Influence of chemical substitution and pressure on structure, resistivity and magnetism of La_(1+x)Ba_(2-x)Fe_3O_(8+δ) (x = 0,0.5,1; 0 < δ < 1)

摘要

Among those Fe-based perovskite $$R hbox {Ba}_{2} hbox {Fe}_{3} hbox {O}_{8+delta }$$ R Ba 2 Fe 3 O 8 + δ which are isomorphous to high- $$T_{c} , R hbox {Ba}_{2} hbox {Cu}_{3} hbox {O}_{7-delta }$$ T c R Ba 2 Cu 3 O 7 - δ superconductors ( $$R=hbox {rare earth}$$ R = rare earth and Y), the cubic $$hbox {LaBa}_{2} hbox {Fe}_{3} hbox {O}_{8+delta }$$ LaBa 2 Fe 3 O 8 + δ is special in that both its magnetism and resistivity are strongly modified when varying a control parameter such as oxygen concentration ( $$8+delta$$ 8 + δ ), La/Ba ratio ( $$1 + x/2 - x$$ 1 + x / 2 - x ), or applied pressure ( p ). With the aim of identifying and optimizing those conditions that induce a reduction in its magnetism and resistivity, we synthesized various samples of $$hbox {La}_{1+x} hbox {Ba}_{2-x} hbox {Fe}_{3} hbox {O}_{8+delta }$$ La 1 + x Ba 2 - x Fe 3 O 8 + δ and studied their structure, magnetism, and resistivity as a function of $$delta$$ δ , p , and x . In this preliminary report, we show that (i) the cubic, $$Pm{ar{3}}m$$ P m 3 ¯ m , structure is stable across the studied ranges, however the lattice a -parameter is reduced on increasing x , $$delta$$ δ , or p ; (ii) the resistivity is reduced on increasing $$delta$$ δ or reducing x ; the influence of pressure, on the other hand, is mostly manifested around and below the onset points of charge and magnetic order. (iii) The magnetism is much reduced as compared to that of the heavier $$R hbox {Ba}_{2} hbox {Fe}_{3} hbox {O}_{8+delta }$$ R Ba 2 Fe 3 O 8 + δ members. We discuss the influence of each of x , $$delta$$ δ and p in terms of the Fe ions disproportionation scenario.