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17 Sep 2012

Volume 101, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He
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Low field giant magnetocaloric effect in RNiBC (R = Er and Gd) and enhanced refrigerant capacity in its composite materials

Lingwei Li, Michiaki Kadonaga, Dexuan Huo, Zhenghong Qian, Takahiro Namiki, and Katsuhiko Nishimura

Appl. Phys. Lett. 101, 122401 (2012); http://dx.doi.org/10.1063/1.4752738 (4 pages) | Cited 2 times

Online Publication Date: 17 September 2012

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The magnetic properties and magnetocaloric effect (MCE) in RNiBC (R = Er and Gd) compounds and its composite materials were investigated. A giant low field reversible MCE was observed in RNiBC compounds at 5 and 13 K for R = Er and Gd, respectively. Under a relative low field change of 2 T, the maximum values of magnetic entropy change (−ΔSMmax) reach 17.1 and 9.3 J/kg K for R = Er and Gd, respectively. A table-like MCE in the temperature of 4-20 K and enhanced refrigerant capacity (RC) were found in the ErNiBC-GdNiBC composite materials. For the magnetic field changes of 1 T and 2 T, the maximum improvement of RC reach 31% (19%) and 30% (8%), in comparison with that of individual compound ErNiBC (GdNiBC), respectively. The excellent MCE properties make the RNiBC composite materials attractive for low temperature magnetic refrigeration.
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75.30.Sg Magnetocaloric effect, magnetic cooling
65.40.gd Entropy

Multiferroic properties of Aurivillius phase Bi6Fe2−xCoxTi3O18 thin films prepared by a chemical solution deposition route

Z. Liu, J. Yang, X. W. Tang, L. H. Yin, X. B. Zhu, J. M. Dai, and Y. P. Sun

Appl. Phys. Lett. 101, 122402 (2012); http://dx.doi.org/10.1063/1.4752748 (4 pages)

Online Publication Date: 17 September 2012

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The magnetic and ferroelectric properties of Co-doped Bi6Fe2Ti3O18 thin films Bi6Fe2−xCoxTi3O18 (BFCTO) (0 ≤ x ≤ 1) are investigated. The coexistence of room-temperature ferromagnetism and ferroelectricity is observed in BFCTO thin films. The x = 0.6 sample exhibits a higher remnant magnetization Mr of 8.41 emu/cm3 and a remnant polarization Pr of 17.6 μC/cm2 compared with other BFCTO thin films. The ferromagnetism can be ascribed to the spin canting of Fe- and Co-based sublattices via the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958); T. Moriya, Phys. Rev. 120, 91 (1960)]. The change in the remnant polarization is discussed in terms of the variation of grain size and oxygen vacancies caused by Co-doping.
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75.85.+t Magnetoelectric effects, multiferroics
77.22.Ej Polarization and depolarization
77.55.Nv Multiferroic/magnetoelectric films
77.80.-e Ferroelectricity and antiferroelectricity
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials

Electric field-induced magnetization reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction

S. Kanai, M. Yamanouchi, S. Ikeda, Y. Nakatani, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 101, 122403 (2012); http://dx.doi.org/10.1063/1.4753816 (3 pages) | Cited 6 times

Online Publication Date: 18 September 2012

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The electric field-induced ∼180° magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy

Spin transfer torque devices utilizing the giant spin Hall effect of tungsten

Chi-Feng Pai, Luqiao Liu, Y. Li, H. W. Tseng, D. C. Ralph, and R. A. Buhrman

Appl. Phys. Lett. 101, 122404 (2012); http://dx.doi.org/10.1063/1.4753947 (4 pages) | Cited 6 times

Online Publication Date: 18 September 2012

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We report a giant spin Hall effect in β-W thin films. Using spin torque induced ferromagnetic resonance with a β-W/CoFeB bilayer microstrip, we determine the spin Hall angle to be |θSHβ-W| = 0.30±0.02, large enough for an in-plane current to efficiently reverse the orientation of an in-plane magnetized CoFeB free layer of a nanoscale magnetic tunnel junction adjacent to a thin β-W layer. From switching data obtained with such 3-terminal devices, we independently determine |θSHβ-W| = 0.33±0.06. We also report variation of the spin Hall switching efficiency with W layers of different resistivities and hence of variable (α and β) phase composition.
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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
75.75.-c Magnetic properties of nanostructures
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport

Rashba spin-orbit-interaction-based quantum pump in graphene

Dario Bercioux, Daniel F. Urban, Francesco Romeo, and Roberta Citro

Appl. Phys. Lett. 101, 122405 (2012); http://dx.doi.org/10.1063/1.4753975 (4 pages) | Cited 2 times

Online Publication Date: 18 September 2012

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We present a proposal for an adiabatic quantum pump based on a graphene monolayer patterned by electrostatic gates and operated in the low-energy Dirac regime. The setup under investigation works in the presence of inhomogeneous spin-orbit interactions of intrinsic- and Rashba-type and allows to generate spin polarized coherent currents. A local spin polarized current is induced by the pumping mechanism assisted by the spin-double refraction phenomenon.
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73.61.Wp Fullerenes and related materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.25.-b Spin polarized transport

Magnetic anisotropy and anomalous transitions in TbMnO3 thin films

Yimin Cui, Yufeng Tian, Aixian Shan, Chinping Chen, and Rongming Wang

Appl. Phys. Lett. 101, 122406 (2012); http://dx.doi.org/10.1063/1.4754544 (5 pages) | Cited 2 times

Online Publication Date: 19 September 2012

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TbMnO3 thin films with different crystallographic orientations were deposited epitaxially on LaAlO3 [100] and SrTiO3 [100] single crystal substrates by using pulsed laser deposition. Magnetization measurements were performed along the [110], [−110], and [001] directions of the films. Obvious magnetic anisotropy and low temperature ferromagnetism were found. Transitions at T ∼ 10, 32, 120, and 125 K along different directions are observed. The susceptibility anomalies, remarkably anisotropic, are discussed on the frame of the domain wall and strain-induced distortion. Particularly, the lattice mismatch and the anisotropic thermal expansion between the films and substrates are likely responsible for the distortion behaviors.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure

Assembly of uniaxially aligned rare-earth-free nanomagnets

B. Balamurugan, B. Das, V. R. Shah, R. Skomski, X. Z. Li, and D. J. Sellmyer

Appl. Phys. Lett. 101, 122407 (2012); http://dx.doi.org/10.1063/1.4753950 (5 pages) | Cited 3 times

Online Publication Date: 19 September 2012

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We report HfCo7 nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K1 ≈ 10 Mergs/cm3, coercivity Hc ≈ 4.4 kOe, and magnetic polarization Js ≈ 10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having Js as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This study suggests HfCo7 as a promising rare-earth-free permanent-magnet alloy, which is important for mitigating the critical-materials aspects of rare-earth elements.
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81.16.Dn Self-assembly
81.40.Gh Other heat and thermomechanical treatments
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.50.Ww Permanent magnets

Perpendicular magnetization of Co20Fe50Ge30 films induced by MgO interface

Manli Ding and S. Joseph Poon

Appl. Phys. Lett. 101, 122408 (2012); http://dx.doi.org/10.1063/1.4754001 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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Epitaxial growth of Co20Fe50Ge30 films on single crystal MgO (001) substrate is reported. Structure characterization revealed (001)-oriented B2 order of Co20Fe50Ge30, well lattice matched with the MgO barrier. Perpendicular magnetic anisotropy was achieved in the MgO/Co20Fe50Ge30/MgO structure with an optimized magnetic anisotropy energy density of 2 × 106 erg/cm3. The magnetic anisotropy is found to depend strongly on the thickness of the MgO and Co20Fe50Ge30 layers, indicating that the perpendicular magnetic anisotropy of Co20Fe50Ge30 is contributed by the interfacial anisotropy between Co20Fe50Ge30 and MgO. With reported low damping constant, Co20Fe50Ge30 films are promising spintronic materials for achieving low switching current.
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75.30.Gw Magnetic anisotropy
75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.A- Nucleation and growth
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Exchange bias coupling of Co with ultrathin La2/3Sr1/3MnO3 films

Y. J. Shi, Y. Zhou, H. F. Ding, F. M. Zhang, L. Pi, Y. H. Zhang, and D. Wu

Appl. Phys. Lett. 101, 122409 (2012); http://dx.doi.org/10.1063/1.4754594 (4 pages)

Online Publication Date: 20 September 2012

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Magnetic properties of epitaxially grown ultrathin La2/3Sr1/3MnO3 (LSMO) films down to a thickness of one unit cell (u.c.) have been systematically investigated by studying their magnetic behaviors with Co capping layers. For LSMO thickness below 3 u.c., the Co/LSMO bilayers exhibit strong exchange bias (EB) effects after field cooling, suggesting the existence of antiferromagnetic (AFM) phase at the interfaces in ultrathin LSMO. The presence of exchange bias effect for the bilayer with 1 u.c. thick LSMO further demonstrates that the AFM ordering of the LSMO is C-type AFM ordering structure. For 10 u.c. LSMO, the magnetic properties are clearly not altered by the capping Co film, suggesting that the observed phenomena are caused by the intrinsic properties of LSMO.
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75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.55.at Other materials

Spintronic oscillator based on magnetic field feedback

D. Dixit, K. Konishi, C. V. Tomy, Y. Suzuki, and A. A. Tulapurkar

Appl. Phys. Lett. 101, 122410 (2012); http://dx.doi.org/10.1063/1.4752008 (4 pages) | Cited 1 time

Online Publication Date: 20 September 2012

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We present a circuit design of a spintronic oscillator based on a magnetic tunnel junction (MTJ). In this design, a dc current is passed through a magnetic tunnel junction which is connected to a “feed-back” wire below it. Any fluctuation in the magnetization direction of the free layer of MTJ, drives a fluctuating current through the feed-back wire, which exerts a magnetic field on the free layer. This in turn can amplify the magnetization fluctuations. If the dc current passing through the MTJ is more than a critical value, periodic precessional states of the magnetization are possible.
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84.30.Ng Oscillators, pulse generators, and function generators
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Spin gating electrical current

C. Ciccarelli, L. P. Zârbo, A. C. Irvine, R. P. Campion, B. L. Gallagher, J. Wunderlich, T. Jungwirth, and A. J. Ferguson

Appl. Phys. Lett. 101, 122411 (2012); http://dx.doi.org/10.1063/1.4752013 (4 pages)

Online Publication Date: 20 September 2012

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The level of the chemical potential is a fundamental parameter of the electronic structure of a physical system, which consequently plays an important role in defining the properties of active electrical devices. We directly measure the chemical potential shift in the relativistic band structure of the ferromagnetic semiconductor (Ga,Mn)As, controlled by changes in its magnetic order parameter. Our device comprises a non-magnetic aluminum single electron channel capacitively coupled to the (Ga,Mn)As gate electrode. The chemical potential shifts of the gate are directly read out from the shifts in the Coulomb blockade oscillations of the single electron transistor. The experiments introduce a concept of spin gating electrical current. In our spin transistor spin manipulation is completely removed from the electrical current carrying channel.
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85.35.Gv Single electron devices
65.40.G- Other thermodynamical quantities
71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors

Magnetization reversal in multisegmented nanowires: Parallel and serial reversal modes

S. Allende, N. M. Vargas, D. Altbir, V. Vega, D. Görlitz, and K. Nielsch

Appl. Phys. Lett. 101, 122412 (2012); http://dx.doi.org/10.1063/1.4754117 (4 pages)

Online Publication Date: 20 September 2012

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We investigate the effect of the dipolar magnetic interaction between magnetic layers mediated by non-magnetic ones in multisegmented nanowires. Multiple symmetric and non-symmetric segments are considered. We observe that due to the dipolar interaction, the magnetization reversal can follow two possible routes, a serial, or a parallel reversal process. We show that by using asymmetrical multi-segmented wires it is possible to stop the magnetization reversal of the system at any particular point.
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75.60.Jk Magnetization reversal mechanisms
75.75.-c Magnetic properties of nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities

Effect of spin drift on spin accumulation voltages in highly doped silicon

Makoto Kameno, Yuichiro Ando, Eiji Shikoh, Teruya Shinjo, Tomoyuki Sasaki, Tohru Oikawa, Yoshishige Suzuki, Toshio Suzuki, and Masashi Shiraishi

Appl. Phys. Lett. 101, 122413 (2012); http://dx.doi.org/10.1063/1.4754285 (4 pages) | Cited 5 times

Online Publication Date: 20 September 2012

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We investigated the effect of spin drift on spin accumulation in highly doped silicon (Si) by using a non-local three-terminal (NL-3T) and four-terminal (NL-4T) methods, and have clarified that the spin accumulation voltages in a NL-3T device were modulated due to spin drift and that spin lifetime can be accurately extracted by employing a modified spin drift-diffusion equation. The extracted spin lifetime is 4-7 ns, which is slightly shorter than the intrinsic spin lifetime (8 ns) measured in the NL-4T method in the same Si device because of spin drift. It is elucidated that the spin drift effect should be considered for the precise estimation of spin lifetime in Si by NL-3T method.
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75.30.Ds Spin waves
75.30.Wx Spin crossover
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
61.72.uf Ge and Si
75.78.-n Magnetization dynamics

Effect of Mg interlayer on perpendicular magnetic anisotropy of CoFeB films in MgO/Mg/CoFeB/Ta structure

Q. L. Ma, S. Iihama, T. Kubota, X. M. Zhang, S. Mizukami, Y. Ando, and T. Miyazaki

Appl. Phys. Lett. 101, 122414 (2012); http://dx.doi.org/10.1063/1.4754118 (5 pages) | Cited 2 times

Online Publication Date: 21 September 2012

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The effects of Mg metallic interlayer on the magnetic properties of thin CoFeB films in MgO/Mg (tMg)/CoFeB (1.2 nm)/Ta structures were studied in this letter. Our experimental result shows that the CoFeB film exhibits perpendicular magnetic anisotropy (PMA) when the CoFeB and MgO layers are separated by a metallic Mg layer with a maximum thickness of 0.8 nm. The origin of PMA was discussed by considering the preferential transmission of the Δ1 symmetry preserved by the Mg interlayer in crystallized MgO/Mg/CoFeB/Ta. In addition, the thin Mg interlayer also contributes to enhancing the thermal stability and reducing the effective damping constant and coercivity of the CoFeB film.
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81.05.Bx Metals, semimetals, and alloys
68.60.Dv Thermal stability; thermal effects
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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