S. Skalski

NMR studies of metal and metalloid site hyperfine field distributions in magnetically ordered amorphous alloys

We report spin‐echo NMR studies of hyperfine field (hf) distributions in a number of magnetically ordered Fe and Co‐based amorphous systems. These distributions are broad and often complex due to the overlap of NMR signals arising from both metal and metalloid atoms. We show that by using isotopic substitutions it is possible to separate the metal and metalloid site hyperfine field distributions in Fe‐based systems. In many instances it is possible to compare these results with those obtained on related crystalline compounds to identify the environments responsible for the hf distributions observed in the amorphous phase. We also present studies of annealing and cold working on electrodeposited amorphous Co‐P samples. Local environmental models provide a good description of our results.

Hyperfine Fields in Fe‐Si Alloys

We have measured the hyperfine field at Fe and Si nuclei in Fe‐Si alloys containing 18.4 to 26.5 at. % Si by the NMR spin‐echo technique at 4.2°K. We observe Fe resonances from nuclei at sites with 3, 4, 5, 6, and 8 Fe nearest neighbors at frequencies which are in good agreement with the reported Mossbauer results. In Fe3Si, we observe an additional line at about 31.5 Mc/sec which we identify with the Si nuclei. In the 23.0 at. % sample, this line is diminished in intensity and another line appears at about 47 Mc/sec which grows in intensity as the Si concentration is decreased below 23.0 at. %. At 22.3 at. % Si and below, the 31.5‐Mc/sec Si line is not observed. In addition, our data shows that a significant change in the Fe hyperfine field at sites with 4 and 8 nearest‐neighbor Fe atoms occurs between 22 and 24 at. % Si. These observations on the hyperfine fields correlate well with the anomalous behavior of the resistivity in this concentration range and indicate a change in the electronic structure of...

31P NMR in the ferromagnetic state of amorphous Fe75P15C10

Abstract The first observation of a metalloid site hyperfine field (hf) distribution in a ferromagnetic amorphous alloy is reported using a spin-echo NMR technique. The 31P nuclei in amorphous Fe75P15C10 show a hf distribution with a maximum at about 27 kOe. The sample was prepared with Fe enriched to 99.93% in 56Fe. A comparison of the NMR spectra on samples containing natural Fe and 56Fe also provides the 57Fe hf distribution whose peak value agrees with Mossbauer results.

Al Hyperfine Fields in Ordered Fe–Al Alloys

In the Fe–Al system a number of ordered phases are possible for compositions between 10 and 30 at.% Al. Since the aluminum site is essentially nonmagnetic, measurements of the hyperfine interaction ought to yield sensitive and detailed information about the conduction electron polarization and its dependence on long‐range crystallographic order. We have studied the Al resonance in alloys containing between 14 and 28 at.% Al by NMR spin‐echo spectroscopy at 4.2°K. For all compositions, the spectra of alloys which have been subjected to cold work are similar and show a single broad asymmetric distribution with a maximum at about 58 MHz which extends to 30 MHz on the low‐frequency side for the higher concentrations. In the 23 to 28 at.% Al region the spectra of annealed alloys are very different having strong sharp lines at 29 and 33 MHz and a broad distribution around 58 MHz which decreases in amplitude with increasing Al content. These spectra seem to be characteristic of Fe3Al order. Since Al sites with 8...

Anisotropic Hyperfine Interactions in ZrFe2 and GdFe2 from a Nuclear Magnetic Resonance Study

We have studied the nuclear magnetic resonance of 57Fe nuclei in the magnetic state of both ZrFe2 and GdFe2, using the technique of spin echoes. The broad spectrum from the iron nuclei in ZrFe2 at 4.2°K could be resolved into one weak and one strong line located at 28.9±0.2 Mc/sec and 30.6±0.1 Mc/sec, respectively. The frequencies of these lines are in good agreement with the Mossbauer results in this system which show two lines, with an intensity ratio of 3 to 1, arising from nuclei in domains. The application of magnetic fields less than 4π/3 Ms to the stronger Zr resonance at 77°K produces a detectable frequency shift and a decrease in intensity of the spin‐echo signal. In GdFe2, a ferrimagnet, a similar spin‐echo spectrum for the iron is observed with one weak and one strong line at 31.3±0.3 Mc/sec and 32.4±0.1 Mc/sec, respectively. The difference between this system and ZrFe2 may be understood in terms of the contribution from the magnetic gadolinium sublattice. We conclude that in these systems, the...

Palladium Hyperfine Field in Ferromagnetic Pd‐Fe Alloys

We have measured the 105Pd hyperfine field distribution in a series of Pd‐Fe alloys ranging in composition from 0.5 to 25.0 at.% Fe by the NMR spin‐echo technique. The features of the observed Pd spectra are strongly concentration dependent, and above 10%, are somewhat heat‐treatment dependent, but always display at least two broad maxima. The ratio HPd/μPd of the average Pd hyperfine field, obtained from our data, to the average Pd moment, as determined from the neutron scattering and magnetization data (assuming a constant value of 3.0 μB for the Fe moment), tends to a constant value of about 525 kOe/μB for Fe concentrations greater than about 4 at.%. As the Fe concentration is reduced below this value, this ratio rises rapidly since μPd→0, but HPd approaches asymptotically a value of about 72 kOe. The interpretation of our data in terms of the long‐range polarization model for the Pd‐Fe system is discussed.

Fe Hyperfine Fields in Dilute Pd–Fe Alloys

We have studied the 57Fe hyperfine field distribution in an alloy of 0.5 at. % Fe in Pd by NMR spin‐echo spectroscopy at temperatures between 1.3° and 4.2°K. The Fe spectrum at 4.2°K is asymmetric. The asymmetry decreases and the frequency of the maximum increases as the temperature is lowered so that at the lowest temperature the Fe line is essentially symmetric about a value corresponding to a field of −299.7 kOe. The interpretation of this data in terms of an enhanced RKKY spin polarization model is presented. The temperature dependence of the maximum is fitted to a T3/2 law and a value of 34°K A2 for the acoustic spin‐wave stiffness constant in this alloy is obtained.

Critical behavior of the magnetic susceptibility of GdNi2

Abstract We find the low field magnetic susceptibility of the ferromagnet, GdNi 2 , is describable by the molecular field model to within approximately 8°K of the ordering temperature below which there are deviations which are consistent with short range order effects.

Investigation of conduction electron polarization effects in Fe3Si based ternary systems

Spin‐echo spectra of transition elements in the ternary alloys Fe3−xTxSi where T=V and show clear satellite structure for small x. For these alloys, it is concluded that changes in the ’’4s’’ CEP alone produce the satellite structure. Studies made on some Fe3Si based quarternary alloys are consistent with the above conclusions.

Evidence for Local Effects on the Nuclear Spin‐Lattice Relaxation Rate in Ferromagnetic Palladium Iron Alloys

For some time there has been considerable theoretical work on the role of local exchange enhancement in highly polarizable systems. To date, there has been little experimental evidence for the importance of these local effects in ferromagnetically polarized alloys. We have measured the nuclear spin‐lattice relaxation rate in ferromagnetic PdFe alloys in the helium temperature range. Our results for the Pd nuclei indicate that the relaxation rate is a strong function of the nearest neighbor environment. Specifically there is a contribution to the relaxation rate which is proportional to the number of iron nearest neighbors, N, for N=0, 1, 2 over the concentration range from 1 to 7.5 at.% Fe. Furthermore, the relaxation rates at both the Pd sites and the Fe site vary with concentration as the square of the measured high‐field susceptibility. This behavior is consistent with either a strong inter‐atomic exchange interaction between a Pd and its nearest neighbors, or a variation in the intra‐atomic exchange i...