Recent developments in low-temperature nuclear orientation

Abstract

A review is given of the techniques associated with low-temperature thermal equilibrium nuclear orientation, detected using nuclear radiations. Following an introductory section that includes a historical summary, a brief description of the formalism and of some experimental aspects of nuclear orientation is presented. Various applications of nuclear orientation are then treated in detail, with emphasis on recent developments and new experiments in the field. The applications are grouped, according to the particular experimental techniques used, into static orientation, nuclear resonance methods, and time-dependent methods.

Nuclear Orientation as a Tool for Investigation of Magnetic Multilayers with Rare Earths

“…Concerning the former, a lot of modern methods are now available and its choice depends on a specific LD system to be studied. The 'classical' NO experiment is well described by Brewer (1990) or Brewer and Chaplin (1986). Here we constrain ourselves only to few remarks which mainly refer to requirements concerning samples, making NO experiments with them possible and useful.…”

“…This is caused by the fact that W is close to the saturation region in the temperature range measured and is predominantly controlled by the population of the two lowest Zeeman nuclear sublevels (m = 3 and 2 for the 160 Tb case), the energy gap of which is given by a linear combination of B hf and V zz only (see e.g. Brewer 1990). Therefore we fixed V zz = 38·9×10 21 V m −2 , which is the value for Tb in bulk Tb (Brewer et al .…”

“…In NO experiments the emission rate is detected in some direction and normalised by the rate from an isotropic nuclear ensemble (temperature T → ∞) to obtain the anisotropy W . The general expression for W and its derivation is somewhat complicated (see Krane 1986;Brewer 1990), but it can be written for our case (γ-rays, radioactive nuclei in thermal equilibrium with lattice, hyperfine interactions with a symmetry high enough etc.) as…”

“…Because of the high sensitivity of NO and its total element selectivity, the magnetic ground state of extremely diluted systems and/or systems consisting of several kinds of magnetically active elements can be studied with advantage. Reviews of such NO studies of bulk magnetic solids were given by Brewer (1986Brewer ( , 1990 and Turrell (1986).…”

Tb magnetic moment behaviour in a Gd single crystal: nuclear orientation study

“…One of the methods, which can give direct information of the magnetic behaviour of individual magnetic sublattices, is low-temperature nuclear orientation (NO). In principle, it can yield (via hyperfine interactions) both the direction and the magnitude of the ionic magnetic moments of a given sublattice in their ground state (T → 0) (see, e.g., review [4]).…”