  An external magnetic field induces large relative changes in the entropy of
one-dimensional quantum spin systems at finite temperatures. This leads to a
magnetocaloric effect, i.e. a change in temperature during an adiabatic
(de)magnetization process. Several examples of one-dimensional spin-1/2 models
are studied by employing the Jordan-Wigner transformation and exact
diagonalization. During an adiabatic (de)magnetization process temperature
drops in the vicinity of a field-induced zero-temperature quantum phase
transition. Comparing different levels of frustration, we find that more
frustrated systems cool down to lower temperatures. For geometrically
frustrated spin models a finite entropy survives down to zero temperature at
certain magnetic fields. This property suggests frustrated quantum spin systems
as promising alternative refrigerant materials for low-temperature magnetic
refrigeration.
