At room temperature a large magnetoresistance, IsR/R(H =0), of 60% has been observed in thin magnetic films of perovskitelike La-Ba-Mn-o, The films were grown epitaxially on SrTi03 substrates by oA'-axis laser deposition. In the as-deposited state, the Curie temperature and the saturation magnetization were considerably lower compared to bulk samples, but were increased by a subsequent heat treatment. The samples show a drop in the resistivity at the magnetic transition, and the existence of magnetic polarons seems to dominate the electric transport in this region. PACS numbers: 75.70.Ak, 72. 15.Gd, 73.50.Jt Giant magnetoresistance (GMR) due to spin-dependent scattering at the interface between ferromagnetic and nonmagnetic regions has been the subject of intense research in the last years [1-4]. At room temperature, resistance changes hR/R(H=0) as high as 40% have been observed in Cu/Co multilayers [2] and up to 11% in heterogeneous Cu/Co alloys [3,4], compared to only 2%-3% for "conventional" materials such as permalloy. A much higher magnetoresistance was found near a metal/insulator and simultaneous magnetic phase transition, e.g. , in Eu~-"Gd"Se [5], but in this material the eAect is restricted to temperatures below 50 K. The anomalous transport phenomena in these Eu-chalcogenide alloys have been explained by the appearance of giant spin molecules [6] and spin polarons [7]. Similar observations have been made in the mixed valence perovskitelike Ndo 5Pbo 5Mno3 in the region around the ferromagnetic phase transition at 184 K [8]. A large drop in resistivity and a high magnetoresistance AR/ R (0) & 50% was found, which is also believed to be caused by the existence of magnetic polarons. La2/3-Ba~g3Mno3 is also well known as a mixed valence metallic ferromagnet, but with a considerably higher Curie temperature of Tc =343 K [9,10]. At the Curie temperature a cusp in the resistivity was found and therefore gives rise to the assumption of a high magnetoresistance eAect at room temperature. Targets of stoichiometric composition were prepared by standard ceramic techniques from the metallic oxides and carbonates of 99.9% purity by repeated grinding and annealing in air. The x-ray diAraction patterns showed no other reAections than those of the rhombohedral unit cell found in Ref. [10] (a =0.3910 nm, y=90. 12'). Thin films of 150~10 nm thickness were grown on SrTi03 10&&10 mm substrates in (100) and (110) orientation. A laser deposition technique in off'-axis geometry was used, which had previously turned out to be a powerful tool in preparing high-T, superconducting thin films with a smooth surface [11]. Different substrate temperatures between 600 and 900 C were used, at a deposition pressure of 0.4 mbar oxygen. Epitaxial films were obtained for a substrate temperature of Tg =600 C as confirmed 250 T= 300K 200 8 A 0 bP c5 150 100 50 0:-0.0~a nnealed O 0.5 1.0 1.5 magnetic field p, H [T] 2.0 FIG. 1. Room temperature magnetization curve for the asdeposited sample (Ts =600'C) showing paramagnetic behav-ior. The ferroma...

Au-Co and Au-Co-B alloys have been prepared by rapid solidification, followed by heat treatment. The precipitation of the ferromagnetic phases Co and Co2B in the Au matrix phase has been observed during annealing. At room temperature, both magnetization and magnetoresistance are determined by the superparamagnetic behavior of the ferromagnetic particles. The magnetoresistance is believed to have the same origin as that in multilayers and granular films. Both Co particles and the precipitates of the Co2B intermetallic phase give rise to a high magnetoresistance. The magnetoresistance effect was less than 1% in the as-quenched samples and increased to about 3% after an appropriate heat treatment.

Cu1−xCox alloys with x=0.1 and x=0.2 have been prepared by conventional melt spinning. The rapid solidification process results in an extended solubility of Co in Cu although some Co precipitates already during quenching. In the as-quenched ribbons, the magnetoresistance (MR) is only of the order of 1.5%. It increases dramatically with the controlled nucleation and growth of Co precipitates from the supersaturated Cu matrix. The highest MR of 11% at 300 K occurs for Cu90Co10 after an aging at about 440 °C when the Co clusters are superparamagnetic. Saturation is possible only after a higher annealing or at lower measuring temperatures. For the optimally annealed samples the MR increases to 36% at 30 K.

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Nd-Fe-B/Fe/Nd-Fe-B trilayers with individual layer thicknesses between 10 and 100 nm have been grown by sputter deposition. The aim of our study is to investigate remanence enhancement due to exchange coupling between the soft-and hardmagnetic layers as a function of the Fe-interlayer thickness d. It is shown that for decreasing d the remanence of the trilayer system is significantly increased due to exchange coupling. The coercivity of the trilayer is also increased for d T 40 nm which can be explained with a higher nucleation field for magnetization reversal.

Micrometer-sized highly sensitive strain sensors are presented. The sensors are based on magnetic tunneling junctions (MTJs) incorporating magnetostrictive free layers. The influence of mechanical strain upon the free layer is explained by a model taking into account the total free energy of the sensing layer. Those MTJ devices prepared in situ with magnetostrictive Fe50Co50 layers exhibit a tunneling magnetoresistance (TMR) ratio of 48%. The changes in strain Δε on the order of 0.4 parts per thousand (‰) result in resistance changes of 24%, which in turn leads to gauge factors [(ΔR/R)/Δε] on the order of 600, whereas gauge factors of 2–4 are typical for metal based, and 40–180 for piezoresistive semiconductor strain gauges.

Magnetically isotropic Nd15Fe77B8 powder is prepared by mechanical alloying and a solid-state reaction from the elemental powders. Due to the extremely short reaction time (for example, 10 min at 700 °C) the magnetically isotropic particles have a very fine microstructure comparable to rapidly quenched samples, show a pinning-type behavior and possess excellent magnetic values such as IHC up to 13 kOe and BHmax up to 12.8 MGOe. Details on the development of the microstructure during milling, the reaction kinetics, and the magnetic properties are reported.

We investigated the magnetoresistance of La2/3Ca1/3MnO3+δ magnetic thin films. Under certain conditions, the magnetoresistance curves show a remarkable hysteresis and the resistance becomes dependent on the magnetic history. A relaxation behavior of the resistance has also been observed. Hysteresis and relaxation of the resistance are very similar to the phenomena of magnetoviscosity of the magnetic moment in spin glasses and the magnetic aftereffect in hard magnets.