Article pubs.acs.org/crystal
Single-Crystal Growth of a Perovskite Ruthenate SrRuO3 by the Floating-Zone Method Naoki Kikugawa,*,†,‡ Ryan Baumbach,‡ James S. Brooks,‡ Taichi Terashima,† Shinya Uji,†,§ and Yoshiteru Maeno∥ †
National Institute for Materials Science, Sakura, Tsukuba 305-0003, Japan National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States § Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8577, Japan ∥ Department of Physics, Kyoto University, Kyoto 606-8502, Japan ‡
S Supporting Information *
ABSTRACT: We report single-crystal growth of a perovskite ruthenate SrRuO3 by the floating-zone method using an infrared image furnace. By employing a cold trap for the growth, we prevented the evaporated RuO2 from coating the inner surface of a quartz tube and were thereby able to maintain a stable molten zone during the growth. Powder Xray and Laue diffraction measurements confirmed the quality of the grown single crystal. The crystal was cut into a 1.4 mm × 1.4 mm × 3.0 mm rectangle that was characterized by magnetic susceptibility, magnetization, and specific heat measurements. The crystal showed a ferromagnetic transition with a Curie temperature of 163.5 K, and the coercive field was as low as 0.004 T. The residual resistivity was 1.05 μΩ cm, corresponding to a residual resistivity ratio of 192. These results indicate that the grown crystal is high-quality. Electrical resistivity measurements show temperature-squared behavior, revealing that a Fermi-liquid-like electron−electron scattering is dominant. Together with a large electronic specific heat coefficient with 30 mJ K−2 mol−1, we confirm that the ferromagnetic SrRuO3 is a strongly correlated material. The system SrRuO3 (n → ∞) in space group Pnma is of interest, in part because it exhibits ferromagnetism.12,13 Because the Curie temperature (TC) is relatively high (∼160 K) and the ordered moment is as large as ∼1.3 μB under a magnetic field (H) of 5 T,14 SrRuO3 has widely been studied from both scientific and application interests.15 For instance, the partial detection of quantum oscillations suggests that the metallic conductivity at low temperatures is explained in the framework of a Fermi liquid theory.16,17 Observation of an anomalous Hall effect has been discussed in terms of a possible magnetic monopole in the momentum space.18 Control of coercivity in the ferromagnetic state using thin films is an application interest.19 Very recently, SrRuO3 thin films on a bulk Sr2RuO4 crystal allowed investigation of the interface.20 A sign of glassy behavior below TC has been reported.21 Thus, a variety of studies have been performed since the synthesis of the material.22 However, fundamental questions remain unsolved, for instance, whether only the itinerant electron picture is applicable.23 Previous studies have been performed using polycrystals,13,24,25 thin films on a variety of substrates,16,19,23,26 and
1. INTRODUCTION Intense research on the Ruddlesden−Popper series of strontium rhuthenates Srn+1RunO3n+1 has revealed attractive physical properties with different values of n. One of the prominent features is unconventional superconductivity1 with evidence of a chiral p-wave spin-triplet Cooper pairing2 in single-layered Sr2RuO4 (n = 1). Bilayered Sr3Ru2O7 (n = 2) exhibits a novel itinerant metamagnetism, which is coupled to quantum criticality with electronic nematicity.3 Trilayered Sr 4 Ru 3 O 10 (n = 3) shows both metamagnetism and ferromagnetism with metallic conductivity.4 For all of these systems, the behaviors are extremely fragile against disorder or defects. For instance, the mean free path exceeds 1 μm in Sr2RuO4 with an intrinsic superconducting transition temperature of 1.5 K.2 However, the superconductivity is completely suppressed when the mean free path is shortened to the order of the superconducting coherence length (∼70 nm) by impurity scattering, even though the carriers are still mobile.5−7 The nematicity in Sr3Ru2O7 is also tied to variations in sample quality.8 The strong dependence of the physical properties on purity in Sr4Ru3O10 has also been discussed.4 Thus, the growth of high-quality single crystals is of great importance for revealing intrinsic physical properties in these ruthenates. For this reason, high-purity single-crystal specimens produced by a crucible-free floating-zone technique are in high demand.4,9−11 © XXXX American Chemical Society
Received: August 28, 2015 Revised: September 30, 2015
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DOI: 10.1021/acs.cgd.5b01248 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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inevitable difficulty associated with the floating-zone technique in ruthenates is the heavy volatility of RuO2 from the feed rods because of its high vapor pressure at the growth temperature.10 Growing the crystals under high pressure is an effective solution for suppressing the volatility, but this becomes less effective for the growth with higher values of n. A systematic procedure in which we evaluate a mass loss, namely, the weight of the evaporated RuO2 during the growth, has been introduced. Then, the loss is fed back to fix the correct nominal Ru/Sr atomic ratio for the preparation of the subsequent feed rods.11 For the sake of simplicity, it is assumed that only RuO2 in the rod is lost during the floating-zone process as follows: Sr2RumOy → Sr2Rum′Oy′ + (m − m′)RuO2. In this case, the optimal value of m was determined using an equation for the series of strontium ruthenates: m′ = m(1 − L) − 1.557L.11 In this equation, L = Mevap/ Mrod is the mass loss ratio, Mevap the mass loss by the volatility, and Mrod the initial mass of the rod. Throughout the attempts described above, m values of 1.15 and 1.68 were the optimal values for obtaining the desirable Sr2RuO4 (m′ = n = 1) and Sr3Ru2O7 (m′ = 2n/3 = 4/3), respectively.11 For SrRuO3 growth, we finally set m to 3.0, as described below. Another significant issue related to the volatility is that the evaporated RuO2 is gradually deposited as a black film on the surface of the quartz tube. The deposition eventually reduces the intensity of light on the molten zone, making it increasingly unstable. This obstruction affects more seriously the growth of ruthenates Srn+1RunO3n+1 with higher values of n. In fact, the mass loss (L) is found to be 6.0 and 10.3% for the growth of Sr2RuO4 (n = 1) and Sr3Ru2O7 (n = 2), respectively.11 It is obvious that the larger mass loss (L) confronts us for the growth of SrRuO3 (n → ∞), and it was one reason that the successful growth of the SrRuO3 crystal by this technique had not been previously achieved.10 To minimize the problem described above, we have employed a cold trap set inside the quartz tube, as shown in Figure 1. The cylinder-shaped trap is located in the slightly upper position from the molten zone. The circulating water inside the trap keeps it cooler than the quartz tube during the growth, allowing the evaporated RuO2 to be deposited mainly on the surface of the trap, rather than on the quartz tube. This results in a reduced level of light blocking by the deposited RuO2 on the quartz tube. Although we increased the lamp power by typically 11% during the growth to compensate for the slight light blocking by the deposited powder on the quartz tube, the light was consequently able to efficiently pass through the quartz tube during the entire growth process. Thus, the successful growth of SrRuO3 has finally been achieved. We note that it was not possible to obtain the pieces of single-phase SrRuO3 without the trap in place. 2.3. Growth Procedures of SrRuO3. The starting materials for the feed rods were SrCO3 (99.99% purity, Rare Metallic Co.) and RuO2 (99.9% purity, Rare Metallic Co.). Both were well ground together with a mortar and pestle. We set the molar ratio of m = 2Ru/ Sr to 3.0 after exploratory growth attempts. The extra RuO2 for SrRuO3 (50%) for our study is much higher than that for Sr2RuO4 (15%),9,11 Sr3Ru2O7 (26%),11 or Sr4Ru3O10 (27−30%).4 The feed rod prepared by hydrostatic compression had typical dimensions of a 10 cm length with a 5 mm diameter and was sintered at 1000 °C in air for 2 h. Here, the length of the rod was limited by the specification of the furnace. We also used the same polycrystalline rods as seeds. During the process described above, great care was taken to avoid any contamination into the rod. The rod was subsequently set in the floating-zone furnace. The optimized growth condition was found to be 7 mm/h with a flowing gas mixture of Ar and O2 (85/15 Ar/O2) at a total pressure of 10 atm. We adopted a slightly oxidized atmosphere for SrRuO3 growth, compared to the growth of other ruthenates (Sr2RuO4,9 Sr3Ru2O7,11 and Sr4Ru3O104) with a 90/10 Ar/O2 mixture, to avoid the reduction process whereby oxide RuO2 transforms into metallic Ru impurities inside the crystal, as was seen previously for the “3K phase” in Sr2RuO4.2
single crystals grown by a flux method.14,17 To the best of our knowledge, crystal growth attempts by a floating-zone technique, which is advantageous for minimizing the disordered level in crystals, have not been achieved.10 A recent successful crystal growth of the isostructural ruthenate CaRuO3 by this technique27 confirmed a paramagnetic ground state with enhanced ferromagnetic fluctuations down to the lowest temperature measured. Obtaining large single crystals is another advantage to this technique, because it allows detailed investigation by many probes (e.g., neutron scattering). Therefore, the growth of the high-quality SrRuO3 crystal by the floating-zone method is highly desirable for deepening our understanding of its underlying physics for the ferromagnetic material SrRuO3. In this article, we present a successful procedure for growing the single crystals of SrRuO3 by the floating-zone technique using a cold trap inside the furnace. Also, we show the characterization of the resulting high-quality single crystals.
2. EXPERIMENTAL SECTION 2.1. Floating-Zone Technique. For the growth of singlecrystalline SrRuO3, we employed a RuO2 self-flux floating-zone technique using an infrared image furnace with double-elliptical mirrors (Canon Machinery, model SC-K15HD-HP). Here, two 2 kW halogen lamps with flat-shaped filaments are placed in the furnace. As shown in Figure 1, the bottom end of the feed rod set to the upper
Figure 1. Photograph of an infrared image furnace. In this study, we employed a cold trap in which water is circulating during the growth. shaft is carried to the focus of the radiation reflected at the mirrors. It has been reported that the rod starts to melt at a typical temperature of as high as ∼2100 °C for ruthenates.9,10 The molten rod is connected to a seed rod set to the lower shaft with counterclockwise rotation. Finally, the single crystal forms as it is pulled continuously from the molten zone. Because a transparent quartz tube separates the growth area from the outside, we are able to control both gas atmosphere and pressure during the growth. We note that one of the advantages of the technique is to minimize the accidental contamination of any kinds of impurities throughout the growth process, because the feed rod, molten zone, and seed crystal never touch any part of the quartz tube and others. Keeping the molten zone stable is an important factor during the growth, because the liquid molten zone is fragilely supported at the cross section of the feed rod and the grown crystal. 2.2. High Volatility of RuO2 and Inserting a Cold Trap. To prepare the feed rod, we followed similar procedures for the growth of Sr2RuO4,9 Sr3Ru2O7,11 and Sr4Ru3O104 with extra RuO2 as self-flux. An B
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indices given in a previous report in space group Pnma.24 The lattice parameters were deduced as a = 0.5567(2) nm, b = 0.7833(2) nm, and c = 0.5529(2) nm. These values are in good agreement with previous reports within experimental error.24 In the Supporting Information, we also show an image of the optical polarized microscopy on the a−c plane of the grown crystal. 3.2. Physical Properties of the Floating-Zone SrRuO3 Crystals. 3.2.1. Magnetic Properties. Figure 3a shows the temperature (T) dependence of the magnetic susceptibility (M/H) in the temperature range between 2 and 300 K under the condition of field cooling at 0.01 T along the [101] direction, using a SQUID magnetometer (Quantum Design, MPMS system). A sharp ferromagnetic transition (TC) is seen around 163 K, and anomalies from other phases were not seen.26 We note that the transition temperature in thin films is slightly lower than that in bulk samples with the same composition: for instance, the transition temperature near 160 K14 in the bulk SrRuO3 is lowered around 150 K in thin films,16,26 probably because of the strains introduced by the mismatch between the substrate and film.16 The inverse susceptibility, (M/H)−1, shown in the inset of Figure 3a, was fitted using Curie−Weiss law above TC. Here, the fit is presented as a black solid line. The Weiss temperature and the effective moment are 167 K and 2.83 μB, respectively. These results were insensitive to the field directions and were in good agreement with previous reports.14,15 Also, we have found a Curie temperature TC of 163.5 K from a conventional Arrott plot analysis (M2 vs H/M) throughout magnetization measurements near TC. In Figure 3b, we show magnetization curves [M(H)] of SrRuO3 at 1.8 K under the field directions of [101] and [010]. Typical ferromagnetic behavior is seen with small hysteresis, and the magnetization increases with fields of up to 7 T without saturation. As shown in the inset of Figure 3b, the coercive field (0.004 T) is lower than that of previous reports.15 These results indicate the suppression of the pinning of domain walls by defects and disorder. We also see the anisotropy of M(H) along the field direction. 3.2.2. Specific Heat. Figure 4 displays the temperature dependence of the specific heat (Cp) of SrRuO3 using the same crystal that was used for the susceptibility measurements. A clear anomaly is seen near TC, which corresponds to the
3. RESULTS AND DISCUSSION 3.1. Characterization of the Grown SrRuO3 Crystals. The SrRuO3 crystal with a single phase was embedded inside the grown crystals. Here, the surface is composed of other phases such as Sr4Ru3O10 (TC ∼ 100 K) and probably Sr5Ru4O13 (TC ∼ 130 K) together with SrRuO3. These phases can be detected by magnetic susceptibility measurements.26 It was straightforward to distinguish the single phase of the SrRuO3 crystal from the other phases, because a shiny flat surface corresponding to the [010] direction is seen in the SrRuO3 crystal, contrary to a powderlike solidification for the mixture phases. This is in contrast to the fact that whole grown boule consists of Sr2RuO49 and Sr3Ru2O711 crystals. Our current result is probably due to a lack of adequate compensation of the volatile RuO2. Under our most optimal condition, we obtained the m′ as 1.54 from a mass loss ratio (L) of 32.1%. We note that the m′ is obtained from the entire mass of the grown material. In Table 1, we summarize the growth condition of SrRuO3 together with other ruthenates. Table 1. Summary of the Growth Condition of a Series of (layered) Perovskite Ruthenates Srn+1RunO3n+1a
Sr2RuO4 (n = 1)9,11 Sr3Ru2O7 (n = 2)11 Sr4Ru3O10 (n = 3)4 SrRuO3 (n → ∞)
m
m′
mass loss L (%)
growth speed (mm/h)
1.15 1.68 1.9−1.95 3.0
0.99 1.33 − 1.54
6.0 10.5 − 32.1
45 20 13−20 7
a
Here, m and m′ represent the nominal (Ru-rich) and obtained 2Ru/ Sr ratio, respectively, throughout the floating-zone process of Sr2RumOy → Sr2Rum′Oy′ + (m − m′)RuO2. Note that the m′ is obtained from the entire mass of the grown material.
A crystal with dimensions of 1.4 mm × 1.4 mm × 3.0 mm was taken from the main shiny boule, as shown in Figure 2a. We confirmed that it was single crystal, as shown in a Laue diffraction picture of the crystal along the [010] axis (Figure 2b). Also, a powder diffraction pattern using the partially crushed crystal is presented in Figure 2c. None of the impurity phases such as Sr2RuO4, Sr3Ru2O7, and Sr4Ru3O10 could be detected in the pattern. All peaks were indexed, following the
Figure 2. (a) Photograph of the grown SrRuO3 single crystal by the floating-zone method. The scale is in millimeters. The crystal was used for magnetization and specific heat measurements. (b) Laue picture of SrRuO3 along the [010] axis. (c) Powdered X-ray diffraction pattern with indices of the crushed SrRuO3 crystals. The inset shows the crystal structure of SrRuO3. C
DOI: 10.1021/acs.cgd.5b01248 Cryst. Growth Des. XXXX, XXX, XXX−XXX
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3.2.3. Resistivity. The temperature dependence of the electrical resistivity (ρ) of SrRuO3 with the current applied parallel to a−c plane is displayed in Figure 5a. Here, for the
Figure 5. Temperature dependence of the electrical resistivity (ρ) in SrRuO3 with the current flow along the a−c plane. For comparison, the resistivity of an isostructural CaRuO3 with enhanced paramagnetism is added. The inset shows the resistivity as a function of tamperature squared focusing on the low-temperature behavior in SrRuO3. The dashed line is a fit within the framework of a Fermi-liquid theory, and the residual resistivity is 1.05 μΩ cm. Figure 3. (a) Temperature dependence of the magnetic susceptibility (M/H) of SrRuO3 under a magnetic field of 0.01 T along the [101] direction. The data were recorded using a field-cooling process. The inset shows the inverse susceptibility [(M/H)−1] as a function of temperature. The black solid line is a fit above TC by a Curie−Weiss law. (b) Magnetization curve of SrRuO3 at 1.8 K in the applied field along the [101] and [010] directions. The inset enlarges the low-field magnetization to emphasize the ferromagnetic hysteresis and small coercive field with 0.004 T.
measurement, we carefully picked up the crystals that are next to the rectangular piece used for the magnetization and the specific heat measurements described above. For comparison, the resistivity of an isostructural ruthenate CaRuO3 is added in Figure 5. Upon cooling from room temperature, both ruthenates have similar temperature dependencies. However, the resistivity of SrRuO3 suddenly changes the temperature dependence to superlinear below TC. On the other hand, the resistivity in CaRuO3 mildly varies from sub- to superlinear temperature dependence with a decrease in T. This difference originates from the differing ground states. The sudden change in the TC of SrRuO3 is attributed to the suppression of the spin scattering in the ferromagnetic state, as seen in typical ferromagnets Fe and Ni.30 In the inset of Figure 5, the low-temperature resistivity as a function of temperature squared is shown. The T2 dependence is satisfied well below 30 K. This result suggests that electron− electron scattering is dominant within the framework of a Fermi-liquid theory.16,17 We also find that the residual resistivity (ρ0), which was defined as the low-temperature resistivity extrapolated to zero temperature by fitting (ρ = AT2 + ρ0), is 1.05 μΩ cm, and the residual resistivity ratio [ρ(300 K)/ρ0] was as high as 192. Here the fit is presented as a dashed line. The ratio directly depends on the crystal quality in metallic materials. The obtained ratio indicates that the floating-zone crystal is a quality higher than those of earlier thin films16 and single crystals grown by the flux method.17 Also, as the coefficient A is determined to be 1.22 × 10−8 Ω cm/K2, the Kadowaki−Woods ratio (A/γN2) is 1.45 × 10−5 Ωcm/(J/K mol)2. The ratio is in good agreement with a universal trend in a series of strongly correlated materials.28 The Fermi-liquid behavior in the resistivity on SrRuO3 appears to be insensitive to sample quality. This is in contrast to the non-Fermi-liquidlike behavior seen in CaRuO3 that is relatively sensitive to disorder.27,31 The difference might correlate with the distinct ground state between them, although the crystal structure is similar.
Figure 4. Temperature dependence of the specific heat (Cp) in SrRuO3. A clear transition around TC represents the ferromagnetic transition in bulk. The inset shows Cp/T as a function of temperature squared in the low-temperature region.
ferromagnetic transition. This suggests that the transition occurs in the bulk. The inset of Figure 4 shows the specific heat divided by temperature (Cp/T) as a function of temperature squared. The electronic part of the specific heat (denoted as γN), which is obtained by the extrapolation of Cp/T to zero temperature, is found to be near 30 mJ K−2 mol−1. The value is consistent with the previous reports,14,25 and the large value of γ N reflects a mass enhancement, as seen in other ruthenates.28,29 D
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(6) Mao, Z.; Mori, Y.; Maeno, Y. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 60, 610−614. (7) Kikugawa, N.; Mackenzie, A. P.; Maeno, Y. J. Phys. Soc. Jpn. 2003, 72, 237−240. (8) Perry, R. S.; Kitagawa, K.; Grigera, S. A.; Borzi, R. A.; Mackenzie, A. P.; Ishida, K.; Maeno, Y. Phys. Rev. Lett. 2004, 92, 166602. (9) Mao, Z. Q.; Maeno, Y.; Fukazawa, H. Mater. Res. Bull. 2000, 35, 1813−1824. (10) Ikeda, S. I.; Azuma, U.; Shirakawa, N.; Nishihara, Y.; Maeno, Y. J. Cryst. Growth 2002, 237−239, 787−791. (11) Perry, R. S.; Maeno, Y. J. Cryst. Growth 2004, 271, 134−141. (12) Longo, J. M.; Raccah, P. M.; Goodenough, J. B. J. Appl. Phys. 1968, 39, 1327−1328. (13) Yoshimura, K.; Imai, T.; Kiyama, T.; Thurber, K.; Hunt, A.; Kosuge, K. Phys. Rev. Lett. 1999, 83, 4397−4400. (14) Cao, G.; McCall, S.; Shepard, M.; Crow, J. E.; Guertin, R. P. Phys. Rev. B: Condens. Matter Mater. Phys. 1997, 56, 321−329. (15) Koster, G.; Klein, L.; Siemons, W.; Rijnders, G.; Dodge, J. S.; Eom, C.-B.; Blank, D. H. A.; Beasley, M. R. Rev. Mod. Phys. 2012, 84, 253−298. (16) Mackenzie, A.; Reiner, J.; Tyler, A.; Galvin, L.; Julian, S.; Beasley, M.; Geballe, T.; Kapitulnik, A. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 58, R13318−R13321. (17) Alexander, C.; McCall, S.; Schlottmann, P.; Crow, J.; Cao, G. Phys. Rev. B: Condens. Matter Mater. Phys. 2005, 72, 24415. (18) Fang, Z.; Nagaosa, N.; Takahashi, K. S.; Asamitsu, A.; Mathieu, R.; Ogasawara, T.; Yamada, H.; Kawasaki, M.; Tokura, Y.; Terakura, K. Science 2003, 302, 92−95. (19) Padhan, P.; Prellier, W. Appl. Phys. Lett. 2006, 88, 263114. (20) Anwar, M. S.; Shin, Y. J.; Lee, S. R.; Kang, S. J.; Sugimoto, Y.; Yonezawa, S.; Noh, T. W.; Maeno, Y. Appl. Phys. Express 2015, 8, 019202. (21) Sow, C.; Samal, D.; Anil Kumar, P. S. A.; Bera, A. K.; Yusuf, S. M. J. Appl. Phys. 2013, 113, 17E122. (22) Randall, J. J.; Ward, R. J. Am. Chem. Soc. 1959, 81, 2629−2631. (23) Shai, D. E.; Adamo, C.; Shen, D. W.; Brooks, C. M.; Harter, J. W.; Monkman, E. J.; Burganov, B.; Schlom, D. G.; Shen, K. M. Phys. Rev. Lett. 2013, 110, 087004. (24) Kobayashi, H.; Nagata, M.; Kanno, R.; Kawamoto, Y. Mater. Res. Bull. 1994, 29, 1271−1280. (25) Kiyama, T.; Yoshimura, K.; Kosuge, K.; Michor, H.; Mbox, M.; Hilscher, G. J. Phys. Soc. Jpn. 1998, 67, 307−311. (26) Tian, W.; Haeni, J. H.; Schlom, D. G.; Hutchinson, E.; Sheu, B. L.; Rosario, M. M.; Schiffer, P.; Liu, Y.; Zurbuchen, M. A.; Pan, X. Q. Appl. Phys. Lett. 2007, 90, 022507. (27) Kikugawa, N.; Balicas, L.; Mackenzie, A. P. J. Phys. Soc. Jpn. 2009, 78, 014701. (28) Maeno, Y.; Yoshida, K.; Hashimoto, H.; Nishizaki, S.; Ikeda, S.; Nohara, M.; Fujita, T.; Mackenzie, A. P.; Hussey, N. E.; Bednorz, J. G.; Lichtenberg, F. J. Phys. Soc. Jpn. 1997, 66, 1405−1408. (29) Ikeda, S. I.; Maeno, Y.; Nakatsuji, S.; Kosaka, M.; Uwatoko, Y. Phys. Rev. B: Condens. Matter Mater. Phys. 2000, 62, R6089−R6092. (30) Schwerer, F. C.; Cuddy, L. J. Phys. Rev. B 1970, 2, 1575−1587. (31) Capogna, L.; Mackenzie, A. P.; Perry, R. S.; Grigera, S. A.; Galvin, L. M.; Raychaudhuri, P.; Schofield, A. J.; Alexander, C. S.; Cao, G.; Julian, S. R.; Maeno, Y. Phys. Rev. Lett. 2002, 88, 076602.
4. SUMMARY We have succeeded in growing high-quality single crystals of the n → ∞ system SrRuO3 by the floating-zone technique. Together with the higher initial Ru/Sr ratio in the feed rod as a self-flux, we employed a cold trap for the growth. Because the evaporated RuO2 was deposited mainly on the surface of the trap set inside the quartz tube, the light was effectively able to pass through the quartz tube. As a result, the molten zone was kept stable during the growth. The shiny SrRuO3 crystal used for magnetization and heat capacity measurements was embedded inside the grown material and was found to have dimensions of 1.4 mm × 1.4 mm × 3.0 mm. We have confirmed the presence of a bulk ferromagnetic ground state with a TC of 163.5 K. The crystal shows low residual resistivity with a residual resistivity ratio of 192. The large electronic coefficient of the specific heat and temperature-squared behavior in resistivity indicate that this system is a highly correlated Fermi liquid. Because the grown crystal is relatively large, it opens a window to clarify the origin of the ferromagnetism on this material. For instance, neutron scattering measurements are of interest. It is also worth attempting the detailed quantum oscillation measurements to fully determine the electronic structure of the ferromagnetic material. Finally, the floating-zone technique combined with the cold trap should be useful to apply to other systems that the high vapor pressure of the feed rods has prevented from forming crystals.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01248. Image of the optical polarized microscopy CIF file (PDF) CIF file (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We acknowledge H. Kitazawa, H. Mamiya, M. Imai, H. Aoki, and K. Nakazato for support and H. Yamase for fruitful comments and discussion throughout the study. N.K. acknowledges the support of the overseas researcher dispatch program in NIMS.
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REFERENCES
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DOI: 10.1021/acs.cgd.5b01248 Cryst. Growth Des. XXXX, XXX, XXX−XXX
