Pinholes in antiferromagnetically coupled multilayers: Effects on hysteresis loops and relation to biquadratic exchange

Bobo, Jean-François; Kikuchi, H.; Redon, O.; Snoeck, E.; Piécuch, M.; White, Robert L.

doi:10.1103/physrevb.60.4131

Cited by 85 publications

(42 citation statements)

References 25 publications

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“…For higher Cu layer thicknesses, the GMR increases monotonically and reaches a maximum in the Cu thickness range of about 3 to 5 nm after which the GMR decreases. The presence of pinholes at low spacer thicknesses was demonstrated experimentally by cross-sectional TEM for sputtered Co/Cu multilayers by Bobo et al 6 and these authors have also studied the influence of pinholes on the interlayer coupling by comparing measured and modeled magnetization curves of the multilayers.…”

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confidence: 99%

Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers Prepared by Two-Pulse (G/P) and Three-Pulse (G/P/G) Plating

Rajasekaran

Pogány

Révész

et al. 2014

J. Electrochem. Soc.

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The giant magnetoresistance (GMR) was investigated for electrodeposited Co/Cu multilayers. In order to better understand the formation of individual layers and their influence on GMR, multilayers produced by two different deposition strategies were compared. One series of Co(2 nm)/Cu(t Cu ) multilayers with t Cu ranging from 0.5 nm to 6 nm was produced with the conventional two-pulse plating by using a galvanostatic/potentiostatic (G/P) pulse combination for the magnetic/non-magnetic layer deposition, respectively, whereby the Cu layer deposition was carried out at the electrochemically optimized potential. Another Co(2 nm)/Cu(t Cu ) multilayer series with the same t Cu range was prepared with the help of a G/P/G pulse combination. In this latter case, first a bilayer of Co(2 nm)/Cu(6 nm) was deposited in each cycle as in the G/P mode after which a third G pulse was applied with a small anodic current to dissolve part of the 6 nm thick Cu layer in order to ensure the targeted t Cu value. The comparison of the two series revealed that the G/P/G pulse combination yields multilayers for which GMR can be obtained even at such low nominal Cu layer thicknesses where G/P multilayers already exhibit bulk-like anisotropic magnetoresistance only. Surface roughness measurements by atomic force microscopy revealed that the two kinds of pulse combination yield different surface roughness values which correlate with the structural quality of the multilayers as indicated by the absence or presence of multilayer satellite reflections in the X-ray diffraction patterns. A separation of the superparamagnetic (SPM) contribution from the total observed GMR provided useful hints at the understanding of differences in layer formation between samples prepared with the two kinds of pulse combination. The results of multilayer chemical analysis revealed that mainly an increased Cu content of the magnetic layer is responsible for the onset of SPM regions in the form of Co segregations in the G/P/G multilayers with small Cu layer thicknesses. Magnetization measurements provided coercive force and remanence data which gave further support for the above interpretation of the GMR data. The giant magnetoresistance (GMR) effect in electrodeposited (ED) multilayer films was extensively studied in the last two decades.

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confidence: 99%

Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers Prepared by Two-Pulse (G/P) and Three-Pulse (G/P/G) Plating

Rajasekaran

Pogány

Révész

et al. 2014

J. Electrochem. Soc.

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“…The magnetic bilayers were covered by 20 ML of protective Au(001). The complete structures are therefore GaAs/Fe (8,11,16,21,31)/40Au/40Fe/20Au(001), where the integers represent the number of MLs. The electron mean free path in thick films of gold is 38 nm [17] and, consequently, the spin transport even in the 40 ML (8 nm) Au spacer is purely ballistic.…”

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confidence: 99%

“…N is assumed thick enough to suppress any RKKY [2], pin-hole [11], and magnetostatic (Néel-type) [12] interactions. We consider ultrathin films with a constant magnetization vector across the film thickness [4], which are nonetheless thicker than λ sc and, therefore, completely absorb transverse spin currents.…”

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Dynamic Exchange Coupling in Magnetic Bilayers

et al. 2003

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A long-ranged dynamic interaction between ferromagnetic films separated by normal-metal spacers is reported, which is communicated by nonequilibrium spin currents. It is measured by ferromagnetic resonance (FMR) and explained by an adiabatic spin-pump theory. In FMR the spin-pump mechanism of spatially separated magnetic moments leads to an appreciable increase in the FMR line width when the resonance fields are well apart, and results in a dramatic line-width narrowing when the FMR fields approach each other.PACS numbers: 75.40. Gb,75.70.Cn,76.50.+g,75.30.Et The giant magnetoresistance [1] accompanying realignment of magnetic configurations in metallic multilayers by an external magnetic field is routinely employed in magnetic read heads and is essential for high-density nonvolatile magnetic random-access memories. These typically consist of ferromagnetic/normal/ferromagnetic (F/N/F ) metal hybrid structures, i.e., magnetic bilayers which are an essential building block of the so called spin valves. The static Ruderman-Kittel-Kasuya-Yosida (RKKY) interlayer exchange between ferromagnets in magnetic multilayers [2] is suppressed in these devices by a sufficiently thick nonmagnetic spacer N or a tunnel barrier. The interest of the community shifts increasingly from the static to the dynamic properties of the magnetization [3]. This is partly motivated by curiosity, partly by the fact that the magnetization switching characteristics in memory devices is a real technological issue. A good grasp of the fundamental physics of the magnetization dynamics becomes of essential importance to sustain the exponential growth of device performance factors.In this Letter we study the largely unexplored dynamics of magnetic bilayers in a regime when there is no discernible static interaction between the magnetization vectors. Surprisingly, the magnetizations still turn out to be coupled, which we explain by emission and absorption of nonequilibrium spin currents. Under special conditions the two magnetizations are resonantly coupled by spin currents and carry out a synchronous motion, quite analogous to two connected pendulums. This dynamic interaction is an entirely new concept and physically very different from the static RKKY coupling. E.g., the former does not oscillate as a function of thickness and its range is exponentially limited by the spin-flip relaxation length of spacer layers and algebraically by the elastic mean free path. This coupling can have profound effects on magnetic relaxation and switching behavior in hybrid structures and devices.The unit vector m = M/M of the magnetization M(t) of a ferromagnet changes its direction in the presence of a noncollinear magnetic field. The motion of m in a single domain is described by the Landau-Lifshitz-Gilbert (LLG) equationwith γ being the absolute value of the gyromagnetic ratio. The first term on the right-hand side represents the torque induced by the effective magnetic field H eff = −∂F/∂M, where the free-energy functional F [M] consists of the Zeeman energy, ma...

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“…[12][13][14] For the PMA-SyF system, the magnetic properties could only be analyzed in the presence of in-plane magnetic fields because, in this case, the magnetization mainly occurs by coherent rotation. In order to include the effects of pinhole coupling, a biquadratic IEC energy term, originating from inhomogeneous IEC, 15,16 was added to the functional, which was expressed as follows:…”

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confidence: 99%

Strong interlayer exchange coupling and high post-annealing stability in perpendicularly magnetized [Pt/Co]/Ru/[Co/Pt] structures

2016

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Strong interlayer exchange coupling (IEC) and high post-annealing stability are demonstrated for perpendicular synthetic ferrimagnets (p-SyFs) with [Pt/Co]6/Ru/[Co/Pt]3 structures. The observed IEC strength was 2.55 ergs/cm2 for a Ru thickness of 0.35 nm, representing the highest value achieved up to date for similar structures. The IEC remained strong even after annealing at 450oC, for the practically important Ru layer thickness of 0.85 nm. The biquadratic IEC, a parameter quantifying the pinhole effects in SyFs, was confirmed by analyzing the experimental results by using the total energy functional, and its strength increased with decreasing the temperature and Ru layer thickness.

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Pinholes in antiferromagnetically coupled multilayers: Effects on hysteresis loops and relation to biquadratic exchange

Cited by 85 publications

References 25 publications

Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers Prepared by Two-Pulse (G/P) and Three-Pulse (G/P/G) Plating

Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers Prepared by Two-Pulse (G/P) and Three-Pulse (G/P/G) Plating

Dynamic Exchange Coupling in Magnetic Bilayers

Strong interlayer exchange coupling and high post-annealing stability in perpendicularly magnetized [Pt/Co]/Ru/[Co/Pt] structures

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