Ac susceptibility and⁵¹V NMR study of MnV₂O₄

Abstract

We report 51 V zero-field NMR of the manganese vanadate spinel compound, MnV 2 O 4 , together with both ac and dc magnetization measurements. The field and temperature dependences of ac susceptibilities show a re-entrant-spin-glass-like behavior below the ferrimagnetic (FEM) ordering temperature. The zero-field NMR spectrum consists of multiple lines ranging from 240 to 320 MHz. Its temperature and field dependences are discussed in terms of the persistence of a small fraction of the cubic phase within the FEM ordered ground state. Due to strong spin-orbit couplings the disordered phase induces an anomalous structural and electronic state in an external field. This suggests a close correlation between magnetism and structure.

Ferrimagnetism of MnV2O4spinel

“…A modified spin-wave theory is developed to describe the two phases and to calculate the magnetization as a function of temperature. The anomalous M (T ) curve reproduces the experimentally obtained ZFC magnetization [2,3].…”

“…A modified spin-wave theory is developed to describe the two phases and to calculate the magnetization as a function of temperature. The anomalous M (T ) curve reproduces the experimentally obtained ZFC magnetization [2,3].Because of the strong spin-orbital interaction it is convenient to consider jj coupling with J A = S A and J B = L B + S B . The sublattice A total angular momentum is j A = s A = 5/2, while the sublattice B total angular momentum is j B = l B + s B , and sublattice A magnetic order is antiparallel with sublattice B one.…”

“…The sublattice B total angular momentum is j B = l B + s B = 5/2, and g-factor g B = 2 which is larger then atomic value, because of the anisotropy. The magnetization of the system g A M A + g B M B as a function of the temperature is depicted in Fig.1 The figure is in a very good agrement with the experimental ZFC magnetization curves [2,3]. (see Fig.1 [9]).…”

“…(see Fig.1 [9]). The anomalous temperature dependence of the magnetization, predicted by Neel, is reproduced, but there is an important difference between Neel's theory, interpretation of NMR results [2,3], and the present modified spin-wave theory. Neel's calculations predict a temperature T N at which both the sublattice A and B magnetization become equal to zero.…”

“…The applied field is antiparallel with vanadium magnetic moment and strongly effect it. On the other hand the experiments show that there is no difference between ZFC and FC magnetization curves when the temperature runs the interval (T * , T N ) [2,3]. They begin to diverge when the temperature is below T * .…”