Sputter deposited, equiatomic Pt-Mn thin films used in giant magnetoresistive spin valves are found not to exist in the antiferromagnetic state required for device operation. Therefore, an annealing step is needed to induce a phase transformation from the as-deposited, paramagnetic A1 ͑fcc͒ phase to the antiferromagnetic L1 0 phase. The L1 0 phase is the thermodynamically stable configuration, but favorable kinetics for the transformation were only found above 260°C. The A1 to L1 0 phase transformation was studied by x-ray diffraction, transmission electron microscopy and differential scanning calorimetry ͑DSC͒. The nucleation and growth conditions were evaluated and an exothermic transformation enthalpy of Ϫ12.1 kJ/mol of atoms was determined. The kinetics of the reaction were simulated using the Johnson-Mehl-Avrami analysis, where the necessary parameters were determined by the Kissinger and Ozawa methods from constant scanning rate DSC experiments ͓H. Yinnon and D. R. Uhlmann, J. Non-Cryst. Solids 54, 253 ͑1983͔͒. The resulting simulations were compared to DSC data as well as isothermal x-ray peak shift data and a reasonable agreement was obtained.
The equilibrium phase diagram of the nickel-manganese system is determined between 500 and 850°C, in the composition range between 25 and 70 at. % Ni. A combination of electron probe microanalysis, x-ray diffraction, and optical microscopy was employed to analyze 47 samples that were annealed anywhere from three to seven months. The equiatomic, antiferromagnetic, L1 0 -NiMn phase that is of considerable technological interest was found to exist continuously between 500 and 700°C. No other intermediate phases were found in this study at low temperatures. These results are in contrast to the currently accepted phase diagram published in most handbooks. A hot-isobaric-pressing method was used to initially bond samples that were subsequently used to determine interdiffusion coefficients in the Ni-Mn system at 650°C. The Boltzmann-Matano method ͓T. Heumann, Z. Phys. Chem. 201, 168 ͑1952͔͒ allowed the calculation of these interdiffusion coefficients across the ␣-Mn, -Mn, ␥-Mn, Equiatomic Ni-Mn thin films are of interest to the magnetic storage industry for use in magnetoresistive sensors. 1 In these sensors, exchange coupling between an antiferromagnetic film, such as NiMn, and a soft ferromagnetic film is required to hold or ''pin'' the magnetization within the ferromagnetic layer. 1 However, the L1 0 phase of NiMn is the only antiferromagnetic phase of this intermetallic, and is thus the only phase suitable for use in these sensors. Therefore, understanding the compositional and temperature ranges over which this antiferromagnetic phase is stable is extremely important but is made very difficult due to the vast inconsistencies between published equilibrium phase diagrams. Furthermore, there is no existing diffusion coefficient information for Ni-Mn alloys in the equiatomic range. Diffusion coefficient information is of significant importance because interlayer diffusion is a primary long-term failure mechanism in magnetoresistive sensors. In the present study, we apply information gained from experiments to resolve the controversy between existing phase diagrams as well as report reliable diffusion coefficients for NiMn alloys.NiMn exists in three solid polymorphic phases at the equiatomic concentration: a high-temperature ͑H͒, chemically disordered, face-centered-cubic ͑fcc͒ A1 phase; a midtemperature ͑M͒, chemically ordered, cubic B2 phase; and a low-temperature ͑L͒, antiferromagnetic, chemically ordered, tetragonal L1 0 phase. 2 The L1 0 structure is simple tetragonal with a two atom basis that resembles a nonBravais, body/face-centered-tetragonal structure. Although all previously published phase diagrams report the existence of these three phases, their reported equilibria are drastically different. For example, the phase diagram as determined by Coles and Hume-Rothery 3 shows a L1 0 phase that is stable from room temperature to 700°C, while Tsiuplakis and Kneller 4 reported a much more complicated phase diagram which claims that no single phase is stable at the equiatomic composition between 480 and 620°C. Th...
The majority of research on Pb-free solders has been done with reflow times sufficient to allow significant intermetallic growth at the liquid solder/pad interface. With the need for small, fine-pitched solder joints and to avoid damage to heat-sensitive read/write sensors, the hard disk drive industry predominantly uses solder jet bonding for electrical connections of the heads. This technique does not use flux and has solidification times on the order of a millisecond, four orders of magnitude smaller than that of conventional solder technology. Therefore, the intermetallic formation is highly nonequilibrium and is localized near the pad interface. Surface finish thicknesses and composition have a significant influence on intermetallic growth and composition of solder joints. The intermetallic microstructure, along with voids, can significantly impact joint reliability. In this paper, results of wettability and mechanical solder ball shear measurements on as-plated and aged samples are reported and correlated with microstructure and growth of intermetallic compounds (IMCs) at the solder/pad interface. A wide range of Au-Sn IMCs are found at the pad interface, and Au-embrittlement effects are not found until Au exceeds 7 wt.%.
Sputter-deposited, equiatomic PtMn thin fi lms have application in giant magnetoresistive spin valves, tunneling magnetoresistive spin valves, and magnetic random access memory. However, the as-deposited fi lms are found to be a disordered A1 phase in a paramagnetic state rather than an antiferromagnetic phase with L1 0 structure, which is needed for device operation. Therefore, a postannealing step is required to induce the phase transformation from the asdeposited A1 face-centered-cubic phase to the antiferromagnetic L1 0 phase. The A1 to L1 0 metastable transformation was studied by x-ray diffraction and differential-scanning calorimetry. An exothermic transformation enthalpy of -12.1 kJ/mol of atoms was determined. The transformation kinetics were simulated using the Johnson-Mehl-Avrami analysis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.