High Quality NiFe/Ag Superlattices Made by Pulsed Laser Deposition (PLD)
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RANDOLPH E. TREECE,t PAUL DORSEY, JAMES S. HORWITZ, SYED QADRI, AND DOUGLAS B. CHRISEY Condensed Matter and Radiation Sciences Division, Naval Research Laboratory, Washington, DC, 20375. ABSTRACT High-quality thin-film superlattices of permalloy (NiFe) and silver (Ag) have been grown by pulsed laser deposition (PLD) for the first time. The alternating metallic layers were grown from individual NiFe and Ag targets utilizing an automated multi-target holder coupled to a conventional PLD system. The targets were ablated at a base pressure of 4x10- 7 Torr and the material deposited on room-temperature (100) silicon and on fused silica substrates. The films were characterized by X-ray diffraction (XRD), magnetic field-dependent resistivity, and ferromagnetic resonance (FMR). XRD was used to confirm uniform bilayer thicknesses. The magnetic field-dependent resistance measurements indicated the presence of magnetoresistance in the deposited films. An as-deposited film with a bilayer thickness of 75 A demonstrated a roomtemperature magnetoresistive effect of 0.15 %. FMR has been used to determine the relationship between NiFe magnetism and the observed magnetoresistance.
INTRODUCTION Materials which display large changes in resistivity (AR/RH%) as a function of applied
magnetic field, an effect known as giant magnetoresistance (GMR), have important applications in magnetic read head devices. GMR was first discovered in ferromagnetic/metallic (Fe/Cr) thin-film multilayers,1 but also has been observed in films of heterogeneous, granular ferromagnetic/metallic alloys, as well. 2 The GMR properties of the deposited films have been shown to depend on the size of the magnetic domain, whether it be the thickness of the magnetic layers in the multilayers or the particle size of the ferromagnetic metals in the granular films. These materials are metastable with respect to complete phase separation into two larger unmixed grains. Excessive grain growth, caused by over heating the multilayers and granular films, destroys the GMR effect. The multilayer films typically are deposited by sputtering techniques. This work describes the first growth of magnetoresistive multilayers by pulsed laser deposition (PLD).3 While a wide variety of thin film materials have been grown by PLD, the technique is most often used to deposit multicomponent oxide films. 4 Recently, as-deposited sputter-grown silver/permalloy (Ag/Ni0.8Fe0. 2 ) multilayer films have been shown to exhibit a AR/R% value as large as 0.22%, which increased to >5% upon annealing at 335 *C.5 We have deposited high-quality Ag/NiFe multilayers by PLD which display as-deposited values of AR/RH% as high as 0.15%.
89 Mat. Res. Soc. Symp. Proc. Vol. 382 01995 Materials Research Society
Figure 1. Pulsed laser deposition system. EXPERIMENTAL DETAILS The Ag/NiFe multilayer films were grown by PLD at a base pressure of 5x10- 7 Torr by ablating individual Ag and Nio.8 Feo. 2 targets held on an automated target holder mounted in a highvacuum chamber (Figure 1), described in detail elsewher
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