Multiferroic.pptx

MULTIFERROIC MATERIALS

SHRUTI K.J SANSKRITA M.TECH (IM) ROLL NO-185503

CONTENT  INTRODUCTION TO MULTIFERROICS

 HISTORY  TYPES OF MULTIFERROICS  Why are there so few magnetic ferroelectrics?

 PEROVSKITE STRUCTURE OF BIFEO3  SYNTHESIS  APPLICATION  FUTURE

MULTIFERROIC

MULTI

More than one

FERROIC

Ferromagnetic, ferroelectric, ferroelastic

Introduction to Multiferroics

FERROMAGNETIC MATERIAL

Materials that can be magnetized by an external magnetic field and remain magnetized after the external field is removed) are ferromagnetic

HYSTERESIS LOOP FOR FERROMAGNETIC MATERIALS

FERROELECTRIC MATERIAL Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field

HYSTERESIS LOOP FOR FERROELECTRIC MATERIALS

FERROELASTIC MATERIAL  Ferroelasticity is the mechanical equivalent

of ferroelectricity and ferromagnetism.  When stress is applied to a ferroelastic material, a phase change will occur .  This stress-induced phase change results in a spontaneous strain in the material.

TYPES OF MULTIFERROIC MATERIAL TYPE I

TYPE II

 Magnetism and FE exist

 Magnetism causes

independently  Weak coupling  Example BiFeO3 BiMnO3 PbVO3

Ferroelectricity vice versa  Strong coupling but net ferroelectric polarization is often very small  Example RMnO3(R = Tb,Tm,Yb, etc)

Why are there so few magnetic ferroelectrics?  The chemistries of ions that tend to be magnetic in solids are different  

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from those that tend to form electric dipoles. For an ion to carry a magnetic moment, its electrons must be arranged such that their magnetic moments do not cancel each other. The magnetic state tends to win the competition when the electrons are localized,which in solids occurs for transition metals with partially filled 3 d shells or lanthanides with partially filled 4 f shells covalent bonds between neighbouring cations and anions provide the stabilizing mechanism for the oppositely charged ions to shift toward each other and form a local dipole. Many ferroelectric materials are transition-metal oxides The ferroelectric state is favoredwhen the transition-metal cations have empty d orbitals. Oxygen ions can form stable dative bonds with such “ d 0 ” cations

Some common Multiferroic with their Tc, TN

THE FIRST MODERN MULTIFERROIC MATERIAL: BIFEO 3  BiFeO3 is the only material that is both magnetic and strong

ferroelectric at room temperature.  As a result, it had an impact on the field of multiferroics with hundreds of publications devoted to it in the past few years.

PEROVSKITE STRUCTUTE OF BiFeO3

PEROVSKITE STRUCTURE OF BIFEO3 1.Distorted Rhombohedral Structure 2. Point Group R3c 3. Perovskite type unit cell with arh =3.965Å and αrh=89.3° 4. Room temperature Polarization is along [111]

Electric-field control of magnetism in BiFeO 3

DOPING IN BIFEO3

Why Bi0.9La0.1Fe1-xCoxO3 ? where x=0, 0.03, 0.05, 0.07, 0.09

Effect of La doping 1. La doping contents indicate that it stabilize the structure of BiFeO3 while the mechanism for the stabilization of BiFeO3 by La doping is not known and also leakage current can be reduced at high applied fields by adding a small amount of La. 2. It was established that even a small fraction of rare-earth (La) additives significantly increases the magnetoelectric affects at room temperature

Effect of Co doping  The magnetic property of BiFeO3 are greatly enhanced due

to Co ions doping at Fe sites.  The undoped BiFeO3 was antiferromagnetic but with the subsitution of Co it becomes ferromagnetic.  Addition of Co improve significantly the ferromagnetic properties of bulk BiFeO3

HISTORY  P. Curie (1894)

Crystal could be ferroelectric and ferromagnetic simultaneously.  J. Valasek (1920) Discovered the switching in ferroelectrics.  Peter Debye (1926) Magnetoelectric (ME) effect.  Dzyaloshinsky (1959) True magnetoelectrically defined free energy was understood theoretically in Cr2O3 .  Astov (1960) Discovered magnetoelectric experimentally in Cr2O3 material.  H. Schmid (1994) Gives the name Multiferroic as the material possess two of the ferroic properties simultaneously.

SYNTHESIS OF MULTIFERROIC MATERIALS  solid state synthesis

 hydrothermal synthesis  sol-gel processing  vacuum based deposition

 Pulsed laser deposition

SOL–GEL SYNTHESIS OF MULTIFERROIC BIFEO3  A transparent multi-component solution was prepared by

mixing bismuth nitrate pentahydrate [Bi(NO3)3.5H2O](Aldrich), and iron nitrate nonahydrate [Fe(NO3)39H2O](Aldrich)  Bismuth nitrate pentahydrate (5 mol% excess) was dissolved at room temperature in the 2-methoxyethanol and acetic acid mixture. After the solution was transparent, it was mixed with iron nitrate nonahydrate by constant stirring at room temperature. The resultant solution was transparent, blackish red, and clear. The precursor solution was dried at 80 -C for about 12 h to obtain the BFO xerogel powder.

 Then the xerogel powder was grinded in an agate crucible,

and the powder was annealed at 600 -C for 30 min in air or N2 atmosphere in the furnace. During the annealing procedure, heating and cooling rates of the furnace were maintained at a rate of 4-C/min.

SEM microstructure of the pure BFO Rphase powder ceramics

APPLICATION OF MULTIFERROIC  Spintronics Devices (that includes a spin-based transistor)

 Information Storage Devices (magnetic tape, floppy disketc)  Spin Valve (device consisting of two or more conducting

magnetic materials, that alternate its electrical resistance)  Quantum Electromagnets (electromagnets are wire coils or loops, which tend to be bulky and difficult to fabricate)  Microelectronic Devices (MOSFETs, Bipolar Transistor etc)  Sensors (measures a physical quantity and converts it into a signal which can be read by an instrument

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