Spectrum of magnetic hyperfine fields at Cd111 probe nuclei in the pseudobinary rare-earth Laves-phase compounds R1−xYxCo2 (original) (raw)
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Investigation of the magnetic hyperfine field of 111Cd in the rare-earth Laves phases RCo2 and RNi2
J. Phys.: Condens. Matter 12, 3423 (2000), 2000
The magnetic hyperfine field Bhf of the closed-shell probe nucleus 111 Cd on the cubic R site of the C15 Laves phase RCo2 (R = Gd, Tb, Dy, Ho, Er, Sm, Nd and Pr) and RNi2 (R = Gd, Sm) has been investigated at 9 K by perturbed angular correlation (PAC) spectroscopy. In RCo2 the hyperfine field increases with increasing R spin, both for the heavy and the light R. The experimental trend suggests that the total hyperfine field has two contributions of opposite sign: Bh f = B 3d - B 4 f , where B 3d is induced by the 3d Co moment and B 4 f is due to indirect 4f - 4f exchange. The 4f contribution can be estimated from the measurement of Bh f in RNi2 where the 3d moment vanishes. The 111 Cd hyperfine fields in GdNi2 and SmNi2 at 9 K are Bh f = 7.5(5) and 2.0(2) T, respectively. Assuming a linear dependence of B 4 f on the projection ( g - 1)J of the R spin on the total angular momentum J , as expected from the Ruderman-Kittel-Kasuya-Yosida (RKKY) theory of indirect 4f - 4f exchange, the variation of B 3d across the R series can be determined from the experimental values of Bhf . In heavy RCo2 (R = Gd, ... ,Er) B 3d follows very closely the variation of the Co moment µCo across the R series with B 3d /µCo = 28.7(2) T µ-1 B . With the same ratio for the light RCo2 (R = Pr, Nd, Sm) the experimental Bh f values indicate an increase of the 3d moment from µCo = 0.45 to 0.7 µB between PrCo2 and SmCo2 . "
Investigation of the magnetic hyperfine field of Ta-181 in the rare earth Laves phases RCo2
SOLID STATE COMMUNICATIONS 122, 155-159, (2002)
The magnetic hyperfine field B-hf of the 5d probe Ta-181 on cubic R sites of the C15 Laves phases RCo2 has been determined at 10 K by perturbed angular correlation spectroscopy for heavy (Gd, Tb, Dy, Ho, Er, Tm) and light (Sm, Nd, Pr) R constituents. For heavy R constituents, B-hf(Ta-181/RCo2) is found to increase with the R atomic number, similar to the trend found for the closed-shell probe Cd-111 in RCo2, but opposite to the decrease of B-hf previously reported for the 5d probe Ta-181 in RFe2. Qualitatively, these opposite trends can be related to the differences in the R dependence of the 3d moments of RCo2 and RFe2.
Phys. Rev. B 68, 014409 (2003), 2003
The order and other properties of the magnetic phase transitions in the rare-earth (R)-cobalt Laves phases RCo2 have been studied for R=Gd, Tb, Dy, Ho, Er, Sm, Nd, and Pr by measuring the temperature dependence of the magnetic hyperfine interaction of the nuclear probe 111Cd on the cubic R sites using the perturbed angular correlation technique. Both for heavy and light R constituents the transitions change from second order (Gd, Tb, Sm) to first order (Dy, Ho, Er, Nd, Pr) at order temperatures of 150–200 K. For heavy R constituents, the order deduced from the hyperfine interaction is in agreement with previous investigations. The observation of first order transitions in NdCo2 and PrCo2, however, is unexpected. In earlier studies the transitions in these compounds are usually classified as second order transitions. Both in the heavy and the light RCo2 the discontinuous jump of the hyperfine interaction at the first order transitions increases with decreasing order temperature. This trend implies that the Co magnetization at the transition increases with decreasing TC which can be related to the temperature dependence of the coefficient of the M4 term of the free energy in the Wohlfarth-Rhodes-Shimizu theory of itinerant electron magnetism. All compounds investigated presented a spread of the order temperature of ∼1–2K which results in a coexistence of the paramagnetic and the magnetically ordered phase near the transition and causes a critical increase of the relative linewidth of the hyperfine frequency diverging as δ∝(1-T/TC)ɛ with ɛ=-1.0(1).
JOURNAL OF PHYSICS-CONDENSED MATTER 18, 253-264 (2006)
The magnetic phase transitions of pseudo-binary rare earth (R) Laves phases R(1-y)Y(x)Co(2) have been investigated by perturbed angular correlation (PAC) measurements of the magnetic hyperfine fields at the probe nucleus (111)Cd for R = Tb, Sm and Ho at various Y concentrations x and for R = Gd, Dy, Er, Nd and Pr at the concentration x = 0.3. First-order transitions were observed in Tb(1-x)Y(x)CO(2) and Sm(1-x)Y(x)Co(2) for x >= 0.3, in Ho(1-x)Y(x)Co(2) for x < 0.4 and in R(0.7)Y(0.3)CO(2) for R = Dy, Ho, Er, Nd and Pr. For Gd(0)(7)(.)Y(0.3)Co(2), the temperature dependence of the average magnetic hyperfine field is compatible with a second-order transition. The discontinuity of the magnetic hyperfine interaction at the first-order transitions of heavy R(1-x)Y(x)Co(2), which mainly reflects the jump of 3d magnetization of the Co subsystem at T(C), was found to increase monotonically with decreasing order temperature. The TC dependence of the normalized magnetic frequency v(M) (T(C))/v(M) (0) proportional to [1-(T(C)/T(0))(2)](1/2) with To = 203(5) K for the boundary temperature between first- and second-order transitions can be explained by the temperature dependence of the coefficient of the M(4) term of the free energy in the Wohlfarth-Rhodes-Shimizu theory of itinerant electron metamagnetism.
Journal of Magnetism and Magnetic Materials 306, 292 (2006), 2006
Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus 111Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl2 as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B4, B6 of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The 111Cd PAC spectrum of EuAl2 at 9 K confirms the antiferromagnetic structure of this compound.
Transferred hyperfine interactions in ferrimagnetic RCo2 cubic Laves phase compounds
Physica B+C, 1977
The ferrimagnetic system (Gd. Y, ~)Co~ has been studied by the M6ssbauer effect of '~'Gd and by the NMR of '65Ho 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.
Hyperfine fields in rare-earth compounds
1969
The 3nper-refj,on.orat:i ve Detector kl 2,2.3 The Spin Echo Apparatus hh 2.3 Other Measurements in Gel Co 2 56 2.3.1 Crystal Structures 56 2.3.2 Bulk Maffneti zation 57 CHAPTER III RESULTS 58 3.1 Spin Echo Observations 5?' 3.1.1 GdCo 0 6k 3.1.2 0d 1 .;Y x Co 2 67 3.1.3 Gel, Dy Co., 6Q 1-x x. .2 3.3-. 'i G d (C o i_ x N i x) 2 70 3.2 Line Widths 71 3.3 Relaxation Measurements 71 j,k Magnetization Measurements 73 3.5 Lattice Parameters lh CHAPTER IV DISCISSION 76 h.l The ^ature of the Resonance Observations 76 •\ .2 Gd. n Y Co_ Compounds 77 l-x x d. k.3 The Gd(Co. ,.Ni)" Series 92 h,k The Dysprosium Substituted Compounds 96 '•I-. 5 Relaxation Rates 9S rage ?\o, CHAPTER V CONCLUSION 101 APPENDIX 106 A.J., The Electron-Nuclear Interaction 106 A.2. The Spin Echo Effect 111 oOo Picture of Spectrometer GdCOg Spin Echo Results GdCOg Resonance Line GdCo,, in External Fields Gd .8l Y .19 C°2 Gd .5l Y .^C°2 Gd j4 Y .6 C°2 Variation in Resonant Frequency with Yttrium Substitution .Dysprosium Substitution Resonant Li n e s 3.8 Gd(Co <9 Ni <;L) 2 J • J ^(CO t8 Ni >2) 2 3.10 Variation of Resonant Frequency
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 306, 292-297 (2006)
Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus Cd-111 in ferromagnetically ordered rare earth (R)-dialuminides RAl2 as a function of temperature for the rare earth constituents R = Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R = Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R = Pr, Nd, Tb, Dy and Ho the parameters B-4, B-6 of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The Cd-111 PAC spectrum of EuAl2 at 9 K confirms the antiferromagnetic structure of this compound