and biophysics. Measurement of the electromagnetic response of materials at microwave frequencies is important for both fundamental and practical reasons. In this paper, we propose a novel near-field microwave sensor with application to material characterization, biology, and nanotechnology. The sensor is based on a subwavelength ferrite-disk resonator with magnetic-dipolar-mode (MDM) oscillations. Strong energy concentration and unique topological structures of the near fields originated from the MDM resonators allow effective measuring material parameters in microwaves, both for ordinary structures and objects with chiral properties.
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84.40.Az Waveguides, transmission lines, striplines
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Effect of antiferromagnetic thickness on thermal stability of static and dynamic magnetization of NiFe/FeMn multilayers

Nguyen N. Phuoc, H. Y. Chen, and C. K. Ong

J. Appl. Phys. 113, 063913 (2013); http://dx.doi.org/10.1063/1.4792223 (6 pages)

Online Publication Date: 14 February 2013

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The influence of antiferromagnetic (AF) thickness on static and dynamic magnetic properties and their thermal stability in NiFe/FeMn multilayered thin films was investigated systematically. It was found that dynamic magnetic anisotropy rises at the AF thickness lower than that of static magnetic anisotropy and exchange bias. This behavior is suggested to be due to the contribution of rotatable anisotropy arising from time-dependent rotatable part of the AF spins. It is also due to the contribution of rotatable anisotropy and exchange bias that makes the thermal stability of static and dynamic anisotropies varied with AF thickness. The temperature dependences of ferromagnetic resonance frequency, Gilbert damping factor and frequency linewidth dependent on AF thickness are also discussed in conjunction with the variations of the dynamic anisotropy and exchange bias field to provide a comprehensive picture of the physical origin of their thermal stability.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Thermally activated magnetization switching in a nanostructured synthetic ferrimagnet

Jong Min Lee and Sang Ho Lim

J. Appl. Phys. 113, 063914 (2013); http://dx.doi.org/10.1063/1.4792303 (5 pages) | Cited 1 time

Online Publication Date: 14 February 2013

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Thermally activated magnetization switching in a nanostructured synthetic ferrimagnet is investigated by micromagnetic simulations and results are analyzed using the Arrhenius-Néel formula. In most of the previous studies, the characteristic attempt time was assumed to be fixed and the parameter extracted from the analysis was the magnetic energy barrier. In this study, however, the assumption of a fixed characteristic attempt time was not used, with resultant advantages of extracting the characteristic attempt time from the analysis and of critically testing the validity of the formula. This was made possible with a precise analytical description of the magnetic field dependence of the energy barrier in the synthetic ferrimagnet. The thermally activated magnetization switching behavior is found to be well described by the Arrhenius-Néel formula with a well-defined characteristic attempt time of 3.1 ns.
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75.75.-c Magnetic properties of nanostructures
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
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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