Unconventional magnetism in the high pressure ‘all transition metal’ double perovskite Mn₂NiReO₆

Abstract

Mn2NiReO6, prepared at high pressure and temperature, has a highly-distorted double perovskite structure. Canted antiferromagnetic order is observed below TM1 = 80 K and an unusual continuous spin rotation of...

Giant coercivity and spin clusters in high pressure polymorphs of Mn2LiReO6.

“…These are comparable to those observed in other Mn 2 BReO 6 (B = Fe, Mn, Co and Ni) high pressure double perovskites. [8][9][10][11][12][13] Nominal Mn 2+ and Li + oxidation states are confirmed from estimated BVS values. However, rhenium shows a lower value than expected (6.2 +, see Table 2), the likely reasons being the strain imposed on the oxygens in order to accommodate Mn 2+ and the more covalent character of the Re-O bonds when compared to Li-O/Mn-O, in accordance with the higherpressures required to obtain this polymorph.…”

“…Since the spins become more ordered on cooling below 20 K while the weak-ferromagnetic component decreases in magnitude, this implies a spin reorientation as observed for instance in Mn 2 NiReO 6 . 13 AC susceptibility measurements provide further evidence of this behaviour showing a plateau for w 0 (T) in the 20-70 K temperature range, below which the magnetisation is reduced (see Fig. S4, ESI †).…”

“…2,6 Although large magnetocrystalline anisotropy is expected in DPv due to low-symmetry crystal structure and the presence of heavy atoms as in La 2 CuIrO 6 , La 2 Ni 1.19 Os 0.81 O 6 and La 2 NiIrO 6 ; 3-5 such large values are without precedent in DPv_Mn 2 BReO 6 A-site manganites (B = Mn, Fe, Co, Ni). [8][9][10][11][12][13] This suggests that for DPv_Mn 2 LiReO 6 , the lack of d electrons for Li + ([He]) and Re 7+ ([Xe]4f 14 ) add a further ingredient in the search for rare-earth-free hard magnets.…”

“…17 In comparison with similar A-site manganites, DPv_Mn 2 LiReO 6 presents exclusive factors that may explain the unprecedented giant coercivity values observed. The other four existent DPv_Mn 2 BReO 6 (B = Mn 2+ , Fe 3+ , Co 2+ , Ni 2+ ) [8][9][10][11][12][13] contain Re in either 5+ (5d 2 ) or 6+ (5d 1 ) oxidation states with not-quenched SOC. The absence of giant coercivities in these compounds discards a possible rhenium spin-orbit-coupling origin in A-site DPv manganites.…”

Complex magnetism in Ni3TeO6-type Co3TeO6 and high-pressure polymorphs of Mn3−xCoxTeO6 solid solutions

“…For instance, localized d 5 (Mn 2+ ) and itinerant d 1 electrons (V 4+ ) coexist in MnVO3. 1 High pressure Mn2BB'O6 double perovskites (DPvs) show a plethora of magnetic behaviours, with simple antiferromagnetic (AFM), [2][3][4][5] collinear, 6 perpendicular 7 and continuously rotating ferrimagnetic structures 8 and more complex incommensurate-elliptical helices. 9 The stacking of honeycomb / triangular magnetic sublattices in ordered-corundum structures such as Ni3TeO6-type (NTO), induces a strong magnetic frustration, usually resulting in the formation of incommensurate helical magnetic structures, 10 sometimes with thermal dependence and lock-in of their propagation vector 2 at low temperatures.…”