In the paper the electric properties and electronic structure of the intermetallic TbxGd1xNi3 compounds are
presented. The partial replacement of Gd by Tb atoms causes the decrease of the Curie temperature (TC) and
the increase of the residual resistivity. According to the Matthiessen rule the scattering mechanisms in  (T) have
been analyzed. Moreover, the reduced form of the electrical resistivity  Z(T  T0) indicates a deviation from the
linearity for x > 0:2. This kind of behaviour can be attributed to density of d states near by the Fermi level (EF)
which are dominated by Ni 3d states. The valence band spectra as well as the core level lines have been analyzed as the in uence of Tb/Gd substitution on the electronic structure

Bajorek, Anna

Chełkowska, Grażyna

Chrobak, Artur

Kwiecień-Grudziecka, Marzena

Acta Physica Polonica A

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Electrical resistivity and electronic structure of the Tb xGd 1-xNi 3 system  Author: Grażyna Chełkowska, Anna Bajorek, Artur Chrobak, Marzena Kwiecień-Grudziecka  Citation style: Chełkowska Grażyna, Bajorek Anna, Chrobak Artur, Kwiecień-Grudziecka Marzena. (2012). Electrical resistivity and electronic structure of the Tb xGd 1-xNi 3 system. "Acta Physica Polonica A" (Vol. 121, nr 5/6 (2012), s. 1139-1141).  Vol. 121 (2012) ACTA PHYSICA POLONICA A No. 56Proceedings of the European Conference Physics of Magnetism 2011 (PM'11), Pozna«, June 27July 1, 2011Electrical Resistivity and Electronic Structureof the TbxGd1 xNi3 SystemG. Cheªkowska, A. Bajorek, A. Chrobak and M. Kwiecie«-GrudzieckaAugust Cheªkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, PolandIn the paper the electric properties and electronic structure of the intermetallic TbxGd1 xNi3 compounds arepresented. The partial replacement of Gd by Tb atoms causes the decrease of the Curie temperature (TC) andthe increase of the residual resistivity. According to the Matthiessen rule the scattering mechanisms in (T ) havebeen analyzed. Moreover, the reduced form of the electrical resistivity Z(T   T0) indicates a deviation from thelinearity for x > 0:2. This kind of behaviour can be attributed to density of d states near by the Fermi level (EF)which are dominated by Ni 3d states. The valence band spectra as well as the core level lines have been analyzedas the inuence of Tb/Gd substitution on the electronic structure.PACS: 71.20.Eh, 71.20.Lp, 72.15. v, 72.10.Di, 79.60. i1. IntroductionThe RT3 compounds where R is rare earth and T isa transition metal show interesting properties due to thecombination of 3d itinerant and 4f localized magnetism[117]. One of the rst studied group is RNi3. Obviously,its properties depends on the type of R atoms. In theGdNi3 compound the Curie temperature TC = 115 K andthe saturation magnetic moment equals 6.55 B/f.u. [1, 4,12, 13]. The TbNi3 compound exhibits non-collinearmagnetic structure where the terbium atoms in the samecrystallographic position are arranged ferromagneticallybut they are turned between two dierent positions [16].Thus, the magnetic susceptibility exhibits a large mag-netic anisotropy with two dierent paramagnetic Curietemperatures k = 9 K and ? = 63 K. The saturationmagnetic moment equals 7.52 B/f.u. The electrical re-sistivity exhibits two magnetic transitions, one at about55 K (helimagnetic structure of terbium moments alongc axis) and the second at about 80 K (transition fromferromagnetic to paramagnetic state) [16].In this paper we are focused on the inuence of terbiumsubstitution on the electric properties and the electronicstructure in the TbxGd1 xNi3 series.2. Experimental detailsThe polycrystalline samples TbxGd1 xNi3 (x = 0:0,0.2, 0.5, 0.8, 1.0) were prepared by arc-melting from highpurity elements under argon atmosphere. All sampleswere wrapped in tantalum foil, placed in quartz tubesand annealed at 900 C for one week. The crystal struc-ture was checked by means of X-ray diraction (XRD)using Siemens D5000 diractometer. The electrical resis-tivity (T ) was measured quasi-continuously at a slowly corresponding author; e-mail: grazyna.chelkowska@us.edu.plchanging temperature (4.2300 K) by a standard four--probe technique. The X-ray photoelectron spectroscopy(XPS) measurements were performed with the use of PHI5700/660 Physical Electronics spectrometer. The spec-tra were analyzed at room temperature using monochro-matized Al K radiation (1486.6 eV). The samples werefractured and measured in vacuum of 10 10 Torr.3. Results and discussion3.1. Electrical resistivityThe (T ) dependence for the Gd1 xTbxNi3 systemsis presented in Fig. 1a. The Tb/Gd substitution causesthe decrease of the temperature of the magnetic phasetransition (TC). Similar behaviour has been observedfrom magnetic measurements [18]. According to theMatthiessen rule the electrical resistivity can be de-scribed as(T ) = 0 + ph(T ) + mag(T ); (1)where 0  residual resistivity, ph  phonon contribu-tion, mag  magnetic part. The ph for pure metals inthe high temperature range follows the BlochGrüneisendependence and changes linearly with T . The mag rep-resents a spin-disorder contribution which is caused bythe scattering of the conduction electrons on 4f momentsand contribution correlated with spin uctuations. In ourcase the value of 0 increases with the terbium substitu-tion (see Table). It may be a result of crystal disorderwhich appears in the crystal lattice during substitution.Analyzing the (T ) curve below TC we have to takeinto account the phonon contribution (ph  T 5) andthe scattering of s electrons to free d states (sd  T 3).Therefore, the following expression has been used:y = ax5   bx3 + cxn: (2)For the compounds with x  0:2 the n is close to 2 whichindicates the scattering on the spin waves (magnons). Inthe case of compounds with x > 0:2 the resistivity below(1139)1140 G. Cheªkowska et al.Fig. 1. Temperature dependence of the electrical resis-tivity for the TbxGd1 xNi3 system.TC can be rather tted by using the equationy = ax5   bx3 + cx2 exp( d=x); (3)where a, b, c are constants and parameter d is propor-tional to the energy gap (d = =2kB). The exponentialcontribution may be the result of a magnetic anisotropywhich was already observed by Hashimoto et al. in theTbNi3 compound [16].The analysis of parameters obtained from the ttingof (T ) dependence indicates that all of them increasewith Gd/Tb substitution. At the same time the value ofenergy gap  in the spin waves spectra also increases (seeTable). This change is caused by using additional energywhich is needed to reverse the localized spins opposite tothe anisotropy eld.The reduced form of the electrical resistivity can berepresented asZ = (T )  (T0)=(T1)  (T0); (4)in the assumption where T0 = 140 K and T1 = 260 K.TABLEThe transport properties of the TbxGd1 xNi3 compounds.x TC [K] 0 [ cm] a 10 10 b 10 5 c 10 3 n[ cm K 5]55113 K3.68 1.33 1.45 2.080.0 115 5.17 4.250 K4.19 1.97 3 1.90T < TC0.2 110 5.29 3.69 1.51 2.73 1.97d [K]  [meV]0.5 101 7.75 6.02 2.04 3.02 2.89 0.250.8 90 7.79 8.50 2.64 3.50 8.22 0.711.0 83 11.45 16.2 3.63 4.31 8.44 0.73The Z(T  T0) concerns paramagnetic range and rep-resents the phonon contribution and the sd scatteringon the non-ordered spins. Thus, Z exhibits linear be-haviour above TC only for the samples with x  0:2.In the case of higher Tb content the Z(T   T0) resis-tivity deviates from the linearity and shows a positivecurvature. This kind of behaviour can be explained asthe strong dependence on density of d states nearby theFermi level.3.2. Electronic structureFor all studied samples valence bands (VB) spectranearby the Fermi level (EF) are dominated by the Ni 3dstates (Fig. 2a). The terbium substitution causes thedecrease of the intensity of Gd 4f line which is locatedat 8 eV. Simultaneously, the multiplet structure of Tbappears. This structure consists of several lines locatedat 2 eV, 7.4 eV, 9.1 eV and 10.2 eV. The broadening ofstates nearby to EF is particularly visible for x = 0:8 and1.0 terbium concentration. It is the result of Tb substi-tution and the increase of the intensity of Tb 4f states(Fig. 2a and b). For the compounds with x  0:5 theslight increase of intensity of states on the EF is visible.This behaviour could be the result of fd interaction. Si-multaneously in the resistivity measurements it has beenshown that for these compounds the resistivity increaseswith the temperature faster than for other compounds(x  0:2). On the one hand, it may be the eect of de-crease of 5d electrons number (terbium has two 4f elec-tron more but one none 5d electron than gadolinium).On the other hand, it may be the result of the decreaseof relaxation time between collisions as a consequenceof higher probability of electrons scattering into free dstates.Electrical Resistivity and Electronic Structure . . . 1141Fig. 2. (a) Valence band spectra in the broad bind-ing energy range and (b) near by the Fermi level forthe TbxGd1 xNi3 series where x = 0:0, 0.2, 0.5, 0.8,and 1.0.4. SummaryThe aim of presented work was to study the elec-tric properties as well as the electronic structure of theTbxGd1 xNi3 series. All results can be concluded as fol-lows: The value of the temperature of phase transition TCobtained from (T ) decreases with Gd/Tb substi-tution. The tting of (T ) dependence for x  0:2below TC indicates the scattering on the spin waveswhereas for x > 0:2 is rather connected with amagnetic anisotropy. Additionally, the reduced re-sistivity Z(T   T0) exhibits linear dependence forx  0:2 samples and for higher Tb content deviatesfrom the linearity. This deviation can be connectedwith the change of the electronic structure. The VB spectra nearby EF are dominated by theNi 3d states. For the compounds with x  0:5the slight increase of intensity of states on the EFhas been observed. Simultaneously, the Z(T  T0)indicates the deviation from the linearity. It may bethe eect of decrease of 5d electron number but alsothe result of the decrease of relaxation time betweencollisions as a consequence of higher probability ofelectrons scattering into free d states.AcknowledgmentsThis work was partially supported by Ministry of Sci-ence and Higher Education, grant no. N N202 200039.References[1] K.H.J. Buschow, Rep. Prog. Phys. 40, 1179 (1977).[2] J. Yakinthos, D. Paccard, Solid State Commun. 10,989 (1972).[3] J. Rossat-Mignod, J. Yakinthos, Phys. Status Solidi B47, 239 (1971).[4] D. Paccard, R. Pauthenet, Compt. Rend. Acad. Sci.Paris 264, 1056 (1967).[5] E. Burzo, J. Laforest, Compt. Rend. Acad. Sci. Paris274, 114 (1972).[6] J.E. Greedan, in: Proc. 9th Rare Earth Res. Conf.,Virginia Polytechnic Inst. and State Univ., Blacks-burg (Va) 1971, p. 208..[7] E. Burzo, D. Seitabla, Solid State Commun. 37, 663(1981).[8] F. Porarian, T. Tajabor, Phys. Status Solidi A 61,537 (1980).[9] S.K. Arif, D.S.P. Bunbury, Phys. Status Solidi A 33,91 (1976).[10] S.C. Tsai, K.S.V.L. Narasimhan, J. Appl. Phys. 45,3582 (1974).[11] K.S.V.L. Narasimhan, R.A. Butera, R.S. Craig,J. Appl. Phys. 44, 879 (1973).[12] A. Chrobak, A. Bajorek, G. Cheªkowska, G. Hane-czok, M. Kwiecie«, Phys. Status Solidi A 206, 731(2009).[13] A. Bajorek, A. Chrobak, G. Cheªkowska,M. Kwiecie«, J. Alloys Comp. 485, 6 (2009).[14] E. Burzo, D. Seitabla, J. Phys. F, Met. Phys. 11,L255 (1981).[15] E. Burzo, D. Seitabla, J. Phys. F, Met. Phys. 12,2675 (1982).[16] Y. Hashimoto, H. Fuji, T. Okamoto, Y. Makihara,J. Magn. Magn. Mater. 70, 291 (1987).[17] P. de V. du Plessis, T. Germishuyse, J. Magn. Magn.Mater. 104-107, 1349 (1992).[18] A. Bajorek, G. Cheªkowska, A. Chrobak,M. Kwiecie«-Grudziecka, Solid State Phenom.170, 109 (2011).

Electrical resistivity and electronic structure of the Tb xGd 1-xNi 3 system

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Electrical resistivity and electronic structure of the Tb xGd 1-xNi 3 system

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