MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

Specific Heat of SrRuO 3
taken in 0 T after application of an 8 T field (circles) shows that the zero-field
data are not hysteretic. On this plot of ∆c/T, the 8 T data (diamonds) show
that the only observed change in the specific heat is a decrease in the linear-T
term.
To further understand the field dependence of γ, specific heat points
between 4 K and 5 K at several intermediate fields were also taken. These
data are shown in Figure B- 3 (open circles) as γ(H) = (c(T,H) - βT 3 )/T using the
value of β measured at 0 T and 8 T. On the same plot, the open squares
indicate the fitted value of γ from the three data sets in Figure B- 1.
Figure B- 3 shows that the coefficient of the linear-T term in the specific heat
decreases approximately linearly with applied magnetic field, H.
To summarize, the specific heat between 3 and 13 K can be described by
c(T,H) = (γ - γ ´H)T+βT 3 .
Although the magnetization of polycrystalline SrRuO 3 is irreversible, the
measured heat capacity is not. Therefore, the heat capacity originates from
processes reversible with respect to a magnetic field, showing that the entropy
associated with random domains is negligible. In this sense, the heat capacity
is a better thermodynamic measure of the low-lying excitations. The
magnetic field dependence of the heat capacity and the magnetization are
related by the following Maxwell relation:
⎛ ∂CH ⎞
⎝ ∂H ⎠ T
= T ∂ 2 M
∂T 2
⎛ ⎞
⎜ ⎟
⎝ ⎠ H
(1)
According to equation 1, the first derivative of the heat capacity with
respect to field gives information about the second derivative of the
magnetization with respect to temperature. This relation is generally valid
for an isotropic system as long as there are no irreversible processes involved
and no PV work is done. Equation 1 is actually three equations since H and M
177