Hyperfine Anomaly inIr193by Mössbauer Effect, and its Application to Determination of the Orbital Part of Hyperfine Fields

Abstract

A 7% hyperfine anomaly is found in Mbssbauer measurements of the 73-keV transition in 193 Ir. A 2% difference is found between the anomalies in antiferromagnetic IrF 6 and Ir-Fe alloy. The difference is ascribed to orbital contributions which differ for the two iridium environments. By using known details of IrF 6 we find the orbital field in the Ir-Fe to be # 7 =+335 ±200 kOe.We have observed a 7% hyperfine anomaly between the ground state and first excited state in i93j r k v Mossbauer effect measurement, and a difference between the anomalies for iridium in ferromagnetic and antiferromagnetic environments. We are able to use the results to partition the hyperfine field at 193 Ir in an Ir-Fe alloy into a contribution due to a Fermi contact interaction and one due to noncontact fields, the latter being primarily orbital in origin. It is chiefly upon this new magnetic technique that we wish to report. The measurements of the anomaly will be treated briefly here and in detail in a later publication. 1 Anomalous hyperfine interaction describes the difference between a nuclear magnetic moment measured in a uniform field and the moment measured in a magnetic field of hyperfine origin. 2 ' 3 Since a hyperfine field is observable only in a product with a nuclear moment, the anomaly is observed by comparing the ratio of two moments or nuclear g factors measured in the two types of field. Many such anomalies between the ground states of a pair of isotopes have been measured, for example by atomic-beam techniques. Grodzins and Blum 4 made the first MSssbauer type measurement of the anomaly between two states of the same nucleus (the ground state and first excited state in 57 Fe), where it was found to be marginally small.A large anomaly might be expected to be present in the iridium nuclei 191 Ir and 193 Ir. 5 The relatively large size of the nucleus results in a considerable variation of electron density over the nuclear radius. The contact hyperfine field, which depends on the density, is thus variable over the radius. The orbital and spin motions of the unpaired nucleons cause different radial distributions of magnetic moment and therefore contribute differently to the overall interaction in the radially varying density. The | + ground state of the odd-proton nucleus 193 Ir, for example, is favored for the effect because insofar as it is d 3/2 in character, the orbital and spin contributions to the nuclear moment tend to cancel, and a minor difference in the separate interactions shows up as a relatively large effect. The | + excited state at 73 keV is not so especially favored. It is the transition between these two states which we use.We measured the ratio g*/g° of excited-state to ground-state nuclear g factors in an external field of 73 kG supplied by a superconducting magnet. The absorber was iridium metal and the source 193 Os from neutron capture in 192 Os metal. The source itself has a small quadrupole splitting 6 which was taken into account in the fitting. The spectrum is incompletely resolved and contains ...

Gyromagnetic ratios of the 4+ and 6+ rotational states of184W

“…The radial decrease of the hyperfine field at the nuclear site of impurity atoms in ferromagnetic hosts may, however, be stronger than for free atoms. In this connection it should be mentioned that hyperfine anomalies in ferromagnetic hosts of our order of magnitude have been reported for several other systems before, see [34][35][36]. We rely in our work on the correctness of the measured g-factor of the 2 + state.…”

The Value of Electronic Hyperfine Anomalies to Nuclear and Solid State Physics

“…values of the hyperfine interaction for both nuclear states involved in the gamma transition under study a single measurement includes a value for gAex between these states provided their moments are known. Thus Perlow et al [13], having established the value of 3 / 2~6 / 2 for the 1931r transition, were able to interpret a spectrum published by Wagner et al [20] Interpretation of hyperfine fields at iridium in ferromagnetic metals using hyperfine anomaly data [21] Contact anomaly 3 1 2~6 '~ 7 -k 6.5 (6) %.…”

“…Both show large anomalies which can be accurately measured. [13]. The crucial hyperfine interaction experiments were done in IrF, and the magnetic moment ratio was obtained from measurements in an external magnetic field applied to nonmagnetic iridium metal.…”

The low-energy level structure and the electromagnetic properties of191Ir and193Ir

“…The ground state magnetic moment has been measured to be 0.1583 (6) nm [22]. The g-factor of the 73 keV (1/2 +) state has been reported to be 0.9400 (19) [23], this value is, however, subject to hyperfine anomaly correction [24]. The correction amounts to 7.2 per cent.…”