Physical properties of double perovskite-type barium neodymium osmate Ba2NdOsO6

Journal of Solid State Chemistry 197 (2013) 236–241

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Physical properties of double perovskite-type barium neodymium osmate Ba2NdOsO6 Makoto Wakeshima a,n, Yukio Hinatsu a, Kenji Ohoyama b a b

Hokkaido University, Division of Chemistry, Graduate School of Science, Sapporo–shi, Hokkaido 060-0810, Japan Institute of Materials Research, Tohoku University, Sendai 980-8577, Japan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 27 July 2012 Received in revised form 28 August 2012 Accepted 28 August 2012 Available online 7 September 2012

The crystal, magnetic structures and physical properties of the double perovskite-type barium neodymium osmate Ba2NdOsO6 are investigated through powder X-ray and neutron diffraction, electrical conductivity, magnetic susceptibility, and specific heat measurements. The Rietveld analysis reveals that the Nd and Os ions are arranged with regularity over the six-coordinate B sites in a distorted perovskite ABO3 framework. The monoclinic crystal structure described by space group P21/n (tilt system a  a  c þ ) becomes more distorted with decreasing temperature from 300 K down to 2.5 K. This compound shows a long-range antiferromagnetic ordering of Os5 þ below 65 K. An antiferromagnetic ordering of Nd3 þ also occurs at lower temperatures (  20 K). The magnetic structure is of Type I and the magnetic moments of Nd3 þ and Os5 þ ions are in the same direction in the ab-plane. & 2012 Elsevier Inc. All rights reserved.

Keywords: Double perovskite Osmate Magnetic properties Magnetic structure

1. Introduction The perovskite family of oxides containing 4d, 5d transition metals is mostly still an unexplored territory in novel physical phenomena that often deviate from conventional expectations, although they present interesting electrical and magnetic properties. We have focused our attention on the crystal structures and magnetic properties of double perovskites Ba2REMO6 (M¼Ru, Ir, Re; RE ¼rare-earths), in which 4d, 5d transition metal and rareearth ions regularly order at the B site of perovskite-type structure. These compounds show a variety of magnetic behavior at low temperatures [1–14]. For the ruthenates, Ba2RERuO6, the Ru5 þ (4d3) and RE3 þ ions are found to be in an antiferromagnetic state below 15 120 K [1–9]. Through their neutron diffraction measurements, the antiferromagnetic structures of Ba2RERuO6 (RE ¼Y, Pr, Nd, Tb, Ho–Lu) are determined to be of Type I [1,3–9], and Ba2LaRuO6 has the antiferromagnetic structure of Type III [2]. In the case of the iridates, Ba2REIrO6 (RE¼Sc, Y, La–Lu), both of the Ir and RE ions are in the tetravalent state for Ba2CeIrO6 and Ba2PrIrO6, while the Ir and RE ions are in the pentavalent and trivalent state, respectively, for the other Ba2REIrO6 compounds [9–11]. In the Ba2REIrO6 series, only the tetravalent iridium (5d5) compounds, Ba2CeIrO6 and Ba2PrIrO6, show an antiferromagnetic transition at 17 and 72 K, respectively [9–11]. A solid-solution Ba2PrRu1  xIrxO6

n

Corresponding author. Fax: þ81 11 746 2557. E-mail address: [email protected] (M. Wakeshima).

0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2012.08.059

shows the valence transition from Ba2Pr4 þ (Ru1 xIrx)4 þ O6 to Ba2Pr3 þ (Ru1 xIrx)5 þ O6 with increasing temperature [12,13]. The rhenates, Ba2REReO6, show the antiferromagnetic ordering of the Re5 þ (5d2) ion and these transition temperatures vary from 30 to 100 K depending on rare-earth ions [14]. For the double perovskite-type rare-earth osmates, Ba2REOsO6, the syntheses and lattice parameters were firstly reported by Treiber et al. [15]. Otherwise, the physical properties of these compounds have not been reported yet. For the double and triple perovskite, the neodymium compounds frequently demonstrate peculiar magnetic behavior, for example, Ba2NdReO6 has the highest Ne´el temperature (TN  100 K) in the Ba2REReO6 [14], and only both of the Ba3NdRu2O9 and Ba3NdIr2O9 compounds shows a ferromagetic transition in the Ba3REM2O9 (M¼ Ru, Ir) series [16,17]. In this study, we have prepared Ba2NdOsO6 and investigated its crystal-magnetic structural and related properties through X-ray and neutron diffraction, magnetic susceptibility, and specific heat measurements.

2. Experimental Stoichiometric mixtures of barium peroxide (BaO2), osmium metal (Os), and neodymium sesquioxide (Nd2O3) was ground with an agate mortar in an Ar atmosphere, and they were put into a platinum crucible in a vacuum-sealed quartz ampoule. In order to remove any moisture, Nd2O3 were preheated in air at 1170 K. An ampoule was heated at 1270 K for 6 h. Silver oxide, Ag2O was added as oxygen donor in a separate platinum crucible.

M. Wakeshima et al. / Journal of Solid State Chemistry 197 (2013) 236–241

The product was annealed at 1270 K with several interval regrinding and repelletizing. Powder X-ray diffraction profile was obtained using a Rigaku RINT2200 diffractometer with graphite-monochromatized Cu-Ka radiation in the range 5r2y/ 1r120 (D2y ¼0.021) below room temperature. The crystal structure was refined by the Rietveld method (RIETAN-FP program [18]). A pseudo-Voigt profile function was used for describing the peak shape. Temperature dependence of the electrical conductivity was measured by a DC four-probe method in the temperature range between 160 and 400 K. Magnetic susceptibility measurements were carried out under both zero-field-cooled condition (ZFC) and field-cooled condition (FC) in the temperature range between 1.8 and 300 K by using a SQUID magnetometer (Quantum Design, MPMS-5S). The ZFC susceptibility measurements were performed under an applied magnetic field of 0.1 T, after the sample was cooled from 300 to 1.8 K in a zero field. For FC susceptibility measurements, the sample was cooled in the presence of 0.1 T field. Specific heat measurement was carried out using a relaxation technique supplied by the commercial specific heat measurement system (Quantum Design, PPMS) in the temperature range from 1.8 to 300 K. The sample in the form of pellet ( 10 mg) was mounted on an alumina plate with apiezon for good thermal contact. Powder neutron diffraction measurements were carried out using the Kinken powder diffractometer for high efficiency and high resolution measurements, HERMES, of Institute for Material Research, Tohoku University, installed at the JRR-3M reactor in Japan Atomic Energy Research Institute, Tokai. Neutrons with wavelength of 1.82035(7) A˚ were obtained by the 331 reflection of the Ge monochromator and 120 -blank-220 collimation [19]. The sample was set in a vanadium cylinder with a diameter of 10 mm and sealed in a standard aluminum cell with helium gas and was cooled down to low temperatures using a liquid helium cryostat. Intensity data from 31 to 1401 were obtained for crystal structure and magnetic structure refinements using Rietveld method program RIETAN-FP [18].

3. Results and discussion 3.1. Crystal structure The results of X-ray diffraction (XRD) measurements indicate that Ba2NdOsO6 was prepared as a double perovskite-type phase. In order to check the symmetry of the crystal structure of Ba2NdOsO6, the XRD measurements were carried out in the temperature range from 20 K to 300 K. Fig. 1(a) shows the XRD profiles between 20 and 300 K. Below 300 K, the peaks of the Bragg reflections become broader with decreasing temperature. We have performed the refinement of the crystal structures with the Rietveld analysis program RIETAN-FP. The XRD profile at room temperature could be fitted with the face-centered cubic lattice (the space group Fm3 m, No. 225, the Glazer symbol for the tilt system a0a0a0 [20]) with crystallographcally ordered arrangements between the Nd and Os ions occupying the B sites. However, the calculated intensities of the 200 reflection at 2y  181 and the 111 reflection at 2y  21o for the face-centered cubic lattice could not be matched to the observed ones. After several attempts of refinement with lower symmetry space groups [20–22], all the splitting Bragg reflections of Ba2NdOsO6 below 300 K could be indexed in a monoclinic lattice with space group P21/n (No. 14, the Glazer symbol a  a  c þ [20]). The calculated intensities for the monoclinic unit cells agree well with the observed ones. A small amount of Nd2O3 was presented in this sample. Since the ratio of the Nd2O3 is below 1.6 wt%, its effect in the magnetic

237

Fig. 1. (a) X-ray diffraction profiles in the temperature range between 20 K and 300 K. (b) Temperature dependence of lattice parameters.

measurements is negligibly small. The variation of the lattice parameters is plotted in Fig. 1(b) as a function of temperature. It is found that the monoclinic distortion becomes smaller pffiffiffiwith increasing temperature. The lattice parameters a, b, and c/ 2 are converging to the same value and b approaching 901 to form a cubic cell at temperatures well above ambient. Fig. 2(a) and (b) shows the result of XRD profile fitting at 20 K and the crystal structure, respectively. Both osmium and neodymium ions are octahedrally coordinated by six oxygen ions and their octahedra are arranging alternately. 3.2. Electrical conductivity The electrical resistivity (r) for Ba2NdOsO6 was  0.9 O m at room temperature. The resistivity was measured in the temperature range between 160 K and 400 K, and its Arrhenius plot is represented in Fig. 3. The resistivity increases with decreasing temperature up to 0.7 kO m at 160 K, but the temperature dependence does not follow the Arrhenius law (log rpT  1). The log r–T  1/4 curve is also plotted in the inset of Fig. 3. On balance, the electrical resistivity shows that Ba2NdOsO6 is a Mott variable-range hopping (VRH) conductor with localized carriers in three-dimension [23] rather than a semiconductor with thermal activation. The result of the electrical conductivity measurements indicates that 5d3 electrons of Os5 þ ions are localized at their sites. 3.3. Magnetic properties Fig. 4(a) shows the temperature dependence of magnetic susceptibilities (w) for Ba2NdOsO6. A small divergence between

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M. Wakeshima et al. / Journal of Solid State Chemistry 197 (2013) 236–241

Fig. 2. (a) The X-ray diffraction profile at 20 K for Ba2NdOsO6. The calculated and observed diffraction profiles are shown on the top solid line and cross markers, respectively. The bottom trace is a plot of the difference between calculated and observed intensities. The upper vertical marks in the middle show positions calculated for Bragg reflections. The lower vertical marks in the middle show positions calculated for Bragg reflections for Nd2O3 impurity. (b) The schematic crystal structure of Ba2NdOsO6. Spheres are Ba atoms, bright octahedra are NdO6 units and dark octahedra are OsO6 units. Fig. 4. (a) Temperature dependence of the magnetic susceptibility (w) of Ba2NdOsO6. The arrow indicates the position of the 65 K anomaly. The inset shows w  1 as a function of temperature. A straight line represents the Curie–Weiss law fitting. (b) The first derivatives of wT in the neighborhood of TN of the Os5 þ moment.

Fig. 3. Temperature dependence of the electrical resistivity (r). The inset shows the plot of r as a function of T  1/4.

be described later. Below this temperature, an increase in the magnetic susceptibility with decreasing temperature is attributable to the paramagnetic behavior of the Nd3 þ ion. The maximum around 20 K indicates that the Nd3 þ moments also order antiferromagnetically below this temperature. The temperature dependence of the reciprocal magnetic susceptibilities (w  1) is shown in the inset of Fig. 4(a). Above 200 K, the reciprocal magnetic susceptibilities obey the Curie-Weiss law, but deviates from the Curie–Weiss law below 200 K. This deviation from the Curie–Weiss law is due to the crystal electric field (CEF) effect of the Nd3 þ ion because the ground state (S¼3/2, L¼0) of the Os5 þ ion shows no CEF effect. The magnetic susceptibilities can be written by

w ¼ wðNd3 þ Þ þ wðOs5 þ Þ ¼ the ZFC and FC susceptibilities is observed in the w–T curve below 70 K. Three magnetic anomalies have been observed, i.e. a shoulder appears around 70 K and a broad maximum exists around 20 K, and an rapid increase is observed below 7 K. Fig. 4(b) shows the d(wT)/dT plots as Fisher [24] in the temperature range between 10 K and 100 K. The maximum at 67 K is indicative of an antiferromagnetic ordering of the Os5 þ ion as will

C , TYW

ð1Þ

From the Curie–Weiss fitting of Eq. (1) to the w  1–T curve in the temperature range between 250 K and 300 K, the Curie constant (C) and the Weiss constant (YW) is derived to be 2.67(1) emu mol  1 and  54.1(5) K, respectively. This Curie constant gives the effective magnetic moment of 4.62 (2) mB. Assuming that the effective magnetic moment (meff) for the Nd3 þ ion in

M. Wakeshima et al. / Journal of Solid State Chemistry 197 (2013) 236–241

Ba2NdOsO6 equals to the value of the 4I9/2 state a free Nd3 þ ion (3.62mB) [8], meff of the Os5 þ ion is estimated to be 2.87mB. This value is considerably lower than that expected from the ‘spinpffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi only’ state with S¼3/2 (i.e., g SðS þ1Þ ¼ 3:87mB ), and is still smaller than that of Ru5 þ (4d3) for Ba2NdRuO6 (3.39mB). Most of the previous studies show that 5d metal ions have effective magnetic moments smaller than the ‘spin-only’ theoretical value, which is attributable to the spin-orbit coupling and/or to the covalency between the 5d metal and the coordinating ligands [14,25–29]. In the case of Ba2NdOsO6 also, such effects should result in the reduction of the effective magnetic moment of the Os5 þ ion.

3.4. Specific heat Fig. 5(a) shows the variation of specific heat (Cp) for Ba2NdOsO6 as a function of temperature (data plotted as solid circles). A l-type anomaly is observed at 65 K and it corresponds to the antiferromagnetic ordering of the Os5 þ moments found as observed in the magnetic measurements (Fig. 4(a), (b)). This temperature of the magnetic ordering is higher than that of the Ru5 þ (4d3) for Ba2NdRuO6 (58 K) [4]. Below 300 K, no specific anomaly due to the structural phase transition is observed. For magnetic compounds, the total specific heat (Cp) is the sum of the lattice (Clat), electronic (Celec), and magnetic (Cmag)

239

contribution. In order to estimate the magnetic contribution (Cmag) of the Os5 þ and Nd3 þ moments to Cp at low temperatures, we need to subtract the lattice contribution (Clat) and the electronic contribution (Celec 0 J mol  1 K  1 for a insulator) from the total Cp. We considered that the Clat and Celec data were estimated from the specific heat data for an insulating and diamagnetic Ba2LuTaO6 (as plotted in dotted curve in Fig. 5(a)) [29] which is isostructural with Ba2NdOsO6. Unfortunately, the large difference in the atomic weight between Nd and Lu led to the different Debye temperatures between Ba2NdOsO6 and Ba2LuTaO6, and gave rise to a quantitatively different specific heat. Therefore, we used the Cp data of Ba2EuTaO6 [30] as a lattice contribution (Clat) (a dashed curve in Fig. 5(a)). For Ba2EuTaO6, the Eu3 þ ion has the nonmagnetic ground state (7F0), and the energy difference (DE) between the ground state and the first excited state (7F1) is 478 K [31]. Considering the contribution of the excited states 7FJ (J¼1, 2, y, 6), the Schottky-type specific heat contributions CSch(Eu3 þ ) with DE¼478 K can be calculated as a dash-dotted curve in Fig. 6(a). We have obtained a lattice contribution (C0 lat) by subtracting the CSch(Eu3 þ ) from Cp(Ba2EuTaO6) (a solid curve in Fig. 5(a)). Then, the magnetic specific heat (Cmag) has been obtained for Ba2NdOsO6 and the temperature dependence of the Cmag/T is shown in Fig. 5(b). In addition to a l-type anomaly at 65 K due to the magnetic ordering of the Os5 þ moment, another specific heat anomaly is clearly observed around 20 K, which is attributable to the antiferromagnetic ordering of the Nd3 þ moment. The magnetic entropy change (Smag) associated with the magnetic ordering is calculated by integrating the magnetic specific heat (C T  1) divided by temperature,  mag RT  Smag(T)¼ 0 C mag =T dT as shown in Fig. 5(b). The Smag change is obtained to be 19.9 J mol  1 K  1 at 100 K. For the isomorphous europium osmate Ba2EuOsO6 showing an antiferromagnetic ordering of the Os5 þ moment at 67 K, the Smag change due to the magnetic ordering of the Os5 þ moment is estimated to be 7.6 J mol  1 K  1 [30]. When the same estimation for Smag of the Os5 þ ion holds for the case of Ba2NdOsO6, the rest of Smag due to the magnetic ordering of the Nd3 þ moment is 12.3 J mol  1 K  1. This value of Smag is close to R ln 4 ( ¼ 11.5 J mol  1 K  1) (R: gas constant) and is much smaller than R ln 6 ( ¼ 14.9 J mol  1 K  1). The 4I9/2 ground state of the Nd3 þ ion should split into one (2) doublet (G6) and two quartet (G(1) 8 , G8 ) by the CEF in the site symmetry of Oh [32]. The ground state of Nd3 þ is expected to be either G6 or G(2) in an ideal NdO6 octahedron. The Smag change 8 below 100 K indicates that the G(2) 8 state forms the antiferromagnetic state of the Nd3 þ moments. 3.5. Magnetic structure

Fig. 5. (a) Temperature dependence of the specific heat Cp for Ba2NdOsO6, Ba2EuTaO6, and Ba2LuTaO6. A dash-dotted curve represents the calculated Schottky-type specific heat (CSch), which is attributable to the excited states 7FJ (J¼ 1, 2,y, 6) of Eu3 þ , on the assumption that the energy splitting (DE) between the ground state (7F0) and the first excited state (7F1) is 478 K. (b) Temperature dependence of Cmag/T and Smag for Ba2NdOsO6.

Since the magnetic anomaly was observed below 70 K, we performed neutron diffraction measurements for Ba2NdOsO6 at 2.5, 10, 20, 40, 60, and 80 K. Fig. 6(a) shows the powder neutron diffraction profile measured at 2.5 K, 60 K, and 80 K, respectively. The diffraction pattern at 80 K could well be refined with the space group P21/n, which is, of course, in agreement with the result by the X-ray diffraction measurements. Table 1 lists the lattice parameters and atomic positions at 80 K. Compared with the pattern at 80 K, several additional peaks appear at low angles in the patterns below 60 K, which indicates that a long-range magnetic ordering occurs below 60 K for Ba2NdOsO6. The integrated intensities of the 001 reflection and the 111, 111 reflections are plotted in Fig. 6(b) as a function of temperature. The intensities of the magnetic Bragg reflections increase with decreasing temperature. The magnetic Bragg reflections observed below 60 K can be indexed simply with the condition that [hþkþl] is an odd integer. From these rules for allowed magnetic

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Table 1 Refined lattice parameters, fractional atom coordinates and temperature factors (B) for Ba2NdOsO6 at 80 K (neutron data). Space group: P21/n (No. 14) ˚ b¼ 5.9974(9) A, ˚ c¼ 8.4648(11) A, ˚ b ¼ 90.180(7)1 a¼ 5.9770(9) A, Rwp ¼7.64%, RI ¼1.38%

Ba Nd Os O(1) O(2) O(3)

Site

g

x

y

z

B/A˚ 2

4e 2c 2d 4e 4e 4e

1.00(1) 0.97(1) 1.00(1) 1 1 1

0.4982(17) 0 1/2 0.279(4) 0.720(3) 0.485(3)

0.5001(21) 1/2 0 0.248(4) 0.256(4) 0.008(2)

0.2444(11) 0 0  0.018(1) 0.021(1) 0.226(1)

0.13(7) 0.14(9) 0.15(7) 0.46(4) 0.46 0.46

2

Note: Rwp ¼ ½Swð9FðoÞ99FðcÞ9Þ2 =Sw9FðoÞ9 1=2 and RI ¼ S9Ik ðoÞIk ðcÞ9=SIk ðoÞ

reflections, the magnetic structure-type is Type I, as Type II and Type III require larger magnetic unit cells [3]. When the magnetic unit cell is equal to the nuclear unit cell, following four magnetic sites are available in the unit cell. Position Nd1 Nd2 Os1 Os2

x 0 1/2 1/2 0

y 1/2 0 0 1/2

z 0 1/2 0 1/2

with respective magnetic moments SNd1, SNd2, SOs1, and SOs2. The directions of SNd1 and SNd2 are antiparallel, and those of SOs1 and SOs2 are also antiparallel. The 100 and 010 reflections are not found and the appearance of the large 001 reflection is recognized in the profile below 60 K compared with the profile at 80 K, as shown in Fig. 6(a). The Magnetic structure factor Fm(hkl) for a hkl reflection is given by X qj bmj exp2piðhxj þ kyj þ lzj Þ ð2Þ Fm ¼ j

with q ¼ eðeUsÞs

ð20 Þ

where bm is the magnetic scattering length, e is the unit scattering vector and s is the unit vector parallel to the magnetic moment. In the case of Ba2NdOsO6, the relations qNd1bNd1 ¼  qNd2bNd2 and qOs1bOs1 ¼ qOs2bOs2 hold. Therefore, the magnetic Bragg reflections 100, 010, and 001 are calculated to be in the following;

Fig. 6. (a) Neutron diffraction profiles at 2.5 K, 60 K and 80 K. The calculated and observed diffraction profiles are shown on the top solid line and cross markers, respectively. The upper vertical marks in the middle show positions calculated for Bragg reflections. The bottom trace is a plot of the difference between calculated and observed intensities. The lower vertical marks in the middle show positions calculated for Bragg reflections for Nd2O3 impurity. (b) Temperature dependence of the integrated intensities of the (001) and (111), (111) reflections for Ba2NdOsO6.

F m ð100Þ ¼ 2ðqNd1 bNd1 qOs1 bOs1 Þ  0

ð3Þ

  F m ð010Þ ¼ 2 qNd1 bNd1 qOs1 bOs1  0

ð4Þ

F m ð001Þ ¼ 2ðqNd1 bNd1 þqOs1 bOs1 Þ a 0

ð5Þ

Here, in order to satisfy the conditions of Eqs. (3)–(5), we suggest that the ordered Os5 þ and Nd3 þ moments orient along the same directions ferromagnetically in the ab-plane and that the absolute value of qOs1bOs1 is nearly equal to qNd1bNd1. The small difference between the lattice parameters a and b leads to the overlap of the magnetic Bragg reflections, and which interferes with determination of the directions of the magnetic moments in the ab-plane. The schematic magnetic structure is illustrated in Fig. 7. Unfortunately, we could not refine the ordered moments using this model, because the magnetic form factor for the 5d metal ions has not been known yet. However, the magnetic structure has been confirmed from the diffraction data at 2.5 K by using the magnetic form factor for the Ru5 þ ion (4d3) [33] instead of that for the Os5 þ ion (5d3). The obtained Nd3 þ and

M. Wakeshima et al. / Journal of Solid State Chemistry 197 (2013) 236–241

241

moment shows a long-range antiferromagnetic ordering below 65 K. An antiferromagnetic ordering of the Nd3 þ moment also occurs at lower temperature (  25 K). The measured moments at 2.5 K are 1.3 and 1.7 mB for Nd3 þ and Os5 þ , respectively. The magnetic structure was determined to be of Type I, and the magnetic moments of the Nd3 þ and Os5 þ ions are in the same direction in the ab-plane.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] Fig. 7. Orientation of the magnetic moments of Nd3 þ and Os5 þ in Ba2NdOsO6. The arrows indicate the direction of the magnetic moments.

Os5 þ moments (m) are 1.3(1) mB and 1.7(2) mB, respectively, and they are smaller than those of Nd3 þ and Ru5 þ (m¼ 2.3 mB for Nd3 þ , m ¼2.2 mB for Ru5 þ ) for Ba2NdRuO6. The magnetic structure for Ba2NdOsO6 (Fig. 8) is the same as that for Ba2NdRuO6. For the rare-earth ruthenates A2RERuO6 (A¼Sr, Ba), the nearestneighbor (NN) interaction of Ru–O–RE determines the magnetic structure, and the next-nearest-neighbor (NNN) interaction of Ru–O–O–Ru is responsible for the magnetic ordering in the Ru sublattice [6,34]. The magnetic structure of Ba2NdOsO6 may be determined by the Os–O–RE interaction in the same way as Ba2RERuO6.

[10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]

4. Conclusion We have synthesized good quality samples of Ba2NdOsO6 and they were prepared for X-ray and neutron diffraction studies to determine its crystal and magnetic structure. In addition, the electrical, magnetic and thermal properties were also characterized to assist our interpretations of the structural findings. The solids crystallize in a monoclinic crystal structure (space group P21/n, No. 14; tilt system a  a  c þ ) with an NaCl-type ordered arrangement of the Nd and Os ions at the B sites in distorted perovskite ABO3. The lattice was further distorted from the perovskite framework with decreasing temperature. Through our susceptibility and specific heat measurements, the Os5 þ

[23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]

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