High-temperature Hall effect inGa1−xMnxAs

Abstract

The temperature dependence of the Hall coefficient of a series of ferromagnetic Ga 1Ϫx Mn x As samples is measured in the temperature range 80 KϽTϽ500 K. We model the Hall coefficient assuming a magnetic susceptibility given by the Curie-Weiss law, a spontaneous Hall coefficient proportional to xx 2 (T), and including a constant diamagnetic contribution in the susceptibility. For all low resistivity samples this model provides excellent fits to the measured data up to Tϭ380 K and allows extraction of the hole concentration (p). The calculated p are compared to alternative methods of determining hole densities in these materials: pulsed high magnetic field ͑up to 55 T͒ technique at low temperatures ͑less than the Curie temperature͒, and electrochemical capacitance-voltage profiling. We find that the anomalous Hall effect ͑AHE͒ contribution to xy is substantial even well above the Curie temperature. Measurements of the Hall effect in this temperature regime can be used as a testing ground for theoretical descriptions of transport in these materials. We find that our data are consistent with recently published theories of the AHE, but they are inconsistent with theoretical models previously used to describe the AHE in conventional magnetic materials.

Scaling relation of the anomalous Hall effect in (Ga,Mn)As

“…Meanwhile the Berry phase mechanism is considered the dominant contribution to the AHE in metallic (Ga,Mn)As. 11,12,13,14,15,16 Whereas most papers concerning the AHE in (Ga,Mn)As are primarily focused on the metallic regime 11,12,13,14,15,16 , only a few systematic studies concentrate on the low-conductivity regime. 13,17,18 Allen et al 18 examined the AHE in digitally doped (Ga,Mn)As structures with hopping transport on the insulating side of the metal insulator transition (MIT).…”

Anomalous Hall effect in insulatingGa1−xMnxAs

“…(2) and the critical parameter mentioned above, we have estimated the critical concentration of holes for Ga 1-x Mn x As (x = 0.085) at T = 10K to be n h ≈ At high temperatures (e.g., 300K), the dependence of ρ xy on the magnetic field is linear for all samples (see Fig.2). This linear behavior allows us to roughly estimate the free carrier concentration in our samples, even though the anomalous Hall effect contribution to ρ xy may still be substantial at these high temperatures 6 . The resistivity and the hole concentration obtained from Hall measurements at 300K for all investigated samples are summarized in Table I.…”

“…In this context magnetotransport measurements -and especially the anomalous Hall effect --have been central in elucidating the essential role of free carriers (holes) in establishing the long-range ferromagnetic order in Ga 1-x Mn x As. 3 While most effort in this area has so far been focused on the AHE in Ga 1-x Mn x As with a high concentration of free carriers, 5,6 relatively little attention has been given to the case of low concentration of free holes, i.e., when this material shows insulating behavior. In this paper we present the results of Hall measurements on Ga 1-x Mn x As ( x = 0.085) which as-grown (i.e., without additional doping) shows insulating type of conductivity.…”

Interplay between Carrier and Impurity Concentrations in AnnealedGa1−xMnxAs: Intrinsic Anomalous Hall Effect

“…Insets depict methods used to determine R S , and the major errors associated, for metallic (top) and insulating (bottom) samples as well as quadratic scaling behavior with n 1:5, 2, 2:5 lines as a guide. [23]. Although some groups have inferred intrinsic origins of AHE in Ga 1ÿx Mn x As by observing n 2 to the scaling relationship xy c xx T n by varying the measurement temperature for a fixed N ÿ Mn and resulting in marginal variation of xx [24], here we vary the magnetic solute concentrations (N ÿ Mn ) to vary xx over 2 orders of magnitude at a fixed low temperature to minimize localization effects, especially for insulatorlike samples.…”