Spin–singlet competition responsible for magnetization plateau associated with magnetocaloric effect in a tetrameric chain

• The quantum phase transitions and magnetocaloric effect (MCE) of a tetrameric chain are investigated by Green’s function theory.
• The spin–singlet competition was proposed to unpuzzle the magnetization plateau.
• The scaling behavior of inverse MCE was unveiled.

The quantum phase transitions (QPTs) and magnetization plateau properties, together with magnetocaloric effect (MCE) of the tetrameric chain are investigated by means of Green’s function theory. We reveal the uniform, dimeric and gapped (gapless) tetrameric phases, which are explicitly confirmed by the field dependence of magnetization. The spin–singlet competition is proposed to make clear the magnetization plateaus and QPTs. Simultaneously, the QPTs and quantum critical points are identified by the dips of the isoentropes, or equivalently the sharp maxima of entropy at ultra-low temperature, as well as the local minima of specific heat and the valley–peak structure of magnetic cooling rate with its sign changed. In addition, the temperature (T)(T) and magnetic field (h)(h) dependence of magnetic entropy change (ΔS)(ΔS) exhibits prominent inverse magnetocaloric effect (IMCE), implying adiabatic magnetization can generate cooling, which follows a power law dependence of hh: ΔS∼hnΔS∼hn. The local exponent n≈2n≈2 is independent of hh and TT at low fields, which was observed in the antiferromagnetic materials experimentally. It is also found that the stronger the dimerization is, the larger the IMCE is, which would provide a clue to design antiferromagnetic refrigerant materials for use in magnetic cooling devices with low field controlling.