Magnetic Field Induced Phase Transition in Distorted Perovskite Eu 0.6 Sr 0.4 MnO 3 300 250 200 150 100 50 0 I (count/A/sec) 50.8 5 0.9 51.0 51.1 51.2 51.3 2 θ θ (deg) Fig. 1. 404 / 080 peaks at 20 K in various applied magnetic fields after the ZFC process ( λ ( λ = 0.8231 λ Å pp Å). A disto rted perovskite Eu 0.6 Sr 0.4 MnO 3 shows a magnetic field-induced insulator-to-metal (IM) transition at approximately below 75 K [1,2]. The magnetic field-induced change in r esistivity ( ρ ) e xceeds 6 figures (10 6 ) at 12 K. It also accompanies a transition from a low magnetization phase ( σ = 25 emu/g) to a high magnetization phase (85 emu/g). The transition fields are 20 kOe at 5 K and 10 kOe at 20 K. Once it takes places, the induced metallic and ferromagnetic states remain stable even in the absence of a magnetic field. There is no evidence in the ρ – T curve that charge ordering occurs. The electronic state of Eu ions remains unchanged through the transition [3]. The transition also accompanies a magnetostriction of – 4 × 10 -4 and the application of a pressure also induces the IM transition [4]. This suggests that the transition also accompanies a structural phase transition. Thus, in this investigation, we m easured the powder X -ray diffraction in a magnetic field and discuss whether the transition accompanies a structural phase transition. Synchrotron X -ray radiation at beamlines BL39XU ( λ = 0.8231 Å ) and BL46XU ( λ = 0.56355 Å ) was used for the diffraction measurements. The measurements were conducted with m agnetic fields up to 20 kOe, perpendicular to the scattering plane [5]. The crystal structure is orthorhombic ( Pnm a ) with lattice constants a = 5.4463(3) Å , b = 7.666 9 ( 4) Å and c = 5.432 9 (3) c Å at room temperature. Mn-O-Mn angles are about 160 . The lattice constants decrease monotonically with decreasing temperature. N o superstructure was detected down to 20 K, which also indicates the absence of charge ordering. At 20 K, the full powder pattern of the insulator phase ( H = 0) and that of the metal phase ( H = 20 kOe) are both well analyzed to reveal a Pnma space gro up. Therefore, no distinct phase transition is realized through the IM transition. In F ig . 1, 404 / 080 diffraction peaks at 20 K are shown for various applied magnetic fields ( H ) after cooled without magnetic field ( ZFC ) . It is seen that with increasing H , both peaks shift toward low 2 θ angle and that the peak intensities increase drastically for H > 10 kOe . In F ig. 2, the lattice constant b , determined from the 080 peak position, is plotted against H . It increases with increasing H , showing a j ump at approximately 10 kOe where IM transition occurs. The j ump ∆ b /b b b is about 4.3 10 -4 , whose magnitude is comparable to that observed in a magnetostriction measurement [4]. After the transition, b decreases with decreasing H , showing no j ump this time, and reaches a value different × 4 0 kO 8 12 16 20 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 5 5 5 5 5 5 50 50 50 50 50 50 50 50 50 50 50 50 50 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 References [ 1] A. Sundaresan e t al. : Phy s. R e v . B 55 ( 1 997) 5596 . [ 2 ] S . N a k a m u ra et al. : . : J . Phy s. S oc . Jp n. 68 ( 1 999) 1 485 . [ 3 ] M . Miz u m a ki et al . l l : J . S y n ch r ot r o n R ad. 8 ( 200 1 ) 440 . [ 4 ] I . Ko sa k a et al. . . Phy s ic a B 281 - 282 ( 2000) 500 . [ 5 ] S . N a k a m u ra , S. S himom ura , N . Ik eda , M . Miz u m a ki, H . Oh su mi, S . Nimo r i, T . T a k eu chi and K . Itoh: J . M a g n. M a g n. M a t er. - i n p ress. Fig. 2. Dependence of b on H . f r om th e i n iti a l o ne a t H = 0 . Thi s i s co ns i s t e n t with th e H d e p enden c es o f m a g ne to res i s t an c e and m a g ne tiz a tio n , and i s su gg es tiv e o f s om e ki nd of p h ase t rans itio n. H e re , w e co ns i de r t h e ch an g e i n p ea k i n t ens ity a g a i ns t H . I n add itio n to 404 a nd 080 p ea k s , th e i n t ens iti es of 400, 004, 440, and 044 p ea k s i n c rease th r o u gh th e IM t rans itio n. O n t h e oth e r h a nd t ho se of 5 11 a nd 11 5 p ea k s de c rease. T h ese i n t ens i ty ch an g es re p resen t t h e d i s p l a c e m en t of a tom s . T a ki n g th e s t ru c t u ra l f a cto rs i n to a cco un t, w e c an de r iv e i n fo r m a tio n o n t h e d i s p l a c e m en t of a tom s t h r o u g h t h e I M t r a n s i t i o n . O n e s i m p l e e xpl ana tio n fo r a ll th ese i n t ens ity ch an g es i s th e d i s p l a c e m en t of oxyg en tow a rd O 1 ( 0 . 5 , 0 . 25, 0) a nd O 2 (0 . 25, 0, -0 . 25) . T h e resu lt a n t d i s p l a c e m en t co rres p o nds to th e r ot a tio n of M n O 6 o c t a h ed r o ns to i n c rease th e M n -O-M n an gl e tow a rd 1 80 . Su c h s ch e m e i s ill us t ra t ed i n Fig . 3 . Thi s s t ru ct ura l ch an g e l eads to a g a i n o f th e e l e ct r o n t rans f e r ener g y i n t h e d o u bl e e xch an g e m e ch a n i s m a nd t h us s t a biliz es th e m e t a llic and f err om a g ne tic s t a t es. I nsulator H Metal S hi n N a k a m ura a a a , Susu m u S himom ura b a a and N a o s hi Ik eda c ( a ) D e p ar tm en t of Phy s ic s , T e ikyo U n iv ers ity (b) D e p ar tm en t of Phy s ic s , K e io U n iv ers ity (c) S P r i n g -8 / J AS R I E-m a il: s hi n @ko a l a. m se. t e ikyo- u.a c . jp Fig. 3. Rotation of MnO 6 octahedrons through the IM transition. H up H down b (Å) 7.649 7.650 7.651 7.652 7.653 7.654 7.655 7.648 0 5 10 15 20 H (kOe) 1 1 1 1 1 1 1 1 1 1 1 1 1 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 51 5 5 5 5 5 5 51 51 51 51 51 51 51 51 51 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
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