Magnetization Measurements of Magnetic Two-Dimensional Electron Gases

Harris, J.; Knobel, R.; Maranowski, K. D.; Gossard, A. C.; Samarth, N.; Awschalom, D. D.

doi:10.1103/physrevlett.86.4644

Cited by 60 publications

(57 citation statements)

References 22 publications

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“…(1). In our sample, M is too small to measure by conventional susceptometry methods and micro-fabricated cantilever measurements require specially-designed heterostructures [20]. Hence, we extract M from the enhanced Zeeman shift of spin-sensitive photoluminescence (PL) [21].…”

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confidence: 99%

Tunable Anomalous Hall Effect in a Nonferromagnetic System

et al. 2006

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We measure the low-field Hall resistivity of a magnetically-doped two-dimensional electron gas as a function of temperature and electrically-gated carrier density. Comparing these results with the carrier density extracted from Shubnikov-de Haas oscillations reveals an excess Hall resistivity that increases with decreasing temperature. This excess Hall resistivity qualitatively tracks the paramagnetic polarization of the sample, in analogy to the ferromagnetic anomalous Hall effect. The data are consistent with skew-scattering of carriers by disorder near the crossover to localization. Although it has been known for almost as long as the Hall effect itself, the AHE in ferromagnetic materials remains the subject of contemporary debate and has gained renewed interest due to its close theoretical connection to the recently discovered spin-Hall effect and to spin transport in general [5,6,7,8,9,10]. Since this AHE often persists above the ferromagnetic Curie temperature, an analogous AHE should be observable in a purely paramagnetic system, in which the charge carriers are spin polarized by an external magnetic field [9]. Unlike ferromagnetic metals whose spin polarization is fixed by their chemistry [11], paramagnetic semiconductors present the additional advantage that their magnetic properties can be smoothly tuned by varying carrier density, magnetic field, or temperature in a given sample. This provides an ideal opportunity to clarify the mechanisms of the AHE. Unfortunately, previous studies in narrow gap semiconductors (e.g. n-InSb) revealed only a very weak AHE, despite large g-factors and strong spin-orbit coupling [9], conditions which should favor observing the AHE. Diluted magnetic semiconductors (DMS) have shown a clear AHE, but only in samples that exhibit hole-mediated ferromagnetism [12], with limited opportunity for tuning with an electric field [13]. Bulk crystals of n-type DMS are not ferromagnetic and, despite their extremely large spin splitting, have exhibited no AHE in previous studies [14].Here, we report the observation of a robust and tunable AHE in a purely paramagnetic two-dimensional electron gas in a DMS quantum well. Surprisingly, the effect is much larger than in earlier studies of paramagnetic semiconductors, despite the presence of a large bandgap and-hence-a weak spin-orbit coupling. We show that the strength of the AHE is electrically tunable in this system, shedding new light on the origins of this class of phenomena and suggesting the possibility of gate-tunable spin transport in similar structures. Finally, we identify a remarkably simple dependence of our AHE on classical scattering in the regime of localization.We have chosen to study the AHE in magneticallydoped two-dimensional electron gases (M2DEGs) [15,16] derived from a II-VI DMS [17]. This choice is dictated by several factors: (a) the carriers have an unusually large paramagnetic susceptibility, resulting in a significant spin polarization that enhances the strength of the AHE; (b) the 2D nature and moderately high mob...

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Tunable Anomalous Hall Effect in a Nonferromagnetic System

et al. 2006

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“…Rings are patterned directly onto cantilevers and the cantilevers are used as torque magnetometers to detect the current in the rings. Sensitive cantilevers are ubiquitous in measurements of small forces; they are used in AFM 15 , mass sensing 16 , magnetization studies of two-dimensional electron gases 17,18 , and have been used to measure the spin resonance of a single electron 19 . Cantilevers are promising for persistent currents because they offer greater sensitivity and a cleaner electromagnetic environment than achieved in previous experiments.…”

Section: Introductionmentioning

confidence: 99%

High sensitivity cantilevers for measuring persistent currents in normal metal rings

Jayich¹,

Shanks²,

Ilic³

et al. 2008

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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We propose a new approach to measuring persistent currents in normal metal rings. By integrating micron-scale metal rings into sensitive micromechanical cantilevers and using the cantilevers as torque magnetometers, it should be possible to measure the rings' persistent currents with greater sensitivity than the SQUID-based and microwave resonator-based detectors used in the past. In addition, cantilever-based detectors may allow for measurements in a cleaner electromagnetic environment. We have fabricated ultra sensitive cantilevers with integrated rings and measured their mechanical properties. We present an estimate of the persistent current sensitivity of these cantilever-based detectors, focusing on the limits set by the cantilever's Brownian motion and the shot noise in the laser interferometer that monitors the cantilever.

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“…The zero-temperature behavior of the magnetization curve can be seen by Eq. (20), which in the absence of edge states is…”

Section: The Magnetization Of 2degmentioning

confidence: 99%

“…On the experimental side, the measurement of the magnetization keeps a most challenging task due to weak signal of the magnetization. A variety of techniques, such as dc superconducting quantum interference device (SQUID) magnetometers 2,3,4,5 , picking up coils lithographed above the gate 6 , torque magnetometers 7,8,9,10,11,12 , torsional magnetometer with optical angular detection 13,14,15 , and micromechanical cantilever magnetometers 16,17,18,19,20,21,22 , have been developed to observe the magnetization oscillations, i.e., the de Haas-van Alphen (dHvA) effect in high-mobility 2DEG. Clear sawtooth dHvA oscillations in the magnetization have been observed for LLs of filling factors up to 52 10 .…”

Section: Introductionmentioning

confidence: 99%

Magnetization in two-dimensional electron gas in a perpendicular magnetic field: The roles of edge states and spin-orbit coupling

Wang

Zhang

2009

Phys. Rev. B

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We study the de Haas-van Alphen (dHvA) oscillations in the magnetization of a two-dimensional electron gas (2DEG) under the influence of the edge states and/or the Rashba spin-orbit interaction (SOI). The boundaries of the systems lift partially the degeneracies of Landau levels (LL's) and the resulting edge states lead to the changes of both the center and the amplitude of the sawtoothlike magnetization oscillation. The SOI mixes the spin-up and spin-down states of neighboring LL's into two unequally spaced energy branches. The inclusion of SOI changes the well-defined sawtooth pattern of the dHvA oscillations in the magnetization. The weaker the magnetic field is, the larger is the change of the dHvA oscillations due to the edge effect and/or the spin-orbit coupling. Some theoretical results are compared with the experimental data.

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Magnetization Measurements of Magnetic Two-Dimensional Electron Gases

Cited by 60 publications

References 22 publications

Tunable Anomalous Hall Effect in a Nonferromagnetic System

Tunable Anomalous Hall Effect in a Nonferromagnetic System

High sensitivity cantilevers for measuring persistent currents in normal metal rings

Magnetization in two-dimensional electron gas in a perpendicular magnetic field: The roles of edge states and spin-orbit coupling

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