Plasma ion heating produces L10 FePt nanoclusters
- PDF / 461,071 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 25 Downloads / 190 Views
1087-V08-08
Plasma ion heating produces L10 FePt nanoclusters Marlann Marinho Patterson1,2, Xiangxin Rui2,3, Xingzhong Li2, Jeff E. Shield2,3, and David Sellmyer2,4 1 Physics, UW - Stout, Wisconsin's Polytechnic University, 103 Jarvis Hall Science Wing, Menomonie, WI, 54751 2 Nebraska Center for Materials and Nanoscience, University of Nebraska - Lincoln, Lincoln, NE, 68588-0113 3 Mechanical Engineering, University of Nebraska - Lincoln, Lincoln, NE, 68588-0656 4 Physics and Astronomy, University of Nebraska - Lincoln, Lincoln, NE, 68588-0113 ABSTRACT In this study, cubic and spherical FePt clusters were created by inert gas condensation in an argon-helium dc sputter discharge under different flow and target power conditions. The plasma recipes for spherical and cubic clusters called for high He:Ar ratio, low target power and low He:Ar ratio, high target power, respectively. As expected, Langmuir probe measurements show the recipes led to larger ion density for the cubic case (2 x 108 cm-3 versus 6 x 106 cm-3 for spherical). We conclude that the larger density of argon ions increased the cluster-ion collision probability, heating the clusters in situ to promote atomic rearrangements and the formation of the ordered L10 crystal structure rather than the disordered fcc structure. INTRODUCTION Nanomagnetic cluster materials have wide applications as high-density storage media precursors [1, 2]. Factors of ten increases in storage density are expected with the use of nanomagnetic clusters over present hard disc drive materials. Several methods to create nanomagnetic clusters exist, among them gas-phase aggregation in a sputter discharge [3]. This method offers a high degree of cluster property control. The nanomagnetic FePt clusters created in the gas phase normally develop a random fcc crystal structure [3]. The ordered phase, however, is necessary to achieve magnetic coercivities commensurate with the memory industry’s future. Typically, a post-processing anneal is needed to achieve this ordered phase. However, it has been shown that in situ anneal is possible [4]. The method used in [4] to produce the cubic, ordered clusters is not well documented, however. Here, we present a method to create these cubic, ordered nanomagnetic FePt clusters in situ and propose a mechanism for the success of the method. There are three possible mechanisms for cubic cluster formation: (1) The plasma conditions offer long residence times and high ion-cluster collision probability. (2) Increased current to the target pre-heats the target atoms before they form clusters. (3) Both effects occur synergistically. To determine which of the three mechanisms is dominant, we performed several inert gas condensation experiments.
EXPERIMENT Fe-Pt clusters are created by inert gas condensation (IGC) [5, 6, 7] from a composite sputtering target consisting of Pt pieces in an Fe target [8]. The target is biased with a DC source immersed in a mixture of argon and helium gas. The bias creates a plasma discharge. A magnet behind the target creates a 10
Data Loading...
