Normal and inverse current-induced magnetization switching in a single nanopillar

Dassow, H.; Lehndorff, R.; Bürgler, D. E.; Büchmeier, M.; Grünberg, P.; Schneider, Claus M.; Hart, A. van der

doi:10.1063/1.2398923

Cited by 20 publications

(25 citation statements)

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“…In our convention, a positive current corresponds to an electron flow from the nanomagnet to the extended layer. In previous experiments with Fe/Ag/Fe pillars 11,15,16 we have established that the spin-transfer torque due to a positive current acts toward an antiparallel alignment. Therefore, the high-resistive state can be identified in terms of antiparallel aligned uniform magnetizations and the low-resistive state as the vortex state.…”

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Magnetization dynamics in spin torque nano-oscillators: Vortex state versus uniform state

et al. 2009

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Current-driven magnetization dynamics in spin torque nano-oscillators ͑STNOs͒ is intensely investigated because of its high potential for high-frequency ͑HF͒ applications. We experimentally study current-driven HF excitations of STNOs for two fundamental magnetization states of the free layer, namely, vortex state and uniform in-plane magnetization. Our ability to switch between the two states in a given STNO enables a direct comparison of the critical currents, agility, power, and linewidth of the HF output signals. We find that the vortex state has some superior properties, in particular, it maximizes the emitted HF power and shows a wider frequency tuning range at a fixed magnetic field. DOI: 10.1103/PhysRevB.80.054412 PACS number͑s͒: 72.25.Ba, 75.60.Jk, 75.70.Kw, 75.75.ϩa The proposal of spin-polarized current-induced magnetization dynamics of Slonczewski 1 and Berger 2 initiated a lot of theoretical and experimental studies in the last years. Promising applications have been found in spin-torque magnetic random access memory and spin torque nanooscillators ͑STNOs͒. The latter shows a steady precession of the magnetization of the free layer under the action of a spin-polarized dc current. Via the giant magnetoresistance or tunnel magnetoresistance ͑GMR or TMR͒ effect this precession generates a high-frequency ͑HF͒ voltage oscillation with frequencies in the GHz range and a rather wide tuning range by dc current and external magnetic field. Still, one drawback of STNOs is their low output power. To achieve useful power levels several groups work on the synchronization of arrays of STNOs.3-5 While this is a very promising approach, maximizing the output power of every single STNO is undeniably the first step to do.There are several possible arrangements for STNOs. Inplane magnetized free and fixed layers with in-plane 6 or outof-plane external fields, 7 in-plane magnetized free and perpendicularly magnetized fixed layers, 8 and free layer magnetized in a vortex state with in-plane magnetized fixed layer 9,10 have been studied experimentally. Comparing the characteristics-especially output power-of HF excitations of these arrangements from different experiments is not conclusive, because impedance and absolute resistance change, ⌬R = R AP − R P , of the samples have a very strong influence on the detected power. Here, we study HF excitations in two of the arrangements mentioned above that we are able to realize in the same sample. While the fixed layer is uniformly inplane magnetized, the free layer is either uniformly in-plane magnetized or in a vortex state. The direct comparison shows some advantages of the vortex state for the application in STNOs.The samples are fabricated by depositing 150 nm Ag/2 nm Fe/6 nm Ag/20 nm Fe/50 nm Au by molecular beam epitaxy on a cleaned and annealed GaAs͑100͒ substrate. All layers grow epitaxially as is confirmed by in situ low-energy electron diffraction measurements. The Fe layers adopt a bcc structure, which yields a cubic magnetocrystalline anisotropy. Bottom electro...

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“…Finally, Ti 15 nm/Au 200 nm top electrodes are formed by optical lithography, thermal evaporation, and lift-off technique. 11 Using this process we fabricate nanomagnets of 230 nm diameter and 20 nm thickness, which are separated by 6 nm Ag from an extended 2-nm-thick Fe layer ͓see inset in Fig. 1͑a͔͒.…”

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Magnetization dynamics in spin torque nano-oscillators: Vortex state versus uniform state

et al. 2009

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“…Here we deal with top and bottom contacted, sub-micron-sized nanopillars made from multilayer stacks comprising ferromagnetic and non-magnetic materials for the study of current-induced magnetization dynamics. We show how the charging effects in a previously established fabrication process for single-crystalline nanopillars by H. Dassow et al (2006) [1] can be significantly reduced by using the bottom electrode layer as charge dissipater and only isolating and disconnecting the bottom electrodes from ground after the fabrication of the delicate nanopillar structure by electron beam lithography. The modified process is successfully applied to Co 2 MnSi/Ag/Co 2 MnSi(001) multilayer stacks grown on highly insulating MgO substrates.…”

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Charging effect reduction in electron beam lithography and observation of single nanopillars on highly insulating substrates

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et al. 2015

Microelectronic Engineering

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“…This kind of structures are interesting model systems, which we are also employing to investigate current-induced magnetization switching. 34 The preparation is described in detail elsewhere. 34 The Cr thickness has been chosen in order to obtain a strong antiferromagnetic coupling in the bottom Fe/Cr/Fe trilayer, which fixes the center reference layer.…”

Section: A Sample Preparation and Experimental Setupmentioning

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“…34 The preparation is described in detail elsewhere. 34 The Cr thickness has been chosen in order to obtain a strong antiferromagnetic coupling in the bottom Fe/Cr/Fe trilayer, which fixes the center reference layer. The top, thin Fe layer is decoupled and can be switched more easily by an external field or a perpendicularly applied current.…”

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Intensity of Brillouin light scattering from spin waves in magnetic multilayers with noncollinear spin configurations: Theory and experiment

et al. 2007

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The scattering of photons from spin waves (Brillouin light scattering -BLS) is a well-established technique for the study of layered magnetic systems. The information about the magnetic state and properties of the sample is contained in the frequency position, width, and intensity of the BLS peaks. Previously [Phys. Rev. B 67, 184404 (2003)], we have shown that spin wave frequencies can be conveniently calculated within the ultrathin film approach, treating the intralayer exchange as an effective bilinear interlayer coupling between thin virtual sheets of the ferromagnetic layers.Here we give the consequent extension of this approach to the calculation of the Brillouin light scattering (BLS) peak intensities. Given the very close relation of the BLS cross-section to the magneto-optic Kerr effect (MOKE), the depth-resolved longitudinal and polar MOKE coefficients calculated numerically via the usual magneto-optic formalism can be employed in combination with the spin wave precessional amplitudes to calculate full BLS spectra for a given magnetic system. This approach allows an easy calculation of BLS intensities even for noncollinear spin configurations including the exchange modes. The formalism is applied to a Fe/Cr/Fe/Ag/Fe trilayer system with one antiferromagnetically coupling spacer (Cr). Good agreement with the experimental spectra is found for a wide variety of spin configurations.

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Normal and inverse current-induced magnetization switching in a single nanopillar

Cited by 20 publications

References 16 publications

Magnetization dynamics in spin torque nano-oscillators: Vortex state versus uniform state

Magnetization dynamics in spin torque nano-oscillators: Vortex state versus uniform state

Charging effect reduction in electron beam lithography and observation of single nanopillars on highly insulating substrates

Intensity of Brillouin light scattering from spin waves in magnetic multilayers with noncollinear spin configurations: Theory and experiment

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