We observe electron magnetism originating from fractional quantum Hall states in single-layered GaAs heterojunctions. This magnetization is entirely governed by electron-electron interaction effects. The studies were performed at temperatures between 0.3 and 7 K on gated high-mobility twodimensional electron systems. We observe oscillations in the magnetic moment at various fractional filling factors, both for n , 1 and n . 1, which persist up to 3.8 K. Most prominent features are found at filling factors 1 3 , 2 3 , 4 5 , and 8 5 . In addition, an intrinsic strongly asymmetric magnetization around n 1 is observed. [S0031-9007(98)08279-9] PACS numbers: 73.40.Hm, 73.20.Dx, 75.30.Cr The magnetization is one of the most fundamental properties of matter and is, besides spin and orbital magnetism, also governed by many-body effects. Manybody interaction effects can be studied advantageously in two-dimensional electron systems (2DES) as realized in a semiconductor heterostructure, which allows one to tune the 2D electron density N S and, in a magnetic field B, the filling factor n N S ͑͞eB͞h͒. Interaction effects lead to a renormalization of the energy states, as it is well known for the exchange enhanced spin gaps at odd filling factors and less well known also for the Landau gap at even n [1]. A most interesting aspect, which has attracted a broad interest in the last years, is the formation of the fractional quantum Hall states (FQHS's) at filling factors p͞q with p integer and q odd by electron-electron interaction [2]. As introduced in the pioneering works of Landau [3] and Peierls [4] in the early 1930s, the magnetization M of conduction electrons has to be considered as a thermodynamic quantityand should thus directly reflect the renormalization effect. U denotes the free energy and N S is the electron density.In particular, it should give rise to a novel type of magnetization for the FQHS's which is entirely governed by the many-body interactions. However, experiments on 2DES magnetization are rather rare and quite a challenge due to the inherent small electron number. It lasted for quite a long time until the first signature of the Landau quantum oscillatory magnetization, i.e., the de Haas-van Alphen (dHvA) effect, was experimentally proven by Eisenstein et al. for conduction electrons in a 2DES [5]. Only very recently, it was possible to resolve the exchange induced enhancement of the spin magnetization at odd n [6,7]. In very high-mobility samples also the sawtooth-like magnetiza-tion [7] was proven in agreement with the 65-year old prediction [4]. Various recent theoretical [8] and experimental works [9] show that in the vicinity of FQHS's additional ground state configurations like skyrmions and spin waves exist, which are so far only partly understood, and their magnetization is not known. The physics of skyrmions and the FQHS's are often probed by activated transport [10] or optical excitation spectroscopy [11][12][13]. However, the former method measures the mobility gap, and within the latter techn...

The stray field of individual nanostructured permalloy (Py) disks has been measured by means of a sub-μm Hall magnetometer which incorporates a ballistic two-dimensional electron system. The circular nanomagnets have diameters of d=500, 600, and 700 nm and thickness of t=20 nm. The characteristic shape of the experimental Hall curves can be explained by the behavior expected from micromagnetic simulations. They indicate that near remanence the disks are in the vortex phase. For the largest Py nanomagnet, if saturated, an averaged value of the stray field of 36 mT is measured in our 300 nm wide Hall sensor.

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