Abstract
The ambient pressure temperature dependence of the magnetization (M) in P1-xSrxCoO3 series (x = 0.4, 0.5, 0.55 and 0.6) indicates the onset of ferromagnetic ordering at high temperatures (TC = 214-226K) and a step-like anomaly at lower temperatures (TS = 69-120 K). In this report we present the pressure dependence of magnetization and zero-field thermal expansion studies for a representative sample x = 0.4. The step-like anomaly in M(T) around TS = 69 K is accompanied by a pronounced peak in thermal expansion coefficient. The application of hydrostatic pressure of P = 1.16 GPa increases TS by 15 K, which is much larger than the increase of the ferromagnetic Curie temperature (ΔTC = 4 K) under the same pressure. The anomalous increase of TS under pressure is attributed to the occurrence of magnetization rotation at a temperature higher than TS = 69 K triggered by the stabilization of low temperature tetragonal phase at the expense of high temperature orthorhombic phase.
Highlights
The perovskite cobaltites such as La1-xSrxCoO3 have attracted much attention because they show a rich variety of phenomena such as temperature- and doping-driven spin state transition of Co ion,[1] coexistence of metallic like resistivity and ferromagnetism,[2,3] giant magnetoresistance,[4,5,6,7,8] giant anisotropic magnetostriction,[9] and nanoscale magnetoelectronic inhomogeneity,[10] etc
Pr0.5Sr0.5CoO3 is a ferromagnetic metal below T C = 230 K but its magnetization shows an unusual feature within the ferromagnetic state: M(T ) shows a downward step around T A = 120 K in a low magnetic field (μ0H = 0.01 T) and it changes to an upward step for μ0H >0.03 T.15–17
The FM Curie temperature increases under pressure, the shift of the latter (∆T C = +4 K) is significantly smaller than the former (∆T S = +15 K)
Summary
The perovskite cobaltites such as La1-xSrxCoO3 have attracted much attention because they show a rich variety of phenomena such as temperature- and doping-driven spin state transition of Co ion,[1] coexistence of metallic like resistivity and ferromagnetism,[2,3] giant magnetoresistance,[4,5,6,7,8] giant anisotropic magnetostriction,[9] and nanoscale magnetoelectronic inhomogeneity,[10] etc. Based on a detailed neutron diffraction and X-ray magnetic dichroism (Co-L23 edge) studies under magnetic fields, Garcia-Munoz et al.[22] concluded that this composition undergoes an orthorhombic (Imma) to tetragonal (I4/mcm) structural transition around 120 K upon cooling and the structural transition is simultaneously accompanied by a coupled rotation of magnetic easy axes (both spin and orbital magnetic moments of the Co sublattice) in the ab plane. This indicates a strong spin-orbital coupling and such a magnetization reorientation transition coupled with structural transition has not been reported in cobaltites with other rare earth ions. There is no previous report of thermal expansion and pressure dependent magnetization studies in this compound
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