Cubic Re⁶⁺ (5d¹) Double Perovskites, Ba₂MgReO₆, Ba₂ZnReO₆, and Ba₂Y_2/3ReO₆: Magnetism, Heat Capacity, μSR, and Neutron Scattering Studies and Comparison with Theory

Abstract

Double perovskites (DP) of the general formula BaMReO, where M = Mg, Zn, and Y, all based on Re (5d, t), were synthesized and studied using magnetization, heat capacity, muon spin relaxation, and neutron-scattering techniques. All are cubic, Fm3̅m, at ambient temperature to within the resolution of the X-ray and neutron diffraction data, although the muon data suggest the possibility of a local distortion for M = Mg. The M = Mg DP is a ferromagnet, T = 18 K, with a saturation moment ∼0.3 bohr magnetons at 3 K. There are two anomalies in the heat capacity: a sharp feature at 18 K and a broad maximum centered near 33 K. The total entropy loss below 45 K is 9.68 e.u., which approaches R ln 4 (11.52 e.u.) supporting a j = 3/2 ground state. The unit cell constants of BaMgReO and the isostructural, isoelectronic analogue, BaLiOsO, differ by only 0.1%, yet the latter is an anti-ferromagnet. The M = Zn DP also appears to be a ferromagnet, T = 11 K, μ(Re) = 0.1 μ. In this case the heat capacity shows a somewhat broad peak near 10 K and a broader maximum at ∼33 K, behavior that can be traced to a smaller particle size, ∼30 nm, for this sample. For both M = Mg and Zn, the low-temperature magnetic heat capacity follows a T behavior, consistent with a ferromagnetic spin wave. An attempt to attribute the broad 33 K heat capacity anomalies to a splitting of the j = 3/2 state by a crystal distortion is not supported by inelastic neutron scattering, which shows no transition at the expected energy of ∼7 meV nor any transition up to 100 meV. However, the results for the two ferromagnets are compared to the theory of Chen, Pereira, and Balents, and the computed heat capacity predicts the two maxima observed experimentally. The M = Y DP, with a significantly larger cell constant (3%) than the ferromagnets, shows predominantly anti-ferromagnetic correlations, and the ground state is complex with a spin frozen component T = 16 K from both direct current and alternating current susceptibility and μSR data but with a persistent dynamic component. The low-temperature heat capacity shows a T power law. The unit cell constant of B = Y is less than 1% larger than that of the ferromagnetic Os (5d) DP, BaNaOsO.

Structural, Magneto‐electronic, Mechanical, and Thermophysical Properties of Double Perovskite Ba2ZnReO6

“…The atomic positions in Wyckoff positions for various atoms in the stable phase are: Ba atoms are located at 8c (0.25, 0.25, 0.25), Zn positioned at 4b (0,0,0), Re sited at 4a (0.5,0.5,0.5), and O atoms at position 24e (0.25,0,0) of the unit cell. The energy variation is shown in Figure with optimized lattice constant is in close agreement with experimental and theoretical results . We have also calculated the optimized parameters analytically found similar in value with others enlisted in Table .…”

“…Further, in two calculation methods there is a negligible change in total magnetic moments where GGA + U incorporation makes exact splitting of the d ‐orbitals of Re +6 due to which a slight increase in its magnetic moment is seen. The reported values of magnetic moments show a good agreement with the experimental results having ferromagnetic character ranging from at 0 K up to 11 K …”

“…Similarly, A defines the height of the material grown is isotropic or anisotropic where its value equal to 1 shows isotropic behavior and deviation from it, anisotropy is present in material . Here, we can see a small deviation from unity confirms its near to isotropic nature and defines that it may grow less micro cracks at the growing process as has been found experimentally . Ductility and brittleness are similarly defined to categories the class of the material for industrial applications.…”

“…BZRO is found to stabilize in cubic Fm‐3m space group as seen from energy verses volume variation in all possible magnetic and non‐magnetic configurations display the ferromagnetic phase as stable. Marjerrison et al, predict the two ferromagnetic configuration of the compound viz ., FM110 and FM100. The author also reported that FM110 is most favorable and stable, while as FM100 existence range is severely limited.…”

Muon Spin Rotation, High-Field Magnetization, and Structural Study on a Spin–Orbit-Entangled Mott Insulator Ba2MgReO6

“…There are only a couple of compounds that have been reported to have J eff = 3/2 (Γ 8 ) quartet ground states thus far: Ba 2 NaOsO 6 [11][12][13], Ba 2 YMoO 6 [14], and A 2 TaCl 6 (A = Rb, and Cs) [15]. Recently, we reported that the 5d DP Ba 2 MgReO 6 [16,17] also has a spin-orbit entangle electronic state [18]. The hallmarks of the J eff = 3/2 state are the reduced effective magnetic moment and the electronic entropy of ~R ln4: when the spin and orbital degrees of freedom of the d 1 system are coupled, the spin and orbital angular momentums cancel each other, resulting in a reduced magnetic moment: the electronic entropy of ~Rln4 is clear evidence of the quartet ground sate.…”