Anomalous Hall effect in thin films of Pr 0.5 Sr 0.5 MnO 3 P. Wagner, * D. Mazilu, † L. Trappeniers, V. V. Moshchalkov, and Y. Bruynseraede Laboratorium voor Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium Received 7 January 1997 We report on the type and density of charge carriers obtained from Hall-effect measurements in the three different magnetic phases of Pr 0.5 Sr 0.5 MnO 3 . The field dependence of the Hall resistivity has two contribu- tions of opposite sign: one is related to skew scattering and dominates in low magnetic fields; the other one is due to the Lorentz-force contribution which prevails at higher fields. This second contribution corresponds to a temperature-independent carrier density in the order of 0.8 holes per chemical unit cell. The skew-scattering contribution is related to the susceptibility of the material and is maximum at the transition temperature from the ferro- to the antiferromagnetic state. S0163-18299751522-0 I. INTRODUCTION The rare-earth perovskites R 1 -x D x MnO 3 R : rare earth, D : divalent dopant are characterized by their intimate rela- tionship between magnetic ordering and electrical conductiv- ity, culminating in the giant negative magnetoresistance ef- fect GMR. 1,2 The conductivity in the paramagnetic state is thermally activated, while a metalliclike behavior, based on the double-exchange mechanism, is observed below the Cu- rie temperature. The magnetic perovskite Pr 0.5 Sr 0.5 MnO 3 exhibits, apart from its para- to ferromagnetic transition at T C =260 K, a second transition to the antiferromagnetic state at T N =160 K. 3,4 In the antiferromagnetic regime the system is semiconducting, which was ascribed to an ordering transi- tion of the charge carriers, provided by the 1 to 1 ratio of Mn 3 + and Mn 4 + ions. 4 In the present paper we address the question of whether the carrier density determined by Hall measurements com- plies with the value expected from the chemical doping. Be- sides the influence of the temperature-dependent magnetic structure of Pr 0.5 Sr 0.5 MnO 3 on the mobility of the carriers, the strong decrease of longitudinal resistivity with increasing field at constant temperature might be caused by an increas- ing concentration of free carriers. 4 A difficult point in the evaluation of the Hall data, however, is the superposition of an extraordinary contribution to the usual Hall voltage, aris- ing from the spin-orbit interaction of the moving carriers with the localized magnetic moments. 5 This ‘‘skew- scattering effect’’ scales with the magnetization of the sample and dominates the measured Hall voltage up to field values where the magnetization becomes saturated. The dif- ferent types of magnetic ordering in Pr 0.5 Sr 0.5 MnO 3 will probably strongly influence the magnitude of this anomalous Hall contribution. It follows that the ordinary Hall effect is only accessible in fields above the saturation field of typi- cally 1 T for all temperatures below T C . These high fields are, however, sufficient to destroy also the antiferromagnetic spin structure found below T N by generating ferromagnetic or canted spin configurations. II. EXPERIMENTAL Thin films of Pr 0.5 Sr 0.5 MnO 3 were prepared in situ by dc-magnetron sputtering from a composite target onto 100-oriented SrTiO 3 substrates. The details of the prepa- ration have been reported in Ref. 6. Epitaxial growth, phase purity, and composition were checked by x-ray diffraction and Rutherford backscattering. Superconducting quantum in- terference device SQUID magnetization measurements en- abled the determination of the Curie point T C =263 K and the Ne ´ el temperature T N =160 K. The Hall measurements were performed on a 3000 Å thick unpatterned film stripe 10 mm2.8 mm, using evaporated and annealed gold con- tacts in a conventional four-point Hall configuration. The transverse resistance R T was measured by an ac technique and the Hall resistance R H was then calculated from the half difference of the two R T measurements with the magnetic- field direction parallel and antiparallel with the film’s normal axis. Typical values for R T were 10  in zero field while the actual Hall contribution was below 5 10 -2 . In order to minimize noise and instabilities we focused on measure- ments at constant temperature, performed according to the following scheme: After carefully stabilizing the tempera- ture, the magnetic field was increased first to +12 T and then reversed to -12 T. The resistance R T was measured while sweeping the field from -12 T to zero field within 6 h. Then the field was switched to +12 T and R T was recorded during the sweep back to zero field, again within 6 h. The sweep rate is a compromise between the requirements of low noise level and sufficient long-term stability of the absolute sample temperature. The special sequence of field sweeps was cho- sen to eliminate artifacts caused by the small remanent mag- netization of the superconducting field coil and by the mag- netic hysteresis of the Pr 0.5 Sr 0.5 MnO 3 film itself. Although Pr 0.5 Sr 0.5 MnO 3 does not show any hysteresis at room tem- perature, we noticed a small coercive field in the range of 100 mT below 150 K. 6 This hysteresis is also observed in the field dependence of the resistivity. The measurements of R T were therefore performed on equivalent branches of the resistive hysteresis loop. Finally, a difficulty arose from the resistive memory effect in Pr 0.5 Sr 0.5 MnO 3 , appearing at 70 K and demonstrating a large amplitude at T →0. These irre- versible and time-dependent changes of resistivity did not allow Hall measurements at very low temperatures. We therefore restricted our studies to temperatures above 50 K. III. RESULTS AND DISCUSSION Figure 1 shows the field dependence of the Hall resistivity  xy =dR H film thickness d  3000 Å measured at different RAPID COMMUNICATIONS PHYSICAL REVIEW B 1 JUNE 1997-II VOLUME 55, NUMBER 22 55 0163-1829/97/5522/147214/$10.00 R14 721 © 1997 The American Physical Society