Resistance Spikes at Transitions Between Quantum Hall Ferromagnets

Abstract

We report a manifestation of first-order magnetic transitions in two-dimensional electron systems. This phenomenon occurs in aluminum arsenide quantum wells with sufficiently low carrier densities and appears as a set of hysteretic spikes in the resistance of a sample placed in crossed parallel and perpendicular magnetic fields, each spike occurring at the transition between states with different partial magnetizations. Our experiments thus indicate that the presence of magnetic domains at the transition starkly increases dissipation, an effect also suspected in other ferromagnetic materials. Analysis of the positions of the transition spikes allows us to deduce the change in exchange-correlation energy across the magnetic transition, which in turn will help improve our understanding of metallic ferromagnetism.Ferromagnetism in metallic systems, also known as itinerant electron ferromagnetism, has thus far revealed few of its secrets to scientists. In one of its well-known occurrences, in transition elements Fe, Co, and Ni, metallic ferromagnetism is believed to stem from a partially filled 3d band of electrons with unbalanced spin populations, although the properties of their magnetic moments at nonzero temperature are still unclear (1) despite some recent theoretical progress (2). In dilute electron gases, the appearance of spontaneous magnetization at sufficiently low densities, as evidenced by recent experiments in doped hexaborides (3), is also subject to debate, with the critical density at the ferromagnetic to paramagnetic transition still uncertain (4). One difficulty in modeling these materials lies in their complexity, because itinerant charged carriers in these systems are subject not only to electron-electron interactions, but also to atomic potentials resulting in an intricate density of states or to local moments of other atoms in the material. Two-dimensional (2D) electron systems in modulationdoped semiconductor heterostructures, on the other hand, provide an ideal system for the study of itinerant electron ferromagnetism, as interactions with their host material are almost entirely contained in the effective mass (m * ) and effective g-factor (g * ) of electrons. Given these two renormalizations, carriers in these structures behave as a nearly free electron gas. In a perpendicular magnetic field (B ⊥ ), 2D electrons condense into a ladder of energy levels, called Landau levels, which are separated by the cyclotron energyhω c =heB ⊥ /m * . The total magnetic field (B tot ) also couples to the electron spin, and leads to an additional (Zeeman) energy ± 1 2 |g * |µ B B tot (where µ B is the Bohr magneton, eh/2m e , and m e is the bare electron mass), which splits each Landau level into two separate levels. The number of occupied spin-split Landau levels at a given field is called the filling factor, ν. This discrete level structure gives rise to the quantum Hall (QH) effect, the vanishing of longitudinal resistance (R xx ) and the quantization of the Hall resistance, that occurs when an integral nu...

Emergent phenomena at oxide interfaces

“…85 Therefore, a quantum Hall ferromagnetic state can be formed. 86 In addition, a ZnO heterostructure is almost free from nuclear spin -the natural abundance of Zn isotopes with nonzero spin ( 67 Zn) is 4%, and that of oxygen with non-zero spin ( 17 O) is 0.038%, and hence the electron -nuclear spin interaction is almost negligible. Therefore, ZnO is an ideal medium for spin transport experiments.…”

Two‐dimensional electrons occupying multiple valleys in AlAs

“…7c), there are "spikes" in the resistance, signalling extra dissipation at such crossings. 25,26,8 Moreover, the position of the spike depends on θ, and the magneto-resistance trace near the spike shows hysteresis as the direction of field sweep is reversed (Fig. 7c).…”

Magnetotransport in high-g-factor low-density two-dimensional electron systems confined inIn0.75Ga0.25Desrat1, Giazotto2, Pellegrini3 et al. 2004Phys. Rev. B354260View full textAdd to dashboardCite

“…In this relatively low-density In 0.75 Ga 0. 25 As quantum well only a limited number of Shubnikov-de Haas oscillations are detected at relatively low magnetic fields which inhibits the conventional determination of the Rashba coupling constant of the heterostructure. Previous studies, in fact, were conducted on samples having densities approaching 1 × 10 12 cm −2 or above [7,15,18].…”

“…25 As quantum well metamorphically grown by molecular beam epitaxy on a (001) GaAs substrate. An In x Al 1−x As step graded buffer with x ranging from 0.15 to 0.85 was inserted between the substrate and the 2DES to achieve almost complete strain relaxation at the quantum-well region.…”

“…25 As single quantum wells. These electron systems display clear quantum Hall states in a large range of temperatures and with electron densities down to n s = 1 × 10 11 cm −2 , the latter controlled by a gate voltage.…”