Mӧssbauer study of Y3Al5O12 (YAG), Y3Fe5O12 (YIG) and Gd3Ga5O12 (GGG) single crystal garnets following dilute implantation of 57Mn+. P. B. Krastev, Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Bulgaria In collaboration with ISOLDE/CERN international group of researchers: H. P. Gunnlaugsson1,2, K. Nomura3, K. Johnston1, A. M. Gerami4, M. Ncube5, H. Masenda5, R. Mantovan6, Y. A. Matveyev7, T. E. Mølholt1, I. Unzueta8, K. Bharuth-Ram9, V. Masondo9 S. Ólafsson10 , Bingcui Qi10 H. Gislason10, G. Langouche2, D. Naidoo5, 1 CERN, PH Div, CH-1211 Geneve 23, Switzerland 2 Instituut voor Kern- en Stralingsfysika, University of Leuven, B-3001 Leuven, Belgium 3 Tokyo University of Science, Tokyo, Japan 4 Department of Physics, K.N. Toosi University of Technology, Tehran, Iran 5 School of Physics, University of the Witwatersrand, South Africa 6 Laboratorio MDM, IMM-CNR, Via Olivetti 2, I-20864 Agrate Brianza (MB), Italy 7 Moscow Institute of Physics and Technology, Russian Federation 8 BC Materials & Elektrizitate eta Elektronika Saila, Bilbao, Spain 9 Durban University of Technology, Durban 4000, South Africa 10 Science Institute, University of Iceland, Dunhaga 3, Reykjavík, Iceland academy of Sciences  

Motivation Synthetic crystalline garnets: Yttrium aluminium garnet (YAG, Y3Al5O12), Yttrium iron garnet (YIG, Y3Fe5O12) and Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) are commonly used as a host materials in solid-state lasers, data storage, acoustic transmitters and numerous nonlinear optics applications (light-emitting diodes, scintillators, magneto–optical films etc.). Ion implantation is one of the most promising methods for affecting surface layers of single crystals in order to study the processes taking place in crystal structures and to obtain information on the distribution of ions inside sub lattices. Text to speak: ISOLDE facility at CERN offers a unique opportunity to study alteration in the physical properties into the chemical compounds during implantation of various atoms. Using a 57Mn beam, 57Fe iron atoms incorporated into the garnets structure provides unusual opportunity to survey the spin variations in different coordination sites and alterations regarding magnetic behavior, especially for the Iron containing garnets (YIG). By substituting specific sites with Rare earth elements, interesting magnetic properties can be obtained through the Mössbauer spectroscopy. =============================== Draft material: (not for speak.) ---------------------------- Yttrium aluminium garnet (YAG, Y3Al5O12) is a synthetic crystalline material of the garnet group. YAG is commonly used as a host material in various solid-state lasers. Verdet constant. These properties make it useful for MOI (magnetic optical imaging) applications in superconductors. Yttrium iron garnet (YIG) is a kind of synthetic garnet. It is a ferrimagnetic material with a Curie temperature of 560 K and high ====================== YAG Additional tasks: One of the promising applications of them is the controlling investigation on different steps in the technological procedures of optical advanced materials, containing as constituent and or dopant the optical and Mössbauer probes. Generally, the Mössbauer spectroscopy can detect the structural changes during the phase transition and in process of crystallization. YAG garnet: ===================================================== It is possible to detect the structural changes during the phase transition by the changes in the spectrum shape and Mössbauer spectral parameters. ----------------------------------------- YIG garnet: The Iron ions in the two coordination sites exhibit different spins, resulting in magnetic behavior. By substituting specific sites with 57Mn we expect to obtain interesting magnetic properties. ========================= Despite the similar chemical structure the three garnets types posses different physical properties. In order to normalize our research we use only single crystal layers without additional dopant ions concentrations.

Preliminary view All the spectra in this presentation have been fitted with “Vinda” software. Spectra calibration have been provided with SS detector test. Velocity calibration gives emission temperature dependant scale relative to α-Fe. All the spectra in this presentation have been fitted with “Vinda” software. Spectra calibration have been provided with SS detector test, using 4846 Bq test-source mounted inside the chamber for 12.95 hours. Velocity calibration gives emission temperature dependant scale relative to α-Fe. ============================ It is interesting to distinguish differences in the spectra, but also is interesting to discuss different models to fit the spectra. In case of the eMS the chosen fitting model have a significant meaning for right spectra components interpretation. There is no observed annealing stages. Spectra has been fitted in temperature range from 298 K to 798 K. The slides shows temperature dependence of the three kind of garnets and confirm YIG sensitivity to high temperatures. GGG spectra subject of our previous study were putted for comparison.

Y3Al5O12 (YAG) DB 3,"Voigt lines shape": Specific of the this model doublet is the possibility two legs of the quadrupole are allowed to have different Gaussian broadening. BT1 and BT2, “Blume-Tjoin line-shape” doublets. This model describe the 57Fe emission Mössbauer relaxation spectra for the indicated relaxation times in a magnetic hyperfine field. Here we can see all YAG spectra series and fitted spectra in all temperature range. ------------------ The overall shape of the spectra is a convolution of three line shapes. One Voight line shape. Voigt lines shape is a convolution between Gaussian with standard deviation σ (given in mm/s) and Lorentzian of FWHM width “Г”. Specific of the doublet is the possibility two legs of the Quadrupole are allowed to have different Gaussian broadening. Two “Blume-Tjoin line-shape” doublets. Simulations according to the Blume-Tjon model [Blume and Tjon, 1968] describing the 57Fe emission Mössbauer relaxation spectra for the indicated relaxation times in a magnetic hyperfine field. With decreasing relaxation time, the lines broaden and finally collapse in pairs.

Spectra analysis YAG DB3 associated with Fe3+ in YAG garnet could be assigned to the slow spin relaxation. All doublets reveal Asymmetric slow temperature dependent structure. The broad lines associated with DB3 suggest Fe in highly distorted lattice environment, due to extended lattice damage resulting from the implantation process. The hyperfine parameters associated with of the BT1 and BT2 are consistent with high-spin Fe2+ in amorphous zones as observed in several ion implanted insulators. The Isomer shift and slow temperature dependence of the Quadrupole splitting of DB3 is consistent with an assignment as originating from high-spin Fe3+. ==================== DB3 acossiated with Fe3+ in YAG garnets could be assigned to the slow spin relaxation in contrast to DB3 acossiated with Fe3+ in our previous GGG garnet Mössbauer investigation where doublet DB3 (assignet with Fe3+ on GaT sites) has been assignet to the fast spin relaxation order due to the interactions between Fe3+ and Gd ions. In present YAG study because there is no actually free electrons in Al3+(i.e. compensation of the Al spin electrons) shell able to interact with Fe3+ ions in crystal structure we can refer interactions between Fe3+ ions and Al3+ ions as slow spin relaxation state.

Gd3Ga5O12 (GGG) DB1 suggest Fe in highly distorted lattice environment. DB2 Probably DB2 is due to intersitial Fe. DB3 hyperfine parameters are consistent with an assignment to high-spin Fe3+. There is no annealing stage between RT and 563 K is observed. High-spin Fe3+ shows fast spin relaxation, presumably due to exchange interactions with Gd3+. DB1 suggest Fe in highly distorted lattice environment, possibly due to amorphous surroundings due to the implantation process. DB2 is characterized by a small line-width suggesting a more regular crystalline site but not amorphous one. Probably DB2 is due to the intersitial Fe, either due to implantation directly on interstitial sites or due to the recoil impared on the 57Fe daughter nucleus in the β– decay of 57Mn. DB3 hyperfine parameters are consistent with an assignment to high-spin Fe3+. The implanted Fe3+ is found to occupy only tetrahedral Ga sites and there is no evidence for octahedral substitution. =============================================== There is no annealing stage between RT and ~ 560 K is observed. High-spin Fe3+ shows fast spin relaxation despite the low concentration (<10–4 at.%) utilized in this study, presumably due to exchange interactions with Gd3+. Dilute ion-implantation results in high-spin Fe3+ on substitutional tetrahedral Ga sites, interstitial Fe and Fe2+ in amorphous zones.

YAG spectra analysis Where: Ϭ0: … ϬSOD.. ϴD - Corrected temperature: Corr.T. = Ϭ0 + ϬSOD [T (K), ϴD] Where: Ϭ0: … ϬSOD.. ϴD - Using the MS excel sheets also let as opportunity to make a comparison between different Mossbauer parameters. In the following charts you can see some interesting correlations between fitted YAG parameters. It is necessary point out that we make comparison between various Mossbauer parameters and so called Corr.T. Transition form T (ºC) in “Corr.T. is necessary because the temperature of the sample is higher than temperature of the sample holder. The temperature that we have on the sample holder, has to be corrected (not the same as the sample). This was done with the following formula…. 1. The isomer shift data for DB3 followed the second order Doppler (SOD) shift with temperature?? 2. dSOD decreasing with temperature. 3. The Area of BT1 and BT1 shows a random distribution in a narrow interval of values ( -238 -> -288). In the same time DB3 Area reveal a slow increasing of the values also in narrow interval.

Quenching Spectra_YAG The Quenching analysis has been done at three different temperatures ranges 300 K, 343,6 K and 517, 6 K followed consequent Liquid Nitrogen measurements. Besides the weak broadening there are no significant differences between the quenched and not quenched spectra at temperature ranges 300K – 517 K.

YAG: Data from Mössbauer spectra parameters It is interesting to pay attention to Mossbauer parameters of the quenched YAG spectra. While there is not clear conclusion between random Area distribution and temperature, the dSOD shows decreasing with the temperature.

Spectra analysis YIG Complex Mössbauer spectra fiited with two distribution models DIST.1 and DIST.2 at tempe-rature range 298 K ÷ 798 K. An additional two doublets have been added to accomplish the fitting analysis at 704 K and 798 K. The overall shape of the spectra is a convolution of two sextets distribution models and two doublets. YIG parameters for spectra fitting: For 298 K, 434 K and 510 K: Two hyperfine split distribution models (DIST) of the Fe spectra. This model uses linear segments for the distribution and a possible coupling, between IS and QS. Line widths and Area fractions are pairwise alike. VDBL: Model : Voigt line shape is a convolution between Gaussian with standard deviation (given in mm/s) and Lorentzian of FWHM width. The lines-shape is calculated using the approximation. ============================================= First three spectra 298K, 434K and 510 K reveal clear broadened magnetic structure typical for the YIG garnet at RT without concentration of the substituting ions of the other rare earth elements. Broadened lines are clear indication for presence at Fe3+ in 24c and 24d positions and prevailing of the Fe-Fe interactions near to 560 K the Curie temperature for the YIG. Magnetic structure order begin to shrink at 604 K and paramagnetic environment arises from a fluctuating magnetic hyperfine field. At 798K domination of the paramagnetic behavior is obvious and we can point out the graduate disappearing of the one quadropule peak. This can be explained with decreasing of the Y atoms substituted from Fe implanted atoms in crystal structure or with relaxation spin – spin interaction and spin lattice interactions due to the increasing of the temperature. --------------------------------------------------------- Draft text: not for speaking. The ferrimagnetic structure develops by antiferromagnetic spin alignments between the tetrahedral (d) and octahedral (a) sublattices (the ratio is 24:16) of YIG. The Mössbauer spectra consist of two sextets, with respect to the tetrahedral and octahedral sites for the Iron. The spectra are indicative for stable crystal structure. Curie temperature for YIG is 560 K.

Spectra analysis YIG As regarding to YIG garnets parameters data, there is too much parameters to consider with. The complexion of the situation is define from the sensitivity if the YIG garnet to the temperature. On other hand Hyperfine parameters in our study are consistent with the results from K. Nomura et All. / Conversion electron Mossbauer spectroscopy of YIG, Hyperfine Interactions 84(1994)421-426. The comparison at RT reveal existing of damages in studied from us YIG garnet structure is, although we can’t see the general structure as this is shown by K. Nomura et al.

YIG: data from Mössbauer spectra parameters There is slow dependence of the Distribution Areas from the temperature but is difficult to make conclusions on the basic of this dependence. The Г (mm/s) width is fixed to 0.34 mm/s which is the characteristic of our eMS experiment. dSOD temperature dependence demonstrate decreasing of the dSOD with increasing of the temperature.

Summarize of the results Summarize of the result for YAG Definite signs of an annealing stage with temperature range RT to 440 ºC are not observed. Annealing at higher temperature is needed to incorporate all ions on regular lattice sites. High spin Fe3+ in this material shows slow spin relaxation presumably due to exchange interaction of Fe ions with Al 3+. Summarize of the result for YIG Although limited to six ranges, the temperature dependence of the Isomer shifts and Quadrupole splitting's of the YIG garnet without impurity atoms concentration are consistent with the values for iron (III). The YIG single crystal garnet show clear temperature dependence at temperatures above the RT. Temperature range from 298K to 798 K is indicative for changes in crystal structure. Curie temperature for YIG is 560 K. After 604 K we observe cleary shrinking of the two line shapes distributions and predomination of the paramagnetic structure.