1 / 18

Colossal Magnetoresistance of Me x Mn 1-x S (Me = Fe, Cr) Sulfides

Colossal Magnetoresistance of Me x Mn 1-x S (Me = Fe, Cr) Sulfides. G. A. Petrakovskii et al ., JETP Lett. 72 , 70 (2000) Y. Morimoto et al ., Nature 380 , 141 (1996). Shimizu-group HANZAWA Akinori. Contents. Introduction Colossal Magnetoresistance (CMR) LaMnO 3

idra
Download Presentation

Colossal Magnetoresistance of Me x Mn 1-x S (Me = Fe, Cr) Sulfides

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Colossal Magnetoresistance of MexMn1-xS (Me = Fe, Cr) Sulfides G. A. Petrakovskii et al., JETP Lett. 72, 70 (2000) Y. Morimoto et al., Nature 380, 141 (1996) Shimizu-group HANZAWA Akinori

  2. Contents • Introduction • Colossal Magnetoresistance (CMR) • LaMnO3 • MexMn1-xS (Me = Fe, Cr) • Motivation • Experimental method • Results and Discussion • Summary

  3. Colossal Magnetoresistance (CMR) • introduction There are 2 types of CMR. At hard disk, Fringing field (漏れ磁場) is very low, so disk head must be magnetic-field-sensitive. • On applied external magnetic field for sample, electrical resistance noticeably increase. • On applied external magnetic field for sample and doped hole, electrical resistance noticeably decrease and phase change from paramagnetic to ferromagnetic. At this paper, they focus on this CMR.

  4. LaMnO3 • introduction Manganese oxides with the cubic perovskite structure. • Crystal structure Perovskite structure • electron state 3d4 (Mn3+) eg electrons are strongly hybridized with the oxygen 2p states, so eg electrons are conduction electron. t2g electrons can be viewed as localized spins with S=3/2. energy state of 3d electron of Mn3+

  5. LaMnO3 • introduction LaMnO3 is Mott insulator. Mott Insulator：Spins are alternately up and down. When coulomb repulsion for two electrons in a Mn is large, Electrons cannot move freely. Antiferromagnetic insulator Carriers are doped in eg orbital. Substitute divalent(2価) cation (Sr2+, Ca2+ etc.) for trivalent(3価) cation (La3+) Electrical conduction is provided. For example,La1-xSrxMnO3 doped cation Mn3+ and Mn4+are present by doping cation.

  6. La1-xSrxMnO3 • introduction • Double-exchange interaction Spins are paralleled in different orbital by Hund’s rule. eg electron can transfer to Mn4+,because energy is not changed if any eg electron is exist which site. (a) t2g electrons (localized spins) are paralleled : (b) t2g electrons (localized spins) are antiparalleled : eg electron cannot transfer to Mn4+,because to transfer results in a loss of energy of Hund’s rule. Paralleled t2g electrons work ferromagnetic interaction. This is double-exchange interaction.

  7. La1-xSrxMnO3 • introduction t2g spins are leant. The formula of transfer integral (t) is this. External magnetic field aligns the t2g spins and reduces the carrier scattering by the local spins. ferromagnetic phase is stabilized for high temperature. ※A steep rise of the magnetization observed around 130 K. T dependence of resistivity for single crystal of (LaxSr1-x)3Mn2O7. The resistivity with the current parallel (rab) and perpendicular (rc). Tc : The critical ferromagnetic transition temperature

  8. MexMn1-xS (Me = Fe, Cr) • introduction S Manganese sulfides with the rock salt structure. • Crystal structure Mn Rock salt structure (NaCl structure) Mn2+ ions are in the octahedral position s of the sulfur cubic lattice. MnS (not doping) is Mott insulator. The features of MexMn1-xS It increases electron orbital overlap. • O → S : • NaCl structure : Rock salt structure is core of Perovskite structure.

  9. Motivation • introduction • To observe Colossal magnetoresistance of non-perovskite MexMn1-xS (Me = Fe, Cr) • To observe magnetic order of MexMn1-xS (Me = Fe, Cr)

  10. Experimental method • sample : MexMn1-xS (Me = Fe, Cr) ← polycrystal x of Fe is 0.29. x of Cr is 0.5 • measurement ・X-ray structural analysis : monochromatic Cu Ka radiation Temperature range 100~300 K ・Electrical resistance measurement : Temperature range 4.2~300 K Magnetic field H = 0, 2, 10, 30, and 50 kOe ・Magnetic properties : measured on vibrating-coil magnetometer with superconducting solenoid at 30 kOe Temperature range 77~300 K ※10 kOe = 1 T

  11. Result Fe0.29Mn0.71S According to X-ray data, the Fe0.29Mn0.71S undergoes a structural transition at Ts ~ 147 K. Similar transition is observed in MnS. Rhombohedral distortion The lattice parameter is independent of temperature at 120~140 K. Lattice distortion is occurred. The conduction in the samples is of the semiconductor type with thermal hysteresis. Temperature-dependent (a) lattice parameter, (b) magnetization, and (c) resistivity of Fe0.29Mn0.71S

  12. Result Fe0.29Mn0.71S At 30 kOe, the negative magnetoresistance dH reaches -450 % at ~50 K. At 50 kOe, this value is -87 %. Temperature curves for the magnetoresistance dH of Fe0.29Mn0.71S at 10, 30, and 50 kOe. It’s found that FexMn1-xS have a colossal magnetoresistance .

  13. Result Cr0.5Mn0.5S This sulfide undergoes the antiferromagnet-ferromagnet transition at 66K. The nature is caused by Jahn-Teller effect. At 30 kOe, the negative magnetoresistance dH reaches -25 % at ~4.2 K. The transition to the negative magnetoresistance occurs in the range of magnetic transition. Temperature curves for the magnetization (a) and magnetoresistance (b) of Cr0.5Mn0.5S at 30 kOe. It’s same behavior of La1-xSrxMnO3 It’s found that CrxMn1-xS have a colossal magnetoresistance .

  14. Discussion Electrical and magnetic properties of MexMn1-xS are similar to those observed for La1-xSrxMnO3. • analogous point ① the cubic lattice is distorted in the range of appeared CMR. ② LaMnO3 and MnS (not doping) are Mott insulator. ③ AF semiconductor-FM metal are produced in cation-substituted LaMnO3 ( or MnS). The regions of antiferromagnetic semiconductor and ferromagnetic metal coexist. (by Mössbauer data) G.V. Loseva et al., Phys, Solid States 25, 2142 (1983) But, the mechanism of CMR effect still remains to be clarified.

  15. Summary • Colossal magnetoresistance is observed in non-perovskite MexMn1-xS (Me = Fe, Cr). • This MexMn1-xS sample has little data. So, this sample must be given results and should be understood the magnetism mechanisms.

  16. My study MexMn1-xS The less interspace of octahedral structure, the more increase electron transfer. MexMn1-xS (Me = Fe, Cr) may appear metallic state. One way is ion substitution. Other way ? • apply hydrostatic pressure For FexMn1-xS, x = 0.29 is critical concentration of metal transition. FexMn1-xS which its concentration is no more than x = 0.29 apply hydrostatic pressure, the sample appear metallic state. I anticipate that CMR will be observed in MexMn1-xS (Me = Fe, Cr) by pressure.

More Related