Large In-Plane Lattice Expansion in NiAs-MnSb Thin Films Induced by ns Laser Recrystallization
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IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099 of Materials Science and Engineering, Stanford University, Stanford, CA 94305
**Department
ABSTRACT
Sputter deposited MnSb thin films were annealed utilizing KrF excimer laser pulses (16ns), and the resulting structural and magnetic changes investigated. These changes are compared to those observed when the samples are subjected to isothermal and rapid thermal annealing treatments. Isothermal and rapid thermal annealing induce significant lateral grain growth, whereas the laser treatment produces vertical grain size refinement with no appreciable lateral growth. Annealing is shown to increase the hexagonal c-axis, reaching an expansion value of 7% for the laser annealed samples. This c-axis expansion has a strong influence on the magnetic properties of the thin films. Mechanisms for the c-axis expansion are discussed. INTRODUCTION
The E-phase of Mn-Sb system is reported to exist for Mn atomic compositions ranging from 44 to 50% as shown in the phase diagram of figure 1. [1] This iE-phase has a hexagonal crystallographic structure and is classified as belonging to the NiAs type. [2] The lattice parameters and magnetic properties are reported to exhibit a strong composition dependence in this range. [2-6] The variations in magnetic moments and Curie temperatures are ascribed to changes in Mn-Mn atomic spacing resulting from changes in lattice parameter as a function of site occupancy. Similarly, Nagasaki et al [5] have studied the pressure dependence of the lattice parameters of MnSb and found dramatic changes in Curie temperatures. In this work, we seek to induce lattice parameter changes by rapid resolidification and recrystallization of fixed composition MnSb thin films. We expect that volume changes due to recrystallization will result in lattice strain and seek to compare the corresponding changes to their magnetic and magneto-optic activity. To this effect we utilized three different time-temperature regimes of annealing; laser quenching (LQ), rapid thermal annealing (RTA) and isothermal furnace annealing (IA). Typical annealing times for each method are 16 ns, 120 sec. and 5 hours, respectively. A variety of structural and magnetic probes are employed to monitor the effect of annealing under this wide temporal range of conditions.
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Mat. Res. Soc. Symp. Proc. Vol. 384 0 1995 Materials Research Society
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30
40
60
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Atomic Percent Antimony
Fignre 1. Mn-Sb phase diagram [I]. Ni-As formation.
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90
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Sb
Note the compositional range for the F,-phase
EXPERIMENTAL TECHNIQUES MnSb thin films were deposi.ed by DC magnetron sputtering (base pressure < IxlO-7 Torr.) from elemental targets at a sputter pressure of 3 mTorr of Argon onto quartz substrates. The film layer structure is substrate / SiN (20 nm) / MnSb (150 nm) / SiN (12.5 um) All layers were grown during the same pumpdown and the SiN was grown by reactive sputteri
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