Chi, Ji (2007-08). A nuclear magnetic resonance probe of Fe-Al and Al20V2Eu intermetallics. Doctoral Dissertation. Thesis uri icon

abstract

  • Al-rich Fe-Al systems (FeAl2, Fe2 Al5 and Fe4Al13) and Al20V2Eu have complicated structures with quasicrystal-like features making these materials potentially of interest for magnetic behavior. However, there is not much work on these materials. To study the variety of magnetic properties, we use NMR, magnetic susceptibility, specific heat and other methods in this work. The microscopic electronic and magnetic properties of the Al-rich Fe-Al system and Al20V2Eu have been studied via 27Al NMR at temperatures between 4 and 500 K. The results of spin lattice relaxation rates reveal a pseudogap in Fe4Al13 and Fe2Al5 around the Fermi-level in the density of states. Besides, a square well gap with a width of 2 meV and center at Fermi energy was detected by specific heat measurements in Fe2Al5. Both Fe4 Al13 and Fe2Al5 are non-magnetic systems with dilute magnetic defects, while FeAl2 is a concentrated local magnetic moment system. In Al20V2Eu, a crossover was observed in NMR, magnetization and transport measurements. Above 40 K, Eu(2+) local magnetic moments dominate; below 40 K, a transition to a Kondo regime is observed, where the Kondo effect leads to the reduction of localized moments due to the formation of a spin-compensated Kondo cloud. With increasing magnetic field, f electrons participate more and more in excitations near the Fermi level and a heavy-Fermion state was observed through specific heat measurements at high magnetic field.
  • Al-rich Fe-Al systems (FeAl2, Fe2 Al5 and Fe4Al13) and Al20V2Eu have complicated
    structures with quasicrystal-like features making these materials potentially of
    interest for magnetic behavior. However, there is not much work on these materials.
    To study the variety of magnetic properties, we use NMR, magnetic susceptibility,
    specific heat and other methods in this work.
    The microscopic electronic and magnetic properties of the Al-rich Fe-Al system
    and Al20V2Eu have been studied via 27Al NMR at temperatures between 4 and 500 K.
    The results of spin lattice relaxation rates reveal a pseudogap in Fe4Al13 and Fe2Al5
    around the Fermi-level in the density of states. Besides, a square well gap with a width
    of 2 meV and center at Fermi energy was detected by specific heat measurements in
    Fe2Al5. Both Fe4 Al13 and Fe2Al5 are non-magnetic systems with dilute magnetic defects,
    while FeAl2 is a concentrated local magnetic moment system. In Al20V2Eu, a
    crossover was observed in NMR, magnetization and transport measurements. Above
    40 K, Eu(2+) local magnetic moments dominate; below 40 K, a transition to a Kondo
    regime is observed, where the Kondo effect leads to the reduction of localized moments
    due to the formation of a spin-compensated Kondo cloud. With increasing
    magnetic field, f electrons participate more and more in excitations near the Fermi
    level and a heavy-Fermion state was observed through specific heat measurements at
    high magnetic field.

publication date

  • August 2007