Growth and characterization of high quality single crystals of NaxCoO2

Anisotropic magnetization and dynamic susceptibility sign change in single-crystalNa0.85CoO2

“…[3] magnetic field of H = 1 T for different crystal orientations of H (ab) and H (c) in the temperature range of 2 K ≤ T ≤ 300 K. The magnetic susceptibility for H (c)-axis (M/H) c (T ) exhibits an antiferromagnetic (AF) transition at T N ≃ 22 K, which is comparable with that in the case of Na 0.83 CoO 2 (T N ≈ 20 K). [15] It follows the Curie-Weiss law from 300 K to 150 K as shown in the inset of Fig. 2 (red square, red line).…”

“…[8] The mixed valence of Co 4+ The static magnetic susceptibility (M/H) ab (T ) under a magnetic field of H = 1 T parallel to the (ab)plane monotonically increases with decreasing temperatures from 300 K to 60 K. With decreasing temperatures, a peak is observed near T ≈ 50 K with a subsequent increase in susceptibility at low temperatures (T ≤ 10 K). Even though this peak (near 50 K) is sharper than that in the other case, [15] the broad shoulder of (M/H) ab in the intermediate temperature region (20 K ≤ T ≤ 50 K) is commonly observed for high Na concentration compounds of Na 0.82 CoO 2 . [11] The authors argue that this may be a signal of a valence fluctuation between Co 3+ and Co 4+ .…”

Growth and magnetic characterization of high-quality α′-Na0.75CoO2 single crystals

“…5 shows temperature dependence of magnetic susceptibility w(T) under magnetic field H=1 T with in-and out-ofplane of the as-grown Na 0.75 CoO 2 crystal in a temperature range of 4pTp300 K. There is a clear and sharp increase in the susceptibility in both directions at 22 K, which is the AF longrange order with Nè el phase temperature transition formed due to spin density wave (SDW) [15,16]. This Nè el phase shows an approximate compositional independence of critical temperature T N $22 for x$0.75, as well as for those at higher sodium content of x$0.83, 0.90 and 1.00 [12]. The inverse magnetic susceptibility w À1 (T) is shown in the inset of which is strongly Curie divergent at low temperature as commonly observed in the two-channel Kondo model [17].…”

“…Therefore, it is crucial to obtain a high-quality single crystal in order to have an accurate characterization of the compound. On the other hand, large single crystal for Na 0.75 CoO 2 is hard to obtain due to the incongruent melt and volatilization of Na leading to decomposition of the compound during sintering [6][7][8]12].…”

Floating zone growth of α-Na0.90MnO2 single crystals

“…This is primarily due to the challenge of dual Na and Mn volatility during growth as well as two competing polymorphic forms for NMO, namely α-NMO and β-NaMnO 2 (β-NMO), with very close energetics [6,7,8,9]. The successful synthesis of large volume FZ grown crystals of Email address: stephendwilson@engineering.ucsb.edu (Stephen D. Wilson) the form ABO 2 , such as Na x CoO 2 [10,11,12,13], have historically provided access to deeper experimental insights. The current absence of high purity, large volume FZ crystals of α-NMO presents an impasse to the community's understanding of this system's rich phase behavior, where recent studies have been limited to polycrystalline specimens [3,7,14,15,16,17].…”