Unconventional magnetization processes and thermal runaway in spin-ice Dy2Ti2O7

We investigate the nonequilibrium behavior of the spin-ice Dy2Ti2O7 by studying its magnetization as a function of the field sweep rate. Below the enigmatic 'freezing' temperature T(equil)≈600 mK, we find that even the slowest sweeps fail to yield the equilibrium magnetization curve and instead give an initially much flatter curve. For higher sweep rates, the magnetization develops sharp steps accompanied by similarly sharp peaks in the temperature of the sample. We ascribe the former behavior to the energy barriers encountered in the magnetization process, which proceeds via flipping of spins on filaments traced out by the field-driven motion of the gapped, long-range interacting magnetic monopole excitations. The peaks in temperature result from the released Zeeman energy not being carried away efficiently; the resulting heating triggers a chain reaction.     

Spectroscopy of nickel chloride: Identification of the [15.0] Π3/2 and [15.0] Δ5/2 states

Vibrational bands belonging to the [15.0] ²Δ_5/2-A²Δ_5/2, [15.0] ²Δ_5/2-X²Π_3/2, and [15.0] ²Π_3/2-X²Π_3/2 electronic transitions of NiCl have been observed in the 14 000-16 000 cm⁻¹ region. The [15.0] ²Δ_5/2 and [15.0] ²Π_3/2 states are identified for the first time. The observed bands have been recorded at high spectral resolution using several techniques, which include intracavity laser spectroscopy (ILS), Fourier transform emission spectroscopy (FTS), and laser induced fluorescence (LIF) spectroscopy. For the ILS absorption spectra, NiCl molecules were produced in a nickel hollow cathode operated with a small amount of CCl₄. For the FTS emission spectra, excited NiCl molecules were produced in a King-type carbon tube furnace loaded with NiCl₂ and heated to 1600 °C. In the LIF work, NiCl molecules were produced by reacting laser-ablated nickel with PCl₃ seeded in argon. Detailed analysis of rotational transition lines indicates that the observed [15.0] ²Δ_5/2 and [15.0] ²Π_3/2 states are only separated by 10 cm⁻¹ and are interacting with each other. Molecular constants for these newly observed electronic states are reported.     

Soft Magnetic Properties of Amorphous CoFeSiB Wire

Thermomagnetic analysis of the initial AC susceptibility of amorphous CoFeSiB wire shows strong stabilization of the domain structure. The initial susceptibility of the as-cast sample drastically decreases in the temperature range (100-250)°C due to directional reordering. A special form of the hysteresis loop is a consequence of large internal stresses introduced in the wire by the rapid melt quenching. It was shown that in the as-cast state the stabilization leads to the reduction of the number of Barkhausen jumps into one large Barkhausen jump at temperatures above 100°C. After stabilization at 150°C, the sample shows almost bistable behaviour even at room temperature.     

Effect of growth parameters on the structure and magnetic properties of thin polycrystalline Fe films fabricated on Si〈1 0 0〉 substrates

This paper deals with the experimental investigation of the structure and magnetic properties of thin polycrystalline Fe films. Two sets of 50 ± 2 nm thick Fe films were fabricated on Si〈1 0 0〉 substrates with native oxides in place by varying (i) the sputter pressure p_Ar and (ii) the Fe sputter power P_Fe. X-ray diffraction (XRD) study revealed that all films grew with strong 〈1 1 0〉 texture normal to the film plane. No higher order peaks were observed in any of the films studied. For both film sets, the lattice constant (a) was less than the bulk Fe lattice constant (a₀ = 2.866 Å), which suggested the existence of compressive strain in all films. Two regions of homogeneous strain were observed over the range of p_Ar studied. Magneto-optical Kerr effect (MOKE) measurements showed that all films exhibited magnetically isotropic behaviour. The magnetic properties were observed to be influenced strongly by p_Ar. The film grown at p_Ar = 4 μbar was the most softest (H_s = 100 ± 8 kA m⁻¹, M_r/M_s = 0.87 ± 0.02) film among all the films studied. The magnetic properties were found to be independent of P_Fe. The effective saturation magnetostriction constant λ_eff determined (using the Villari method) was positive (4 ± 1 ppm) and observed to vary within the calculated error.