  In this study, we investigate the finite-temperature properties of the
spin-1/2 $J_1-J_2$ Heisenberg model on the kagome lattice using the
orthogonalized finite-temperature Lanczos method. Under a zero magnetic field,
the specific heat exhibits a double-peak structure, as $|J_2|$ increases.
Additionally, at approximately $J_2=0$, the magnetic entropy remains finite,
even at low temperatures. The finite-temperature magnetization curve reveals
the asymmetric melting behavior of the 1/3 plateau around $J_2=0$. As $|J_2|$
increases, the 1/3 plateau becomes more stable, exhibiting symmetric melting
behavior. Specifically, for $J_2 > 0$, the $\bf Q=0$ up-up-down structure is
stabilized, whereas for $J_2 < 0$, the $\sqrt{3} \times \sqrt{3}$ up-up-down
structure is stabilized.
