The intermetallic compounds YbxGd1¡xNi5 crystallize in the hexagonal CaCu5-type structure. Based on
wide ranging SQUID-type magnetometer, it was shown that the saturation magnetization decreases with growing
concentration of ytterbium. The opposite tendency was observed for the Sommerfeld coefficient obtained in the
heat capacity measurements. These results are confirmed using ab initio band structure calculations

Bajorek, Anna

Chełkowska, Grażyna

Chrobak, Artur

Szajek, A.

Werwiński, M.

Acta Physica Polonica A

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: The Electronic and Magnetic Properties of YbxGd1-xNi5 Systems  Author: A. Szajek, M. Werwiński, Grażyna Chełkowska, Anna Bajorek, Artur Chrobak  Citation style: Szajek A., Werwiński M., Chełkowska Grażyna, Bajorek Anna, Chrobak Artur. (2010). The Electronic and Magnetic Properties of YbxGd1-xNi5 Systems. "Acta Physica Polonica A" (Vol. 118, nr 5 (2010), s. 905-906).  Vol. 118 (2010) ACTA PHYSICA POLONICA A No. 514th Czech and Slovak Conference on Magnetism, Košice, Slovakia, July 6–9, 2010The Electronic and Magnetic Propertiesof YbxGd1−xNi5 SystemsA. Szajek, M. WerwińskiInstitute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, PolandG. Chełkowska, A. Bajorek and A. ChrobakA. Chełkowski Institute of Physics, Silesian University, Uniwersytecka 4, 40-007 Katowice, PolandThe intermetallic compounds YbxGd1−xNi5 crystallize in the hexagonal CaCu5-type structure. Based onwide ranging SQUID-type magnetometer, it was shown that the saturation magnetization decreases with growingconcentration of ytterbium. The opposite tendency was observed for the Sommerfeld coefficient obtained in theheat capacity measurements. These results are confirmed using ab initio band structure calculations.PACS numbers: 71.20.−b, 75.25.−j1. IntroductionThe RNi5 compounds (R = rare earth) have been in-tensively studied in recent decades [1–12]. Newly ob-tained series of the YbxGd1−xNi5 compounds (x ≤ 0.5)exhibit interesting properties [5]. All studied compoundscrystallize in the hexagonal CaCu5 type structure. How-ever, the Yb/Gd substitution causes the increase in c(x)lattice parameter in the whole range of studied concen-trations. This kind of change is connected with differentionic radii for gadolinium and ytterbium ions. The devia-tion from the linear change of a(x) and V (x) for x > 0.4may be related to an intermediate valence of Yb ions.The properties of the YbxGd1−xNi5 compounds are veryinteresting and were the motivation to study their elec-tronic and magnetic properties more in detail using abinitio calculations and SQUID measurements.2. Experimental and computational detailsPolycrystalline samples of the YbxGd1−xNi5 serieswith x = 0.0, 0.2, 0.4, 0.5 were prepared by an arc melt-ing technique from high purity elements under the argonatmosphere. The purity of materials used for preparingsamples were 99.99% for Ni and Yb and 99.9% for Gd.The crystal structure of all samples was checked by meansof X-ray diffraction (XRD) using Siemens D5000 diffrac-tometer. The magnetic properties of YbxGd1−xNi5 com-pounds were measured with the use of SQUID magne-tometer (MPMS XL7 Quantum Design). All measure-ments were performed in the 2–400 K temperature rangeup to 7 T magnetic field.In the band structure calculations we employed thefull potential linear augmented plane wave (FP LAPW[13]) method in Wien2k code implemented in the latestversion of the original Wien code. The calculations wereperformed within the density-functional theory for exper-imental lattice constants [5]. We started for x = 0 fromthe CaCu5-type unit cell and for other concentrationsappropriate supercells were constructed to get an exper-imental stoichiometry. We used the generalized gradientapproximation (GGA) [14] to the potential parameter-ized in the form proposed by Perdew et al. [14]. Theself-consistent criterion for the total energy was equal toat least 10−6 Ry.3. Results and discussionThe isothermal magnetization curves M(H) for theYbxGd1−xNi5 system were measured at 2 K and upto 7 T. The magnetization saturates faster for the Gd--rich compounds. The highest value of the satura-tion magnetization MS is observed for x = 0.0 andslowly decreases with the increase of ytterbium concen-tration up to x = 0.5 (see Table).The value of MS forTABLEThe electronic and magnetic characteristics forYbxGd1−xNi5 series: saturation magnetization MS andtotal magnetic moment m [µB/f.u.], measured (γ) andcalculated (γ0) Sommerfeld coefficient [mJ/(mol K2)],density of states (DOS)at the Fermi level [states/(eV spinf.u.). In parenthesis there are collected calculated magneticmoments on Gd and Yb atoms.x MS γDOS(EF)spin ↑ / ↓ γ0 m0.0 6.52 45.3 4.66/4.54 21.7 7.08 (Gd:6.88)0.2 5.72 73.1 1.45/5.71 16.9 7.68(Gd1:6.82/Gd2:6.82/Yb:0.80)0.4 4.66 73.6 2.74/6.85 22.6 3.43(Gd1:6.82/Gd2:-6.94/Yb:0.50)0.5 4.36 104.2 9.23/1.83 26.1 0.96 (Gd:6.94/Yb:-0.81)the GdNi5 compound is smaller than for free Gd3+ ion(7 µB). As we suppose from X-ray photoemission spec-troscopy (XPS) measurements [5] the ytterbium ions inthe YbxGd1−xNi5 series are visible in trivalent state.Moreover, magnetic Yb3+ ions have a smaller magnetic(905)906 A. Szajek et al.moment than Gd3+. Therefore Yb/Gd substitutioncauses the gradual decrease of the MS(x) value.The Sommerfeld coefficient γ was fitted from specificheat measurements C(T ) = γT + CD(T ), where CD(T )is the Debye expression for the phonons, for T > TC, andresults are collected in Table. Their values increase withan increasing content of Yb atoms. For related compoundDyNi5 γ = 36 mJ/(mol K2) [15].In Fig. 1 we present DOS plots for YbxGd1−xNi5 sys-tems calculated based on Wien2k code within the GGAapproach. It is our first attempt to this problem in spiteof known limitations of GGA, which are manifested bywrong positions of 4f peaks. The calculated values ofDOS at the Fermi level together with the Sommerfeldcoefficients are collected in Table. Values of γ0 are muchlower than γ experimental, the difference indicates im-portant role of many-body effects in these systems, whichare described by the simple formula γ = γ0(1+λ), whereλ is the mass enhancement factor.Fig. 1. Total and spin projected DOS plots forYbxGd1−xNi5 systems (x = 0.0, 0.2, 0.4, and 0.5).To get magnetic moments we started calculations fromdifferent initial moments assuming their anti- or parallelalignment, then the total energy was compared. Resultspresented in Fig. 1 and Table are for the case with theminimum energy. The general tendency in the calculatedmagnetic moment per formula unit and Sommerfeld co-efficient is compatible with experimental results, but toimprove the description of the strongly correlated 4f elec-trons, crucial role of many-body effects should be takeninto account (see [16] for elemental, metallic Yb). Themagnetic structure of considered systems is complicated,usually Ni atoms treated as non-magnetic are magneticwith moments up to 0.4 µB/atom and have different ori-entations.4. ConclusionsPresented results may be summarized as follows:— the substitution of Yb for Gd atoms up to x = 0.5in the GdNi5 crystalline compound causes the decreaseof the saturation magnetization, from 6.52 µB/f.u. to4.36 µB/f.u. for x = 0 to x = 0.5, respectively;— the Sommerfeld coefficient increases with increasingcontent of Yb;— above conclusions are confirmed by ab initio calcu-lations.AcknowledgmentsThis work was supported by MNiSW within grant No.NN202134933.References[1] K.H.J. Buschow, Rep. Prog. Phys. 40, 1169 (1977).[2] E. Burzo, A. Chełkowski, H.R. Kirchmayr, LandoltBörnstein Handbook, Vol. III/19d2, Springer, Berlin1990.[3] M. Coldea, S.G. Chiuzbaian, M. Neumann,D. Todoran, M. Demeter, R. Tetean, V. Pop,Acta Phys. Pol. A 98, 629 (2000).[4] D. Gignoux, D. Givord, A. Del Moral, Solid StateCommun. 19, 891 (1976).[5] A. Bajorek, G. Chełkowska, Acta Phys. Pol. A 115,188 (2009).[6] E. Burzo, V. Pop, I. Costina, J. Magn. Magn. Mater.157/158, 615 (1996).[7] E.A. Nesbitt, H.J. Williams, H.J. Wernick, R.C. Sher-wood, J. Appl. Phys. 33, 1674 (1962).[8] A. Bajorek, D. Stysiak, G. Chełkowska,J. Deniszczyk, W. Borgieł, M. Neumann, Mater. Sci.Poland 24, 867 (2006).[9] K. Balkis Ameen, J. Alloys Comp. 347, 165 (2002).[10] M.A. Fremy, D. Gignoux, J. Less-Common Met. 106,251 (1985).[11] A. Palenzona, S. Cirafici, J. Less-Common Met. 33,361 (1973).[12] J. He, N. Tsujii, M. Nakanishi, K. Yoshimura, K. Ko-suge, J. Alloys Comp. 240, 261 (1996).[13] P. Blaha, K. Schwarz, G.K.H. Madsen, D. Kvasnicka,J. Luitz, WIEN2k_9.1, An Augmented Plane Wave +Local Orbitals Program for Calculating Crystal Prop-erties, Karlheinz Schwarz, Techn. Universität Wien,Austria 2007.[14] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett.77, 3865 (1996).[15] R. Radwański, N.H. Kim-Ngan, F.E. Kayzel,J.J.M. Franze, Int. J. Mod. Phys. B 7, 379 (1993).[16] E.R. Ylvisaker, J. Kuneš, A.K. McMahan, W.E. Pick-ett, Phys. Rev. Lett. 103, 246401 (2009).

The Electronic and Magnetic Properties of YbxGd1-xNi5 Systems

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The Electronic and Magnetic Properties of YbxGd1-xNi5 Systems

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