R. Cywinski

Moment localisation in β-MnAl

Abstract μSR has been used to map the magnetic phase diagram of β-Mn 1− x Al x and to investigate the evolution of spin fluctuations with increasing Al concentration. There is a marked change in the spin fluctuation spectrum at x = 0.08, below which simple exponential relaxation is observed, while for higher concentrations Kohlrausch relaxation, associated with spin-glass behaviour is found. This change is accompanied by a sudden increase in the magnetic transition temperature.

DIFFUSE MAGNETIC SCATTERING OF POLARISED NEUTRONS

Abstract Neutron polarisation studies of the diffuse scattering from disordered magnetic alloys and compounds have provided unique and detailed insights into the nature and extent of magnetic inhomogeneities and their dependence upon local atomic environments. In this paper, we briefly review the application of polarised neutron methods in the characterisation of magnetic and structural defects in ferromagnets, antiferromagnets, spin glasses and topologically frustrated systems and present some new polarisation analysis measurements of the spin correlations in β-MnAl.

Evolution of magnetic order in (Tb1−xHox)Mn2 and (Tb1−xDyx)Mn2

Abstract High intensity neutron diffraction has been used to study the evolution of magnetic order in (Tb 1− x Ho x )Mn 2 and (Tb 1− x Dy x )Mn 2 for x ⩽0.25. The substitution of Ho or Dy for Tb is found to lead to an inhomogeneous transition from a TbMn 2 -like magnetic phase to a DyMn 2 -like magnetic phase beyond x =0.15 and 0.20 respectively.

De Gennes scaling in Er1-xTbxNi2B2C superconductors

Abstract The magnetic and superconducting phase diagram of the pseudo-quaternary system Er 1- x Tb x Ni 2 B 2 C has been determined by magnetisation measurements. We find that T c decreases linearly with de Gennes factor reaching zero at x ∼ 0.3, whereas the Neel temperature, T N , remains almost constant at ∼6.5 K for concentrations up to x = 0.5, beyond which a rapid but non-linear increase to 15 K at x = 1 is observed.

Spin dynamics in the concentrated spin-glass system Y(Al1−xFex)2

The zero-field μSR spectra obtained from Y(Al1−xFex)2 alloys at concentrations below x<0.75 are stretched exponential in form and characteristic of those of a concentrated spin glass in which an increasingly broad distribution of spin relaxation rates evolves as the glass temperature is approached. These μSR results are discussed within the context of recent high-field Mossbauer effect measurements on Y(Al1−xFex)2 alloys from which estimates of the lifetime of magnetic correlations have been obtained.

A μSR study of anomalous rare-earth spin dynamics in RNi2B2C (R = Er, Tb)

Abstract Stretched exponential muon spin relaxation is observed in the paramagnetic phase of superconducting ErNi 2 B 2 C ( T c = 10.5 K, T N = 6.5 K) and nonsuperconducting TbNi 2 B 2 C ( T N = 15 K). This result suggests anomalous, broadly distributed rare-earth spin dynamics in these compounds.

Evolution of magnetic order and loss of superconductivity in Er1−xTbxNi2B2C

Abstract The magnetic phase diagram of the Er 1− x Tb x Ni 2 B 2 C has been mapped using neutron powder diffraction. It is noted that a marked discontinuity in the evolution of the magnetic structure coincides with the loss of superconductivity at x ∼0.3.

Dynamic spin correlations in (Dy1 − xYx)Mn2

Abstract Zero-field μSR has been used to study spin dynamics in (Dy 1 − x Y x )Mn 2 . Antiferromagnetic compounds close to the DyMn 2 and YMn 2 compositions exhibit the expected simple exponential muon depolarisation in the paramagnetic state. However, at intermediate compositions, where there is no long-range magnetic order, stretched exponential depolarisation, similar to that observed for spin glasses, is observed.

Comparison of high-field Mössbauer and μSR investigations on spin glasses

Abstract We report on the analysis of μSR and Mossbauer measurements of the metallic spin glasses Y(Fe 0.65 Al 0.35 ) 2 and Y(Fe 0.4 Al 0.6 ) 2 above the freezing temperature ( T f ) in terms of a model taking into account a dynamical process of stochastic formation and decay of magnetically correlated regions. By this model a comparison of the autocorrelation function determined by the two different measuring techniques is possible. For the temperature dependence of the autocorrelation time we find fair agreement between both experiments for T >2 T f .

Superparamagnetic CuCo studied by μSR

Abstract Zero-field μSR has been used to probe cluster dynamics in two superparamagnetic samples of Cu-2 at% Co with mean cluster moments of 77 and 237 μ B . The temperature dependence of the fluctuation rates of both samples is found to follow an Arrhenius law indicating activation energies of 35.4 and 48.4 K and intrinsic relaxation rates of 0.7 × 10 9 and 2.7 x 10 9 Hz for the two samples.