Disordered magnetism and spin glasses

Chapter 1 Magnetism of ternary intermetallic compounds of uranium

We investigate the effect of geometrical frustration on the competition between the Kondo coupling and the Ruderman-Kittel-Kasuya-Yosida interaction in Kondo lattice systems. By variational Monte Carlo simulations, we reveal an emergent quantum phase with partial ordering in which the frustration is relieved by forming a magnetic order on a sublattice and leaving the rest in the Kondo screening with spin-singlet formation. The role of quantum fluctuations and spin-charge interplay is elucidated.

Partial Kondo Screening in Frustrated Kondo Lattice Systems

Publisher Summary Stimulated by technological prospects of high-density magneto-optical (MO) recording and by fundamental research on magnetism, a wealth of experimental data on MO Kerr spectra had been collected until the beginning of the nineties. The theoretical explanation of magneto-optical Kerr effect (MOKE) spectra because of first-principles band-structure calculations was at that time in its infancy, and consequently all the insight that theory could give in the microscopic mechanism leading to large Kerr rotations was mainly speculative, because nothing could be proven by first-principles calculations. This situation has profoundly changed, due to the rapid development of first-principles computational research on MO Kerr spectra during the nineties.

Chapter 3 Magneto-optical kerr spectra

Publisher Summary The muon spin rotation/relaxation/resonance (μSR) spectroscopy has become an important tool for probing local static and dynamic magnetic properties. In over two decades a quite substantial body of μSR data has been collected from rare-earth and actinide materials, the latter, however, mostly restricted to samples containing uranium. μSR is the measurement of the temporal development of the spatial orientation of the spins of muons, which have been implanted in the material of interest with all spins initially fixed in one direction (complete muon spin polarization). μSR can be performed either with positive or negative muons. The latter behave like heavy electrons and will be captured into Bohr orbits by the atoms in the sample material. They will quickly reach the ls ground state, whose orbital radius, however, is comparable to nuclear radii. Negative muons thus sense predominantly the effects of the protonic charge distribution and the result is primarily of interest to nuclear physics. The magnetic field at the site of the muon in a magnetic compound is, at least in part, created by the dipole moments on neighboring paramagnetic atoms or ions.

Chapter 206 μSR studies of rare-earth and actinide magnetic materials

We have determined unusual magnetic ordering of the hexagonal intermetallic uranium compound U${\mathrm{N}}_{\mathrm{i}4}$B via neutron diffraction. In the easy basal plane the U moments have triangular symmetry with antiferromagnetic interactions. Along the hard $c$ axis ferromagnetic coupling occurs. Below ${T}_{N}=20$ K only two out of every three U moments of $1.2{\ensuremath{\mu}}_{B}$ order in vortexlike arrangements around the third paramagnetic spin. This novel magnetic structure is related to the occurrence of a crystallographic superstructure. Previously observed anomalies in bulk properties below ${T}_{N}$ are attributed to unconventional spin-wave excitations associated with this type of ordering.

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Magnetic ordering and frustration in hexagonal UNi4B

The hexagonal uranium intermetallic compound ${\mathrm{UNi}}_{4}$B orders antiferromagnetically below ${\mathit{T}}_{\mathit{N}}$=20 K in a magnetic structure, where, in zero applied magnetic field, one-third of the spins remains paramagnetic. Here, we report on the high-field (B\ensuremath{\le}50 T) magnetic and transport properties of this material. We establish the magnetic structures and phase diagram and the influence of magnetic field on the paramagnetic spins. Model calculations of the magnetization assuming two independent spin systems are in qualitative agreement with the observed magnetization.

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Magnetization and resistivity of UNi4B in high magnetic fields

We have studied the magnetic anisotropy on a single crystal of the new heavy-fermion compound CePd 2 Al 3 . The magnetic moments lie in the hexagonal ( a , b )-plane, but do not order antiferromagnetically, in contrast to annealed polycrystalline samples. The Kondo effect can account for the large specific heat at low temperatures. The small crystal-field splitting causes a field-induced electric-quadrupole moment, which orders in fields larger than 4.3 T.

Kondo effect and quadrupolar interactions in single-crystal CePd2Al3

Low-temperature structure of UNi2Sn

We have determined the Kondo temperature and crystal-field splitting of the new heavy-fermion compound CePd2Al3 by thermopower and inelastic neutron scattering. The absence of static, magnetically ordering cerium moments in single crystals is demonstrated by zero-field μ+SR. Small deviations of aluminum stoichiometry yield significant variations of TN of CePd2Al3 and Tc of UPd2Al3 in different samples.

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A. Drost

Papers

Magnetic ordering and frustration in hexagonal UNi4B

Magnetization and resistivity of UNi4B in high magnetic fields

Kondo effect and quadrupolar interactions in single-crystal CePd2Al3

Low-temperature structure of UNi2Sn

Crystal symmetry and electronic properties of heavy-fermion MPd2Al3 (M = Ce, U)☆