jap banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

SECTION LISTING

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

1 Apr 2009

Volume 105, Issue 7, Articles (07xxxx)

Page 1 of 2 Pages Return to All Sections Next Page
back to top
RSS Feeds
back to top Magnetic Tunnel Junctions

Origin of asymmetry of tunneling conductance in CoFeB/MgO/CoFeB tunnel junction

Youngman Jang, Kisu Lee, Seungkyo Lee, Seungha Yoon, B. K. Cho, Y. J. Cho, K. W. Kim, and Kwang-seok Kim

J. Appl. Phys. 105, 07C901 (2009); http://dx.doi.org/10.1063/1.3055344 (3 pages) | Cited 1 time

Online Publication Date: 29 January 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigated the top and bottom interfaces of a CoFeB/MgO/CoFeB tunnel junction using transmission electron microscope (TEM) and x-ray photoemission spectroscopy (XPS) in order to understand the origin of the asymmetry of dI/dV in terms of bias polarity. It was found, from a TEM image, that there is no clear cut at the top interface, while the bottom interface has relatively clean boundary. Furthermore, XPS data show that more hydroxides were formed at the top interface than at the bottom interface. These indicate that the hydroxides would hinder the epitaxial crystallinity at the interface in CoFeB/MgO/CoFeB tunnel junctions. Therefore, it is most likely that the asymmetry of dI/dV is caused by the disappearance of minority Bloch state, which is closely correlated with the existence of hydroxides at the top interface of a CoFeB/MgO/CoFeB tunnel junction.
Show PACS
75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
79.60.Jv Interfaces; heterostructures; nanostructures

The band gap of ultrathin amorphous and well-ordered Al2O3 films on CoAl(100) measured by scanning tunneling spectroscopy

V. Rose and R. Franchy

J. Appl. Phys. 105, 07C902 (2009); http://dx.doi.org/10.1063/1.3056577 (3 pages) | Cited 5 times

Online Publication Date: 29 January 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The structural and electronic properties of ultrathin insulator Al2O3 films on CoAl(100) have been studied using a combination of scanning tunneling spectroscopy and microscopy. The analysis of the differential conductance yields a band gap of 2.6–2.9 eV for amorphous Al2O3. In the case of a well-ordered alumina film, the band gap is increased to 4.5 eV. On each of the oxide phases, the barrier height is to a large extent independent of local variations such as the surface corrugations or oxide steps.
Show PACS
71.23.-k Electronic structure of disordered solids
73.61.-r Electrical properties of specific thin films
68.60.-p Physical properties of thin films, nonelectronic
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Tunnel magnetoresistance effect in magnetic tunnel junctions using epitaxial Co2FeSi Heusler alloy electrode

Mikihiko Oogane, Masatsugu Shinano, Yuya Sakuraba, and Yasuo Ando

J. Appl. Phys. 105, 07C903 (2009); http://dx.doi.org/10.1063/1.3062814 (3 pages) | Cited 4 times

Online Publication Date: 30 January 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Magnetic tunnel junctions (MTJs) using epitaxially grown (100)-oriented and (110)-oriented Co2FeSi Heusler alloy bottom electrodes and amorphous Al-oxide barriers were fabricated. The tunnel magnetoresistance (TMR) ratios were 80% at 2 K and 48% at room temperature for the MTJ with the (100)-Co2FeSi bottom electrode. The MTJ with the (100)-Co2FeSi bottom electrode had a smaller TMR ratio than the MTJ with (100)-Co2FeSi electrode. The TMR ratio in MTJs with Co2FeSi electrode is smaller than that of a MTJ with Co2MnSi electrode. Tunnel conductance characteristics were investigated, revealing no half-metallic character in MTJs with Co2FeSi electrode in the conductance-voltage curves.
Show PACS
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Rectifying characteristics and transport behavior of the La0.9Hf0.1MnO3/Nb-doped SrTiO3 heterojunction

L. Wang and J. Gao

J. Appl. Phys. 105, 07C904 (2009); http://dx.doi.org/10.1063/1.3063670 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
La0.9Hf0.1MnO3 (LHMO) films were grown on (001) SrTiO3 (LHMO/STO) and (001) 0.7% Nd-doped STO (LHMO/STON) substrates under the same conditions by using pulsed laser deposition technique. The x-ray diffraction and rocking curve measurements demonstrated high epitaxy and good crystallinity obtained in our films. The curves of resistance versus temperature indicated that the as-grown LHMO film exhibits a paramagnetic-ferromagnetic transition at Curie temperature TC. The LHMO/STON heterojunctions exhibited asymmetric current-voltage characteristics similar to those of traditional semiconductor junctions and a typical temperature-dependent rectifying property in a wide temperature range from 20 to 300 K. The diffusion voltage (Vd) of the junction decreases almost linearly with the decrease in temperature. At a negative bias voltage, the dependence of the junction resistance (V/I) on temperature showed an insulator-metal transition in the vicinity of TC, as the voltage decreased from −2 to −7 V. The results were discussed by considering the band diagram of LHMO/STON junction and the tunneling current through the junction.
Show PACS
73.40.Ei Rectification
73.40.Gk Tunneling
73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
68.55.aj Insulators

Enhanced magneto-Coulomb effect in asymmetric ferromagnetic single electron transistors

M. B. A. Jalil, S. G. Tan, and M. J. Ma

J. Appl. Phys. 105, 07C905 (2009); http://dx.doi.org/10.1063/1.3055271 (3 pages)

Online Publication Date: 2 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate the magneto-Coulomb (MC) effect in a ferromagnetic single electron tunneling transistor (FM-SETT), with asymmetric junction resistances and FM electrodes. The MC effect enables the conductance of the FM-SETT by an applied magnetic B-field in addition to the usual gate-bias modulation. Under optimal biasing of the asymmetric FM-SETT near the sawtooth edge of its gate oscillation, the sensitivity γB = dI/dB can be enhanced by a factor math, where α = R1/R2 denotes the junction resistance asymmetry. The enhanced B-field modulation is, however, susceptible to thermal smearing effects. Finally, an asymmetry in the magnetic properties of the FM leads results in a complex magnetoconductance response, with distinct conductance states.
Show PACS
85.35.Gv Single electron devices
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Experimental study of time-dependent switching current in MgO based magnetic tunnel junction

Wenzhong Zhu, Xiaobin Wang, and Dimitar Dimitrov

J. Appl. Phys. 105, 07C906 (2009); http://dx.doi.org/10.1063/1.3056578 (3 pages) | Cited 1 time

Online Publication Date: 2 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Spin-transfer induced magnetization switching in MgO based magnetic tunnel junction has been studied at a wide time range. We observed a discrepancy between experimental data and thermal activation model prediction on switching current mean and variation as a function of pulse width. The discrepancy is mainly due to Joule heating and the theoretical limitation of the analytical model. It can be overcome by using the notion of an effective temperature. We also compare the fitting result of the averaged switching current versus pulse width to that of switching current probability at each individual pulse width. Finally, we present the identically switching currents measured by both finite pulse width and current sweep rate schemes.
Show PACS
75.47.De Giant magnetoresistance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Pq Other materials

Manganite-based magnetic tunnel junction with piezoelectric barrier

R. Mundle, R. B. Konda, O. Bamiduro, O. Yasar, F. Williams, M. Bahoura, A. K. Pradhan, D. R. Sahu, J.-L. Huang, and D. E. Nikonov

J. Appl. Phys. 105, 07C907 (2009); http://dx.doi.org/10.1063/1.3054380 (3 pages)

Online Publication Date: 3 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report on the fabrication and tunneling characteristics of pulsed-laser deposited LaSrMnO (LSMO)/PbZrTiO(PZT)/LSMO/SrTiO3 multilayers, using PZT layer as a tunnel barrier. The trilayer films show magnetic onset at about 360 K with ferromagnetic hysteresis at room temperature. The microscopic studies show that the effective barrier thickness is reduced due to the presence of defects in the barrier region. Our results suggest that the asymmetric deformation of the barrier potential profile induced by the ferroelectric polarization of PZT influences the tunneling characteristics and can be used for electrically controlled readout in quantum-computing schemes.
Show PACS
75.47.Lx Magnetic oxides
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Dd Nonmetallic ferromagnetic materials

Phenomenological analysis for spin-Seebeck effect in metallic magnets

K. Uchida, S. Takahashi, J. Ieda, K. Harii, K. Ikeda, W. Koshibae, S. Maekawa, and E. Saitoh

J. Appl. Phys. 105, 07C908 (2009); http://dx.doi.org/10.1063/1.3056581 (3 pages) | Cited 9 times

Online Publication Date: 3 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The two-band spin diffusion model has been extended to nonequilibrium systems to investigate the recently discovered spin-Seebeck effect in a ferromagnetic metal. A calculation using this model well reproduces the experimental results for a Ni81Fe19 film; the gradient of electrochemical potential is different between up- and down-spin bands affected by a temperature difference between the ends of the film.
Show PACS
72.15.Jf Thermoelectric and thermomagnetic effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
65.40.gk Electrochemical properties

Manipulating the crystallographic properties of Fe/MgO/Fe trilayers

Xiaoxi Liu, Hidetoshi Matsuoka, Hong Zhang, and Akimitsu Morisako

J. Appl. Phys. 105, 07C909 (2009); http://dx.doi.org/10.1063/1.3068420 (3 pages)

Online Publication Date: 5 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An ultrathin MgO/Fe seed layer was introduced to manipulate the crystal orientation and crystallinity of Fe/MgO/Fe trilayers. The crystallographic properties and magnetic properties of the trilayer are investigated. It is concluded that the texture of the MgO layer is strongly dependent on the texture of the Fe layer. (001) oriented Fe layer can assist the growth of (001) oriented MgO barrier upon annealing. A 0.5 nm MgO seed layer can introduce (001) orientation in the following Fe layer. It is also found that the crystal orientation of the Fe/MgO/Fe trilayer is independent of the initial Fe seed layer thickness. However, the crystallinity of both the Fe layer and the MgO layer is dependent on the initial Fe seed layer.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
75.60.Nt Magnetic annealing and temperature-hysteresis effects
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Theoretical study on the stability of magnetic structures in the surface and interfaces of Heusler alloys, Co2MnAl and Co2MnSi

A. Sakuma, Y. Toga, and H. Tsuchiura

J. Appl. Phys. 105, 07C910 (2009); http://dx.doi.org/10.1063/1.3058622 (3 pages) | Cited 16 times

Online Publication Date: 5 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We carry out the first principles calculations for bulk, surface, and bilayer system of Heusler alloys Co2MnAl and Co2MnSi. In the bulk system, the Mn moments feel much larger exchange (molecular) field than the Co moments. In the surface density of states of Co, the half-metallicity disappears in both systems, even though the magnetic moments are enhanced due to localization of d-states. The exchange constant of the surface Co is much reduced in Co2MnSi. In the bilayer system with MgO, both the magnetic moments and exchange constants of Co atoms at the interface are remarkably decreased. We suppose that such instability of Co moments at the interface is responsible for the strong dependences of the magnetoresistance ratio on both the temperature and bias voltage, which was measured in the magnetic tunnel junction of Co2MnAl(Si)/MgO.
Show PACS
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Rf Surface magnetism
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions

Fabrication of MgO-based magnetic tunnel junctions with CoCrPt perpendicularly magnetized electrodes

Daisuke Watanabe, Shigemi Mizukami, Mikihiko Oogane, Hiroshi Naganuma, Yasuo Ando, and Terunobu Miyazaki

J. Appl. Phys. 105, 07C911 (2009); http://dx.doi.org/10.1063/1.3062816 (3 pages) | Cited 7 times

Online Publication Date: 6 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The applicability of perpendicularly magnetized CoCrPt films to the MgO-based magnetic tunnel junctions (MTJs) was investigated. For this study, CoCrPt films deposited on the Ru buffer exhibited hcp(0002)-oriented growth by sputtering method using the low substrate temperature of 250 °C, low saturation magnetization of around 360 emu/cm3, and high magnetic anisotropy field of 6 kOe, which is sufficient to retain the thermal stability of the magnetization direction. The MgO-based MTJs with a synthetic ferrimagnetlike structure were fabricated: CoFe was coupled magnetically with CoCrPt through the thin Ru layer. Transport properties with a magnetic field applied perpendicular to the film plane revealed a tunnel magnetoresistance ratio of about 6% at room temperature.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.30.Gw Magnetic anisotropy

Spin polarized transport in an asymmetric ferromagnetic/quantum dot/ferromagnetic system

M. J. Ma, M. B. A. Jalil, and S. G. Tan

J. Appl. Phys. 105, 07C912 (2009); http://dx.doi.org/10.1063/1.3063078 (3 pages) | Cited 3 times

Online Publication Date: 9 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate the tunnel magnetoresistance (TMR) of the double barrier magnetic tunnel junction, where a quantum dot (QD) with discrete electron and hole energy levels is sandwiched between ferromagnetic leads. The effects of the symmetry of the coupling between the leads and the dot on both the TMR and spin accumulation (SA) are studied for voltage ranges corresponding to the QD’s single and double occupancies. When the QD is singly occupied, both the TMR and SA assume at their minimum values for symmetrical junctions with identical coupling strengths. For the doubly occupied QD, the opposite occurs with the highest TMR and SA being observed for symmetrical junctions with identical coupling strengths. The TMR is found to be strongly correlated with the spin accumulation in the QD.
Show PACS
73.63.Kv Quantum dots
72.25.-b Spin polarized transport
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Measurement of spin current using spin relaxation modulation induced by spin injection

K. Ando, H. Nakayama, Y. Kajiwara, D. Kikuchi, K. Sasage, K. Uchida, K. Ikeda, and E. Saitoh

J. Appl. Phys. 105, 07C913 (2009); http://dx.doi.org/10.1063/1.3063081 (3 pages) | Cited 7 times

Online Publication Date: 9 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ferromagnetic resonance spectra affected by the spin-Hall effect (SHE) and the spin torque were measured for a Ni81Fe19/Pd bilayer film. A charge current applied to the Pd layer is converted into a spin current via SHE, which propagates into the Ni81Fe19 layer through the interface as a spin current. The spin current exerts the torque on the magnetization, modulating the spin relaxation in the Ni81Fe19 layer. By monitoring the spin relaxation modulation, we estimated the spin current amplitude injected into the Ni81Fe19 layer. This method enables the quantitative measurement of spin currents without assuming any microscopic material parameters.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Ba Spin polarized transport in metals
72.25.Hg Electrical injection of spin polarized carriers
72.25.Rb Spin relaxation and scattering
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Pressure sensor based on magnetic tunnel junctions

D. Meyners, T. von Hofe, M. Vieth, M. Rührig, S. Schmitt, and E. Quandt

J. Appl. Phys. 105, 07C914 (2009); http://dx.doi.org/10.1063/1.3063662 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Magnetic tunnel junctions consisting of a magnetically stable reference layer plus a magnetostrictive sense layer separated by an insulating MgO tunnel barrier have been fabricated and characterized particularly with regard to their application as strain and pressure sensors. Using a four-point-bending apparatus it has been proven that the application of mechanical stress causes the magnetization of the sense layer to rotate, while simultaneously the resistance of the strained magnetic tunnel junction changes. So far gauge factors up to 840 have been reached in resistance versus strain measurements. It has been demonstrated that these magnetic tunnel junctions also work as highly sensitive pressure gauges when placed on bulk or surface micromachined membranes.
Show PACS
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction

Enhancement of tunneling magnetoresistance by optimization of capping layer thicknesses in CoFeB/MgO/CoFeB magnetic tunnel junctions

Philip W. T. Pong and William F. Egelhoff

J. Appl. Phys. 105, 07C915 (2009); http://dx.doi.org/10.1063/1.3063664 (3 pages) | Cited 4 times

Online Publication Date: 9 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The main focus of improving the tunneling magnetoresistance (TMR) of magnetic tunnel junctions (MTJs) has been on optimizing the structure and thickness of the MgO barrier layer [ Moriyama et al., Appl. Phys. Lett. 88, 222503 (2006) ; Yuasa et al., Nat. Mater. 3, 868 (2004) ]. However, in this paper, we found that the thicknesses of the capping layers also play an important role in TMR. We studied the influence of the capping layers above the CoFeB/MgO/CoFeB. It was intuitively believed that these capping layers did not affect the TMR because they were deposited after the critical CoFeB/MgO/CoFeB structure. Surprisingly, we found that the thicknesses of the capping Ta and Ru layers have significant influence on the TMR. The stress or strain applied onto the MgO barrier by these capping layers appear to be responsible. The results in this paper shed light on optimizing TMR of MgO MTJs.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Ns Metal-nonmetal contacts
68.65.Ac Multilayers
68.55.jd Thickness
75.47.Pq Other materials

Spin polarization of Co–Fe alloys estimated by point contact Andreev reflection and tunneling magnetoresistance

S. V. Karthik, T. M. Nakatani, A. Rajanikanth, Y. K. Takahashi, and K. Hono

J. Appl. Phys. 105, 07C916 (2009); http://dx.doi.org/10.1063/1.3058699 (3 pages) | Cited 3 times

Online Publication Date: 9 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The compositional dependence on spin polarization of Co100−xFex alloys has been studied by point contact Andreev reflection (PCAR) and tunneling magnetoresistance (TMR) measurements. The intrinsic spin polarization for bcc Co75Fe25 alloy is P = 0.58±0.03  at 4.2 K contrary to the pure Fe (P = 0.46±0.03) and Co (P = 0.45±0.03). The tunneling spin polarization values of Co75Fe25 (110) textured polycrystalline electrode and (001) epitaxially grown electrode was estimated to be PT = 0.5±0.01  and PT = 0.57±0.01  at 8 K from the TMR ratios using Julliere’s model for the MTJs prepared on oxidized Si and MgO (001) substrates. The spin polarization obtained from the tunneling junctions and PCAR experiments have been discussed.
Show PACS
72.25.Ba Spin polarized transport in metals
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys

Thickness dependence of ferromagnetic- and metal-insulator transition in thin EuO films

Martina Müller, Guo-Xing Miao, and Jagadeesh S. Moodera

J. Appl. Phys. 105, 07C917 (2009); http://dx.doi.org/10.1063/1.3063673 (3 pages) | Cited 6 times

Online Publication Date: 13 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have studied the thickness dependence of the magnetic and transport properties of thin EuO films in the range of 10–60 Å. The ferromagnetic phase transition shows a systematic dependence of the critical temperature Tc with decreasing EuO film thickness. This behavior has been attributed to the interface layers which play a major role by reducing the number of average magnetic neighbors; we find the effect of interface intermixing becoming relevant in low thickness regime. In addition, we could identify a clear dependence of the onset of the metal-to-insulator transition on the ferromagnetic ordering of thin EuO films.
Show PACS
71.30.+h Metal-insulator transitions and other electronic transitions
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.61.Ng Insulators

Magneto- and electroresistance of La0.7Sr0.3MnO3/Nb(1.0%):SrTiO3 junctions

Y. F. Chen and M. Ziese

J. Appl. Phys. 105, 07C918 (2009); http://dx.doi.org/10.1063/1.3068421 (3 pages)

Online Publication Date: 17 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The current-voltage characteristics and magnetotransport properties of La0.7Sr0.3MnO3/Nb(1.0%):SrTiO3 junctions under various currents ranging from 10−6 to 10−3 A and different temperatures ranging from 10 to 300 K were investigated. The current-voltage curves exhibit rectifying behavior. The resistance, magnetoresistance, and electroresistance of the junctions are strongly dependent on bias-current direction, current, temperature, and magnetic field. A detailed analysis of the conductance-voltage curves showed that quantum mechanical tunneling was the dominating transport mechanism.
Show PACS
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.40.-c Electronic transport in interface structures
73.40.Gk Tunneling

Spin-polarized tunneling through a ferromagnetic insulator

M. Kok, J. N. Beukers, and A. Brinkman

J. Appl. Phys. 105, 07C919 (2009); http://dx.doi.org/10.1063/1.3068643 (3 pages)

Online Publication Date: 17 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The polarization of the tunnel conductance of spin-selective ferromagnetic insulators is modeled, providing a generalized concept of polarization including both the effects of electrode and barrier polarization. The polarization model is extended to take additional non-spin-polarizing insulating layers into account. These additional tunnel barriers are found to have a large effect on the tunneling polarization, both positively and negatively, depending on the material parameters. The model is applied to spin-filter devices containing the promising spin filter material EuO.
Show PACS
72.25.-b Spin polarized transport
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.50.Dd Nonmetallic ferromagnetic materials

Tunnel magnetoresistance effect in double magnetic tunnel junctions using half-metallic Heusler alloy electrodes

Yusuke Ohdaira, Mikihiko Oogane, and Yasuo Ando

J. Appl. Phys. 105, 07C920 (2009); http://dx.doi.org/10.1063/1.3072023 (2 pages) | Cited 2 times

Online Publication Date: 19 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Double magnetic tunnel junctions (DMTJs) using half-metallic Co2MnSi Heusler alloy electrodes were fabricated. Their tunnel magnetoresistance (TMR) effects were then investigated. Large TMR ratios were observed as 25% at room temperature and as 320% at 6 K. The bias voltage dependence of tunnel conductance suggests a half-metallic nature of the Co2MnSi electrode. These results show that high-quality DMTJ with half-metallic Heusler alloy electrodes was fabricated and that the DMTJ exhibited the expected performance.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Gk Tunneling
75.47.Np Metals and alloys

Performance of shape-varying magnetic tunneling junction for high-speed magnetic random access memory cells

H. Honjo, S. Fukami, R. Nebashi, T. Suzuki, N. Ishiwata, S. Miura, and T. Sugibayashi

J. Appl. Phys. 105, 07C921 (2009); http://dx.doi.org/10.1063/1.3062825 (3 pages) | Cited 2 times

Online Publication Date: 20 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have developed a shape-varying magnetic tunneling junction (MTJ) (SVM) which has a high MR ratio and low write current for use in high-speed magnetic random access memory (MRAM) cells. Combining NiFe that has low anisotropy to CoFeB which has high anisotropy through the nonmagnetic layer by interlayer exchange coupling (synthetic ferromagnetic coupling free layer: SFF), the anisotropy of SFF was reduced much more than that of CoFeB, and the MR ratio was improved much more than that of NiFe. The switching magnetic field (Hsw) of SFF was reduced as the thickness of NiFe increased. The Hsw of SFF for 0.24×0.48 μm2 MTJ was 30 Oe when the thickness of CoFeB was 1.5 nm and that of NiFe was 3.0 nm. Furthermore Hsw was reduced to 18 Oe by varying the shape of the MTJ of NiFe to 0.48×0.48 μm2; the shape of the MTJ of CoFeB was not changed (0.24×0.48 μm2). Combining the SVM and a write-line-inserted structure, we obtained a write current of 0.9 mA and an MR ratio of 140%. The Hsw was 40 Oe and its thermal stability factor was 82. These properties are sufficient for operating MRAMs over 500 MHz.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Tunable coupling in CrO2 via RuO2 layers

H. Sims and W. H. Butler

J. Appl. Phys. 105, 07C922 (2009); http://dx.doi.org/10.1063/1.3068417 (3 pages) | Cited 1 time

Online Publication Date: 20 February 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Theoretical calculations of the magnetic structure of CrO2–RuO2 interfaces and multilayer structures are presented. The antiferromagnetic coupling between Ru ions and neighboring Cr ions in such interfaces is explored both for contiguous layers of CrO2 and RuO2 and for Cr layers separated by RuO2 spacers. The Fermi surface of the RuO2 spacer is calculated and kF100 is utilized to determine the oscillatory behavior of the interlayer exchange coupling as described by Bruno [ Phys. Rev. B 52, 411 (1995) ]. The first-principles calculations are found to be qualitatively consistent with the Bruno theory, which suggests that CrO2–RuO2 layered structures could be designed to give the desired magnetic ordering between CrO2 layers given sufficient control over the composition and roughness of the deposited material.
Show PACS
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.)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
75.50.Ee Antiferromagnetics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.30.Et Exchange and superexchange interactions

Spin-dependent tunneling through NiFe nanoparticles

K. J. Dempsey, A. T. Hindmarch, C. H. Marrows, H.-X. Wei, Q.-H. Qin, Z.-C. Wen, and X.-F. Han

J. Appl. Phys. 105, 07C923 (2009); http://dx.doi.org/10.1063/1.3072721 (3 pages) | Cited 3 times

Online Publication Date: 3 March 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Double magnetic tunnel junctions (DMTJs) have been fabricated using alumina barriers with NiFe particles ( ∼ 1.8 nm) embedded within. The junctions exhibit spin-dependent transport properties and Coulomb blockade effects. We study differences between control samples and the DMTJs; specifically I-V characteristics and tunnel magnetoresistance (TMR) versus bias voltage characteristics. Clear differences in the systems are evident: the DMTJ with NiFe particles shows a marked peak in TMR at low bias, whereas the dependence of TMR on bias is much weaker for the control MTJ without embedded particles. Hence the TMR at low bias is enhanced by the Coulomb blockade effects.
Show PACS
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.47.Pq Other materials
73.23.Hk Coulomb blockade; single-electron tunneling

Inelastic tunneling spectra of MgO barrier magnetic tunneling junctions showing large magnon contribution

Do Bang, T. Nozaki, D. D. Djayaprawira, M. Shiraishi, Y. Suzuki, A. Fukushima, H. Kubota, T. Nagahama, S. Yuasa, H. Maehara, K. Tsunekawa, Y. Nagamine, N. Watanabe, and H. Itoh

J. Appl. Phys. 105, 07C924 (2009); http://dx.doi.org/10.1063/1.3063674 (3 pages) | Cited 3 times

Online Publication Date: 9 March 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigated bias-voltage and temperature dependence of conductivity arising from the magnon contribution in MgO-based magnetic tunneling junctions (MTJs) with different ferromagnetic electrodes. Second derivative conductance curves showed broad peak structure, which extends from 5 to 200 mV, accompanied by additional peaks at around 23, 54, and 85 mV. The peak intensities were larger for antiparallel configuration than for parallel configuration except that at 85 mV. This difference in the peak intensity was observed to be larger for the MTJs having higher tunneling magnetoresistance ratio, indicating a magnetic origin of these peaks. Abrupt increase in the second derivative conductance at very low biasing voltage in the antiparallel configuration suggests the important role of the surface magnon excitation.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Pq Other materials
85.75.Mm Spin polarized resonant tunnel junctions

Tunnel magnetoresistance for magnetic tunnel junctions with Co2FeAl0.5Si0.5 full Heusler electrodes fabricated by molecular beam epitaxy system

N. Tezuka, N. Ikeda, F. Mitsuhashi, and S. Sugimoto

J. Appl. Phys. 105, 07C925 (2009); http://dx.doi.org/10.1063/1.3072448 (3 pages) | Cited 3 times

Online Publication Date: 9 March 2009

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The authors fabricated Co2FeAl0.5Si0.5 full Heusler alloy thin films by using a molecular beam epitaxy system on Cr buffered MgO single crystal substrates and investigated their structural and magnetic properties. It was revealed that Co2FeAl0.5Si0.5 films formed ordered L21 and B2 structures after annealing above 500 °C and below 400 °C, respectively. Then magnetic tunnel junctions with these electrodes and Al-oxide or MgO barriers were also fabricated, and the bias voltage dependence of tunnel magnetoresistance ratio was investigated. It was found that the tunnel magnetoresistance ratio of the junction with Al-oxide barrier has a larger asymmetric bias voltage dependence compared with that with MgO barrier, and the negative tunnel magnetoresistance ratio at high negative bias voltage is observed for both junctions.
Show PACS
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth
Page 1 of 2 Pages Return to All Sections Next Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close