Transversal magnetic anisotropy in nanoscale PdNi-strips

Steininger, D.; Hüttel, A. K.; Ziola, M.; Kiessling, Matthias; Sperl, Matthias; Bayreuther, G.; Strunk, Christoph

doi:10.1063/1.4775799

Journal of Applied Physics

2013

DOI: 10.1063/1.4775799

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Transversal magnetic anisotropy in nanoscale PdNi-strips

D. Steininger

A. K. Hüttel

M. Ziola

et al.

Abstract: We investigate submicron ferromagnetic PdNi thin-film strips intended as contact electrodes for carbon nanotube-based spintronic devices. The magnetic anisotropy and micromagnetic structure are measured as function of temperature and aspect ratio. Contrary to the expectation from shape anisotropy, magnetic hysteresis measurements of Pd 0.3 Ni 0.7 on arrays containing strips of various width point towards a magnetically easy axis in the sample plane, but transversal to the strip direction. Anisotropic magnetore… Show more

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Cited by 2 publications

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References 22 publications

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“…( 1) ranges over a large fraction of the d-band. SQUID measurements allow us to determine a magnetic moment of µ = 0.58 µ B /atom for our PdNi alloy [17], implying an effective magnetization of M = 0.116. Ab-initio calculations of the band structure provide a filling fraction of F = 0.853 [18].…”

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Universality of the Kondo Effect in Quantum Dots with Ferromagnetic Leads

et al. 2011

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We investigate quantum dots in clean single-wall carbon nanotubes with ferromagnetic PdNi-leads in the Kondo regime. In most odd Coulomb valleys the Kondo resonance exhibits a pronounced splitting, which depends on the tunnel coupling to the leads and an external magnetic field B, and only weakly on gate voltage. Using numerical renormalization group calculations, we demonstrate that all salient features of the data can be understood using a simple model for the magnetic properties of the leads. The magnetoconductance at zero bias and low temperature depends in a universal way on gµB(B − Bc)/kBTK, where TK is the Kondo temperature and Bc the external field compensating the splitting.PACS numbers: 73.23. Hk, 73.63.Fg, 72.15.Qm, The Kondo effect resulting from the exchange interaction of a single spin with a bath of conduction electrons [1], is one of the archetypical phenomena of many-body physics. Its competition with ferromagnetism and possible applications in spintronics [2] have raised wide interest in the past few years. The Kondo effect in quantum dots [3,4] has, in recent experiments, been investigated in the presence of ferromagnetic (FM) leads [5][6][7]. It was found that the Kondo resonance, usually observed at zero bias in the odd Coulomb blockade (CB) valleys, is split into two peaks at finite bias [5]. The splitting consists of a term depending logarithmically on gate voltage [6,7], and, as demonstrated here, a second term nearly independent of gate voltage. These phenomena were predicted theoretically [8][9][10][11], attributing the splitting of the Kondo resonance to a tunneling induced exchange field, which results from the magnetic polarization of the leads. So far no detailed and quantitative comparison of the measured conductance with the theory has been undertaken to verify whether the simplistic description of FM leads used in Refs. 8-11 has quantitative predictive power. The latter would be needed for future spintronics applications that exploit the lead-induced local spin splitting, e.g., spin filtering.In this Letter we present low-temperature transport measurements of a single wall carbon nanotube quantum dot with PdNi leads. We concentrate on the less studied gate-independent contribution of the exchange splitting of the Kondo resonance and attribute it to the saturation magnetization of the contact material. We show that the evolution of the conductance with magnetic field and gate voltage can be understood within a simple model for the magnetization and polarization in the FM leads, by presenting numerical renormalization group (NRG) calculations for this model, using parameters extracted from experiment. Moreover, by comparing resonances of different transparency, we demonstrate a universal scaling of the magnetic field dependence of the Kondo conductance, proving that the magnetization of the leads can indeed be viewed as an exchange field, which acts analogously to an external magnetic field. Experimental setup.-The nanotubes are grown by chemical vapor deposition on a highly doped ...

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Universality of the Kondo Effect in Quantum Dots with Ferromagnetic Leads

et al. 2011

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“…Therefore, while it was possible to make MR measurements, FePd is far from an ideal contact material [7]. NiPd proved to be more successful [11,12], showing a clear, reproducible MR. However, NiPd-contacted devices had an unexpected easy axis transverse to the main axis of the contacts, indicating competition between shape anisotropy and other anisotropy effects.…”

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confidence: 93%

Effect of contact geometry on magnetoresistance in CoPd-contacted carbon nanotubes

Morgan

Metten

Schneider

et al. 2013

Phys. Status Solidi B

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We present local magnetoresistance measurements on carbon nanotubes contacted with the ferromagnetic alloy Co50 Pd50. A sample with contacts of dimensions thickness=10nm, normallength=4thinmathspaceμm exhibited the typical sharp switching expected at the coercive fields of the contacts. However, a sample with the same in‐plane geometry but a thickness of 40 nm displayed a complicated switching behavior indicative of gradual domain wall rotation. In both samples, the contact widths were varied to control shape anisotropy. Further characterization of the contacts and similar contact‐like structures via remanent state magnetic force microscopy suggested a single or few domain structure in the 10 nm thick contacts. The thicker contacts exhibited a complex domain structure characteristic of a hard or intermediate magnetic axis along the long axis of the contact, despite the effect of shape anisotropy. This result is discussed with respect to the influence of both thickness and in‐plane geometry on competing anisotropy contributions within the device. The characterization allows for the pinpointing of precise dimensions that will determine the magnetic easy axis of contacts, thereby controlling magnetotransport.

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Transversal magnetic anisotropy in nanoscale PdNi-strips

Cited by 2 publications

References 22 publications

Universality of the Kondo Effect in Quantum Dots with Ferromagnetic Leads

Universality of the Kondo Effect in Quantum Dots with Ferromagnetic Leads

Effect of contact geometry on magnetoresistance in CoPd-contacted carbon nanotubes

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