Materials Science and Engineering B51 (1998) 216 – 218 Observation of a new type of giant magnetoresistance with possible sensor applications N. Overend a , A. Nogaret a , B.L. Gallagher a, *, P.C. Main a , M. Henini a , R. Wirtz b , R. Newbury b , C. Marrows c , M.A. Howson c , S.P. Beaumont d a Department of Physics, Uniersity of Nottingham, Nottingham NG72RD, UK b School of Physics, Uniersity of New South Wales, Sydney, NSW 2052, Australia c Department of Physics, Uniersity of Leeds, Leeds LS92JT, UK d Department of Electrical Engineering, Glasgow Uniersity, Glasgow G12 8QQ, UK Abstract We demonstrate the existence of a new type of giant magnetoresistance (GMR) in hybrid semiconductor/ferromagnetic devices. We observe up to a 1000% increase in resistance for applied fields of only 100 mT at a temperature of 4 K and 1% at 300 K. The GMR has a strong angular dependence and it can also be strongly hysteretic. Optimisation of device parameters is expected to increase considerably the magnitude of GMR. Such devices may have applications as magnetic sensors and memories. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Magnetoresistance-giant; Semiconductors; Devices; Heterostructures 1. Introduction The discovery of giant magnetoresistance (GMR) in magnetic multilayers and granular films has led to promising new magnetic sensor and non-volatile mag- netic memory designs. However, such applications re- quire integration with standard semiconductor devices which is not straightforward. An attractive alternative approach is to try to use integrated ferromagnetic/semi- conductor devices in which the resistance of the semi- conductor is controlled by the ferromagnetic element. In this paper we demonstrate one way in which this can be achieved using a ferromagnetic grating defined on the surface of a semiconductor device. The induced GMR in the semiconductor is up to 1000% at low temperatures and is 1% at 300 K. The GMR is due to a strong modification of the electron dynamics and is a generic effect which will be present for any combina- tion of ferromagnet/semiconductor material. Optimisa- tion of material should lead to considerably larger GMRs. The types of device used, illustrated schematically in Fig. 1, are similar to those use in several related studies [1–4]. The 2DES is formed in a 22 nm wide GaAs/ (AlGa)As quantum well, the centre of which is only 35 nm beneath the surface of the heterostructure. The electron density is 4.5 ×10 15 m -2 . The electron mobil- ity is 70 m 2 V -1 s -1 at 4.2 K, corresponding to an electron mean free path of l e =7 m. Arrays of cobalt stripes with period, a =500 nm are fabricated by elec- tron beam lithography directly on the surface of the heterostructure. The stripes are taken to be along the y -direction. The stripes have nominal width, d =200 nm and height, h =120 nm. In order to avoid any strain-induced electric modulation at the 2DES [1 – 3] due to the differential thermal contraction of Co and GaAs, the stripes are oriented normal to the [100] direction which is non piezo-electric [5]. The grating covers the entire active area of the Hall bar devices, which are 50 m wide and which have voltage probes separated by 130 m. The current is perpendicular to the direction of the stripes. Fig. 2 shows the longitudinal MR of the device measured with the external magnetic field perpendicular to the plane of the 2DES ( =0°) and at  =80° with the in-plane component perpendicular to the stripes * Corresponding author. Fax: +44 115 9515139, e-mail: ppzblg@ppn1.physics.nottingham.ac.uk 0921-5107/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S09 21- 5 1 07(97)00 2 63 - 8