a Magnetization and Nuclear Magnetic Resonance Study of Nickel-Based Metallic Glasses.
Abstract
This work presents and discusses the results of nuclear magnetic resonance (NMR) (both pulse and continuous wave) and magnetization measurements of the melt spun metallic glass systems: Ni_{100-x}P_ {x} (18 <=q x <=q 22), (Ni_{0.20}Pt_ {0.80})_{100-x}P_{x } (23 <=q x <=q 30) and Ni_{80}(P_{1 -z}B_{z})_{20} (0 <=q z <=q 0.75). The magnetization measurements have been carried out for temperatures 4.2 ^circ K <=q T <=q 295^circ K and magnetic fields H <=q 20 kOe. ^{31 }P and ^{195}Pt NMR spectra have been obtained for temperatures 4.2 ^circ K <=q T <=q 295^circ K and resonance frequencies 4 MHz <=q v_{o} <=q 16 MHz. The three systems studied in this work, along with the three systems previously studied ((Ni_{0.50}Pd _{0.50})_{100-x}P_ {x}, (Ni_{y}Pd_{1 -y})_{80}P_{20} and (Ni_{y}Pt_{1-y })_{75}P_{25}), represent a complete and systematic combination of amorphous alloys in which both the metalloid concentration and relative transition metal composition are varied. Both the ^{31}P Knight shift and nuclear spin-lattice relaxation rate in these systems decrease with increasing P concentration, x, however, they do not depend on the relative Ni composition, y, nor whether the second transition metal is Pd or Pt. The ^ {31}P resonance line is somewhat asymmetric with a linewidth that increases with increasing frequency, which is indicative of a broadening mechanism resulting from a distribution of Knight shifts, and a direct consequence of the P atoms having a variety of environments in the glassy atomic structure. The magnetization measurements yielded susceptibility values which also decreased with increasing P concentration, x, and, in addition, demonstrated a systematic variation with the relative transition metal composition, y, which correlated with the ^ {195}Pt Knight shift behavior. The Ni _{100-x}P_{x} magnetic susceptibilities contained a local moment contribution which could be described by the Curie law (theta ~ 0) and was attributed to superparamagnetic Ni clusters. Fittings to the Brillouin function yielded the same local magnetic moment value of approximately 7.0 mu_{B} for all five Ni_{100-x}P_{x} alloys, however, different moment concentrations. All of these results are discussed in the light of various band models for the electronic structure, electronic charge transfer from the metalloid atoms to the transition metal d-states and covalent bonding (molecular orbital) methods. Finally, there is no evidence for any minimum in the electronic density of states as predicted by the Nagel and Tauc model. (Abstract shortened with permission of author.).
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1988
- Bibcode:
- 1988PhDT.......107P
- Keywords:
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- Physics: Condensed Matter