Transport and magnetic properties in one dimensional A 3 ABO 6 family

Transcription

1 Transport and magnetic properties in one dimensional A 3 ABO 6 family M. Costes 1, J.M. Broto 1, B. Raquet 1, M.N. Baibich 2, H. Rakoto 1, A. Maignan 3, Ch. Martin 3, D. Flahaut 3, S. Hebert 3 1 Laboratoire National des Champs Magnétiques Pulsés, LNCMP, Toulouse, France 2 Instituto do Fisica UFRGS, Porto Alegre, RS, Brazil 3 CRISMAT, ISMRA et Université de Caen, France

2 OUTLINE The low dimensional A 3 ABO 6 magnetic oxides Ca 3 Co 2 O 6 -Magnetic properties -Electronic properties Other compounds: Sr 3 NiIrO 6 and Ca 3 CoIrO 6 -Sr 3 NiIrO 6 -Ca 3 CoIrO 6 Conclusion

3 The low dimensional A 3 ABO 6 magnetic oxides A = Ca, Sr. A = Co, Ni, Cu, Fe, Zn B = Co, Fe, Rh, Ru, Ir An impressive variety of complex magnetic phenomena Typical 1-D magnetism varying with : A & B Spin and Oxidation States Crystal fields Ions size Crystallographic distortions Existence of unpaired electrons.. A B Sr 3 ZnIrO 6 : 1D Ising Antiferro with S = ½ Sr 3 CuPtO 6 : 1D Heisenberg Antiferro with S = ½ Sr 3 CuIrO 6 : 1D Heisenberg Ferro with S = ½ Sr 3 CuPt 0.5 Ir 0.5 O 6 : Random Spin Chain Para. [See for instance, NiiTaka & al. J. Sol. Stat. Chem 1999]

4 Elaboration and crystallographic structure for Ca 3 Co 2 O 6, Ca 3 CoIrO 6, Sr 3 NiIrO 6 Elaboration: -samples elaborated via solid state reactions at CRISMAT of Caen Ca 3 Co 2 O 6 : mixture of Ca 3 Co 4 O 9 and K 2 CO 3 in a weight ratio 1/7, heating up to 880 C for 48h in an Eur.Phys.J. B 15, Maignanet al alumina boat in air and then cooling down to room temperature at 100 C/h. needle shaped crystals of several mm length Ca 3 CoIrO 6 : stoichiometric mixture of CaO, Ca 3 Co 4 and IrO 2, heated in air at 900 C, 950 C for 12h for each temperature, after pressed in the form of bars under 1 ton/cm² and heated at 1000 C for 3 days, 1100 C for 2 days and 1200 C for 3 days powders samples non stoichiometric Ca 3 Co 1.03±0.08 Ir 0.66±0.06 Sr 3 NiIrO 6 : stoichiometric mixture of SrCo 3, NiO and IrO 2, calcinated in air at 800 C, 900 C, 1000 C for 24h, after pressed in the form of bars under 1 ton/cm² and heated at 1150 C for 2 weeks, and then cooled down to room temperature at 100 C/h. powders samples Sr 3 Ni 1.1±0.04 Ir 0.9±0.04

5 Crystallographic structure : Maignan et al, Eur.Phys.J. B 15, (1999) Common characteristics: -rhombohedral structure - phase group R-3c,[ABO 6 ] 6- along hexagonal cell c axis - alternating [ABO 6 ] 6- chains, separated by ions Sr 2+, Ca 2+, with 2 configurations: - trigonal prism (A) - octahedral (B) For instance, in Ca 3 Co 2 O 6 different inter-atomic distances : - inter-chain d(co-co) = nm - intra-chain d(co-co) = nm One dimensional compounds

6 Magnetic Properties 3,0x10-4 2,5x10-4 T N = 12 K H//c H=10oe - T c 24 K : Ferro intra-chain coupling 2,0x10-4 χ(emu) 1,5x10-4 T * = 6.5 K - T N 12 K : AF inter-chain coupling 1,0x10-4 T c = 24 K 5,0x T* 6.5 K : frozen temperature 0, T(K) DC - Susceptibility (T) in ZFC and FC, H//c : 10 oe Spin and valence states: Co oct III -d 6, low spin with µ 0 µ B and Co trig III - d 6, high spin with µ 4 µ B Whangbo et al, Solid State Com, 125(7-8), (2003)

7 Magnetization M/M S M/M S M/M S 1,0 0,5 0,0 1,0 0,5 0,0 1,0 0,5 0, K µ o H( T) 4.5K 9.6K M/M s M/M s M/M s K H c1 H c2 10 K K T<T*: large dynamic effects at low temperature T*<T<T N : plateau at 1/3 of M sat T>T C : disappearing of plateau µ 0 H (T) DC-magnetization at 9T for several temperatures 4.5K, 9.6K, 20K Pulsed field magnetization at 11T for several temperatures 2K, 10K, 25K basal plane : Triangular AF Ising Spin configuration : 1 chain = 1 macro-spin

8 Large dynamic effects at low temperature Ca 3 Co 2 O 6 -(a) χ'(emu) 7,0x10-6 6,0x10-6 5,0x10-6 4,0x10-6 3,0x10-6 f=33hz f=111hz f=666hz f=1000hz T c Partially Disordered AF T(K) Para Ferri Ferro 2,0x10-6 1,0x10-6 0,0 f=5000hz f=10000hz T N Frozen Spin T(K) real part of AC - susceptibility for several frequencies - Large dynamic effects - time constant between 1ms and 1s Magnetic phase diagram PDA Ferri Unpaired electrons + magnetic frustrations + strong structural anisotropy Model system for the spin dependent conductivity study in a low dimensional frustrated magnetic oxide

9 ρ(t) (Ω.cm) T (K) Resistivity function of temperature Localization length : α nm Optimum hop: R opt (70 K) 0.52 nm Electronic properties ln( δlnρ / δlnt ) T o = 600 K ν = ln (T) VRH-3D Efros- Shklovskii T o = 87 K ν = 0.9 Logarithmic derivative function of logarithm of temperature 1D Resistivity expression for a VRH model ρ(t) = ρ o exp (T o /T) υ

10 High magnetic field effect R/R (%) R/R (%) T (K) 2 K MR function of field insert: MR function of temperature Ln(R(B)) K (M/Ms) 2 logarithm of R(H) function of (1- (M/Ms)²) at 4K Resistivity under high field at 15T - under T C : VRH-3D type ES VRH-3D type Mott Localization length : α nm Optimum hop: R opt = 1.3/T 1/4 nm let R opt (20K) 0.6 nm Magnetoresistance isn t directly linked with magnetization reversal under field effect : Coulomb gap suppression

11 Surprising dynamic effects on magnetoresistance!! B (T) MR function of magnetic field at 4.2K Insert: MR function of field in parallel and transverse configuration at c axis Superposition of MR and magnetization at 10K function of magnetic field Temps (s) Pulsed magnetic field function of time - Appearance of planar components magnetization during the reversal process {S.Miyashita, J.Phys.Jpn 55, 3605 (1986)}? OR - Magneto-caloric effects due to large dm/dt?

12 Conclusion Conduction mechanisms -T < T C : VRH-3D type ES at zero field VRH-3D type Mott under high field -70 K < T < 230 K : conductivity 1D along chains -T > 230 K : conductivity 3D Large dynamic effects on the magnetoresistance due to magnetization reversal

13 Other compounds: Sr 3 NiIrO 6 and Ca 3 CoIrO 6 DC-Susceptibility for Sr 3 NiIrO 6 T 2 =20 K T 1 =70 K Curie Temperature: θ P = K AF interactions along chains Curie Weiss law :µ(mes) = 3.67 µ B /fu combination of Ni 3+,HS(S=1) and Ir 4+,LS(S=1/2) : µ(calc) = 3.39 µ B /fu

14 Pulsed field magnetization for Sr 3 NiIrO 6 M(µB/fu) Sr 3 NiIrO 6-15K T < T 2 = 20 K: large transition H c around 23 T H c increases when T decreases M(B) 1 ere aim M(B) 0.4 T= 180K T= 77K M(µB/fu) M(µB/fu) T 2 < T < T 1 = 70K:. Plateau at 1/3 of M sat AF polycrystals T > T 1 : paramagnetic state M(µB/fu) T= 40K M(µB/fu) T= 20K AF ordering along chains and inter-chains

15 DC-Susceptibility for Ca 3 CoIrO 6 M/H (emu/g) 4.0x x x x x x x x G 1T Ca 3 CoIr T T(K) 2 transition temperatures : T N = 30 K :frozen temperature and AF interchain coupling T C 200 K : appearance of ferro intra-chain interactions. Curie Temperature: θ P = 145 K F interactions along chains Curie Weiss law :µ(mes) = 4.17 µ B /fu combination of Co 2+,HS(S=3/2) and Ir 4+,LS(S=1/2) : µ(calc) = 4.24 µ B /fu

16 Pulsed field magnetization for Ca 3 CoIrO 6 2 M(µB/fu) M(µB/fu) K K M(µB/fu) M(µB/fu) K 77K M(µ B /fu) T = 4.2 K: no transition below 35 T T < 20 K: 2 transitions, Hc (transition 1 st magnetization 5 T more than Hc on cycle). Hc increases when T decreases Ferro ordering intra-chain and no Ferri state during magnetization reversal

17 Similarities and differences... χ'(emu.mol -1 ) χ"(emu.mol -1 ) f T(K) f 10 Hz 100 Hz 1000 Hz T(K) 10 Hz 100 Hz 1000 Hz AC-susceptibility in Sr 3 NiIrO 6 for f = 10, 100, 1000 Hz Fig. 4 Shift of T f with f given by K = Tf / (Tf logf) K is very high for these compounds -Ca 3 Co 2 O 6 = Sr 3 NiIrO 6 = Ca 3 CoIrO 6, Ca 3 CoRhO 6 = 0.10 superparamagnets K 0.3 spin glasses K 10-2 Very low spin dynamic on frozen state!!!

18 Compound c/a Magnetic state Ca 3 Co 2 O f-pda below T 2 (12K) Sr 3 NiIrO f-pda below T 2 (21K) Ca 3 CoRhO f-pda below T 2 (30K) Ca 3 CoIrO Glassy magnetic state below T 2 (30K) Niitaka et al, PRL 87, , (2003)