S.H. Kilcoyne

Pressure dependence of the magnetic order in YMn2 and TbMn2

Abstract The P-T magnetic and structural phase diagrams of YMn2 have been mapped over the ranges 0

Temperature dependent SANS from ferritin and apoferritin

Abstract SANS from deuterated ferritin and apoferritin solutions over the temperature range 5 to 300 K is presented. Above the freezing point the SANS is well described by Percus-Yevick hard sphere packing. On freezing, highly correlated, partially crystallised, clusters of the proteins form and grow with decreasing temperature. The resulting scattering, characterised by a squared Lorentzian structure factor, indicates a spatial extent of 1000 A for the protein clusters.

High resolution neutron powder diffraction studies of microtwinning and stoichiometry variations in the high Tc superconductor, YBa2Cu3O7−x

Abstract High resolution time-of-flight neutron powder diffraction has been used to investigate simultaneously the atomic structure and average microstructure of the high T c superconductor YBa 2 Cu 3 O 7− x . The neutron data reveal the presence of microtwinning ( x ≈0.1) and oxygen concentration variations ( x ≈1/0).

Suppression of local moment formation in Ce doped YMn2

Abstract The evolution of magnetic and structural order in Y 1− x Ce x Mn 2 with (0≤ x ≤0.3) has been mapped using neutron powder diffraction. As little as 5 at% substitution of Ce for Y is found to destabilise the magnetic moment at the Mn site and inhibit both the first order transition to antiferromagnetism and associated expansion of the unit cell observed for pure YMn 2 .

Low temperature structural distortions in RMn2 compounds

Abstract The low temperature crystal structures of the C15 Laves phase compounds TbMn 2 , DyMn 2 and HoMn 2 have been determined using high resolution time-of-flight neutron powder diffraction. At the Neel point of 50 K TbMn 2 exhibits a first order volume expansion of 1.68% accompanied by a monoclinic distortion. DyMn 2 displays a slight rhombohedral distortion, while HoMn 2 remains cubic down to 5 K.

Kinetic neutron studies of the recrystallisation of amorphous Bi-Sr-Ca-Cu-O

Abstract Recrystallisation of amorphous Bi-Sr-Ca-Cu-O, with nominal cation ratios of 2-2-1–2, has been studied in-beam using high intensity neutron powder diffraction. Eutectic crystallisation, proceeding via formation of the n =1, Bi 2 Sr 2 CuO 6 , and n = 2, Bi 2 Sr 2 Ca 1 Cu 2 O 8 phases is observed.

Magnetic correlations in YBa2(Cu1−xFex)3O6+y

Abstract Neutron scattering techniques have been used to establish the state of magnetic order in YBa 2 (Cu 1− x Fe x ) 3 O 6+ y for x =0.06 and 0.1, and for values of y in the range 0.3≤ y ≤0.9. For the x =0.1 samples an unusual magnetic structure for the 1-2-3 family of compounds has been found in which a large moment at the Cu(1) site is coupled antiferromagnetically to those at the neighbouring Cu(2) sites.

Magnetic correlations in amorphous terbium alloys

Abstract We report studies of a series of amorphous rare earth alloys: a-Tb 2 (Fe 1− x Ni x ). Small angle neutron scattering has been used to determine the magnetic correlations as a function of alloy concentration and temperature. Results are compared with magnetisation data and are found to agree with scaling theory.

The magnetic phase diagram of (DyxY1−x)Mn2 alloys

Abstract The evolution with temperature and concentration of the magnetic structure of the C15 Laves phase alloys (Dy x Y 1− x )Mn 2 has been studied using neutron powder diffraction, ac susceptibility and high field dc magnetisation techniques. The phase diagram can be divided into three principal regions: for x ⩽0.2, the magnetic behaviour is closely similar to YMn 2 , although for x = 0.2 the Mn moment has decreased to about 2.0μ B at 2 K. For x ⩾0.8, the DyMn 2 magnetic structure is found, but at x = 0.7 a second type of antiferromagnetic structure has developed. This coupling persists as short range correlations into a remarkably wide range of intermediate compositions (0.7> x ⩾0.3) where there is no long range magnetic order down to low temperatures.

A μSR study of magnetic order in Y6(Mn0.55Fe0.45)23

Abstract Low-temperature zero- and longitudinal-field μSR in Y 6 (Mn 0.55 Fe 0.45 ) 23 is characterized by a field independent relaxation function of the root-exponential form, exp [−(λ d t) 1 2 ] , indicating that below 100 K the magnetic state of this compound is dominated by dynamic random magnetic fields. No evidence of static local field distributions was obtained down to 12 K.