Measurements of the magnetic properties, the electrical conductivity and the Seebeck effect were performed
on single crystals (CdxAly)[Cr2]Sez between 77 and 300 K. All samples have a ferromagnetic order with the Curie temperature of 130 K and the paramagnetic Curie–Weiss temperature of 155 K. Both these temperatures do not depend significantly on the Al substitution. The electrical conductivity of single crystals CdCr2Se4 doped with Al. was p-type and showed the change of log ¾ versus 1=T slope above 150 K. This fact is interpreted as being due to the onset of impurity conduction and structural defects

Duda, Henryk

Groń, Tadeusz

Kusz, Joachim

Malicka, Ewa

Rduch, Paweł

Acta Physica Polonica A

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Ferromagnetic order in single-crystalline (CdxAl y)[Cr2]Sez semiconductors  Author: Henryk Duda, Paweł Rduch, Ewa Malicka, Tadeusz Groń, Joachim Kusz  Citation style: Duda Henryk, Rduch Paweł, Malicka Ewa, Groń Tadeusz, Kusz Joachim. (2011). Ferromagnetic order in single-crystalline (CdxAl y)[Cr2]Sez semiconductors. "Acta Physica Polonica A" (Vol. 119, nr 5 (2011), s. 702-704).  Vol. 119 (2011) ACTA PHYSICA POLONICA A No. 5XXXIX “Jaszowiec” International School and Conference on the Physics of Semiconductors, Krynica-Zdrój 2010Ferromagnetic Order in Single-Crystalline(CdxAly)[Cr2]Sez SemiconductorsH. Dudaa, P. Rducha, E. Malickab, T. Grońa and J. KuszaaInstitute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, PolandbInstitute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, PolandMeasurements of the magnetic properties, the electrical conductivity and the Seebeck effect were performedon single crystals (CdxAly)[Cr2]Sez between 77 and 300 K. All samples have a ferromagnetic order with the Curietemperature of 130 K and the paramagnetic Curie–Weiss temperature of 155 K. Both these temperatures do notdepend significantly on the Al substitution. The electrical conductivity of single crystals CdCr2Se4 doped with Alwas p-type and showed the change of log σ versus 1/T slope above 150 K. This fact is interpreted as being due tothe onset of impurity conduction and structural defects.PACS: 72.80.Jc, 75.50.Pp, 75.50.Dd1. IntroductionFerromagnetism has been found in several ternarychromium compounds crystallizing in spinel structure[1, 2]. These compounds are both semiconducting andferromagnetic with relatively high Curie temperature.Pure CdCr2Se4 combines p-type semiconducting andferromagnetic properties with the Curie temperatureTC = 142 K and the Curie–Weiss temperature θCW =190 K [1]. In literature some reports appeared on theproperties mentioned above, in particular an anomaloustemperature dependence of the electrical conductivity ofIn-doped and Ga-doped n-type CdCr2Se4 [2–4]. Newerreports concern isostructural single-crystalline CdCr2Se4spinel systems doped with In [5], Sb [5–7] and Ga [8, 9]as well as polycrystalline CdxCryVzSe4 spinel series [10].They are ferromagnets and p-type semiconductors forsmall In, Sb, Ga and V content. For higher content an-tiferromagnetic order, spin-glass and n-type conductionoccur.This paper reports the electrical and magnetic prop-erties of CdCr2Se4 single crystals doped with Al in thecompositional range of Al up to y = 0.04.2. Experimental detailsNew nonstoichiometric single crystals of(CdxAly)[Cr2]Sez (where 0.02 ≤ y ≤ 0.04) wereprepared using a chemical vapour transport method. Asthe starting materials, binary selenides (CdSe, Al2Se3)and anhydrous chromium chloride (CrCl3) were used.The chemical composition of the (CdxAly)[Cr2]Sez singlecrystals were determined using an electron microscopeJEOL (7600F) with a microprobe EDS OXFORD.Good quality samples of the (CdxAly)[Cr2]Sez spinelseries were selected under a stereoscopic microscope.The structure refinements of the spinels under studywere done using a KM 4-circle diffractometer (KumaDiffraction) and a SHELXL-93 computer program [11].The single crystals under study crystallize in the cubicsystem with the space group Fd3¯m (No. 227). Twodiamagnetic ions, Cd and Al, differing in ionic radii andcharge (rCd2+ = 78 and rAl3+ = 39 pm [12]), occupytetrahedral 8a positions, while the magnetic Cr ionsare in the octahedral 16e sites. Refinement of the siteoccupation factors (SOFs) revealed a certain amount ofthe Se deficit in the anion 32e sites (Table I).The electrical conductivity has been measured with thefour-probe dc method using the apparatus with KeithleyK181 digital multimeters. The thermoelectric power wasmeasured with a differential method using the tempera-ture difference ∆T of about 2 K. The electrical and ther-mal contacts between the single crystal and the copperrods were maintained with a silver lacquer mixture (De-gussa Leitsilber 200). The thermoelectric power and theelectrical conductivity of the same sample were measuredalong the 〈001〉 direction. The crystal orientation aboutthe 〈001〉 crystallographic zone axis was based on 12–18centred X-ray diffraction reflections with the Bragg an-gles in the range 107◦ ≤ 2θ ≤ 144◦ (Mo Kα radiation).The crystal data are summarized in Table I. The electri-cal measurements in the 〈111〉 direction, performed forcomparison, showed unimportant difference with thosealong 〈001〉. Ac and dc magnetization and magnetic sus-ceptibility were measured using a Quantum Design Sys-tem (MPMS XL) at magnetic field up to 70 kOe and inthe temperature range 4.2–300 K.3. Results and discussionMagnetic and electrical measurements carried out onthe (CdxAly)[Cr2]Sez single crystals are presented inTable II and Figs. 1–3. They revealed a ferromagneticorder with a Curie temperature TC ≈ 130 K and a para-magnetic Curie–Weiss temperature θCW ≈ 155 K as wellas a p-type conduction. TC and θCW do not significantlydepend on the Al substitution. The effective magneticmoment slightly decreases from 6.40 µB/f.u. for y = 0.02(702)Ferromagnetic Order in Single-Crystalline . . . 703TABLE IChemical composition, crystal data, structure refine-ments, atomic positions, selected distances and angles for(CdxAly)[Cr2]Sez spinel system. a and u are the lattice andanion positional parameters, respectively, d is the calculateddensity, R1 and wR2 are the final factors.Chemical compositionx 0.98 0.97 0.96y 0.02 0.03 0.04z 3.95 3.93 3.88Crystal system: cubic; space group: Fd3¯mCrystal dataa [pm] 1074.39(2) 1074.28(2) 1073.82(2)u 0.26431(1) 0.26431(1) 0.26428(1)d [Mg/m3] 2.55 2.556 2.559Refinementfinal R1 [%] 1.68 1.56 1.93final wR2 [%] 4.38 3.59 4.41Site occupation factor (SOF)Cd 0.982 0.969 0.958Al 0.018 0.031 0.042Cr 1.0 1.0 1.0Se 0.987+vac. 0.983+vac. 0.971+vac.Isotropic displacement parameter Ueq [×103 Å2]Cd 3.27(4) 1.65(3) 3.04(4)Al 3.27(4) 1.65(3) 3.04(4)Cr 2.55(5) 1.20(4) 2.64(5)Se 2.39(3) 0.92(3) 2.16(3)Selected interatomic distances in pmCd–Se(2) 259.21(2) 259.11(2) 259.18(2)Al–Se(1) 254.13(2) 259.11(2) 259.18(2)Cr–Se(1) 254.19(1) 254.02(1) 254.19(1)Selected angles in degSe–Cd/Al–Se(4) 109.47(1) 109.47(1) 109.47(1)Se(3)–Cr–Se(1) 96.71(1) 96.71(1) 97.12(1)Se(3)–Cr–Se(2) 82.87(1) 82.86(1) 82.88(1)The atom positions are: (Cd/Al) site: 8a: (1/8, 1/8, 1/8);[Cr] site: 16d: (1/2, 1/2, 1/2); Se site: 32e: (u, u, u).to 6.06 µB/f.u. for y = 0.4. The magnetic isothermsmeasured up to 70 kOe and at 2 K exhibit a saturationmagnetization at 2 kOe which remains almost constantas Al content slowly increases.Below 2 kOe a linear increase in magnetization withincreasing magnetic field indicates a lack of spontaneousmagnetization. These results suggest the strong ferro-magnetic coupling of the magnetic moments both in the(001) planes and between them. One can conclude thatin comparison with the CdCr2Se4 matrix a dilution ofmagnetic sublattice by the spin defects (Al-ions) weak-ens both the long and short range ferromagnetic superex-Fig. 1. The ac molar susceptibility χac vs. temperatureT for single crystals of the (CdxAly)[Cr2]Sez spinel sys-tem recorded at Hac = 3 Oe, and inverse susceptibility1/χac versus T indicating Curie–Weiss behaviour.Fig. 2. Magnetization σ vs. magnetic field H recordedat 2 K for (CdxAly)[Cr2]Sez.704 H. Duda et al.Fig. 3. The electrical conductivity (lnσ) vs. reciprocaltemperature T−1 for (CdxAly)[Cr2]Sez.TABLE IIElectrical and magnetic parameters of the(CdxAly)[Cr2]Sez spinel system. µeff is the effec-tive magnetic moment, CM is Curie constant, χ0 is thetemperature independent susceptibility, TC and θCW arethe Curie and Curie–Weiss temperatures, respectively,σ is the electrical conductivity, Ea is the activationenergy and S is the thermopower at 300 K.y 0.02 0.3 0.04µeff [µB/f.u.] 6.40 6.09 6.06CM [K/mol] 5.12 4.639 4.59χM [emu/mol] 56.83 37.87 25.53TC [K] 131.4 130.4 130.1θCW [K] 155.9 150.7 158.8lnσ [Ω−1 m−1] −4.68 −4.7 1.05Ea [eV] – 0.1 0.1S [µV/K] 30 25 120change interactions in the spinels under study. The Al--substitution strongly affects on the value of the electricalconductivity, but not on the thermal activation, close to0.1 eV, as well as on the sign of thermopower (see Table IIand Fig. 3). A Se non-stoichiometry could change thecarrier concentration, too.AcknowledgmentsThis work is partly founded from science Grant No. NN204 145938.References[1] P.K. Baltzer, H.W. Lehmann, M. Robbins, Phys. Rev.Lett. 15, 493 (1965).[2] P.K. Baltzer, P.J. Wojtowicz, M. Robbins,E. Lopatin, Phys. Rev. 151, 367 (1966).[3] H.W. Lehman, Phys. Rev. 163, 488 (1967).[4] A. Amith, L. Friedman, Phys. Rev. B 2, 434 (1970).[5] A. Waśkowska, L. Gerward, J. Staun Olsen, W. Mor-genroth, E. Malicka, D. Skrzypek, J. Phys., Condens.Matter. 20, 425209 (2008).[6] E. Malicka, A. Waśkowska, D. Skrzypek, R. Sitko,D. Kaczorowski, J. Solid State Chem. 182, 3149(2009).[7] E. Malicka, H. Duda, T. Groń, S. Mazur,A. Waśkowska, R. Sitko, J. Alloys Comp. 442, 186(2007).[8] I. Okońska-Kozłowska, E. Malicka, A. Waśkowska,J. Heimann, T. Mydlarz, J. Solid State Chem. 158,34 (2001).[9] T. Groń, A. Krajewski, J. Kusz, E. Malicka,I. Okońska-Kozłowska, A. Waśkowska, Phys. Rev. B71, 035208 (2005).[10] T. Groń, H. Duda, E. Malicka, B. Zawisza, J. Krok--Kowalski, A.W. Pacyna, Acta Phys. Pol. A 116, 969(2009).[11] G.M. Sheldrick, SHELXL-93, program for the refine-ment of crystal structures, University of Göttingen,1993.[12] R.D. Shannon, Acta Crystallogr. A 32, 751 (1976).

Ferromagnetic order in single-crystalline (CdxAl y)[Cr2]Sez semiconductors

https://rebus.us.edu.pl/bitstream/20.500.12128/8201/1/Duda_Ferromagnetic_order_in_single_crystalline.pdf

Ferromagnetic order in single-crystalline (CdxAl y)[Cr2]Sez semiconductors

Abstract

Similar works

Full text

Available Versions

Repozytorium Uniwersytetu Śląskiego RE-BUŚ