Indice
The tetragonal unit cell is that of La8Ni6O16, a=3.9633 Å, b=3.9633 Å, c=26.0373 Å space group I4/mmm, Int Tables number=139
| Layers along c
|
| charge order on Ni
|
| no charge order on Ni
|
|
|
|---|
| Ni1 2(O1)
|
| 2+ + 2(2-) = 2-
|
| 1.33 + 2(2-) = 2.67-
|
| La1 Ni2 2(O2)
|
| 3+ + 1+ + 2(2-) = 0
|
| 3+ + 1.33+ + 2(2-) = 0.33+ (x2)
|
| La
|
| 3+
|
| 2O3
|
| 2(2-) = 4-
|
| La
|
| 3+
|
| Ni2 La1 2(O2)
|
| 2(O1) Ni1
|
| Ni2 La1 2(O2)
|
| 2(La2) 2(O3)
|
| La1 Ni2 2(O2)
|
| Ni1 2(O1)
|
Muon site There is an analogy with T' La2CuO4, where DFT indicates that most stable muon site A is in the O2 plane of the La2O2 blocks, negatively charged, whereas a local minimum is somewhere in between O1 and O2, site B. First choice for site A would be ca. 1.12 Å from O3 in the direction of a neighbour O3.
Ref. [1] indicates a SDW with Q=(1/3 1/3 0), hence three distinct low spin Ni1 and three distinct low spin Ni2, negligible spin on O and the following moments
| inequiv. Ni1,2
| Ni1 (µB)
| Ni2 (µB)
|
Fig. S6 from ref. [1]
| TO BE CORRECTED The contrast is not very large, the total imbalance is small (0.04 µB), and there is a 5:4 ratio of up to down spin (or viceversa) in each layer. This means that, assuming isotropic hyperfine coupling, a muon bound to O in between a green and a yellow, two yellow or two blue Ni ions will experience a local ferromagnetic environment (10 cases in the figure), hence a net hyperfine field from Ni, whereas the muon bound to O in between a yellow and a blue Ni will experience a nearly AF environment, hence a near cancellation of the hyperfine field (8 cases in the figure). This predicts two groups of fields, with and without a hyperfine contribution, in the ratio 5:4. Dipolar sums will provide further subtle differences. This could justify a high multiplicity of internal fields.
|
|---|
| G
| 0.75
| -0.74
|
| Y
| 0.73
| -0.66
|
| B
| -0.83
| 0.82
|
|
Sketch of µ sites distinguished by the dipolar environment.
|
To start with, let's consider only the nn configuration (labelling it by the colour of Ni, GYB. Check!) There are 16 BB sites, 8 YY sites, 16 GY sites, 32 BY sites that will be further subtly differentiated by their nnn-and-farther configuration. Keeping in mind the symmetry I count 9 distinct sites, numbered in the sketch, all with multiplicity 8. The Ni spin direction (in plane?) can further increment the multiplicity by a factor 2.
On second thoughts experimentally we have a strong 20 MHz frequency (~0.15T) and a bunch of lower frequencies (1.5, 2.4, 3.8 and 7.5 MHz, i.e. 0.01, 0.018, 0.028 0.055 T)
|
La4Ni3O8 con musa2
References
[1] V. Poltavets et al. Phys. Rev. Lett. 104 206403 (2011)
Indice
