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Specific-heat and magnetic-susceptibility measurements are reported for the polycrystalline spinel compounds GeNi 2 O 4 and GeCo 2 O 4 in magnetic fields up to 14 T and 0.5 K Յ T Յ 400 K. Both compounds have first-order antiferromagnetic transitions. There are two sharp closely spaced magnetic-ordering anomalies for GeNi 2 O 4 at Néel temperatures T N1 ͑0͒ = 12.080 K and T N2 ͑0͒ = 11.433 K in zero magnetic field. There is also a broad anomaly in the specific heat centered at ϳ5 K, which is present for all fields. Spin waves with an average gap of 10.9 K are associated with this anomaly, which is confirmed by neutron-scattering measurements. An unusual feature of the antiferromagnetism for GeNi 2 O 4 is the simultaneous presence of both gapped and ungapped spin waves in the Néel state, inferred from the specific-heat data. GeCo 2 O 4 has a single anomaly at T N ͑0͒ = 20.617 K in zero magnetic field. Spin waves with an average gap of 38.7 K are derived from fitting the low-temperature specific heat and are also observed by neutron scattering. For both compounds ϳ50% of the derived magnetic entropy is below the ordering temperatures, and the total magnetic entropies are only ϳ60% of that predicted for the Ni 2+ and Co 2+ single-ion ground-state configurations. The missing entropy is not linked to magnetic disorder in the ground state or hidden ordering below 0.5 K. It is postulated that the missing entropy is accounted for by the presence of substantial magnetic correlations well above the Néel temperatures. Fitting the GeNi 2 O 4 susceptibilities to the Curie-Weiss law yields parameters that are consistent with those found for Ni 2+ ions in a crystal-electric-field environment including octahedral and trigonal components. The application of the Curie-Weiss law to the GeCo 2 O 4 susceptibilities is not valid because of low-lying crystal-electric-field states.

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The lithium-storage material Li(0.6)FePO(4) was studied by inelastic neutron scattering and differential scanning calorimetry. Li(0.6)FePO(4) undergoes a transformation from a two-phase mixture (heterosite and triphylite) to a disordered solid-solution at 200 degrees C. Phonon densities of states (DOS) obtained from the inelastic neutron scattering were similar for the two-phase sample measured at 180 degrees C and the disordered sample measured at 220 degrees C. The vibrational entropy of transformation is 1.8 +/-0.9 J/(K mol), which is smaller than the configurational entropy difference of approximately 3.1 J/(K mol). The measured enthalpy of the disordering transition was estimated as 2.5 kJ/mol. The phonon data show a small change in lattice dynamics upon disordering.