230% room-temperature magnetoresistance in CoFeB∕MgO∕CoFeB magnetic tunnel junctions

Djayaprawira, D.D.; Tsunekawa, K.; Nagai, M.; Maehara, H.; Yamagata, S.; Watanabe, Naoki; Yuasa, Shinji; Ando, Koji

doi:10.1063/1.1871344

Cited by 906 publications

(498 citation statements)

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“…While the cubic L2 1 Heusler alloys are virtually isotropic, their tetragonal cousins can display very high uniaxial magnetic anisotropy coupled with tunable saturation magnetization and high spin polarization. This is especially true in the case of D0 22 Mn 3 Ga. [15][16][17][18] Thin films of this material exhibit high, perpendicular, uniaxial anisotropy and grow with ease on both MgO and SrTiO 3 substrates, as well as a number of lattice matched seed layers like Cr and Pt.…”

Section: Introductionmentioning

confidence: 99%

“…At present, the most often used material combination for achieving high on-off ratios (magnetoresistance, MR) is the CoFeB/MgO/CoFeB trilayer. 1 These tunnel junctions can provide MR above 200% at room temperature thanks not solely to the spin polarization of the electrodes, but also to the k-dependent transmission of the CoFe electron wave through the MgO barrier. 2,3 There are, however, several improvements possible to this solution.…”

Section: Introductionmentioning

confidence: 99%

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Site-specific order and magnetism in tetragonal Mn3Ga thin films

et al. 2013

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Mn 3 Ga bulk material and thin films deposited on several different substrates have been investigated using x-ray and neutron diffraction, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and electronic structure calculations using density-functional theory with the aim of determining the atomic site occupancy, magnetic moments, and magnetic structure of this tetragonal D0 22 -structure compound. The Mn 3 Ga has close to ideal site occupancy, with Ga on 2a sites and Mn on 2b and 4d sites. The magnetic structure is basically ferrimagnetic, with the larger Mn moment of about 3 μ B on the 2b site, which is coordinated by 8 Mn 4d and 4 Ga, and the smaller one on the 4d site, which is coordinated by 4 Mn 2b, 4 Ga, and 4 Mn 4d. The Mn d-band occupancy is close to 5 on both sites, and the orbital moments are small, <0.2 μ B . The material nevertheless exhibits substantial uniaxial anisotropy, K u = 1.0 MJ m −3 , which originates from the 4d site. The 2b site has hard axis anisotropy, which together with an oscillatory exchange coupling from the first and second nearest neighbors, leads to a soft component of the magnetization in the c plane, coexisting with c-axis hysteresis loops exhibiting coercivity of up to 1.2 T, and magnetization in the range 110-220 kA m −1 at room temperature, depending on preparation conditions. Tetragonal Mn 2 Ga films behave similarly. Manganese is lost from both sites, but the films have substantially larger magnetization (480 kA m −1 ) and anisotropy constant (2.35 MJ m −3 ) than Mn 3 Ga.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Site-specific order and magnetism in tetragonal Mn3Ga thin films

et al. 2013

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“…1a) were used to provide very large magnetoresistance 11,14 . Such MTJs are now useful as data storage cells in magnetic random-access memories (M-RAMs) and as magnetic-field sensors in magnetic hard disk drives [11][12][13] . The MTJs with a layer structure of Ir-Mn/Co-Fe/Ru/Co 60 Fe 20 B 20 /MgO/Co 60 Fe 20 B 20 were prepared on a MgO substrate using an ultrahigh-vacuum sputtering system (C-7100; Canon ANELVA).…”

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confidence: 99%

“…Yet, such measurements are crucial to refining our understanding of the mechanisms responsible and the theories that describe them 9,10 . To address this, we present quantitative experimental measurements of the spin torque in MgO-based magnetic tunnel junctions [11][12][13][14] for a wide range of bias currents covering the switching currents. The results verify the occurrence of two different spin-torque regimes with different bias dependences that agree well with theoretical predictions 10 .…”

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Quantitative measurement of voltage dependence of spin-transfer torque in MgO-based magnetic tunnel junctions

et al. 2007

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When an electric current passes from one ferromagnetic layer via a non-magnetic layer into another ferromagnetic layer, the spin polarization and subsequent rotation of this current can induce a transfer of angular momentum that exerts a torque on the second ferromagnetic layer 1-4 . This provides a potentially useful method to reverse 3,5-7 and oscillate 8 the magnetic momenta in nanoscale magnetic structures. Owing to the large current densities required to observe spin-torqueinduced magnetization switching and microwave emission (∼10 7 A cm −2 ), accurately measuring the strength, or even the direction, of the associated spin torque has proved difficult. Yet, such measurements are crucial to refining our understanding of the mechanisms responsible and the theories that describe them 9,10 . To address this, we present quantitative experimental measurements of the spin torque in MgO-based magnetic tunnel junctions 11-14 for a wide range of bias currents covering the switching currents. The results verify the occurrence of two different spin-torque regimes with different bias dependences that agree well with theoretical predictions 10 .Magnetic tunnel junctions (MTJs) consisting of a MgO insulating layer sandwiched between two ferromagnetic layers (S 1 and S 2 in Fig. 1a) were used to provide very large magnetoresistance 11,14 . Such MTJs are now useful as data storage cells in magnetic random-access memories (M-RAMs) and as magnetic-field sensors in magnetic hard disk drives [11][12][13] . The MTJs with a layer structure of Ir-Mn/Co-Fe/Ru/Co 60 Fe 20 B 20 /MgO/Co 60 Fe 20 B 20 were prepared on a MgO substrate using an ultrahigh-vacuum sputtering system (C-7100; Canon ANELVA). The 3-nm-thick bottom Co-Fe-B layer (S 1 ) acts as a spin polarizer. The top Co-Fe-B layer (S 2 ), a 2-nm-thick free layer, is excited by the spin torque. The MgO tunnel barrier is about 1 nm thick. The MTJs are rectangular with dimensions of approximately 70 nm × 250 nm (see the Methods section for preparation details).Resistance-magnetic-field (R-H ) curves measured at a small bias voltage (0.1-0.3 mV) and different in-plane field directions, that is, θ H = 0 and 45 • , are shown in Fig. 1b. θ H is the angle between the applied field direction and the easy axis of the magnetic cell along the long axis of the rectangular cell (see Fig. 1a). The magnetoresistance ratio is defined as MR = (R AP − R P )/R P , where R P and R AP respectively represent resistance in the parallel and antiparallel magnetization alignments of S 1 and S 2 . A positive bias current denotes electron flow from S 2 to S 1 . The magnetoresistance ratio and R P at a small bias voltage are, respectively, 154% and about 120 (R P × (Junction area) = 2 µm 2 ). Figure 1c shows the bias voltage, V b , dependence of the tunnelling resistance, as measured in four different fields (A-D), which are indicated by arrows in Fig. 1b. For antiparallel alignment (curves A and B), the resistance decreases with increasing V b because new tunnelling channels open at higher bias voltages 1...

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“…However, postdeposition annealing turned out to be crucial for achieving "giant" TMR ratios of 230% [9], later even above 600% [10] at room temperature, and more than 1000% at 5 K [10,11]. CoFeB grows amorphous when sputtered, while MgO grows polycrystalline beyond five atomic layers with a pronounced (001) out-of-plane texture [12].…”

Section: Introductionmentioning

confidence: 99%

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

et al. 2014

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The I -V characteristics of CoFeB/MgO/CoFeB magnetic tunnel junctions show pronounced nonlinearities which are relevant both for sensor applications and for the basic understanding of spin-dependent tunneling. To study the relation between the tunnel characteristics and the tunnel magnetoresistance (TMR) ratio, a series of CoFeB/MgO/CoFeB junctions was annealed with stepwise increasing annealing time at different temperatures. The related TMR ratio and the I -V characteristics were measured in the temperature range between 15 K and 300 K. This allowed the comparison of I -V characteristics of the same junction for TMR ratios between 25% and 150% at 300 K thus eliminating the influence of variations in the preparation process of separate individual samples. In addition to a zero bias anomaly observed in particular at low temperatures and for large TMR ratios, a conductance anomaly in the I -V curves was observed around a bias voltage of 350 mV. A general correlation between the deviation from Ohmic I -V characteristics and the TMR ratio was found both for parallel and antiparallel magnetizations of both ferromagnetic layers. This means that the shape of the I -V curves directly scales with the spin polarization of the tunneling current and the proportion of coherent electron tunneling. Both the 350 mV conductance anomaly and the correlation between non-Ohmic characteristics and the TMR ratio can be explained by considering the contributions of the relevant majority and minority spin bands of the ferromagnetic contacts.

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230% room-temperature magnetoresistance in CoFeB∕MgO∕CoFeB magnetic tunnel junctions

Cited by 906 publications

References 14 publications

Site-specific order and magnetism in tetragonal Mn3Ga thin films

Site-specific order and magnetism in tetragonal Mn3Ga thin films

Quantitative measurement of voltage dependence of spin-transfer torque in MgO-based magnetic tunnel junctions

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

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