A⁷Li-NMR Study on Spinel LiMn₂O₄: the Evidence of an Antiferromagnetic Transition at ∼ 40 K

Evidence of a Cationic Substitution Domain in Lithium-Manganese Spinels

“…The features at about 80,45 and 35 K can be well accounted for by the presence of the other phases identified by XRD analysis. As evidenced in Figure 3b, where the l/xm curves of Mn 2 0 3 , Mn 3 0 4 and Li 2 Mn0 3 pure samples are reported for comparison, the shoulder at 80 K, observed in samples with x < 0.33, corresponds to the maximum of the Mn 2 0 3 susceptibility at the antiferromagnetic transition at T = 80 K, and the rise of x m just below 50 K to the ferrimagnetic transition of Mn 3 0 4 at T = 49 K. Similarly, the flexion below 40 K in samples with x > 0.33 can be attributed to the antiferromagnetic transition of Li 2 Mn0 3 at 35 K. By contrast, the change in the slope at about 40 K in the x m curve of the stoichiometric spinel, also observed by other authors [11], cannot be reasonably assigned to spurious phases, but probably indicates the onset of antiferromagnetic ordering [16]. Note that the presence of Mn 3 0 4 in samples with x < 0.33 is not revealed by XRD except for the x = 0.31 sample.…”

Microscopic magnetic and structural nature of spinelLi[LixMn2−x]O4

“…This is presumably the main reason for the discrepancy of T N and the magnetic structure of LiMn 2 O 4 in past reports. [5][6][7][8] We wish to emphasize that the present + SR experiment confirms the existence of the magnetic transition for LMO with x Ͼ 0, because, based only on the measurements, it is difficult to judge whether the origin of T N and/or T f is intrinsic.…”

“…The stoichiometric compound ͑LMO with x =0͒ exhibits two phase transitions; one is a structural transition from a high-T cubic phase to a low-T orthorhombic phase at T JT ϳ 280 K induced by a cooperative Jahn-Teller ͑JT͒ distortion of Mn 3+ ions, [2][3][4] and the other is an AF transition with T N ϳ 60 K, which was found by 7 Li− NMR, 5 and then confirmed by neutron diffraction experiments. [6][7][8] Since both neutron and electron diffraction analyses indicated charge ordering of Mn 3+ and Mn 4+ below T JT that is probably stabilized by the cooperative JT distortion, 9 the AF order is also considered to be strongly coupled with charge ordering.…”

Charge and spin ordering inLiMn2O4

“…7-9,14 -19 The existence of the spin-glass behavior is a point in question. 15,16 The inverse susceptibility Ϫ1 starts to deviate from linearity on cooling at temperatures ranging from 70 to 40 K. 8,16 -18 Sugiyama et al 18 reported the existence of an antiferromagnetic phase below 40 K by means of 7 Li-NMR measurements. However, Oohara, Sugiyama, and Kontani 19 observed the absence of a magnetic long-range order even at 8 K in their neutron diffraction experiment.…”