The static (dc) and dynamic (ac) magnetic measurements of CdCr2Se4 and Cd[Cr1:89Ti0:08]Se4 showed
their ferromagnetic properties with a Curie temperature TC   130 K and revealed on the real component of ac
susceptibility curve, the peaks near TC at 200 Oe, 450 Oe and 1 kOe, characteristic for the Hopkinson ones.
The meaningful reduction of saturation moment to 4.73  B/f.u. for Cd[Cr1:89Ti0:08]Se4 suggests the diamagnetic
con guration of Ti ions, which dilutes the ferromagnetic sublattice of Cr ones and causes reducing of the energy
losses visible on the imaginary components of ac susceptibility curve. Close for zero values of higher susceptibility harmonics above TC are pointing out to the lack of the spin  uctuations in the paramagnetic state

Duda, Henryk

Groń, Tadeusz

Krok-Kowalski, Józef

Malicka, Ewa

Pacyna, A.W.

Acta Physica Polonica A

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Hopkinson-like effect in single-crystalline CdCr 2Se 4 and Cd[Cr 1.89Ti 0.08]Se 4  Author: Ewa Malicka, Tadeusz Groń, A.W. Pacyna, Henryk Duda, Józef Krok-Kowalski  Citation style: Malicka Ewa, Groń Tadeusz, Pacyna A.W., Duda Henryk, Krok-Kowalski Józef. (2012). Hopkinson-like effect in single-crystalline CdCr 2Se 4 and Cd[Cr 1.89Ti 0.08]Se 4. "Acta Physica Polonica A" (Vol. 121, nr 3 (2012), s. 690-693).  Vol. 121 (2012) ACTA PHYSICA POLONICA A No. 3Hopkinson-Like Eect in Single-Crystalline CdCr2Se4and Cd[Cr1:89Ti0:08]Se4E. Malickaa, T. Gro«b, A.W. Pacynac, H. Dudab and J. Krok-KowalskibaInstitute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, PolandbInstitute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, PolandcThe Henryk Niewodnicza«ski Institute of Nuclear Physics, Polish Academy of SciencesE. Radzikowskiego 152, 31-342 Kraków, Poland(Received June 25, 2011)The static (dc) and dynamic (ac) magnetic measurements of CdCr2Se4 and Cd[Cr1:89Ti0:08]Se4 showedtheir ferromagnetic properties with a Curie temperature TC  130 K and revealed on the real component of acsusceptibility curve, the peaks near TC at 200 Oe, 450 Oe and 1 kOe, characteristic for the Hopkinson ones.The meaningful reduction of saturation moment to 4.73 B/f.u. for Cd[Cr1:89Ti0:08]Se4 suggests the diamagneticconguration of Ti ions, which dilutes the ferromagnetic sublattice of Cr ones and causes reducing of the energylosses visible on the imaginary components of ac susceptibility curve. Close for zero values of higher susceptibilityharmonics above TC are pointing out to the lack of the spin uctuations in the paramagnetic state.PACS: 72.80.Jc, 75.50.Pp, 75.50.Dd1. IntroductionThe magnetization of many compounds shows a peaknear the ordering temperature when heating the samplein a xed (small) magnetic eld [1]. This behavior iscommonly called the Hopkinson eect [2]. The acceptedexplanation [3] of this eect is based only on domain wallmotion. This mechanism is obviously inapplicable to thecase of single-domain particles. However, a thermomag-netic eect which is quite similar to the Hopkinson eecthas been experimentally observed in most of the amor-phous magnetic materials as well as in some spin glasseswhere the existence of multi-domain particles is question-able or even practically impossible [2]. In Nd2Fe14B-typeribbons the existence of a maximum in the thermomag-netic curves of thermally demagnetized samples in lowelds was connected with the processes of irreversiblerotation of magnetic moments of non-interacting uni-axial single domain particles according to the StonerWohlfarth model [2, 4].The CdCr2Se4 spinel combines the p-type semicon-ducting and ferromagnetic properties with the Curie tem-perature TC = 142 K and the CurieWeiss temperatureCW = 190 K [5, 6]. Magnetization of CdCr2Se4 reaches Proceedings of the 40th Jaszowiec International School andConference on the Physics of Semiconductors, Krynica-Zdrój,Poland, June 25July 1, 2011.the full saturation of 5.98 B per molecule [7]. The ferro-magnetic properties of CdCr2Se4 are a result of dominat-ing interactions between the nearest-neighbour chromiumions and of weaker superexchange couplings between themore distant chromium ones [8]. The Cr 2p X-ray pho-toelectron spectra (XPS) of CdCr2Se4 showed the spinorbit splitting between the nal Cr 2p3=2 and Cr 2p1=2states of 9.5 eV. The Cr 2p3=2 states are split into twopeaks at 574.2 and 575.2 eV. The peak separation withthe binding energy dierence E about 1 eV is typicalof the 3d3 elements with localized magnetic moment of3 B [9]. CdCr2Se4 crystallizes in the cubic structure(Fd3m). The X-ray renements showed that the (Cd)ions have a preference to be located in the tetrahedralsites and the [Cr] ions prefer to be located in the octahe-dral sites of the spinel structure [10]. In slightly dopedwith gallium, CdCr1:985Ga0:015Se4 [10], and with vana-dium, Cd0:87Cr1:93V0:06Se4 [11], a step-like structure ofthe electrical conductivity and a mictomagnetic order [12]were observed.2. Experimental detailsThe single-crystal X-ray diraction data were collectedon Gemini A Ultra diractometer equipped with CCDdetector and using Mo K radiation. The structurewas rened by the full-matrix least-squares method bymeans of SHELX-97 program package [13]. Chemi-cal compositions of the single crystals were determined(690)Hopkinson-Like Eect in Single-Crystalline . . . 691non-destructively by energy-dispersive X-ray uorescencespectrometry (EDXRF) [14]. The samples were excitedby an X-ray beam from the air-cooled side-window Rhtarget of the X-ray tube with Be window of 125 m thick-ness and nominal focal spot size of ca. 100 m (XTF5011/75, Oxford Instruments, USA). The quantitativeEDXRF analysis was performed using the fundamentalparameter method based on the Sherman equation [15]and Pella et al. algorithm [16, 17] to calculate the X-raytube spectrum. The X-ray diraction revealed a single--phase material with the cubic spinel structure (Fd3m)with a lattice parameter a = 1073:3(8) pm for CdCr2Se4and a = 1068:32(13) pm for Cd[Cr1:89Ti0:08]Se4.Dc magnetization, ac and dc magnetic susceptibilityof the single crystals under study were measured in thezero-eld-cooled mode using a Lake Shore 7225 dc mag-netometer/ac susceptometer in the temperature range4.3300 K and in applied external magnetic elds up to60 kOe. The in-phase 01(T ) and out-of-phase 001(T )components of the ac fundamental susceptibility wererecorded in the temperature range 4.5160 K using anoscillating eld Hac = 1 Oe with frequency of 120 Hz forexternal magnetic elds Hdc = 0:100 Oe, 200 Oe, 450 Oeand 1 kOe. The signals of the second (2) and third(3) harmonics were detected at the same temperaturerange, for the same amplitude and frequency as the ac 1measurements without an external static magnetic eld.3. Results and discussionFigures 13 show the ferromagnetic order with TC =130 K, CW = 150 K and the saturation magnetizationof 5.91 B/f.u. at 4.5 K and at 60 kOe for CdCr2Se4,and with TC = 129 K, CW = 138 K and the saturationmagnetization of 4.73 B/f.u. at 4.3 K and at 60 kOe forCd[Cr1:89Ti0:08]Se4. The values of TC and CW charac-terize the long- and short-range superexchange magneticinteractions, respectively. The strongly reduced satura-tion magnetization for Cd[Cr1:89Ti0:08]Se4 in comparisonwith the CdCr2Se4 matrix (5.98 B/f.u. [7]) seems tobe partially connected with the solution of the magneticCr-sublattice by the diamagnetic Ti4+ ions. Other hypo-thetical possibility is a mixed-spin state of the Cr ions inthe t2g orbital.The tting procedure of the CurieWeiss law [18] showsthat the experimental (blue) curve of  1 (T ) in Fig. 1deviates upward from its linear part (red curve). It in-dicates the diamagnetic temperature independent con-tribution to the magnetic susceptibility with the valueof 0 =  1:74  10 6 cm3/g for CdCr2Se4 and of 0 = 1:2310 5 cm3/g for Cd[Cr1:89Ti0:08]Se4, for which thePearson correlation coecient R is over 99% [18]. Usu-ally 0 contains the orbital and Landau diamagnetism,the Pauli and Van Vleck paramagnetism as well as oth-ers, as they cannot be separated. Because the CdCr2Se4matrix is the semiconductor [5] the Landau and Paulicontributions can be neglected.The ac magnetic susceptibility measurements pre-sented in Figs. 4 and 5 revealed the spectacular peaksFig. 1. Dc magnetic susceptibility  and inversesusceptibility 1= vs. temperature T at 1 kOe forCdCr2Se4. TC is marked by arrow.Fig. 2. Dc magnetic susceptibility  and inverse sus-ceptibility 1= vs. temperature T at 1 kOe and 2 kOefor Cd[Cr1:89Ti0:08]Se4. TC is marked by arrow.for both single crystals under study at 200 Oe, 450 Oeand at 1 kOe on the 01(T ) curve near TC, characteristicfor the Hopkinson peak. Both (T ) (measured at thestatic magnetic eld Hdc = 1 kOe) and 01(T )(measuredat the oscillating magnetic eld Hac = 1 Oe and at theconstant frequency of 120 Hz) show the same orderingtemperature TC, but dierent magnetic state. With in-creasing Hdc up to 100 Oe, 01(T ) correlates well with(T ). Starting from 200 Oe, Hdc suppresses the mag-netic susceptibility intensity of 01(T ) showing character-istic peaks at 200 Oe, 450 Oe and at 1 kOe near TC. Thisfeature could be connected with the processes of irre-692 E. Malicka et al.Fig. 3. MagnetizationM vs. magnetic eldH at 4.5 K.Fig. 4. In phase 01 (a) and out of phase 001 (b) compo-nents of ac magnetic susceptibility vs. temperature T forCdCr2Se4 recorded at Hac = 1 Oe with f = 120 Hz forexternal magnetic elds Hdc changing from 0 to 1 kOe.versible rotation of magnetic moments of non-interactinguniaxial single domain particles [2, 4]. Small and posi-tive values of 001(T ) below TC for CdCr2Se4 (Fig. 4) in-dicate the energy loss, connected, for example, with themagnetic-domain-wall motion or with rotation of magne-tization within domains [19]. However, the sample richerin titanium (Fig. 5) is showing the slight energy loss (thevalues of 001(T ) are close to zero) which can suggest thatin this case the magnetizing processes do not appear.The second 2(T ) and third 3(T ) harmonics of acmagnetic susceptibility are shown in Fig. 6 for CdCr2Se4and in Fig. 7 for Cd[Cr1:89Ti0:08]Se4. These higher har-monics have one feature in common: their values are closeto zero below TC in accordance with the simple molecu-lar eld theory [20]. Moreover, zeroing their values aboveFig. 5. In phase 01 (a) and out of phase 001 (b) com-ponents of ac magnetic susceptibility vs. temperatureT for Cd[Cr1:89Ti0:08]Se4 recorded at Hac = 1 Oe withf = 120 Hz for external magnetic elds Hdc changingfrom 0 to 1 kOe.Fig. 6. In phase 02;3 (a) and out of phase 002;3 (b) com-ponents of second and third harmonics of zero eld sus-ceptibility vs. temperature T for CdCr2Se4 recorded atHac = 1 Oe with f = 120 Hz.TC is the evidence of the lack of the spin uctuationsin the paramagnetic state characteristic, e.g., in case ofZnCr2Se4 [21], ZnCr2 xAlxSe4 [22] and ZnCr2Se4 dilutedwith Ga, In and Ce [23].4. ConclusionsThe Hopkinson-like eect using the complex ac dy-namic magnetic susceptibility measurements in single-Hopkinson-Like Eect in Single-Crystalline . . . 693Fig. 7. In phase 02;3 (a) and out of phase 002;3 (b)components of second and third harmonics of zero eldsusceptibility vs. temperature T for Cd[Cr1:89Ti0:08]Se4recorded at Hac = 1 Oe with f = 120 Hz.-crystalline CdCr2Se4 and Cd[Cr1:89Ti0:08]Se4 ferromag-netic semiconductors was observed. Its existence in asystem of non-interacting single-domain particles close tothe ordering temperature is probable. One can suggestthat the complex ac dynamic magnetic susceptibility isa sensitive tool for the studies of exotic phenomena andfascinating ground states in the materials with the spinelstructure.AcknowledgmentsThis work is partly founded from science grant No. NN204 145938.References[1] J. Hopkinson, Proc. R. Soc. Lond. 48, 1 (1890).[2] O. Popov, M. Mikhov, J. Magn. Magn. Mater. 75,135 (1988).[3] M. Kersten, Z. Angew. Phys. 8, 313 (1956).[4] E.C. Stoner, E.P. Wohlfarth, Philos. Trans. R. Soc. A240, 599 (1948).[5] H.W. Lehmann, Phys. Rev. 163, 488 (1967).[6] P.K. Baltzer, H.W. Lehmann, M. Robbins, Phys. Rev.Lett. 15, 493 (1965).[7] R.C. LeCraw, H. von Philipsborn, M.D. Sturge,J. Appl. Phys. 38, 965 (1967).[8] P.K. Baltzer, M. Robbins, P.J. Wojtowicz, J. Appl.Phys. 38, 953 (1967).[9] V. Tsurkan, St. Plogmann, M. Demeter, D. Hart-mann, M. Neumann, Eur. Phys. J. B 15, 401 (2000).[10] T. Gro«, A. Krajewski, J. Kusz, E. Malicka,I. Oko«ska-Kozªowska, A. Wa±kowska, Phys. Rev. B71, 035208 (2005).[11] T. Gro«, H. Duda, E. Malicka, B. Zawisza, J. Krok--Kowalski, A.W. Pacyna, Acta Phys. Pol. A 116, 969(2009).[12] T. Gro«, E. Malicka, B. Zawisza, H. Duda, J. Krok--Kowalski, A.W. Pacyna, Acta Phys. Pol. A 119, 714(2011).[13] G.M. Sheldrick, 1997 SHELXL-97, Program for Crys-tal Structure Renement, University of Göttingen.[14] R. Sitko, B. Zawisza, E. Malicka, Spectrochim. Acta B64, 436 (2009).[15] J. Sherman, Spectrochim. Acta 7, 283 (1955).[16] P.A. Pella, L. Feng, J.A. Small, X-ray Spectrum 14,125 (1985).[17] P.A. Pella, L. Feng, J.A. Small, X-ray Spectrum 20,109 (1991).[18] T. Gro«, A.W. Pacyna, E. Malicka, Solid State Phe-nom. 170, 213 (2011).[19] T. Sato, T. Ando, T. Watanabe, S. Itoh, Y. Endoh,M. Furusaka, Phys. Rev. B 48, 6074 (1993).[20] T. Hashimoto, A. Sato, Y. Fujiwara, J. Phys. Soc.Jpn. 35, 81 (1973).[21] J. Hemberger, H.-A. Krug, V. von Nidda, A. Tsurkan,Loidl, Phys. Rev. Lett. 98, 147203(4) (2007).[22] E. Malicka, T. Gro«, A. lebarski, A.W. Pacyna,J. Goraus, M. Fijaªkowski, J. Heimann, J. Phys.Chem. Solids 72, 974 (2011).[23] E. Malicka, T. Gro«, A. lebarski, A. G¡gor,A.W. Pacyna, R. Sitko, J. Goraus, T. Mydlarz,J. Heimann, Mater. Chem. Phys. 131, 142 (2011).

Hopkinson-like effect in single-crystalline CdCr 2Se 4 and Cd[Cr 1.89Ti 0.08]Se 4

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Hopkinson-like effect in single-crystalline CdCr 2Se 4 and Cd[Cr 1.89Ti 0.08]Se 4

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