Superparamagnetism in MgO-based magnetic tunnel junctions with a thin pinned ferromagnetic electrode

Feng, Jinchao; Chen, Junyang; Venkatesan, M.; Feng, G.; Han, X. F.; Coey, J. M. D.

doi:10.1103/physrevb.81.205212

Cited by 14 publications

(9 citation statements)

References 27 publications

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“…It was suggested that the effect of Ta migration to the CoFeB/MgO interface accounts for the reduction of and thus degradation of PMA at high annealing temperatures. In addition, it has been suggested that superparamagnetic nanoparticles are formed in the thin CoFeB layer adjacent the MTJ interface [9], [10]. In the study of the tunneling resistance as a function of temperature, Feng et al observed an abnormal temperature dependence of the junction resistance [9].…”

Section: Introductionmentioning

confidence: 98%

“…In addition, it has been suggested that superparamagnetic nanoparticles are formed in the thin CoFeB layer adjacent the MTJ interface [9], [10]. In the study of the tunneling resistance as a function of temperature, Feng et al observed an abnormal temperature dependence of the junction resistance [9]. They have suggested that the anomaly may arise either from spin-flip scattering associated with thermal fluctuations of interfacial superparamagnetic nanoparticles [11] or an extra magnetic coupling occurs due to the blocking of the nanoparticles at low temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Superparamagnetic States and Perpendicular Magnetic Anisotropy in Ultrathin MgO/CoFeB/Ta Structures

et al. 2014

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High perpendicular magnetic anisotropy (PMA) has been observed in MgO/CoFeB/Ta thin films if the thickness of CoFeB is in the range between 1.1 and 1.5 nm. However, both the coercivity and remanence vanish when the thickness of CoFeB is less than 1.1 nm, indicating a characteristic of superparamagnetic state. The magnetization versus external field of these thinner films shows a fit with a Langevin model. In addition, a temperature dependent study identifies a blocking temperature of 160 K by field cool and zero field cool measurements. The particle size of nm in diameter is estimated for a pancake shape cluster and the small particles are probably formed at the CoFeB/MgO interface at the beginning of the growth. Moreover, even the thicker films, which show ferromagnetic response at room temperature, also exhibit the temperature-dependent characteristic of superparamagnetic state due to the pinning at the edge of the small particles.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Superparamagnetic States and Perpendicular Magnetic Anisotropy in Ultrathin MgO/CoFeB/Ta Structures

et al. 2014

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“…We are still not sure the origin of this difference. However, as pointed out in [54], a dipole field (H dip ) from the SAF pinned reference layer, which is different from H offset inducing the overall shift of RH loops, may stabilize one of the magnetic configurations, while destabilize the other, i.e., the actual H offset for AP and P states are different.…”

Section: Methodsmentioning

confidence: 98%

“…As expected from the I-PMA, H c increases as t FL decreases until t FL < 1 nm. For t FL > 1 nm, the PMA becomes unstable due to formation of superparamagnetic phase [53], [54]. As EF is confined within a few monolayers at the interface, the influence of EF on the PMA is effectively only at the interface.…”

Section: Methodsmentioning

confidence: 99%

Perspectives of Electric Field Controlled Switching in Perpendicular Magnetic Random Access

et al. 2015

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Based on requirements for spin-transfer torque (STT)-magnetic random access memory (MRAM), fundamental challenges in current CoFeB-and MgO-based STT-MRAM with perpendicular magnetic anisotropy (PMA) are addressed when scaling down to sub-20 nm. Electric-field (EF)-induced PMA modulation has been proposed to significantly reduce the switching current. As EF alone is unable to induce the magnetization reversal but PMA reduction, additional mechanisms should be applied to realize EF switching. We discuss difficulties in the implementation of currently reported two switching approaches and propose a new approach using Oersted field guided EF switching in MRAM arrays. Our latest experimental results on the EF effect show that the spin reorientation transition can be realized at an EF of 0.8 V/nm for the top-pin CoFeB/MgO magnetic tunnel junctions (MTJs) with the thermal stability factor of as high as 57 in the absence of EF. However, the bidirectional switching of the free layer cannot be achieved at a fixed biasing field, which is attributed to small STT effect and switching uncertainty due to unipolar feature of EF-induced PMA modulation. Perspective of EF-MRAM is analyzed based on currently published data on EF efficiency. We show that the EF switching is very promising for future MRAM applications in spite of challenges in materials and MTJ stack engineering. Index Terms-Electrical field (EF), low-power switching, magnetic random access memory (MRAM), spin-transfer torque (STT). = 2ē h 2α P J M S V (H K − H eff ) 1 + P 2 J (1) I AP→P C0 = 2ē h 2α P J M S V (H K + H eff ) 1 − P 2 J0018-9464

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“…[11][12][13][14] When the free layer thickness is below a critical value, it breaks up into nanoislands on the MgO surface, which are superparamagnetic. [11][12][13][14][15] Realizing a linear response in DBMTJs, which have better bias dependence of TMR compared to SB-MTJs, [16][17][18] is advantageous for sensor applications. In addition to the linear response, a low noise level is necessary for sensor applications.…”

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confidence: 99%

Field sensing in MgO double barrier magnetic tunnel junctions with a superparamagnetic Co50Fe50 free layer

Feng

Liu

et al. 2012

Journal of Applied Physics

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Linear response and low frequency noise have been investigated in MgO double barrier magnetic tunnel junctions with a superparamagnetic Co 50 Fe 50 free layer. Linear and hysteresis-free switching was observed for the Co 50 Fe 50 thickness t 1 nm. A tunneling magnetoresistance ratio of up to 108% and large magnetic field sensitivity value of 61%/mT were obtained at room temperature when t ¼ 1.0 nm. The angular dependence of magnetoresistance suggests that weak coupling between superparamagnetic islands in a 1.0 nm free layer permits continuous rotation of magnetization, whereas the islands in a 0.8 nm layer switch rather independently. The frequency dependence of noise power spectrum density and field dependence of Hooge parameter (a) also behave differently for junctions with 0.8 and 1.0 nm free layers. The noise sensitivity of 1.0 nm free layer junctions is independent of bias, and it is estimated to reach 400 pT/Hz 0.5 at 500 kHz. V C 2012 American Institute of Physics. [http://dx

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Superparamagnetism in MgO-based magnetic tunnel junctions with a thin pinned ferromagnetic electrode

Cited by 14 publications

References 27 publications

Superparamagnetic States and Perpendicular Magnetic Anisotropy in Ultrathin MgO/CoFeB/Ta Structures

Superparamagnetic States and Perpendicular Magnetic Anisotropy in Ultrathin MgO/CoFeB/Ta Structures

Perspectives of Electric Field Controlled Switching in Perpendicular Magnetic Random Access

Field sensing in MgO double barrier magnetic tunnel junctions with a superparamagnetic Co50Fe50 free layer

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