Magnetic transformations in reentrant region of the x–T diagram of Li0.5Fe2.5−xGaxO4 spin-glass system

Abstract

Reentrant spinels Li0.5Fe2.5−xGaxO4 with x=0.9 and 1.2 display peaks on the temperature dependences of heat capacity C at T1=13.4 K (x=0.9) and 14.2 K (x=1.2) respectively, which are typical of a first-order phase transition. This transition is identified with the transformation of the collinear ferrimagnetic structure into a noncollinear structure preceding on the temperature scale the state of ferrimagnetic spin glass existing in the temperature range 0 K⩽T⩽Tf, where transition temperatures Tf are 9 K (x=0.9) and 12 K (x=1.2).

Low-temperature specific heat of frustrated ferrimagnets BaFe12−xInxO19 with x=3.0 and x=3.6

“…9. We note that a third first-order phase transition quite likely exists in reentrant magnets in the temperature region T f ϽTϽT C , as we observed previously 14,15 in the the spin-glass system Li 0.5 Fe 2.5Ϫx Ga x O 4 .…”

“…Clearly the phonon contribution to the specific heat has about the same value in both samples and in the temperature interval under study is probably proportional to T 3 . At low temperatures the magnetic contribution is ordinarily larger than the lattice contribution; 8,14,16 the magnetic contributions in samples with different In 3ϩ concentrations can in principle have not only different values but also different temperature trends. For a qualitative check of this, Fig.…”

“…3; the correlation coefficient is 0.99. netic states in the vicinity of the multicritical point of the x -T diagram, one has C m ϰT both in the SG and in the FSG states. 14,16 Moreover, in the context of the question under discussion it is appropriate to recall another example ͑they are not yet numerous͒ 20,21 in which a dependence C m ϰT 3/2 is observed simultaneously with pronounced spin-glass properties. In the dilute spinels Li 0.5 Fe 1.6 Ga 0.9 O 4 the linear dependence C m ϰ(T) gives way to a T 3/2 law if ϳ2 mole% Co 2ϩ is added to its composition.…”