Relaxation Phenomena in Mössbauer Spectra of Magnetically Ordered Erbium Ions in ErFeO3

Abstract

Wiedemann and Zinn 1 have recently reported unusual Mossbauer spectra for Er 3+ in ErFe0 3 , at sample temperatures below the N£el temperature (4.3°K) 2 of the erbium sublattice (the ferromagnetic iron-lattice Curie temperature is 3 640°K). The Mossbauer transition employed was the 2 + -0 + , 80.6-keV gamma transition of Er 166 . We show below that these spectra may be readily interpreted in terms of spin-relaxation effects. The ErFeO s system, therefore, appears to be the first reported example of such behavior in the Mossbauer-effect (ME) spectra from a magnetically ordered system.The spin-relaxation interpretation differs from that of Wiedemann and Zinn, who suggested that there are several magnetically inequivalent Er 3+ sites in ErFe0 3 and that the effective magnetic fields acting on the erbium nuclei in the various sites have different temperature dependences, thus leading to the observed spectra. 1 However, crystal structure, 4 mag-(1965) [translation: Opt. Spectry. (USSR) Jj), 252 (1965)].10 The phase-coherent detection, made possible by the coherence between the light modulation and the applied rf field, makes the effective bandwidth much smaller, and hence the detection much easier than in the detection of incoherent light beats as performed by A. T. . netic structure, 2 and recent ME spectra 5 of Dy 3+ in isomorphous DyFe0 3 argue for at most two magnetically inequivalent Er 3+ sites. The magnetic and Mossbauer data are, in fact, well represented by a single magnetic rare-earth site. With this assumption relaxation spectra were computed and excellent agreement between experiment and theory was obtained.In order to discuss the rare-earth hyperfine fields, it is first necessary to decide on a model for the pertinent electronic properties of the magnetic erbium ions. In the temperature range of interest, the erbium ions are exposed to an exchange field made up of two contributions: (1) an effectively constant exchange field from the iron atoms, and (2) at T^ T c (Er 3+ ), an induced molecular field in the erbium sublattice arising from exchange between the rareearth ions. Near the transition temperature, the constant iron field dominates the erbium exchange field. The induced field in the erbium sublattice which gives rise to collective Recent low-temperature Er 166 Mossbauer data, reported by Wiedemann and Zinn in a study of ErFe0 3 , are interpreted in terms of spin-relaxation effects. This appears to be the first time relaxation effects have been observed in the Mossbauer spectra from a magnetically ordered system. 949

High magnetic ordering temperature in the perovskites Sr4−La Fe3ReO12 (x=0.0, 1.0, 2.0)

“…9) clearly shows that all Fe ions are equivalent; this suggests that the RT ''smeared'' spectra result from spin fluctuations, frequently observed in magnetically ordered materials [51]. The parameters of the fitted Mössbauer spectra in terms of inequivalent sites, are summarized in Table 4.…”

Effect of Fe substitution on the magnetic ordering inCa3(Co1−xFex)2Nowik1, Jain2, Yusuf3 et al. 2008Phys. Rev. BSelf Cite20291View full textAdd to dashboardCite

“…2͒ were analyzed in terms of the spin relaxation theory, 14 and it yields perfect fits in terms of 2 values, and confirms the earlier conclusions 1 that the iron occupies only one site ͑Co2͒, with a negative quadrupole interaction, EQ = 1 4 e 2 qQ ͑=−0.62 mm/ s at 90 K͒. The analysis also yields ͑assuming a fluctuating magnetic hyperfine field of 45 T͒ the room temperature spin relaxation rates, which are 1.5 ϫ 10 11 and 7.7ϫ 10 10 s −1 for x = 0.2 and x = 0.1, respectively, indicating the dominance of Fe-Fe spin-spin relaxation.…”

“…The spectra for the x = 0.1 and 0.2 samples, at 90 and 300 K, were fitted in terms of spin up-down relaxation theory formulas. 14 The spectra for the x = 0.5 sample were analyzed in terms of full diagonalization of the Hamiltonian of magnetic and quadrupole interactions, where the magnetic field is at an angle relative to the local axis of the electric field gradient ͑EFG͒, for simplicity, assuming axial symmetry for two different sites of iron.…”

Personal recollections of 52 years of Mössbauer spectroscopy research

“…The phenomenon in magnetically ordered systems was very shortly also observed [8]. Typical relaxation spectra in paramagnetic Dy 3 Al 5 O 12 are shown in Fig.…”

“…All thermodynamic phase transitions were studied. New unexpected dynamic phenomena, directly observable in the spectrum like: spin relaxation [8,9] in iron, and in all rare earths and actinides, spin crossover and transitions in iron compounds [10], intermediate valence and valence changes [11] in iron, europium, samarium and even neptunium, and bound diffusion [12], were all discovered in a very wide range of compounds. Fig.…”