S. Sakarya

Magnetic density of states at low energy in geometrically frustrated systems

Using muon-spin-relaxation measurements we show that the pyrochlore compound Gd(2)Ti(2)O(7), in its magnetically ordered phase below approximately 1 K, displays persistent spin dynamics down to temperatures as low as 20 mK. The characteristics of the induced muon relaxation can be accounted for by a scattering process involving two magnetic excitations, with a density of states characterized by an upturn at low energy and a small gap depending linearly on the temperature. We propose that such a density of states is a generic feature of geometrically frustrated magnetic materials.

Spin dynamics in geometrically frustrated compounds

Abstract We have probed the low temperature spin dynamics in two pyrochlore lattice compounds R2Ti2O7, where the rare earth (R3+) form a sublattice of tetrahedra linked by their corners such that geometrically derived magnetic frustration is possible. In Yb2Ti2O7 (Yb3+: S′=1/2, XY anisotropy), we show that below 0.24 K , the temperature of the known specific heat λ transition, there is no long range order. The transition, in fact, corresponds to a first-order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate is in the GHz range and it follows a thermal excitation law, whereas below the transition, the rate is in the MHz range and it is temperature independent. In Gd2Ti2O7, where the S-state Gd3+ ions are antiferromagnetically coupled, there is a magnetic phase transition near 1 K . As the temperature is lowered through the critical region, λZ, the spin-lattice relaxation increases. On lowering the temperature to 21 mK , λZ tends to a temperature independent value. Concomitant with the persisting electronic spin fluctuations, we observe oscillating components evidencing long-range spin correlations. Therefore, temperature independent spin dynamics is observed even after passing through a magnetic phase transition and even when the magnetic correlations are long range.

Dilatometry study of the ferromagnetic order in single- crystalline UrhGe

Thermal expansion measurements have been carried out on single-crystalline URhGe in the temperature range from 2 to 200 K. At the ferromagnetic transition (Curie temperature T C =9.7 K), the coefficients of linear thermal expansion along the three principal orthorhombic axes all exhibit pronounced positive peaks. This implies that the uniaxial pressure dependencies of the Curie temperature, determined by the Ehrenfest relation, are all positive. Consequently, the calculated hydrostatic pressure dependence dT C /dp is positive and amounts to 0.12 K/kbar. In addition, the effective Gruneisen parameter was determined. The low-temperature electronic Gruneisen parameter Γ s f = 14 indicates an enhanced volume dependence of the ferromagnetic spin fluctuations at low temperatures. Moreover, the volume dependencies of the energy scales for ferromagnetic order and ferromagnetic spin fluctuations were found to be identical.

Determination of the magnetic domain size in the ferromagnetic superconductor UGe2 by three-dimensional neutron depolarization

Three-dimensional neutron-depolarization measurements have been carried out on single-crystalline

A combined study of the magnetic properties of GdCrO4

\mathrm{U}{\mathrm{Ge}}_{2}

Critical Scaling of the Magnetization and Magnetostriction in the Weak Itinerant Ferromagnet UIr

between 4 and

Evidence for an antiferromagnetic component in the magnetic structure of ZrZn2

80\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Studies of R2Ti2O7R2Ti2O7 (R=GdR=Gd and Yb); new results

in order to determine the average ferromagnetic domain size

Testing the self-consistent renormalization theory for the description of the spin-fluctuation modes of MnSi at ambient pressure

d

Thermal Behaviour of the μSR Relaxation Rate at High Temperature in Insulators

. It is found that below