Nanoconstriction microscopy of the giant magnetoresistance in cobalt/copper spin valves

Theeuwen, S.J.C.H.; Caro, J.; Wellock, K. P.; Radelaar, S.; Marrows, C. H.; Hickey, B. J.; Козуб, В. И.

doi:10.1063/1.125426

Cited by 25 publications

(11 citation statements)

References 14 publications

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“…Experimental efforts to research these topics then disappeared for many years before the discovery of current driven switching effects in multilayer point contacts [413] and nanopillars [414] by the group of Buhrman at Cornell. These experiments were the first confirmations of the theoretical idea of a spin-transfer torque of Slonczewski [415], and built on previous experimental results where hints of the presence of this torque had been observed [416,417,418]. The basic principle of current driven switching is that a current driven from one magnetic layer into another that is antiparallel must relax its spin polarisation to match that of the layer it is entering over the scale of a spin diffusion length.…”

Section: Resultsmentioning

confidence: 77%

Spin-polarised currents and magnetic domain walls

Marrows

2005

Advances in Physics

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216

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Electrical currents flowing in ferromagnetic materials are spinpolarised as a result of the spin-dependent band structure. When the spatial direction of the polarisation changes, in a domain structure, the electrons must somehow accommodate the necessary change in direction of their spin angular momentum as they pass through the wall. Reflection, scattering, and a transfer of angular momentum to the lattice are all possible outcomes, depending on the circumstances. This gives rise to a variety of different physical effects, most importantly a contribution to the electrical resistance caused by the wall, and a motion of the wall driven by the spin-polarised current.Historical and recent research on these topics is reviewed. * Phone: +44(0)113 3433780

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Section: Resultsmentioning

confidence: 77%

Spin-polarised currents and magnetic domain walls

Marrows

2005

Advances in Physics

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216

163

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“…For example, STM has been used to study the formation and evolution of nanocontacts between an STM tip and Au [20][21][22] Ni, Cu, or Pt [23] films. Studies have also been performed on nanocontacts made between a metallic tip and a multilayered ferromagnetic film in an attempt to probe the local MR behaviour [24][25][26]. STM has proven useful here by providing a means to establish and control the nanocontacts [27].…”

Section: Introductionmentioning

confidence: 99%

Magnetoresistance of oblique angle deposited multilayered Co/Cu nanocolumns measured by a scanning tunnelling microscope

Morrow

Parker

et al. 2008

Nanotechnology

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In this work we present the first magnetoresistance measurements on multilayered vertical Co(∼6 nm)/Cu(∼6 nm) and slanted Co(x nm)/Cu(x nm) (with x≈6, 11, and 16 nm) nanocolumns grown by oblique angle vapour deposition. The measurements are performed at room temperature on the as-deposited nanocolumn samples using a scanning tunnelling microscope to establish electronic contact with a small number of nanocolumns while an electromagnet generates a time varying (0.1 Hz) magnetic field in the plane of the substrate. The samples show a giant magnetoresistance (GMR) response ranging from 0.2 to 2%, with the higher GMR values observed for the thinner layers. For the slanted nanocolumns, we observed anisotropy in the GMR with respect to the relative orientation (parallel or perpendicular) between the incident vapour flux and the magnetic field applied in the substrate plane. We explain the anisotropy by noting that the column axis is the magnetic easy axis, so the magnetization reversal occurs more easily when the magnetic field is applied along the incident flux direction (i.e., nearly along the column axis) than when the field is applied perpendicular to the incident flux direction.

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“…The gradual evolution of the resistance and thus of the magnetization is regularly observed. [3][4][5][6]39 In many cases this behavior has a threshold character and is observed only for one of the magnetic configurations of the system. In Refs.…”

Section: Comparison To Experimental Situationmentioning

confidence: 99%

“…In connection to this short history of the field, it is noted that the very idea that the evolution of the magnetic state of a spin valve or multilayer system of nanoscale lateral dimension may arise from generation of nonequilibrium magnons was first formulated in Ref. 4, mostly in a qualitative picture.…”

Section: Introductionmentioning

confidence: 99%

Voltage-dependent electron distribution in a small spin valve: Emission of nonequilibrium magnons and magnetization evolution

Козуб

Caro

2007

Phys. Rev. B

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We describe spin transfer in a ferromagnet/normal metal/ferromagnet spin-valve point contact. Spin is transferred from the spin-polarized current to the magnetization of the free layer by the mechanism of incoherent magnon emission. Our approach is based on the rate equation for the magnon occupation, using Fermi's golden rule for magnon emission and absorption and the nonequilibrium electron distribution for a voltagebiased spin valve. The magnon emission reduces the magnetization of the free layer. Depending on the sign of the applied voltage for parallel or antiparallel magnetizations, a magnon avalanche, characterized by a diverging effective magnon temperature, sets in at a critical voltage. This critical behavior can result in magnetization reversal and consequently to suppression of magnon emission. However, magnon-magnon scattering can lead to saturation of the magnon concentration at a high but finite value. The further behavior depends on the parameters of the system. In particular, gradual evolution of the magnon concentration followed by magnetization reversal is possible. Another scenario is the steplike increase of the magnon concentration followed by a slow decrease. In this scenario a spike in the differential resistance is expected due electron-magnon scattering. Then, a random telegraph noise in the magnetoresistance can exist, even at zero temperature. A comparison of the obtained results to existing theoretical approaches and experimental data is given. We demonstrate that our approach for magnetization configurations close to collinear corresponds to the voltagecontrolled regime. Namely, the magnetization evolution is related to nonequilibrium spin-dependent electron distribution controlled by the total voltage applied to the device. In this regime the evolution has an exponential character. In contrast, the existing spin-torque approach corresponds to a current-controlled regime, and the evolution rate is restricted by value of the total spin current through the "analyzing" ferromagnetic layer. It is shown that our scenario dominates at mutual magnetization orientation close to the parallel or antiparallel.

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Nanoconstriction microscopy of the giant magnetoresistance in cobalt/copper spin valves

Cited by 25 publications

References 14 publications

Spin-polarised currents and magnetic domain walls

Spin-polarised currents and magnetic domain walls

Magnetoresistance of oblique angle deposited multilayered Co/Cu nanocolumns measured by a scanning tunnelling microscope

Voltage-dependent electron distribution in a small spin valve: Emission of nonequilibrium magnons and magnetization evolution

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