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13 Dec 2010

Volume 97, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 97, 241101 (2010); http://dx.doi.org/10.1063/1.3525583 (3 pages)

Kanghee Lee and Jaewook Ahn
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Experimental and theoretical evidence of enhanced ferromagnetism in sonochemical synthesized BiFeO3 nanoparticles

Liang Fang, Jian Liu, Sheng Ju, Fengang Zheng, Wen Dong, and Mingrong Shen

Appl. Phys. Lett. 97, 242501 (2010); http://dx.doi.org/10.1063/1.3525573 (3 pages)

Online Publication Date: 13 December 2010

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BiFeO3 nanoparticles were synthesized by a sonochemical method and their magnetic behavior was investigated both experimentally and theoretically. With an aid of ultrasonic irradiation, the saturated magnetization of BiFeO3 nanoparticles at room temperature was found to be increased effectively, from 0.007 to 0.012 μB/Fe. The postannealing and x-ray photoemission spectroscopy results demonstrate that oxygen vacancies can be generated due to the ultrasonic irradiation and play an important role to increase the ferromagnetism. Our first-principles calculation results are in good agreement with the experimental observations.
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75.75.-c Magnetic properties of nanostructures
75.78.-n Magnetization dynamics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
81.16.-c Methods of micro- and nanofabrication and processing

Magnetostriction and anisotropy compensation in TbxDy0.9−xNd0.1Fe1.93 [0.2 ≤ x ≤ 0.4]

S Narayana Jammalamadaka, G. Markandeyulu, and Krishnan Balasubramaniam

Appl. Phys. Lett. 97, 242502 (2010); http://dx.doi.org/10.1063/1.3525577 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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Structure and magnetostriction of TbxDy0.9−xNd0.1Fe1.93 (0.2 ≤ x ≤ 0.4) compounds are investigated. All the compounds are found to stabilize in MgCu2-type C15 cubic Laves phase structure. The easy magnetization direction changes from 〈100〉(x = 0.2) to 〈111〉(x = 0.3) through an intermediate state at x = 0.25. Anisotropy compensation is realized near x = 0.25 for the TbxDy0.9−xNd0.1Fe1.93 compounds. The Laves phase compound Tb0.4Dy0.5Nd0.1Fe1.93 has large spontaneous magnetostriction (1670×10−6) and a low anisotropy at room temperature which could make it a good candidate material for magnetostriction applications.
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75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic domain-wall depinning with reduced current density by short pulse rise time

Hauke H. Langner, Lars Bocklage, Benjamin Krüger, Toru Matsuyama, and Guido Meier

Appl. Phys. Lett. 97, 242503 (2010); http://dx.doi.org/10.1063/1.3518486 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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The depinning probability of magnetic domain walls at constrictions by current pulses depends on the external magnetic field and on the temporal shape of current pulses. We investigate the depinning of domain walls in permalloy nanowires in dependence of the rise time of a current pulse. We observe a change in the depinning probability when varying the pulse rise time and the pulse amplitude at a constant magnetic field. The experiments reveal that the current density for domain-wall depinning can be strongly reduced by current pulses with short rise times.
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75.75.-c Magnetic properties of nanostructures
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.78.Fg Dynamics of domain structures
75.60.Ch Domain walls and domain structure

Real-time direct measurement of field rise time and dynamic instability of perpendicular writers

Peter Czoschke, Shehzaad Kaka, N. J. Gokemeijer, and Scott Franzen

Appl. Phys. Lett. 97, 242504 (2010); http://dx.doi.org/10.1063/1.3525927 (3 pages) | Cited 3 times

Online Publication Date: 13 December 2010

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A method is presented to measure the dynamic write field of a perpendicular recording head directly in the time domain using a tunneling magnetoresistive read sensor. The method is used to measure the magnetic field rise time of two different writer designs and real-time measurements of the write field without averaging are demonstrated, enabling investigation of transient switching behavior that would not be observed with stroboscopic or frequency-domain techniques. A dynamic instability is observed and characterized in a particular writer design and is attributed to the insertion of an antiferromagnetic coupling layer in the writer pole.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Ss Magnetic recording materials
75.50.Ee Antiferromagnetics
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Origin of ferromagnetism in self-assembled Ga1−xMnxAs quantum dots grown on Si

S. L. Wang, L. Chen, K. K. Meng, P. F. Xu, H. J. Meng, J. Lu, W. S. Yan, and J. H. Zhao

Appl. Phys. Lett. 97, 242505 (2010); http://dx.doi.org/10.1063/1.3526378 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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Self-assembled Ga1−xMnxAs magnetic semiconductor quantum dots have been grown on Si (001) substrates using droplet epitaxy by molecular-beam epitaxy. Structural characterization reveals that these dots possess a zinc-blende lattice. The Ga1−xMnxAs quantum dots with 8% Mn content are ferromagnetically soft and slightly anisotropic at low temperature, and show the superparamagnetic behavior with a blocking temperature of 20 K in the in-plane direction. Moreover, the results of x-ray absorption near edge structure provide direct evidences for the substitutional Mn2+ ion with a half-filled d5 configuration for the Ga site, suggesting the hole-mediated ferromagnetism in zero-dimensional Ga1−xMnxAs quantum dots.
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75.50.Pp Magnetic semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
78.70.Dm X-ray absorption spectra

Collapse of charge ordering and enhancement of magnetocaloric effect in nanocrystalline La0.35Pr0.275Ca0.375MnO3

M. H. Phan, S. Chandra, N. S. Bingham, H. Srikanth, C. L. Zhang, S. W. Cheong, T. D. Hoang, and H. D. Chinh

Appl. Phys. Lett. 97, 242506 (2010); http://dx.doi.org/10.1063/1.3526380 (3 pages) | Cited 9 times

Online Publication Date: 13 December 2010

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We demonstrate the possibility of enhancing both the magnetocaloric effect (MCE) and refrigerant capacity (RC) in nanostructured mixed phase manganites. A comparative study of the magnetic and magnetocaloric properties of La0.35Pr0.275Ca0.375MnO3 in single crystalline and nanocrystalline forms is presented. While the conventional trend is reduction of magnetization and MCE with nanostructuring, we show that the opposite is true in the case of mixed phase manganites. The charge-ordered state is largely suppressed and ferromagnetic order is established in the nanocrystalline sample with an average particle size of 50 nm. Consequently, a strong enhancement of MCE and RC and a strong reduction of thermal and field hysteresis losses are achieved in the nanocrystalline sample. This finding opens up a way of exploring magnetic refrigerant materials at the nanometer scale for active magnetic refrigerators.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Pseudomorphic strain induced strong anisotropic magnetoresistance over a wide temperature range in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films

L. F. Wang, Z. Huang, X. L. Tan, P. F. Chen, B. W. Zhi, G. M. Li, and W. B. Wu

Appl. Phys. Lett. 97, 242507 (2010); http://dx.doi.org/10.1063/1.3524193 (3 pages) | Cited 4 times

Online Publication Date: 15 December 2010

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Strong anisotropic magnetoresistance (AMR) was observed in La0.67Ca0.33MnO3 films grown coherently on the orthorhombic NdGaO3(001) substrates. With an increased orthorhombic lattice distortion due to the pseudomorphic strain, the films show not only a ferromagnetic-metal (FM) transition at TC of ∼ 265 K, but also the phase coexistence of FM and antiferromagnetic-insulator below ∼ 250 K. The phase competitions are very sensitive to the magnetic field, and more strikingly, to its orientations with respect to the crystal axes resulting in a large AMR in a broad temperature range, in addition to the conventional one peaked near TC. The films also show uniaxial magnetic anisotropy with the easy axis along the elongated b axis, suggesting that it is the strain induced spin-orbit-lattice coupling and the resultant phase competitions that control the AMR in epitaxial manganite films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Lx Magnetic oxides

Nontunnel transport through CoFe2O4 nanometric barriers

M. Foerster, D. F. Gutierrez, F. Rigato, J. M. Rebled, F. Peiro, and J. Fontcuberta

Appl. Phys. Lett. 97, 242508 (2010); http://dx.doi.org/10.1063/1.3527921 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2010

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Electric transport through ultrathin CoFe2O4 (CFO) films of different thicknesses is studied using current sensing atomic force microscopy. Analysis of current distribution maps and I-V characteristics reveals anomalous thickness dependence. Results indicate the existence of an Ohmic conduction channel in parallel with the tunnel one. The origin of the nontunneling, likely non-spin-preserving, channel is discussed in the context of recent results on spin-filtering CFO-based devices.
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73.61.Ng Insulators
72.25.-b Spin polarized transport
68.55.-a Thin film structure and morphology

Magnetism and clustering in Cr-doped InN

A. Belabbes, A. Zaoui, and M. Ferhat

Appl. Phys. Lett. 97, 242509 (2010); http://dx.doi.org/10.1063/1.3527978 (3 pages) | Cited 2 times

Online Publication Date: 17 December 2010

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Density functional theory was applied to study the electronic and magnetic coupling of Cr-doped InN, in which magnetic configurations have been investigated. We found that the calculated ferromagnetic stabilizing energy is strongly linked to the Cr–Cr distance. The local magnetic moment of Cr is 2.3μB, and it weakly depends on the Cr–Cr distance. The coupling between the Cr d and the N p states is found to be the origin of ferromagnetism in the InCrN system. The generalized gradient approximation-1/2 correction procedure increases the polarization of InCrN, making this system a robust half-metallic ferromagnetic alloy.
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75.30.Cr Saturation moments and magnetic susceptibilities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Cc Other ferromagnetic metals and alloys
71.55.Eq III-V semiconductors
FREE

Ultrafast switching in magnetic tunnel junction based orthogonal spin transfer devices

H. Liu, D. Bedau, D. Backes, J. A. Katine, J. Langer, and A. D. Kent

Appl. Phys. Lett. 97, 242510 (2010); http://dx.doi.org/10.1063/1.3527962 (3 pages) | Cited 11 times

Online Publication Date: 17 December 2010

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Orthogonal spin-transfer magnetic random access memory (OST-MRAM) uses a spin-polarizing layer magnetized perpendicularly to a free layer to achieve large spin-transfer torques and ultrafast energy efficient switching. We have fabricated and studied OST-MRAM devices that incorporate a perpendicularly magnetized spin-polarizing layer and a magnetic tunnel junction, which consists of an in-plane magnetized free layer and synthetic antiferromagnetic reference layer. Reliable switching is observed at room temperature with 0.7 V amplitude pulses of 500 ps duration. The switching is bipolar, occurring for positive and negative polarity pulses, consistent with a precessional reversal mechanism, and requires an energy of less than 450 fJ.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
75.78.Jp Ultrafast magnetization dynamics and switching
75.76.+j Spin transport effects
75.60.Jk Magnetization reversal mechanisms
75.50.Ee Antiferromagnetics

Increasing the coherence time of single electron spins in diamond by high temperature annealing

Boris Naydenov, Friedemann Reinhard, Anke Lämmle, V. Richter, Rafi Kalish, Ulrika F. S. D’Haenens-Johansson, Mark Newton, Fedor Jelezko, and Jörg Wrachtrup

Appl. Phys. Lett. 97, 242511 (2010); http://dx.doi.org/10.1063/1.3527975 (3 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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Negatively charged nitrogen-vacancy (NV−) centers in diamond produced by ion implantation often show properties different from NVs created during the crystal growth. We observe that NVs created from nitrogen ion implantation at 30–300 keV show much shorter electron spin coherence time T2 as compared to the “natural” NVs and about 20% of them show switching from NV− to NV0. We show that annealing the diamond at T = 1200 °C substantially increases T2 and at the same time the fraction of NVs converting from NV− to NV0 is greatly reduced.
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61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies
61.72.up Other materials

Concentration dependence of magnetic moment in Ni50-xCoxMn50-yZy (Z = In,Sn) Heusler alloys

W. Ito, X. Xu, R. Y. Umetsu, T. Kanomata, K. Ishida, and R. Kainuma

Appl. Phys. Lett. 97, 242512 (2010); http://dx.doi.org/10.1063/1.3525168 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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The concentration dependence of magnetic properties in the austenite phase of NiCoMnIn and NiCoMnSn Heusler alloys was systematically investigated by the magnetization measurements. The TC for Ni(50-x)CoxMn(50-y)Sny alloys linearly increases with increasing the Co content and fixed Sn content. Although showing a concave curve for Ni50Mn(50-y)Sny ternary alloys, the Sn content-dependence of magnetic moment per formula unit changes from the concave curve to a straight line when Co is substituted for Ni. On the other hand, the In content-dependence of the magnetic moment for Ni45Co5Mn(50-y)Iny alloys is perfectly linear as is that in the Ni50Mn(50-y)Iny ternary alloys.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Giant exchange bias based on magnetic transition in γ-Fe2MnGa melt-spun ribbons

X. D. Tang (唐晓丹), W. H. Wang (王文洪), W. Zhu (朱伟), E. K. Liu (刘恩克), G. H. Wu (吴光恒), F. B. Meng (孟凡斌), H. Y. Liu (刘何燕), and H. Z. Luo (罗鸿志)

Appl. Phys. Lett. 97, 242513 (2010); http://dx.doi.org/10.1063/1.3526377 (3 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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Giant exchange bias with a shift up to 3.86 kOe has been observed in γ-Fe2MnGa alloy in which a ferromagnetic to antiferromagnetic transition takes place at 250 K. The transition can be suppressed to lower temperatures by higher magnetic fields at a shift rate of 10.3 K/kOe. Exchange bias and enhanced coercivity occur simultaneously, revealing an exchange coupling between the coexisting antiferromagnetic and ferromagnetic phases. Meanwhile, the internal exchange coupling inside the antiferromagnetic clusters dynamically ensures their unidirectional anisotropy during their size changing following the external magnetic field.
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75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Enhancement of perpendicular exchange bias in [Pd/Co]/FeMn thin films by tailoring the magnetoelastically induced perpendicular anisotropy

Lin Lin, Naganivetha Thiyagarajah, Ho Wan Joo, Jang Heo, Ky Am Lee, and Seongtae Bae

Appl. Phys. Lett. 97, 242514 (2010); http://dx.doi.org/10.1063/1.3526735 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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The effects of magnetoelastically induced perpendicular anisotropy, KFM,me, on the perpendicular exchange bias (PEB) characteristics in [Pd/Co]5/Fe50Mn50 thin films have been explored by inserting ultrathin CoFe magnetic layers with different thicknesses, compositions, and Ar sputtering gas pressures (PAr,CoFe) at the interface between [Pd/Co]5 and FeMn. It was clearly found that the [Pd/Co]5/CoFe/FeMn with CoFe sputtered at a low PAr,CoFe showed great enhancement in PEB due to the development of intrinsic compressive stress in the CoFe resulting in improving KFM,me and interfacial exchange coupling. Additionally, this effect was more significant for Co80Fe20 insertion than Co90Fe10 due to its larger magnetostriction.
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75.30.Gw Magnetic anisotropy
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
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