Spin-diffusion lengths in metals and alloys, and spin-flipping at metal/metal interfaces: an experimentalist’s critical review

Bass, J.; Pratt, W. P.

doi:10.1088/0953-8984/19/18/183201

Cited by 544 publications

(631 citation statements)

References 118 publications

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“…The overall reduction in the SOF and SOT is mainly because the Cu partially shorts the current through the Pt. Another possible effect is that the Cu/CoFeB interface may have a different spin-mixing conductance than the Pt/CoFeB interface, resulting in a different spin transfer torque efficiency 27,28 . Despite the significant reduction in both SOF and SOT, the ratio between the two remains near 0.2 when the Cu is thicker than 0.75 nm, as shown in Fig.…”

Section: Current-induced Magnetization Reorientationmentioning

confidence: 99%

Quantifying interface and bulk contributions to spin–orbit torque in magnetic bilayers

et al. 2014

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Spin-orbit interaction-driven phenomena such as the spin Hall and Rashba effect in ferromagnetic/heavy metal bilayers enables efficient manipulation of the magnetization via electric current. However, the underlying mechanism for the spin-orbit interaction-driven phenomena remains unsettled. Here we develop a sensitive spin-orbit torque magnetometer based on the magneto-optic Kerr effect that measures the spin-orbit torque vectors for cobalt iron boron/platinum bilayers over a wide thickness range. We observe that the Slonczewskilike torque inversely scales with the ferromagnet thickness, and the field-like torque has a threshold effect that appears only when the ferromagnetic layer is thinner than 1 nm. Through a thickness-dependence study with an additional copper insertion layer at the interface, we conclude that the dominant mechanism for the spin-orbit interaction-driven phenomena in this system is the spin Hall effect. However, there is also a distinct interface contribution, which may be because of the Rashba effect.

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Section: Current-induced Magnetization Reorientationmentioning

confidence: 99%

Quantifying interface and bulk contributions to spin–orbit torque in magnetic bilayers

et al. 2014

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“…Note that the measured emitted power is therefore only a fraction of the actual emitted power from the pillars. Both transport and frequency measurements have been performed at room temperature and with in-plane magnetic field.The torques of Fig.1a have been calculated by introducing in the models of Refs.[16] and [17] parameters mostly derived from CPP-GMR experimental data [22][23]. For respectively Au, Py, Cu, Co and Ta, these parameters are: bulk resistivity ρ (μΩ.cm) = 2, 15, 2.9, 24, 170; bulk spin asymmetry coefficient β = 0, 0.76, 0, 0.46, 0; spin diffusion length l sf (nm) = 35, 4, 350, 38, 10.…”

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confidence: 99%

“…In addition, the observation of a wavy angular dependence of the torque represents a valuable test of the theory and shows that realistic predictions of the spin transfer torque and its angular dependence in a given structure are now possible. As we will see, in the models we consider here [15][16], the torque is calculated from parameters which, for most of them, can be derived from former CPP-GMR experiments [22][23]. The usual behaviour observed in pillars with in-plane magnetizations along an anisotropy axis corresponds to the standard angular dependence of the inset of Fig.1a, in which the torque starts from zero at ϕ = 0 (P equilibrium state with parallel magnetizations of the fixed and free magnetic layers) and keeps the same sign till it comes back to zero at ϕ = π (AP antiparallel state).…”

mentioning

confidence: 99%

“…We present the results of calculations in the models of Fert et al [15] and Barnaś et al [16][17] for a Py(8)/Cu(10)/Co(8) pillar. With respect to standard structures like Co/Cu/Co or Py/Cu/Py, the difference we have introduced is a large asymmetry between the spin diffusion lengths (SDL) in the magnetic layers, with a long SDL in Co ≈ 38 nm (at room temperature) and a short SDL in Py ≈ 4 nm [22][23]. The smaller spin asymmetry of the resistivity in Co could also affect the angular dependence but we have checked by additional calculations that the wavy variation comes primarily from the shorter SDL in the Py free layer and not from the different spin asymmetry coefficients, as this has been mistakenly written in Ref.…”

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Shaped angular dependence of the spin-transfer torque and microwave generation without magnetic field

et al. 2007

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The generation of oscillations in the microwave frequency range is one of the most important applications expected from spintronics devices exploiting the spin transfer phenomenon. We report transport and microwave power measurements on specially designed nanopillars for which a non-standard angular dependence of the spin transfer torque (wavy variation) is predicted by theoretical models. We observe a new kind of current-induced dynamics that is characterized by large angle precessions in the absence of any applied field, as this is also predicted by simulation with such a wavy angular dependence of the torque. This type of non-standard nanopillars can represent an interesting way for the implementation of spin transfer oscillators since they are able to generate microwave oscillations without applied magnetic field. We also emphasize the theoretical implications of our results on the angular dependence of the torque. 2The magnetization of a ferromagnetic body can be manipulated by transfer of spin angular momentum from a spin-polarized current. This is the concept of spin transfer introduced by Slonczewski [1] and Berger [2] in 1996. In most experiments, a spin-polarized current is injected from a spin polarizer into a "free" magnetic element, for example in pillar-shaped magnetic trilayers [3][4][5][6]. The phenomenon of spin transfer has a great potential for applications. It can be used either to switch a magnetic configuration (the configuration of a magnetic memory for example) [3][4][5] or to generate magnetic precessions and voltage oscillations in the microwave frequency range [6][7]. In the most usual situations, such oscillations are observed in the presence of a magnetic field.From a fundamental point of view, spin transfer effects raise two different types of problems [8]. First the spin transfer torque acting on a magnetic element is related to the transverse spin polarisation of the current (transverse meaning perpendicular to the magnetization axis of the element) and can be derived from spin-dependent transport equations [8][9][10][11][12][13][14][15][16][17]. On the other hand, the description of the magnetic excitations generated by the spin transfer torque raises problems of non-linear dynamics [8,[18][19][20]. For example, in the simple limit where the excitation is supposed to be a uniform precession of the magnetization (macrospin approximation), this precession can be determined by introducing the spin transfer torque into a Landau-LifshitzGilbert (LLG) equation for the motion of the magnetic moment. However, the determination of the spin transfer torque and the description of the magnetization dynamics cannot be regarded as independent problems. In standard trilayered structures with in-plane magnetizations and with the usual angular dependence, a switching regime is found at zero and low magnetic field and the precession regime with generation of voltage oscillations is mainly observed above some threshold field [8]. We will show that a new behavior, characterized by large a...

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“…This difference can be attributed to the thickness dependence of the spin diffusion length due to that of the conductance and the spin memory loss effect at the interfaces. [25][26][27] The spin diffusion length decreases at a smaller thickness because of the interfacial scattering, 5,12,28) such that the decreased spin-current transmission reduces the SMR magnitude. Similarly, the spin memory loss effect reduces the spin current transmission through the interface.…”

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confidence: 99%

Spin-current-induced magnetoresistance in trilayer structure with nonmagnetic metallic interlayer

Iguchi

Sato

Uchida

et al. 2017

Jpn. J. Appl. Phys.

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We have theoretically investigated the spin Hall magnetoresistance (SMR) and Rashba-Edelstein magnetoresistance (REMR), mediated by spin currents, in a ferrimagnetic insulator/nonmagnetic metal/heavy metal system in the diffusive regime. The magnitude of both SMR and REMR decreases with increasing thickness of the interlayer because of the current shunting effect and the reduction in spin accumulation across the interlayer. The latter contribution is due to driving a spin current and persists even in the absence of spin relaxation, which is essential for understanding the magnetoresistance ratio in trilayer structures. © 2017 The Japan Society of Applied Physics M agnetoresistance effects are important for applications in sensor and memory devices and for investigation of spin-dependent transport. [1][2][3] Recently, a new type of magnetoresistance has been demonstrated, in which a spin current generated via spin-orbit coupling from an applied charge current plays a central role. [4][5][6][7][8][9][10][11][12] The generated spin current interacts with magnetization and magnetic field and changes its magnitude. 6,8,11,13) When the spin current is converted back to a charge current by spin-orbit coupling, 14,15) the spin-current transport modulates the conductivity of the system, and then gives rise to magnetoresistance. This spin-current-induced magnetoresistance is now recognized as an indispensable tool for investigating the spin transport in ferromagnetic material=metal heterostructures. [16][17][18][19] The spin Hall magnetoresistance (SMR) refers to the resistance change due to the spin current generated by the spin Hall effect (SHE), which interacts with a ferromagnetic material. 4,6) Typically in materials consisting of heavy metals such as Pt and W, 4,9) a spin current is induced by an applied charge current, j c , due to the SHE. This spin current propagates in the material and forms spin accumulation, s , around the system edges. 20) When s acts on a ferromagnetic material, it exerts spin transfer torque on the magnetization m, which is given by 13)Here, the spin current is defined to be positive when it flows out of the F layer, and e > 0, G r , m, and s j interface respectively denote the elementary charge, the real part of the mixing conductance per unit area, and the magnetization unit vector, the spin accumulation at the interface. Since j STT s is absorbed by the magnetization, the resultant spin accumulation s decreases, which results in the reduction in backflow spin current and thus the additional charge current due to the SHE (Fig. 1). As j STT s depends on the magnetization direction, the spin-current absorption finally appears as a magnetoresistance effect, under which the total conductivity σ shows a different dependence on m from the conventional anisotropic magnetoresistance, 6) i.e.,where n, σ 0 , and Δσ SMR respectively denote the unit vector normal to the junction interface and the conductivities insensitive and sensitive to the magnetization. In the context of SMR research, an interla...

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Spin-diffusion lengths in metals and alloys, and spin-flipping at metal/metal interfaces: an experimentalist’s critical review

Cited by 544 publications

References 118 publications

Quantifying interface and bulk contributions to spin–orbit torque in magnetic bilayers

Quantifying interface and bulk contributions to spin–orbit torque in magnetic bilayers

Shaped angular dependence of the spin-transfer torque and microwave generation without magnetic field

Spin-current-induced magnetoresistance in trilayer structure with nonmagnetic metallic interlayer

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