Thermal Hysteresis Of The Pumped Spin Current In The Spin-transition Materials

In this paper,a two-layer film system composed of spin-transition material / paramagnetic metal is studied.The competition between the crystal field energy and the electron pairing energy can result in the transition between the low-spin state and the high-spin state by the modulation of the temperature.When the high-spin spin-transition material is ferromagnetic and an excitation magnetic field perpendicular to the external magnetic field,both in-plane,is applied in the spin-transition material paramagnetic metal bilayer,a spin current can be pumped into the adjacent paramagnetic metal,due to the inverse spin Hall effect,the DC and AC voltages can be found in paramagnetic metals in different directions.Firstly,we studied the relationship between the occupancy probability of high spin state and the temperature in the spin transition materials.The results show that the high-spin molar fraction increases with the temperature,i.e.,the material transitions from the low-spin state into the high-spin state,the thermal hysteresis can appear under certain conditions.Secondly,the dependence of the DC and AC voltages from the inverse spin Hall effect due to the pumped spin current on the external magnetic field is investigated.The results show that the dc and ac voltages peak when the system is in ferromagnetic resonance,but the dc and ac voltages decay immediately if the external magnetic field deviates from resonance.Thirdly,thedependence of both voltages on the temperature is studied and the lagging effect of the magnitude of both voltages can be found during the increasing and decreasing temperature processes,i.e.,the appearance of the thermal hysteresis phenomena.Finally,the modulation amplitude of both voltages in the thermal hysteresis range increases when the spin-transition material is insulating and/or the thickness of the paramagnetic metal decreases.