Transferred hyperfine interactions in ferrimagnetic RCo2 cubic Laves phase compounds

doi:10.1016/0378-4363(77)90268-6

Physica B+C

Volumes 86–88, Part 1, January–March 1977, Pages 158-160

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Abstract

The ferrimagnetic system (Gd_xY_1−x)Co₂ has been studied by the Mössbauer effect of ¹⁵⁵Gd and by the NMR of ¹⁶⁵Ho as a substitutional impurity. The data are interpreted in terms of a simple model which involves transferred hyperfine fields from the lanthanide and cobalt ions and which allows for crystal field quenching of the holmium moment.

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Cited by (12)

Chapter 94 NMR in intermetallic compounds
1991, Handbook on the Physics and Chemistry of Rare Earths
Nuclear magnetic resonance (NMR) is a radiofrequency technique using frequencies v_rf up to several hundreds of MHz. An NMR spectroscopist has to tackle the problem of the skin depth for electromagnetic radiation in metals. The most frequently adopted procedure of solving the sensitivity problem is, therefore, to use powder samples for the NMR of intermetallic compounds with grain sizes smaller than the skin depth. An annealing treatment after powdering is generally recommended to heal spurious strains to reduce line broadening at least if nuclei susceptible to quadrupolar broadening are studied. Most investigations use pulsed NMR spectrometers. Appropriate instruments for the lower radiofrequency range (3–200 MHz) are commercially available; they have to be equipped with a reliable system for controlling tuning, sensitivity, rf field amplitude, and pulse shape to allow the analysis of broad line profiles or relative intensities. An automatic broadband frequency variable spectrometer working in the frequency range from 10 to 1000 MHz has been introduced recently for the study of hyperfine fields in ferromagnetic materials. The NMR spectrum can be measured in two different modes: by varying the frequency or by varying the magnetic field strength. The latter is generally much easier to perform.
Study of the variation of the cobalt moment in the (Tb<inf>1-x</inf>Y<inf>x</inf>)Co<inf>2</inf> compounds
1986, Journal of Magnetism and Magnetic Materials
A detailed study has been made of the series (Tb_1−xY_x)Co₂ by means of high field magnetization measurements and spin-echo NMR of ¹⁵⁹Tb.
At the TbCo₂ end of the series NMR data gives (8.44±0.15)μ_B for the terbium moment while magnetization measurements gives (8.93±0.10)μ_B.
By assuming a constant crystal field interaction across the series we have estimated the exchange parameter within the molecular field model and thereby have obtained the variation of the terbium moment μ_Tb across the series. We have also obtained μ_Tb from the quadrupolar parameter of ¹⁵⁹Tb NMR for x ⩽ 0.6.
By combining μ_Tb with the saturation magnetization per formula unit we have obtained the variation of the mean cobalt moment across the series.
The study shows that cobalt is not magnetic for x ⩾ 0.9.
Mössbauer effect study of the 105.3 keV transition in <sup>155</sup>Gd
1986, Nuclear Inst. and Methods in Physics Research, B
Mössbauer effect studies on the 105.3 keV transition of ¹⁵⁵Gd using the single line source and absorber combination of SmPd₃ and GdCo₂ have shown that the previously reported narrowing in the linewidth is due to the formation of antipeaks on the spectrum. These antipeaks occur on the 105.3 keV spectrum at positions which correspond to maximum resonant absorption of the 86.5 keV radiation in ¹⁵⁵Gd. They are observed at a very low amplifier output count rate of 6 kHz which corresponds to a multichannel analyzer recording rate of 200 counts per channel per minute for the 105.3 keV spectrum. The antipeaks were not present on the 105.3 keV spectrum after attenuating the 86.5 keV radiation with a thallium acetate filter. The resultant linewidth of the 105.3 keV transition, after correcting for finite source and absorber thickness, was found to be Γ₀=1.129 mms⁻¹ in comparison with the theoretical value of 1.112 mms⁻¹ calculated from the lifetime of the 105.3 keV energy level.
The change in the character of phase transition with nickel in the Ho(Co, Ni)<inf>2</inf> compounds
1982, Journal of Magnetism and Magnetic Materials
The series Ho(Co_1-cN_c)₂ has been investigated in the composition range c⩽0.15 by spin-echo NMR of ¹⁶⁵Ho and by magnetic measurements. From NMR data a value of (9.5±0.1)μ_B is estimated for holmium in HoCo₂. Magnetisation measurements on the same compound give (7.9±0.1)μ_B/fu. An assumption of 0.8μ_B for the cobalt moment aligned antiparallel to that of holmium leads to a value of 9.5μ_B for holmium in agreement with the value estimated from NMR. The substitution of nickel for cobalt causes a rapid fall in both the hyperfine field, and the ordering temperatures, while the molecular moment shows a simultaneous rise. These are attributed to a rapid fall in the cobalt moment which leads to a bootstrap process involving the strength of the exchange field and the magnitude of the cobalt moment. Nickel substitution also leads to a change in the character of the magnetic phase transition. Initially first order, this transition becomes second order on exceeding ≈ 9 at% Ni.
Rare earth compounds
1980, Handbook of Ferromagnetic Materials
This chapter discusses rare earth compounds. The number of stable binary intermetallic compounds in which one of the components is a rare earth element is of the order of a thousand. Combination with elements of much smaller metallic radii then encompasses a much larger number of possible atomic arrangements of sufficiently high space filling than would be the case for two components of almost equal size. A meaningful study of the physical properties of intermetallic compounds can only be made on single phase materials. Only a fraction of the compounds is in single phase condition after the melting together of the components. The chapter explains the compounds with non-magnetic elements and compounds with d-transition metals. It also explains ternary compounds or hydrides.
Hyperfine interactions in intermetallic compounds between Gd and 3d transition metals
1977, Solid State Communications
Measurements of hyperfine interactions at ¹⁵⁵Gd nuclei in metallic compounds between Gd and 3d transition metals and at ⁶¹Ni in GdNi compounds by Mössbauer spectroscopy are reported. The results are discussed in terms of various models proposed for the electronic structure of these compounds. The Gd isomer shifts with respect to metallic Gd are at variance with the model of a strong d electron transfer from rare earths to transition metal ions. From the observation of a linear relation between magnetic hyperfine fields at Gd and at Dy nuclei in corresponding compounds it is inferred that crystal-field induced variations of Dy moments are neglible and that the conduction electron polarization induced by 4f moments is directly related to that caused by 3d moments.

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Transferred hyperfine interactions in ferrimagnetic RCo2 cubic Laves phase compounds

Abstract

Phys. Lett.

Phys. Lett.

Transferred hyperfine interactions in ferrimagnetic RCo₂ cubic Laves phase compounds