Weak Ferromagnetism in Dilute Manganese-Nickel Alloys
Open Access
- Author:
- Podolak, Kenneth Ryan
- Graduate Program:
- Physics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 05, 2008
- Committee Members:
- Roy F Willis, Committee Chair/Co-Chair
Peter E Schiffer, Committee Member
Renee Denise Diehl, Committee Member
Darrell Schlom, Committee Member - Keywords:
- magnetism
ferromagnetism
spin disorder
spin glass - Abstract:
- Nickel manganese alloys are interesting due to their novel magnetic behavior. At low concentrations of manganese, the alloys show increased ferromagnetism at room temperature. Increasing the concentration to 25% manganese in nickel results in a frozen spin glass with reduced ferromagnetism. The transition from one state to the other is of fundamental interest. Furthermore, magnetic alloy thin films have widespread application in magnetic memory devices. By diffusing manganese into a nickel single-crystal substrate, spin scattering effects in the sp bands were explored. The behavior was compared with that of chromium and iron-doped nickel alloys. The results show that the behavior in manganese-doped nickel to be different in both the change in the exchange field and the spin transport properties. I have built a vapor deposition system to investigate nickel manganese alloys characterized with surface science techniques, namely reflection high energy electron spectroscopy (RHEED), low energy electron diffraction (LEED), and scanning electron microscopy (SEM). Samples were grown on Si(100) with buffer layers of copper sandwiching the nickel manganese alloy. Magnetic hysteresis loops and magnetic circular dichroism (MCD) signatures show a transition in the magnetism at 15% manganese in nickel when measured at 100K. This transition is a sign of this alloy entering a re-entrant spin glass (RSG) magnetic phase. Thermal hysteresis measurements confirm that the spin glass freezing temperature for a 10% manganese in nickel sample is around 100K. The measurements endorse the unusual precursor spin-glass behavior of dilute ferromagnetic alloys of manganese in nickel. With increasing doping, the nickel first shows increased ferromagnetism followed by spin disordering and the formation of a spin glass.