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

Tsai, C. C.; Cheng, Chih Chia; Tsai, Michael; Chern, G.

doi:10.1109/tmag.2013.2274458

Cited by 11 publications

(8 citation statements)

References 16 publications

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“…The latter presents simultaneously both types of responses, sharp hysteretic ones with TMR values up to ∼200% (t > t critical ) and linear responses with TMR values down to 40%, translating the thin CoFeB evolution from the ferromagnetic to the SPMlike regime (t ≤ t critical ). This transition is also illustrated in the inset of Figure 20a with the abrupt drop in coercive field at t critical ∼ 1.45 nm which is in accordance with other reported values [79][80][81][92][93][94]. Tsai et al estimated ∼23 nm as the average lateral size of the ferromagnetic particles at the sensing layer [94] while Shen et al obtained 40-120 nm [95] which for the given t critical implies that the clusters have a pancake-like shape.…”

Section: -P11supporting

confidence: 89%

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Linearization strategies for high sensitivity magnetoresistive sensors

Silva

Leitao

Valadeiro

et al. 2015

Eur. Phys. J. Appl. Phys.

102

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Abstract. Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of ∼40 pT/ √ Hz at 30 Hz, representing a step forward the low field detection at room temperature.

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Section: -P11supporting

confidence: 89%

“…In this ultra thin CoFeB layers, even for temperatures below the blocking temperature the thermal ambient energy is sufficient to change the magnetization direction of the grains [94]. The resulting relaxation of magnetization orientation causes the magnetic moment of the entire grain to align with any applied magnetic field.…”

Section: -P11mentioning

confidence: 99%

Linearization strategies for high sensitivity magnetoresistive sensors

Silva

Leitao

Valadeiro

et al. 2015

Eur. Phys. J. Appl. Phys.

102

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“…It therefore seems preferable to use Fe or an Fe-rich alloy in contact with the MgO barrier to minimize the roughness of the stack and internal stress in the MgO barrier which could promote dielectric breakdown of the tunnel barrier. Furthermore, a discontinuous magnetic layer has a greater tendency to become superparamagnetic at small thickness (Tsai et al, 2014). Despite these advantages, it has also been shown that Fe in contact with the barrier, especially when positioned below the barrier, may form an FeO layer which could reduce the TMR amplitude (Meyerheim et al, 2001).…”

Section: Influence Of Cofeb Composition On Pma Amplitude and Thermal mentioning

confidence: 99%

Perpendicular magnetic anisotropy at transition metal/oxide interfaces and applications

2017

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International audienceSpin electronics is a rapidly expanding field stimulated by a strong synergy between breakthrough basic research discoveries and industrial applications in the fields of magnetic recording, magnetic field sensors, nonvolatile memories [magnetic random access memories (MRAM) and especially spin-transfer-torque MRAM (STT-MRAM)]. In addition to the discovery of several physical phenomena (giant magnetoresistance, tunnel magnetoresistance, spin-transfer torque, spin-orbit torque, spin Hall effect, spin Seebeck effect, etc.), outstanding progress has been made on the growth and nanopatterning of magnetic multilayered films and nanostructures in which these phenomena are observed. Magnetic anisotropy is usually observed in materials that have large spin-orbit interactions. However, in 2002 perpendicular magnetic anisotropy (PMA) was discovered to exist at magneticmetal/oxide interfaces [for instance Co(Fe)/alumina]. Surprisingly, this PMA is observed in systems where spin-orbit interactions are quite weak, but its amplitude is remarkably large—comparable to that measured at Co/Pt interfaces, a reference for large interfacial anisotropy (anisotropy ∼1.4 erg/cm2 = 1.4 mJ/m2). Actually, this PMA was found to be very common at magnetic metal/oxide interfaces since it has been observed with a large variety of amorphous or crystalline oxides, including AlOx, MgO, TaOx, HfOx, etc. This PMA is thought to be the result of electronic hybridization between the oxygen and the magnetic transition metal orbit across the interface, a hypothesis supported by ab initio calculations. Interest in this phenomenon was sparked in 2010 when it was demonstrated that the PMA at magnetic transition metal/oxide interfaces could be used to build out-of-plane magnetized magnetic tunnel junctions for STT-MRAM cells. In these systems, the PMA at the CoFeB/MgO interface can be used to simultaneously obtain good memory retention, thanks to the large PMA amplitude, and a low write current, thanks to a relatively weak Gilbert damping. These two requirements for memories tend to be difficult to reconcile since they rely on the same spin-orbit coupling. PMA-based approaches have now become ubiquitous in the designs for perpendicular STT-MRAM, and major microelectronics companies are actively working on their development with the first goal of addressing embedded FLASH and static random access memory-type of applications. Scalability of STT-MRAM devices based on this interfacial PMA is expected to soon exceed the 20-nm nodes. Several very active new fields of research also rely on interfacial PMA at magnetic metal/oxide interfaces, including spin-orbit torques associated with Rashba or spin Hall effects, record high speed domain wall propagation in buffer/magnetic metal/oxide-based magnetic wires, and voltage-based control of anisotropy. This review deals with PMA at magnetic metal/oxide interfaces from its discovery, by examining the diversity of systems in which it has been observed and the physicochemical methods through which the ...

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“…On the other hand, fitting the dependence below t c gives us the value of magnetic dead layer thickness t D , however, in this thickness regime the magnetic moment is additionally reduced. This reduction may be explained by incomplete crystallization of CoFeB and coexistence of an amorphous phase [21] or other modification of a film structure [22,23]. In our system we have obtained a magnetic dead layer thickness of 0.35 ± 0.03 nm after the deposition process, which increases to 0.5 ± 0.05 nm after annealing at the highest temperature of 450 • C. The estimated interface anisotropy is already high and equals K i,V=0 = 1.19 ± 0.2mJ/m 2 .…”

Section: B W Buffermentioning

confidence: 99%

Underlayer material influence on electric-field controlled perpendicular magnetic anisotropy in CoFeB/MgO magnetic tunnel junctions

et al. 2015

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We study the dependence of the perpendicular magnetic anisotropy on the underlayer material in magnetic tunnel junction. Using several different 4d and 5d metals we identify an optimal seed layer in terms of high anisotropy, low mixing, and high thermal stability. In such systems we investigate the tunability of the anisotropy by means of electric fields. Especially, by using W as the underlayer of the CoFeB/MgO/CoFeB trilayer we could obtain good thermal stability that allows for annealing in the temperatures up to 450 • C, which results in high perpendicular anisotropy.

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

Cited by 11 publications

References 16 publications

Linearization strategies for high sensitivity magnetoresistive sensors

Linearization strategies for high sensitivity magnetoresistive sensors

Perpendicular magnetic anisotropy at transition metal/oxide interfaces and applications

Underlayer material influence on electric-field controlled perpendicular magnetic anisotropy in CoFeB/MgO magnetic tunnel junctions

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