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3 Dec 2012

Volume 101, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 101, 233101 (2012); http://dx.doi.org/10.1063/1.4749281 (3 pages)

S. A. Studenikin, J. Thorgrimson, G. C. Aers, A. Kam, P. Zawadzki, Z. R. Wasilewski, A. Bogan, and A. S. Sachrajda
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Magnetotransport properties of dual MgO barrier magnetic tunnel junctions consisting of CoFeB/FeNiSiB/CoFeB free layers

D. K. Kim, J. U. Cho, B. S. Chun, K. H. Shin, K. J. Lee, M. Tsunoda, M. Takahashi, and Y. K. Kim

Appl. Phys. Lett. 101, 232401 (2012); http://dx.doi.org/10.1063/1.4768931 (4 pages)

Online Publication Date: 3 December 2012

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We report the transport properties of a dual MgO barrier magnetic tunnel junction (DMTJ) where a FeNiSiB layer was inserted in a CoFeB free layer. Upon post-deposition annealing at 330 °C, the tunneling magnetoresistance (TMR) ratio of the DMTJ with a hybrid CoFeB/FeNiSiB/CoFeB free layer reached 195% which is higher than the TMR ratio of 121% from the DMTJ with the single CoFeB free layer. The bias voltage dependence profile was more symmetric for the hybrid case. Boron depth profiling result suggests that the FeNiSiB layer dragged boron atoms more to it rather than letting them diffuse toward CoFeB/MgO interfaces, resulting in improved MTJ performances.
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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

Exchange-biased magnetic tunnel junctions with antiferromagnetic ε-Mn3Ga

H. Kurt, K. Rode, H. Tokuc, P. Stamenov, M. Venkatesan, and J. M. D. Coey

Appl. Phys. Lett. 101, 232402 (2012); http://dx.doi.org/10.1063/1.4768941 (4 pages)

Online Publication Date: 3 December 2012

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Oriented c-axis films of the hexagonal triangular antiferromagnetic ε-Mn3Ga have been used in bottom-pinned synthetic antiferromagnet magnetic tunnel junctions with MgO barriers, which show up to 150% tunneling magnetoresistance at room temperature. Exchange bias fields as high as 150 mT can be achieved for samples field-cooled from 100 °C. Thin films of the antiferromagnet have a Néel temperature in excess of 650 K and provide an interface exchange energy with CoFe of 0.09 mJ m−2. They show an isotropic uncompensated magnetization of Ms = 48 kA m−1, with a coercivity μ0Hc > 3 T.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Depth-selective electronic and magnetic properties of a Co2MnSi tunnel magneto-resistance electrode at a MgO tunnel barrier

B. Krumme, D. Ebke, C. Weis, S. I. Makarov, A. Warland, A. Hütten, and H. Wende

Appl. Phys. Lett. 101, 232403 (2012); http://dx.doi.org/10.1063/1.4769180 (4 pages)

Online Publication Date: 3 December 2012

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We investigated the electronic structure as well as the magnetic properties of a Co2MnSi film on MgO(100) element-specifically at the interface to a MgO tunnel barrier by means of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The electronic structure of the Co atoms as a function of the capping layer thickness remained unchanged, whereas the XA spectra of Mn indicate an increase of the unoccupied d states. The experimental findings are consistent with the interfacial structure proposed in the work by B. Hülsen et al. [Phys. Rev. Lett. 103, 046802 (2009)], where a MnSi layer is present at the interface to the MgO with oxygen atoms at top positions in the first MgO layer.
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75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
72.20.My Galvanomagnetic and other magnetotransport effects

Effect of the magnetic domain structure in the ferromagnetic contact on spin accumulation in silicon

Y. Ando, S. Yamada, K. Kasahara, K. Sawano, M. Miyao, and K. Hamaya

Appl. Phys. Lett. 101, 232404 (2012); http://dx.doi.org/10.1063/1.4769221 (4 pages) | Cited 1 time

Online Publication Date: 4 December 2012

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We show a marked effect of magnetic domain structure in an epitaxial CoFe contact on spin accumulation signals in Si devices detected by three-terminal Hanle effect measurements. Experimental results indicate that magnetic domain structures cause large discrepancies in the estimation of spin lifetime and bias-current dependence of the spin accumulation signal. By introducing the domain walls in CoFe contact, spin accumulation signals are reduced, which is caused by the lateral spin transport in the Si channel. Thus, to understand precisely the physical properties of Si spintronic devices, it is important to take into account the control of magnetic domain structure in the contacts.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.76.+j Spin transport effects
72.25.Mk Spin transport through interfaces
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Asymmetric hysteresis loops and its dependence on magnetic anisotropy in exchange biased Co/CoO core-shell nanoparticles

Sayan Chandra, Hafsa Khurshid, Manh-Huong Phan, and Hariharan Srikanth

Appl. Phys. Lett. 101, 232405 (2012); http://dx.doi.org/10.1063/1.4769350 (5 pages)

Online Publication Date: 4 December 2012

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The origin of asymmetry in field cooled (FC) hysteresis loops exhibiting exchange bias (EB) is investigated by studying the static and dynamic magnetic properties of core-shell Co/CoO nanoparticles. Two distinct freezing temperatures coresponding to the core (Tf-cr ∼ 190 K) and the shell moments (Tf-sh ∼ 95 K) are obtained from the energy barrier distribution. The FC loops are symmetric in the temperature range Tf-sh ≤ T ≤ Tf-cr, however, asymmetry in hysteresis is observed immediately below Tf-sh. These intriguing features are also probed by radio frequency transverse susceptibility (TS) experiments. We show that the first anisotropy fields obtained from the demagnetization and return curves of field cooled TS measurement, shift along the negative field axis and strikingly resemble the temperature dependence of EB. Field cooled TS measurements reveal the effect of competing Zeeman and anisotropy energy above and below Tf-sh to account for the development of asymmetry. Our study indicates that asymmetry in FC hysteresis loops is intrinsic to core-shell nanoparticles and develops only below the freezing temperature of the shell due to enhanced magnetic anisotropy.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Jn Dynamics of magnetic nanoparticles
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Sg Magnetocaloric effect, magnetic cooling

Microwave reflection imaging using a magnetic tunnel junction based spintronic microwave sensor

L. Fu, Z. X. Cao, S. Hemour, K. Wu, D. Houssameddine, W. Lu, S. Pistorius, Y. S. Gui, and C.-M. Hu

Appl. Phys. Lett. 101, 232406 (2012); http://dx.doi.org/10.1063/1.4769837 (4 pages)

Online Publication Date: 5 December 2012

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A far-field microwave imaging technique has been developed using a spintronic sensor based on a magnetic tunnel junction (MTJ). Such a sensor can directly rectify a microwave field into a dc voltage signal using the Seebeck effect. Thanks to the high conversion efficiency of the microwave rectification in MTJs, the microwave power sensitivity of the spintronic sensor is on the order of 1–10 mV/mW. This high sensitivity allows the sensor to directly measure the coherent spatial scattered microwave field distribution, which gives it the ability to non-destructively detect hidden objects down to a few wavelengths in size.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
07.55.-w Magnetic instruments and components

Room-temperature ferromagnetism induced and controlled by electric field in BaNbO3 films

Ensi Cao, Hongwei Qin, Yongjia Zhang, and Jifan Hu

Appl. Phys. Lett. 101, 232407 (2012); http://dx.doi.org/10.1063/1.4769901 (4 pages)

Online Publication Date: 6 December 2012

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The application of electric field can induce the room-temperature ferromagnetism (FM) in paramagnetic BaNbO3 films on the conductive Nb:SrTiO3 substrate. The electric field-induced ferromagnetism in BaNbO3 is connected with the hybridization between electrons of Nb-4d1 and the injected electrons from the conductive substrate, possibly leading to large density of states at the Fermi level and satisfying the Stoner criterion for ferromagnetism. By application of electric field in forward and reversed directions, the magnetization of electric field-induced FM can be adjusted in some extent. The application of electric field can also enhance the oxygen vacancies-induced room-temperature ferromagnetism in BaNbO3 films.
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75.70.Ak Magnetic properties of monolayers and thin films
61.72.jd Vacancies
71.20.Ps Other inorganic compounds
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Abnormal substrate temperature dependent out-of-plane anisotropy in FeCoNbB amorphous films

Youxing Yu, Youran Yang, Yijiao Shan, and Xiaofang Bi

Appl. Phys. Lett. 101, 232408 (2012); http://dx.doi.org/10.1063/1.4767952 (4 pages)

Online Publication Date: 7 December 2012

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Out-of-plane magnetic anisotropy (OMA) of FeCoNbB amorphous films has been studied. The OMA is abnormally enhanced by elevating the substrate temperature from room-temperature to 500 °C, being much different from most soft-magnetic amorphous films. Furthermore, the films show a slightly decay in the OMA when annealed at a temperature lower than the respective deposition temperature. But when annealed at a temperature 50 °C higher than the respective deposition temperature, the OMA suddenly disappears. Such results indicate a distinguishing mechanism of non-magnetoelastic-anisotropy dominated OMA. A model of co-effects of magnetoelastic anisotropy and microshape anisotropy is proposed.
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75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.15.Cd Deposition by sputtering
68.55.at Other materials
75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
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