The Er2¡xRxFe14C (R=Gd, Pr) polycrystalline compounds have been synthesized and investigated with
57Fe Mössbauer spectroscopy and magnetic measurements. The spin reorientation phenomena were studied
extensively by narrow step temperature scanning in the neighborhood of the spin reorientation temperature.
Obtained Mössbauer spectra were analyzed using a procedure of simultaneous fitting and the transmission integral approach. Consistent description of Mössbauer spectra were obtained, temperature and composition dependencies of hyperfine interaction parameters and subspectra contributions were derived from fits and the transition temperatures were determined for all the compounds studied. Initial magnetization versus temperature measurements (in zero and non-zero external field) for Er2¡xGdxFe14C compounds allowed to establish the temperature regions of reorientation, change of magnetization value during the transition process. The results obtained with different methods were analyzed and the spin arrangement diagrams were constructed. Data obtained for Er2¡xGdxFe14C were compared with those for Er2¡xGdxFe14B series

Bogacz, B.F.

Kaczorowski, D.

Kapusta, Cz.

Krawiec, K.

Przewoźnik, J.

Pędziwiatr, A.T.

Talik, Ewa

Acta Physica Polonica A

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Influence of carbon on spin reorientation processes in Er 2-xRxFe14C (R = Gd, Pr) - Mossbauer and magnetometric studies  Author: A.T. Pędziwiatr, K. Krawiec, B.F. Bogacz, Cz. Kapusta, J. Przewoźnik, D. Kaczorowski, Ewa Talik  Citation style: Pędziwiatr A.T., Krawiec K., Bogacz B.F., Kapusta Cz., Przewoźnik J., Kaczorowski D., Talik Ewa. (2011). Influence of carbon on spin reorientation processes in Er 2-xRxFe14C (R = Gd, Pr) - Mossbauer and magnetometric studies. "Acta Physica Polonica A" (Vol. 119, nr 1 (2011), s. 48-51).  Vol. 119 (2011) ACTA PHYSICA POLONICA A No. 1Proceedings of the All-Polish Seminar on Mössbauer Spectroscopy, Warsaw, Poland, June 18–21, 2010Influence of Carbon on Spin Reorientation Processesin Er2−xRxFe14C (R = Gd, Pr) — Mössbauerand Magnetometric StudiesA.T. Pe¸dziwiatra, K. Krawieca, B.F. Bogacza, Cz. Kapustab, J. Przewoźnikb,D. Kaczorowskic and E. TalikdaM. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krakow, PolandbAGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, PolandcW. Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy of SciencesOkólna 2, 50-950 Wrocław, PolanddA. Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, PolandThe Er2−xRxFe14C (R=Gd, Pr) polycrystalline compounds have been synthesized and investigated with57Fe Mössbauer spectroscopy and magnetic measurements. The spin reorientation phenomena were studiedextensively by narrow step temperature scanning in the neighborhood of the spin reorientation temperature.Obtained Mössbauer spectra were analyzed using a procedure of simultaneous fitting and the transmission integralapproach. Consistent description of Mössbauer spectra were obtained, temperature and composition dependenciesof hyperfine interaction parameters and subspectra contributions were derived from fits and the transition tem-peratures were determined for all the compounds studied. Initial magnetization versus temperature measurements(in zero and non-zero external field) for Er2−xGdxFe14C compounds allowed to establish the temperature regionsof reorientation, change of magnetization value during the transition process. The results obtained with differentmethods were analyzed and the spin arrangement diagrams were constructed. Data obtained for Er2−xGdxFe14Cwere compared with those for Er2−xGdxFe14B series.PACS: 76.80.+y, 75.25.–j, 75.50.–y, 75.50.Bb1. Introduction.Since the discovery of unique magnetic properties ofNd2Fe14B permanent magnets, a great number of studieswere devoted to R2Fe14B compounds, where R is a rare-earth [1–7]. Less attention was put on carbides R2Fe14C,which are known to be less stable than borides. However,higher anisotropy field of carbides as well as fact thatcarbon doesn’t have negative influence on health and en-vironment during processing, made R2Fe14C compoundsworthy of investigations.Similar to Er2Fe14C compound [8], Er2−xGdxFe14Cand Er2−xPrxFe14C have a tetragonal crystal lattice ofthe P42/mmm space group with 68 atoms in elementarycell, where Fe atoms occupy six different positions de-noted: 16k1, 16k2, 8j1, 8j2, 4e, 4c; rare earth atoms locatethemselves at 4f and 4g positions; and carbon atom at 4gposition. Planar anisotropy of rare earth sublattices hasstronger temperature dependences than axial anisotropyof iron sublattice. Gadolinium or praseodymium atomsreplace Er atoms on 4f and 4g sites and weaken rare earthanisotropy. Due to the weak coupling between sublat-tices in comparison with coupling within the particularsublattice and a competition between planar and axialtendency in rare earth and Fe sublattice, the direction ofeasy magnetization changes from planar (in basal plane)to axial (along the c-axis) with increasing temperature.The spin reorientation temperature, TSR, determinesthe onset of axial anisotropy region, and it is sensitive tothe R-content (R=Gd, Pr) in the sample.The spin reorientation phenomenon in R2Fe14B com-pounds was confirmed by neutron diffraction investiga-tions on single crystals [9]. It was studied previouslyfor different rare earth ions [1–2] in borides and for fewcarbide compounds R=Nd, Er, Gd. Also, change of mag-netic structure with increasing temperature (axis/plane)takes place in Er2−xFe14+2xSi3 compound [10] withP63/mmc structure type.The main goal of this work was to synthesize the car-bides and study the influence of carbon on the spin re-orientation phenomena in substitutions R=Gd, Pr — us-ing 57Fe Mössbauer spectroscopy and magnetic measure-ments. Additional tasks were: to get a consistent descrip-tion of Mössbauer spectra in the whole range of temper-atures and to establish spin structure phase diagram forthe Er2−xGdxFe14C compounds.We also investigated the influence of spin reori-entation process on hyperfine interaction parametersand compared this process in Er2−xGdxFe14C andEr2−xGdxFe14B compounds.(48)Influence of Carbon on Spin Reorientation Processes in Er2−xRxFe14C (R = Gd, Pr). . . 492. Experimental methodsThe samples Er2−xRxFe14C (R=Gd, Pr) were pre-pared by means of induction or arc melting stoichiomet-ric proportions of the starting materials in a high purityargon atmosphere followed by annealing in quartz am-poules at 900 ◦C for two weeks and then rapid cooling inwater to room temperature.X-ray diffraction analysis performed at room temper-ature on randomly oriented powdered samples with theuse of Cu-radiation exhibit a small amount of naturaliron impurity in the samples (the worst case was 10%).The amount of iron impurity has a tendency to increasewith increasing Gd amount in the sample. These im-purity patterns were subtracted from the experimentalspectra by the numerical procedure.The absorbers for Mössbauer investigations, were pre-pared in the form of thin layer of powdered material.As for the polycrystalline material the distribution of ori-entation of magnetic moments is random, so there is nopreferential orientation of powder sample, and it wouldgive 3:2:1 ratio for line intensities in a single Zeeman pat-tern for a thin absorber.The Mössbauer spectra of Er2−xGdxFe14C wererecorded in the temperature range 80–330 K, with 2 Kstep in the vicinity of reorientation temperature TSR, us-ing a 57Co (Rh) source and a computer driven constantacceleration mode spectrometer. The velocity scale wascalibrated with a high purity iron foil. Isomer shift wasestablished with respect to the center of the room tem-perature iron Mössbauer spectrum.Magnetic measurements were performed on Physi-cal Property Measurement System (PPMS) device onEr2−xGdxFe14C compounds by recording magnetizationversus temperature, M versus T , curves in zero and non-zero external magnetic field. Reorientation temperaturesTSR, change of magnetization value during the transi-tion process in the sample were determined from thesemeasurements.3. Results and discussionFor the Er2−xGdxFe14C (x = 0.25, 0.5, 1.5, 2) andEr2−xPrxFe14C (x = 0.25) a large number of spectrawas obtained by 57Fe Mössbauer spectroscopy methodin regions below, above and during the transitions. Allspectra were analysed by fitting six Zeeman subspecrtaaccording to six iron occupations of the crystallographicsublattices, using “exponential” approximation [11] of thetransmission integral, which takes into account the influ-ence of sample thickness on the ratio of line intensities inMössbauer spectrum.Each subspectrum was characterized by the threehyperfine interaction parameters: isomer shift (IS),quadrupole splitting (QS), define as [(v6 − v5) − (v2 −v1)]/2, where vi are velocities corresponding to Möss-bauer line positions, and hyperfine magnetic field — B.One common set of three line widths was used for all Zee-man subspectra. A procedure of simultaneous fitting ofseveral spectra with interconnected parameters, similarto previous studies [8, 12], was applied in order to get aconsistent description of spectra throughout the series.Exemplary spectra are presented in Fig. 1. The spec-tra at the top and the bottom of the figure are relatedto the planar and axial spin arrangements, respectively.The spectra below and above the transition process weredescribed with six Zeeman sextets called “low” and “hightemperature”, respectively with relative intensities ac-cording to iron occupations of the crystallographic sub-lattices (4:4:2:2:1:1).Fig. 1. The selected experimental 57Fe Mössbauerspectra of Er2−xGdxFe14C, x = 1.5 intermetallic com-pound. The solid lines are fits to the data. The stickdiagrams show the line positions and their relative in-tensities.The intermediate spectra were measured inside thespin reorientation region, where a coexistence of the “low”and the “high temperature” Zeeman subspectra was as-sumed, and described with twelve Zeeman sextets in thespectrum. During the transition, these “low” and “hightemperature” Zeeman sextets exchange gradually (be-tween themselves) their contributions Cl, Ch to the totalspectrum, (Cl+Ch = 1). The separation of the sixth lineof 8j2 sublattice from other lines in “high temperature”spectra allow us to establish precisely those contributionsto the spectrum and to determine the spin reorientationtemperature from Mössbauer studies, TSRM , taken as in-tersection points of Cl and Ch curves (Fig. 2).50 A.T. Pe¸dziwiatr, K. Krawiec, B.F. Bogacz, Cz. Kapusta, J. Przewoźnik, D. Kaczorowski, E. TalikFig. 2. The temperature dependencies of subspectracontributions for Cl — low temperature (solid triangle)and Ch — high temperature (open triangle) Zeemansextets for Er2−xGdxFe14C.Fig. 3. The temperature dependencies of the hyperfinefields, B, for different crystal sites of Er1.75Pr0.25Fe14C.The average error is 0.1 T.A common linear temperature dependence of IScaused by second order Doppler shift effect was assumedfor “low” and “high temperature” Zeeman sextets. Thesystematic changes with temperature of QS (linear) andB (square polynomial) were taken into account. Fig-ure 3 shows the temperature dependencies of the hyper-fine fields for the Er1.75Pr0.25Fe14C system. The valueof B for subspectrum 8j2 is the largest because this sub-lattice has the largest number of Fe ions in its nearestneighbourhood. For all sublattices the hyperfine field de-creases with the increase in temperature.Quadrupole splitting is related to the angle betweenthe easy axis of magnetization and the electric field gradi-ent direction [13]. The QS values are different for “high”and “low temperature” sextets and almost independentof temperature.Magnetization curves obtained at low external mag-netic field for solid polycrystalline Er2−xGdxFe14C piecesexhibited some anomalies in the vicinity of reorientations.This enabled the estimation of the spin reorientation tem-perature, TSRH , which was taken as an inflection pointof the descending portion of curve [12]. Changes of mag-netization value during the transition process in the sam-ples were determined from magnetization measurementsat high external magnetic field (see Table).TABLEValues of the spin reorientation temperatures forEr2−xRxFe14C (R=Gd, Pr) compounds: TSRH — frommagnetic measurements, TSRM — from Mössbauer stud-ies, ∆M — change of magnetization value.x, Gd TSRH [K] TSRM [K] ∆M [emu/cm3] TSRM [K],boroncompounds0 — 316 — 3250.25 306 307 144 —0.5 299 290 183 3061.5 211 212 23 220x, Pr0.25 — 267 — 269TSRH error is ±2 K, TSRM and TSRM error is ±2 K,∆M error is ±5 emu/cm3.The reorientation temperatures obtained for the seriesare listed in Table. The values of reorientation tempera-ture obtained with different methods for the carbide se-ries are approximately 10 K lower than those for corre-sponding borides.Fig. 4. Spin structure phase diagram for theEr2−xGdxFe14C compounds. TSRM — spin reori-entation temperature determined from Mossbauermeasurements, TSRH — spin reorientation temperaturedetermined from magnetic measurements. TC —Curie temperature [1]. Dotted line — hypotheticalline to guide the eye. Vertical solid lines refer to thetemperature range of reorientation process.Figure 4 shows the magnetic phase diagram for theEr2−xGdxFe14C. The values of spin reorientation tem-peratures obtained with different methods show a goodagreement for all compounds studied. The increasingcontent of gadolinium results in a decrease of the valueInfluence of Carbon on Spin Reorientation Processes in Er2−xRxFe14C (R = Gd, Pr). . . 51of TSR temperature as well as Curie temperature. Substi-tution of boron by carbon in the compounds mentionedabove, retains the region of axial spin arrangement ap-proximately the same, but moves it to lower tempera-tures. Significant difficulty is the preparation of single-phase carbide samples.References[1] J. Herbst, Rev. Mod. Phys. 63, 819 (1991).[2] E. Burzo, Rep. Prog. Phys. 61, 1099 (1998).[3] K.H.J. Buschow, in: Ferromagnetic Materials, Eds.E.P. Wohlfarth, K.H.J. Buschow, Vol. 4, Amsterdam1988.[4] K.H.J. Buschow, Rep. Prog. Phys. 54, 1123 (1991).[5] M.R. Ibarra, Z. Arnold, P.A. Algarabel, L. Morellon,J. Kamarad, J. Phys. Condens. Matter 4, 9721 (1992).[6] A.T. Pędziwiatr, W.E. Wallace, J. Less-CommonMet. 126, 41 (1996).[7] C. Piqué, R. Burriel, J. Bartolomé, J. Magn. Magn.Mater 154, 71 (1996).[8] A.T. Pędziwiatr, B.F. Bogacz, K. Krawiec, S. Wróbel,J. Alloys Compd. 490, 11 (2010).[9] P. Wolfers, M. Bacmann, D. Fruchart, J. AlloysCompd. 317–318, 39 (2001).[10] J. Żukrowski, A. Błachowski, K. Ruebenbauer,J. Przewoźnik, D. Sitko, N.-T.H. Kim-Ngan, Z. Tar-nawski, A.V. Andreev, J. Appl. Phys. 103, 123910(2008).[11] B.F. Bogacz, Mol. Phys. Rep. 30, 15 (2000).[12] A.T. Pędziwiatr, B.F. Bogacz, A. Wojciechowska,S. Wróbel, J. Alloys Compd. 396, 54 (2005).[13] P. Gütlich, R. Link, A. Trautwein, Mössbauer Spec-troscopy and Transition Metal Chemistry, Springer-Verlag 1978.

Influence of carbon on spin reorientation processes in Er 2-xRxFe14C (R = Gd, Pr) - Mossbauer and magnetometric studies

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Influence of carbon on spin reorientation processes in Er 2-xRxFe14C (R = Gd, Pr) - Mossbauer and magnetometric studies

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