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2 Jul 2012

Volume 101, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 101, 013701 (2012); http://dx.doi.org/10.1063/1.4730945 (5 pages)

Frederick Gertz, Rustam Azimov, and Alexander Khitun
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Magnetoresistance and magnetocaloric properties involving strong metamagnetic behavior in Fe-doped Ni45(Co1−xFex)5Mn36.6In13.4 alloys

L. Chen, F. X. Hu, J. Wang, L. F. Bao, J. R. Sun, B. G. Shen, J. H. Yin, and L. Q. Pan

Appl. Phys. Lett. 101, 012401 (2012); http://dx.doi.org/10.1063/1.4732525 (4 pages) | Cited 3 times

Online Publication Date: 2 July 2012

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Here, we report the co-substitution of Fe and Co for Ni atoms on metamagnetic behavior, martensitic transformation, and transport and magnetocaloric properties in Ni45(Co1−xFex)5Mn36.6In13.4 (x = 0∼0.05) alloys. It is found that the introduction of Fe atoms stabilizes martensitic phase and shifts martensitic temperature (TM) to higher temperature. Meanwhile, the Curie temperature TC of parent phase notably decreases. Upon Fe doping, the low magnetization of martensitic phase keeps nearly unchanged while the magnetization of parent phase slightly decreases. As a result, the Fe-doped samples maintain strong metamagnetic behavior and show great MR and MCE in an extended temperature range around room temperature. The hysteresis loss is reduced upon Fe-doping, which leads to an enhancement of effective RC by 15%.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.30.Kf Martensitic transformations

Magnetic and dielectric properties of Aurivillius phase Bi6Fe2Ti3O18 and the doped compounds

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

Appl. Phys. Lett. 101, 012402 (2012); http://dx.doi.org/10.1063/1.4732526 (4 pages) | Cited 1 time

Online Publication Date: 2 July 2012

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The magnetic and dielectric properties of Bi6Fe2Ti3O18, Bi6FeCoTi3O18, and Bi5LaFeCoTi3O18 are investigated. The room-temperature ferromagnetism is observed in the samples Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 compared with the paramagnetic behavior in Bi6Fe2Ti3O18 at room temperature. The ferromagnetism in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 can be ascribed to spin canting of the Fe-based and Co-based sublattices via the antisymmetric Dzyaloshinskii-Moriya interaction. The frequency-dependent behavior of the dielectric loss peak in Bi6FeCoTi3O18 and Bi5LaFeCoTi3O18 manifests itself a thermally activated relaxation process. The rather large activation energy (2.62 ± 0.11 eV for Bi6FeCoTi3O18 and 1.97 ± 0.07 eV for Bi5LaFeCoTi3O18) implies that the relaxation process is not due to the thermal motion of oxygen vacancies inside ceramics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
77.22.Gm Dielectric loss and relaxation
61.72.jd Vacancies
61.72.U- Doping and impurity implantation

Demonstration of magnetoelectric effect in ultrathin Cr2O3/Fe2O3 nano-oxide layer by training effect

Naoki Shimomura, Kazuya Sawada, Tomohiro Nozaki, Masaaki Doi, and Masashi Sahashi

Appl. Phys. Lett. 101, 012403 (2012); http://dx.doi.org/10.1063/1.4731274 (4 pages)

Online Publication Date: 3 July 2012

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We identified magnetoelectric effect in an ultrathin (Cr2O3/Fe2O3) nano-oxide layer structure (thickness ∼1 nm) formed on the surface of a Co0.9Fe0.1 metal layer by investigating the training effect as a function of sense current/bias voltage and its direction. A system-dependent constant κMR, which reflects changes in the surface spin, increases (decreases) with increasing current in the pinned (inverse pinned) direction. Furthermore, κMR varies for temperatures up to ∼200 K with current despite the extreme thinness, thus suggesting the current contributes to the surface spin changes. The results indicate the demonstration of the magnetoelectric effect in ultrathin Cr2O3.
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77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics

Spin-polarized scanning tunneling microscopy study of Mn/Co/Cu(001) using a bulk Fe ring probe

Chii-Bin Wu (吳啟彬), Jiaming Song (宋佳明), and Wolfgang Kuch

Appl. Phys. Lett. 101, 012404 (2012); http://dx.doi.org/10.1063/1.4733343 (5 pages)

Online Publication Date: 3 July 2012

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A bulk ring probe made of pure iron wire with diameter of 0.125 mm was prepared for spin-polarized scanning tunneling microscopy at room temperature in ultrahigh vacuum. The layerwise antiferromagnetic spin contrast of 2.8 atomic monolayers (ML) Mn/4.5 ML Co/Cu(001) observed with such a probe revealed a spin asymmetry of 14% and a signal-to-noise ratio of 1.8. Areas of reversed spin contrast on the same atomic layer of Mn were observed and attributed to the influence from underlying Co steps and islands. This demonstrates the simplicity of preparation and capability of such bulk Fe ring probes.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films

Long coherence time of spin qubits in 12C enriched polycrystalline chemical vapor deposition diamond

K. D. Jahnke, B. Naydenov, T. Teraji, S. Koizumi, T. Umeda, J. Isoya, and F. Jelezko

Appl. Phys. Lett. 101, 012405 (2012); http://dx.doi.org/10.1063/1.4731778 (5 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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Single defects in diamond and especially negatively charged nitrogen vacancy (NV) centers are very promising quantum systems with wide applications in physics and biology. It was shown that their coherence properties can be strongly improved by growing ultrapure diamond with low concentration of parasitic spins associated with nitrogen electron spins and nuclear spins related to 13C carbon isotope. Here we report a high quality 12C-enriched polycrystalline chemical vapor deposition diamond material with properties comparable with single crystals. We find single NVs in the grains of this material, which show extremely long electron spin coherence time T2>2ms.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
03.67.Lx Quantum computation architectures and implementations
61.72.jd Vacancies

Chemical diffusion: Another factor affecting the magnetoresistance ratio in Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junction

Y. Yang, W. X. Wang, Y. Yao, H. F. Liu, H. Naganuma, T. S. Sakul, X. F. Han, and R. C. Yu

Appl. Phys. Lett. 101, 012406 (2012); http://dx.doi.org/10.1063/1.4732463 (3 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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This letter investigates the microstructure and mean inner potential (MIP) profile of Ta/CoFeB/MgO/CoFeB/Ta magnetic tunnel junctions (MTJs) by high resolution transmission electron microscopy (HRTEM) and electron holography, respectively. The inconspicuous crystallization of MgO barrier is confirmed by HRTEM in the post-annealed sample at 250 °C. An obvious MIP difference is displayed in the Ta layers between the top and bottom of the MTJ, and elemental content difference of them is confirmed by energy dispersive spectroscopy. These results imply that the chemical diffusion can also give rise to a lower tunnel magnetoresistance ratio besides the inconspicuous crystallization of MgO barrier.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
66.30.Ny Chemical interdiffusion; diffusion barriers

Exchange bias and its thermal stability in ferromagnetic/antiferromagnetic antidot arrays

W. J. Gong, W. J. Yu, W. Liu, S. Guo, S. Ma, J. N. Feng, B. Li, and Z. D. Zhang

Appl. Phys. Lett. 101, 012407 (2012); http://dx.doi.org/10.1063/1.4733341 (4 pages) | Cited 2 times

Online Publication Date: 5 July 2012

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The exchange bias (EB) effect and its thermal stability in nanoscale Co/NiO antidot arrays and sheet films have been investigated. The EB field HE increases with increasing Co thickness (tCo) and reaches a maximum at tCo = 8 nm in the antidot arrays, whereas HE decreases with tCo in the sheet films. Compared with the sheet films, HE in the antidot arrays is either enhanced or decreased, depending on the thickness of the ferromagnetic Co layer, which is due to the three-dimensional effects in the antiferromagnetic NiO and ferromagnetic Co layers caused by the nanopores. A higher thermal stability is observed in the antidot arrays due to the out-of-plane anisotropy constant K1 of the misaligned antiferromagnetic magnetization component.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures

Domain-related origin of magnetic relaxation in compressively strained manganite thin films

S. R. Bakaul, B. F. Miao, W. Lin, W. Hu, A. David, H. F. Ding, and T. Wu

Appl. Phys. Lett. 101, 012408 (2012); http://dx.doi.org/10.1063/1.4733320 (4 pages) | Cited 4 times

Online Publication Date: 6 July 2012

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Magnetic relaxation is ubiquitous in magnetic materials, and elucidation of the underlying mechanisms is important for achieving reliable device operations. Here, we systematically investigate the magnetic relaxation in compressively strained La0.7Sr0.3MnO3 thin films. Upon the removal of external magnetic field, the slow time-dependent increase of in-plane magnetization is correlated with the break-up of magnetic domains and the emergence of additional domain walls, whereas a reduction of magnetization for the initial short period dominates the magnetic relaxation at lower temperatures in thinner films. These relaxation effects underline the importance of domain dynamics in the properties of magnetic thin films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.78.Fg Dynamics of domain structures
75.60.Ch Domain walls and domain structure

Magnetic properties of Co2C and Co3C nanoparticles and their assemblies

Kyler J. Carroll, Zachary J. Huba, Steven R. Spurgeon, Meichun Qian, Shiv N. Khanna, Daniel M. Hudgins, Mitra L. Taheri, and Everett E. Carpenter

Appl. Phys. Lett. 101, 012409 (2012); http://dx.doi.org/10.1063/1.4733321 (5 pages) | Cited 2 times

Online Publication Date: 6 July 2012

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Nano-composite material consisting of Co2C and Co3C nanoparticles has recently been shown to exhibit unusually large coercivities and energy products. Experimental studies that can delineate the properties of individual phases have been undertaken and provide information on how the coercivities and the energy product change with the size and composition of the nanoparticles. The studies indicate that while both phases are magnetic, the Co3C has higher magnetization and coercivity compared to Co2C. Through first principles electronic structure studies using a GGA+U functional, we provide insight on the role of C intercalation on enhancing the magnetic anisotropy of the individual phases.
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75.75.Lf Electronic structure of magnetic nanoparticles
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A tunable spin filter in periodic diluted magnetic semiconductor/semiconductor superlattices

Yong Guo, Fei-Ruo Shen, and Xin-Yi Chen

Appl. Phys. Lett. 101, 012410 (2012); http://dx.doi.org/10.1063/1.4733668 (4 pages)

Online Publication Date: 6 July 2012

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We propose a tunable spin filter based on periodic diluted magnetic semiconductor/semiconductor (DMS/S) superlattices. It is found that periodic DMS/S superlattices can filter high efficiently not only spin-up electrons but also spin-down ones over a broad range of incident energies. The positions and widths of spin-filtering bands can be manipulated by adjusting the parameters of the superlattices or the external magnetic field. It is also found that the defect layer within the system generally leads to a strong suppression of spin-dependent transmission and makes the superlattices filter single-energy electrons. The results obtained may lead to potential applications in the field of spintronics.
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85.35.Gv Single electron devices
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