Spin-dependent tunneling in discontinuous metal/insulator multilayers

Diény, B.; Sankar, S.; McCartney, Martha R.; Smith, David J.; Bayle–Guillemaud, Pascale; Berkowitz, A. E.

doi:10.1016/s0304-8853(98)00028-6

Cited by 80 publications

(40 citation statements)

References 27 publications

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“…1 They are represented, e.g., by discontinuous metal-insulator multilayers ͑DMIMs͒ that resemble frozen ferrofluids to a large extent. 2,3 Due to magnetic interparticle interactions, e.g., of dipolar or tunneling exchange origin, different kinds of collective behavior are encountered, viz. modified superparamagnetism, 4 superspin glass ͑SSG͒ behavior, 5 or superferromagnetism ͑SFM͒.…”

Section: Introductionmentioning

confidence: 99%

Superferromagnetic domain state of a discontinuous metal insulator multilayer

et al. 2005

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Polarized neutron reflectivity ͑PNR͒ and magnetometry studies have been performed on the granular multilayer ͓Co 80 Fe 20 ͑1.3 nm͒ /Al 2 O 3 ͑3 nm͔͒ 10 . Due to strong interparticle interactions, a collective superferromagnetic state is encountered. Cole-Cole plots drawn from the complex ac susceptibility are measured as functions of frequency, temperature, and field amplitudes that hint at the relaxation, creep, sliding, and switching regimes of pinned domain walls that are in close agreement with results obtained from simulations. Very slow switching with exponential relaxation under near-coercive fields is confirmed by PNR measurements. The complete absence of spin-flip scattering confirms that the magnetization reversal is achieved merely by domain nucleation and growth.

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Section: Introductionmentioning

confidence: 99%

Superferromagnetic domain state of a discontinuous metal insulator multilayer

et al. 2005

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“…Ferromagnetic metal-based DMIMs show moderate room-temperature ͑RT͒ tunneling magnetoresistance ͑TMR͒ that originates from spin-dependent tunneling between adjacent metallic granules. [1][2][3][4][5] Significant lowfield sensitivity in the current-in-plane ͑CIP͒ configuration and relative ease of preparation make DMIMs promising materials for sensors and read heads. 3 Although DMIMs were actively studied during the past decade, only structures with amorphous insulator layers have been prepared so far by different groups ͑see for instance Ref.…”

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confidence: 99%

Tunneling magnetoresistance in epitaxial discontinuous Fe/MgO multilayers

García-García

Pardo

Strichovanec

et al. 2011

Applied Physics Letters

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Epitaxial discontinuous Fe/MgO multilayers have been grown by pulsed laser deposition on MgO͑001͒ single-crystal substrates. The multilayers with 0.6 nm nominal Fe layers thickness are superparamagnetic and demonstrate tunneling magnetoresistance ͑TMR͒ in the current-in-plane configuration. Increasing deposition temperature causes an improvement in crystal quality and is accompanied by higher TMR ratios. The maximum value ͑9.2% TMR at room temperature and 18 kOe magnetic field͒ trebles that of polycrystalline samples deposited simultaneously on glass substrates. A model formula for TMR ratio that includes both spin-dependent tunneling and spin-filtering effect is proposed to explain these results. © 2011 American Institute of Physics. ͓doi:10.1063/1.3569149͔ Discontinuous metal-insulator multilayers ͑DMIMs͒ are cermet structures prepared by repeated alternate deposition of a continuous insulating and a discontinuous metal layer composed of nanometer-sized islands. The size and shape of the nanoparticles can be controlled by the nominal thickness of the metallic layer ͑typically of the order of 1 nm͒ and deposition parameters. Ferromagnetic metal-based DMIMs show moderate room-temperature ͑RT͒ tunneling magnetoresistance ͑TMR͒ that originates from spin-dependent tunneling between adjacent metallic granules. 1-5 Significant lowfield sensitivity in the current-in-plane ͑CIP͒ configuration and relative ease of preparation make DMIMs promising materials for sensors and read heads. 3 Although DMIMs were actively studied during the past decade, only structures with amorphous insulator layers have been prepared so far by different groups ͑see for instance Ref. 5 and references therein͒. No studies on the influence of the substrate nature, deposition temperature, and degree of crystallinity of the insulator layer on transport properties of DMIMs have been reported previously.In planar magnetic tunnel junctions ͑MTJs͒ a substantial increase in TMR ratios appeared when single-crystal MgO replaced amorphous alumina tunnel barriers. 6 This is due to the crucial role of the electron band symmetry of the electrodes and the barrier in epitaxial Fe/MgO/Fe MTJs. 6,7 Recently, [8][9][10] we studied Fe/MgO DMIMs deposited on glass substrates by pulsed laser deposition ͑PLD͒. In these materials the TMR ratio is defined as TMR= 100ϫ ͓R͑H͒ − R͑H =0͔͒ / R͑H =0͒, R being the electrical resistance and H the magnetic field. For Fe layers with 0.61 nm nominal thickness, TMR ratiosϷ −3% at RT were achieved in 18 kOe magnetic field. In this case, the MgO spacers grew in polycrystalline state with a tendency to form large columnar grains through the Fe layers. This suggests that increasing the degree of texturing of Fe/MgO DMIMs could lead to an enhancement of TMR.In this letter, we report on the preparation, structural characterization, and CIP TMR of epitaxial Fe/MgO DMIMs deposited by PLD on single-crystal MgO͑001͒ substrates. The effect of elevated substrate temperature during deposition ͑T S ͒ on the microstructure and transport properti...

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“…Whereas many studies were made on spin-dependent tunneling and magnetoresistance in DMIM, e.g., [27][28][29][30][31][32][33][34] only few applied the CPP configuration, where the gap in the tunneling conductance can be observed at low temperature. Sankar et al 27 measured the transport properties of CoFe/HfO 2 multilayers with 20 bilayers.…”

Section: B Charging Energy and Interactionsmentioning

confidence: 99%

Tunneling and charging effects in discontinuous superparamagneticNi81Fe19/Al2O3
Bručas
¹
,
Hanson
²
,
Apell
³

et al. 2010
Phys. Rev. B
11
0
7
0
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The magnetic and transport properties of films based on discontinuous layers of Ni 81 Fe 19 ͑Py͒ embedded in Al 2 O 3 were investigated. In films with nominal Py thicknesses 6 and 8 Å superparamagnetic particles with median diameters D med = 2.8 and 3.1 nm and distribution widths D = 1.2 and 1.3 nm were formed. Current voltage ͑IU͒ curves were measured with the current perpendicular to the film plane. The analyses show that the charge transport occurs via tunneling; with the charging energy supplied by thermal fluctuations at high temperature, T Ն 100 K, and by the electric field at low temperature, T Ͻ 10 K. The separation of the two regimes allows independent estimates of the mean charging energy ͗E C ͘Ϸ40 meV for both samples; from the resistance R versus T analyzed in an effective-medium model at high temperature and from I versus U at 4 K. In order to obtain a consistent description of the transport properties, the size distributions must be included to account for the deviation from the single size behavior R ϳ exp͑E C / k B T͒ at high T. The scaling parameter in the relation I ϰ ͑ U U th −1͒ ␥ , where U th is the threshold for conduction, is estimated to ␥ Ϸ 2 at 4 K. The superparamagnetic relaxation of the particles becomes blocked below a temperature T Ϸ 20 K respective 30 K for 6 and 8 Å. The magnetic field ͑B͒ dependence of the resistance R͑B͒ displays a single maximum of the ratio MR= ͓R͑B͒ − R͑2 T͔͒ / R͑2 T͒ in zero field at room temperature and a characteristic splitting of the peak at 4 K, attributed to the blocking. The maxima, Ϸ0.9% for 6 Å and 1.1% for 8 Å, are positioned at fields about a factor of two to three higher than the coercive fields of the samples.

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Spin-dependent tunneling in discontinuous metal/insulator multilayers

Cited by 80 publications

References 27 publications

Superferromagnetic domain state of a discontinuous metal insulator multilayer

Superferromagnetic domain state of a discontinuous metal insulator multilayer

Tunneling magnetoresistance in epitaxial discontinuous Fe/MgO multilayers

Tunneling and charging effects in discontinuous superparamagneticNi81Fe19/Al2O3
Bručas
¹
,
Hanson
²
,
Apell
³

et al. 2010
Phys. Rev. B
11
0
7
0
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Spin-dependent tunneling in discontinuous metal/insulator multilayers

Cited by 80 publications

References 27 publications

Superferromagnetic domain state of a discontinuous metal insulator multilayer

Superferromagnetic domain state of a discontinuous metal insulator multilayer

Tunneling magnetoresistance in epitaxial discontinuous Fe/MgO multilayers

Tunneling and charging effects in discontinuous superparamagneticNi81Fe19/Al2O3Bručas1, Hanson2, Apell3 et al. 2010Phys. Rev. B11070View full textAdd to dashboardCite

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Tunneling and charging effects in discontinuous superparamagneticNi81Fe19/Al2O3
Bručas
¹
,
Hanson
²
,
Apell
³

et al. 2010
Phys. Rev. B
11
0
7
0
View full text Add to dashboard Cite