Antiferromagnetic correlations in the metallic strongly correlated transition metal oxide LaNiO3

The material class of rare earth nickelates with high Ni3+ oxidation state is generating continued interest due to the occurrence of a metal-insulator transition with charge order and the appearance of non-collinear magnetic phases within this insulating regime. The recent theoretical prediction for superconductivity in LaNiO3 thin films has also triggered intensive research efforts. LaNiO3 seems to be the only rare earth nickelate that stays metallic and paramagnetic down to lowest temperatures. So far, centimeter-sized impurity-free single crystal growth has not been reported for the rare earth nickelates material class since elevated oxygen pressures are required for their synthesis. Here, we report on the successful growth of centimeter-sized LaNiO3 single crystals by the floating zone technique at oxygen pressures of up to 150 bar. Our crystals are essentially free from Ni2+ impurities and exhibit metallic properties together with an unexpected but clear antiferromagnetic transition.


Supplementary Note 2 Thermogravimetric measurements
Supplementary Figure 2 shows a typical thermogravimetric (TG) measurement of one of our nickelate samples that was heated to 900 • C in a flow (100ml/min.) of 20% H 2 and 80% Ar gas. The oxygen concentration amounts to ∼3.005 according to the graphical analysis and ∼2.998 as derived from weighing initial and final masses before and after the reduction of the sample. Both values basically indicate the absence of Ni 2+ impurities in our LaNiO 3 crystals. The small difference between these values is comfortably within the typical error of TG measurements and can be attributed to the impact of the gas flow which is affecting the buoyant force that has non-negligible influence on the weighing of the sample mass during the reaction.

Supplementary Note 3 Crystal structure
Moreover, we determined the atomic positions of LaNiO 3 by means of single crystal X-ray diffraction. The structural parameters are listed in Supplementary Table 1

Supplementary Note 4 Physical properties
We also re-measured the magnetic susceptibility and electrical resistivity for six different single crystals from three batches that we have grown, see Supplementary If the crystal is a single crystal and not polycrystalline it shows the kink in the magnetic susceptibility and a low value of the electrical resistivity, see Supplementary  Figure 4. However, if the crystal is not single crystalline, we also observe a magnetization without any kink, similar as in Supplementary Ref. [1]. Therefore, we could imagine that magnetic ordering only appears in LaNiO 3 single crystals where domain sizes are very large and samples are very pure.
Finally, there seems to be no field dependence (up to 9 T) of the electrical resistivity of LaNiO 3 -see Supplementary Figure 5. Since the single crystals are twined (and pseudocubic) also no direction dependence on the magnetic field direction can be expected.

Supplementary Note 5 Magnetic structure
Since our single crystal is fully twinned we decided to make a magnetic symmetry analysis for the high symmetry cubic (undistorted perovskite) structure with space group Pm3m. The integrated intensities of the (0 0 1) and (1 1 0)  magnetic peaks have been obtained from Gaussian fits to the corresponding Q scans (note, that an analyzer was used in our triple-axis measurements,) and normalized by the monitor and by the attenuation factor (plexi: 7.5) for the nuclear reflections. The scale factor was determined from the nuclear intensities and fixed for the subsequent magnetic structure refinement. The magnetic structure was determined by irreducible representation (IR) analysis for space group Pm3m and for a propagation vector (0.25 0.25 0.25). The reducible magnetic representation for the Ni ions at the 1b site is decomposed into two IRs as: The basis vectors for the IRs are listed in Supplementary Table 2. and a comparison of observed and calculated intensities is listed in Supplementary Table 3. For the cubic symmetry the appearance of the (3/4 3/4 3/4) reflection excludes the model with longitudinal modulation of the magnetic moments (see Supplementary Figure 6(a)) which is also reflected by the large R-and weighted R values that amount to 65.0% and 69.4%. The model with helical arrangement of the magnetic moments perpendicular to the propagation vector (see Supplementary Figure 6(b)) is consistent with our data (R-and weighted R values amount to 16.3% and 17.7% respectively) and yields an ordered moment of about 0.3 µ B .
Supplementary Figure 1: Laue diffraction images A photo of one of our LaNiO 3 single crystals (batch 2) together with Laue diffraction images measured at different spots on the sample which are indicated by the blue arrows.