magnetoresistance

1. Magnetoresistance
Intorduction
Types
Colossal Magnetoresistance
Manganites
Mechanisms
Few samples discussions
-P.Anusha

2. Magnetoresistance
 ''Magnetoresistance is the tendency of a material
(preferably ferromagnetic) to change the value of
its electrical resistance in an externally-applied
magnetic field.''
 Magnetoresistance (MR) %:
 MR% =

(H) - (H=0)
(H=0)
 x100
(H) - (H=0)
(H=0)
 x100
 MR% =

3. Technological interest
 The global market for nonmagnetic materials and devices will
rise at an AAGR(Average Annual Growth Rate) of 22.6% from
$4.3 billion in 2004 to $12 billion in 2009
 Information stoarage application account for the vast
majority,over 90% and will continue to dominate.

4. Technological interest
 The global market for nonmagnetic materials and devices will
rise at an AAGR(Average Annual Growth Rate) of 22.6% from
$4.3 billion in 2004 to $12 billion in 2009
 Information stoarage application account for the vast
majority,over 90% and will continue to dominate.

5. Magnetoresistance depends upon the strength
and relative orientation of the magnetic field
withrespect to the current.
There are different types of MR:
1.Ordinary MR (OMR)
2.Anisotropic MR (AMR)
3.Giant MR (GMR)
4.Colossal MR (CMR)
5.Tunnelling MR (TMR)
6. Ballistic MR (BMR), etc.

6. Magnetization Vs.
Resistivity
1.Conductive phase :
 external applied magnetic field

 magnetic order
2.Insulating phase :
 high temperatures
 paramagnetic phase

7. 
Significance of Colossoal
Magnetoreistance
In present days science based society largely depends
on several gadgets where magnetic field sensors play
crucial role. The primary requirement for
magnetoresistive sensor is the large magnetoresistance.
Perovskite manganites was in the fore-front of the
experimental research and resulted several thousand
research articles with the primary focus on large
magnetoresistance (MR).

8. Technological
applications:
Magnetic storage technology :
MR materials have been used
for years in reading-heads
of hard disks
Future spintronic devices :
Spin-driven electronic
devices :
spin-valves
spin-injectors
tunnel junctions

9. Colossal Magnetoresistance
 Colossal magnetoresistance is a property of some
materials, mostly manganese-based perovskite
oxides, that enables them to dramatically change
their electrical resistance(by orders of magnitude) in
the presence of external magnetic field.
 Colossal magnetoresistance has recently been
discovered in Lal-xMxMn03+8 (M = Ca, Sr)
 perovskite structures. The largest effects have been
observed for x=O.33.

10. The resistivity of the material undergoes a low
temperature transition from an insulating to a
metallic behavior.
The colossal magnetoresistance effect is
observed in the metallicregime.

Recent research has shown that the insulating to
metal transition and CMR effect can beraised up
to room temperature.

11. Manganites
Theory

12. Doped manganites
 Chemical Formula
A1-x Bx MnO3
A = Trivalent rare earth elements(LaNd,Sm,Y,Tb,Eu,..)
B = Divalent alkaline earth ions(Sr,Ca,Ba,..)
The CMR materials have the perovskite structure
A = La3+, Y3+…
B = Sr2+, Ca2+…
Mn3
+
Mn4+
A1-x Bx MnO3

13. The Mn in the MnO planes are aligned
ferromagnetically within the a-b plane, with planes
along the c axis aligning in an antiferromagnetic
order.
The application of a field switches the ordering
ofthe Mn ions along the e axis, so that all ofthe Mn
ions are magnetized in the same direction.
Application of a magnetic field most likely
increases the alignment ofthe spins, and
decreases the resistivity.

14. CMR Materials

15. 21 Sc Scandium
39 Y Yttrium
57 La Lanthanum
58 Ce Cerium
59 Pr Praseodymium
60 Nd Neodymium
61 Pm Promethium
62 Sm Samarium
63 Eu Europium
64 Gd Gadolinium
65 Tb Terbium
66 Dy Dysprosium
67 Ho Holmium
68 Er Erbium
69 Tm Thulium
70 Yb Ytterbium
71 Lu Lutetium
beryllium (Be)
magnesium (Mg)
calcium (Ca)
strontium (Sr)
barium (Ba)
radium (Ra)
Divalent
Alkalline
Trivalent Rare Earth
Elements

16. Local structure and magneto-transport
properties
 Magneto transport
Magnetic
transition (TC)
Metal-to-Insulator
transition (TMI)
Structural
transition (TS)
(TC TMI TS)
paramagnetic
insulating
enhanced distortion
ferromagnetic
conductive
reduced distortion

17. Temperature Vs Doping
Doped manganites have complex
phase diagram.
FM = FerroMagnetic
AF = AntiFerromagnetic
CAF = Canted AF
FI = FM Insulator
CO = Charge Ordered
FM-MR
conductiv
e
phase
LaMnO
3
CaMnO3

18. Superexchange

19. Double exchange Mechanism

21. Double Exchange mechanism :LaSrMNO3

22. Jahn-Teller distortion
 In the electronically degenerate state, the orbitals
are said to be asymmetrically occupied and get more
energy. Therefore the system tries to get rid of this
extra energy by lowering the overall symmetry of
the molecule i.e., undergoing distortion, which is
otherwise known as Jahn Teller distortion.

23. Enhanced CMagnetoresistance?
 The primary requirement for magnetoresistive
sensor is the large magnetoresistance.
 Last two decades perovskite manganites was in the
fore-front of the experimental research,in
manganites most of the cases large
magnetoresistance occurs at very high (several
tesla or more) magnetic field.
 Achieving the significant enhancement of the same
material even at the lower magnetic field and at
room temerature is the main objective of our
research.

24. Doped Manganite samples
Among the manganite families
La1−xCaxMnO3 (LCMO) is very well known
compound. According to its phase diagram, this
compound shows rich physical properties depending
on the ‘Ca’ doping concentration 'x'.
For lower doping concentration (0.2< x < 0.5), the
ferromagnetic ground state is observed.
Whereas in the doping region 0.5 < x < 0.87 the
ground state of the LCMO shows the charge-ordered
antiferromagnetic nature with lowering the
temperature.

25. Most of the recent work has focused on Ca- and Sr-
substituted compounds( La1−xSrxMnO3, and the CMR
trends in encountered as a function of divalent ion
concentration, x, are observed for both dopant types.

Substitution on the La site modifies the phase behaviour
through size effects for (Nd1−ySmy )0.5Sr0.5MnO3 .
This compound exhibits an instability towards either the
FM ground state (y = 0.875, TC = 110 K) or a high-ρ,low-
M (y = 0, Tins = 160) state, most likely either charge
ordered or antiferromagnetic (or both). Similar behaviour
is also found in Pr0.5Sr0.5MnO3 [10] and Pr0.7(Sr,
Ca)0.3MnO3−
Sr Doping

26. Ca Doping
 It is similar to that for Sr doping, especially in the
 region for x < 0.5. For 0.2 <x< 0.5.
 For x > 0.5, a well defined critical line with
maximum around T ≈ 270 K is seen in the TC–x
plane (figure 5(b)). This phase boundary defines the
CO transition which is directly seen by TEM.
 Charge order is also seen in La1−xCaxMnO3 for x ≈
0.51.

27. Ba doping
 The series La(2−x)/3Ba(1+x)/3Mn1−xCuxO3 for which the end members of
the series are the ferromagnetic La2/3Ba1/3MnO3 and the superconducting
La1/3Ba2/3CuO7−δ . In the Mnrich region, the perovskite phase is found for
x < 0.4.


28. Doped Manganite samples
CMR in hole doped LaMnO3
In hole-doped rare earth manganite compounds, the
colossalmagnetoresistance (CMR) peaks at a transition
from a hightemperature(T) insulating paramagnetic
phase to a low-T conducting
ferromagnetic phase.

29. The combinations
 La0.67Ca0.33MnO31x Al2O3 ~with x50%,5,5%,
8%, 15%, and 25% in volume.
The low temperature
value (T577 K) is increased nearly three times by
adding
8% of alumina to pure LCMO

30. MR vs. T -plots of rare earth doped LBMO
manganites at 5 T magnetic field.
Fig shows the variation of MR%
vs. temperature at H=¼5 T for all
the samples. As the temperature
is decreased from 300 K, MR%
values of all the samples are
found to increase upto their metal
insulator transition temperature
and remain almost constant on
further decrease of temperature.
With decreasing ionic radius,
MR% values are increasing,
exhibiting a maximum value of
96% for Gadolinium doped
sample which may be exploited
for magnetic sensor applications
at low temperatures.

31. An extraordinarily large magnetoresistance (MR)
has been achieved in La0.7Ca0.3MnO3 by
optimal substitution.
A large MR has been observed in optimally doped
(La0.5Y0.5)0.7Ca0.3MnO3 (x = 0.5). In this compound,
an MR value as high as 1.5 × 10pow 7 % at a
temperature of 50 K and 3.6 × 104% at 80 K has been
achieved for an external magnetic field of 90 kOe.
Moreover at 80 K, for the x = 0.5 compound, the MR is
reversible in nature.

33.  Since mid-1990s, an enormous amount of
 work has been devoted to the manganites after the discovery of
the so-called CMRin manganites (e.g., up to 127000% in
La2/3Ca1/3MnO3 thin film at 77 K and 6 T)
 Phase separation in a wide temperature range is observed in
La0.7Ca0.3MnO3. Single films where the metallic and insulating
areas are strongly temperature and magnetic field
dependent.The similar phase separation phenomena were also
found in Pr0.5Sr0.5MnO3,
 Pr1-xCaxMnO3,
 Nd1-xSrxMnO3,
 La0.45Sr0.55MnO3-δ.
In La0.67Ca0.33Mn1−xGaxO3(x=0.0,0.02,0.05,0.1)-large
variation of the resistivity coefficient B and the polaronactivation
energy Ea with Ga doping was found.

34. La0.7Sr0.3MnO3 (LSMO)
manganite, that is robust ferromagnet, showing
the highest Curie
temperature among manganites. in the
La0.7Sr0.3MnO3
(LSMO), the sharp drop of the electric resistance
around room temperature together with
the occurrence of a metallic phase with a fully
spin-polarized conduction band

35. The colossal magnetoresistive (CMR) manganites have the perovskitic structure.
The generalformula was identied by Jonker and van Santen [7] as ABO3, where
A is a trivalent rareearth (La, P r, N d) ion and B is a trivalent Mn ion. The
susbtitution of the rare earth witha divalent alkaline (Sr, Ca, Ba) ion (doping)
determines a mixed valence Mn3+ − Mn4+state. Fig.illustrates the structure of a
LSMO compound, where the trivalent La3+1−xanddivalent Sr2+x
ions are located at the corners of the unit perovskite cell (A site), the oxygen
ions occupy the center of the faces in the unit cell, and the smallest Mn3+1−x
and Mn4+xionsare in the center of the octahedral oxygen ions (B site).

36. Metal-Insulator Transition
The doping x in LSMO manganite controls the
number of carriers, actually holes, at the Fermi
level. At the optimal doping (x = 0.3) the LSMO is
a robust ferromagnet with Curie temperature TC
well above room temperature. It exhibits a
transition from the high temperature paramagnetic
(P) semi-conducting or insulating (I) phase to the
low temperature ferromagnetic metallic (FM )
phase. The phase diagram of the La1−xSrxMnO.

37. Thank You.
-
Dr.M.Sreenath Reddy Sir
Dr.Y.Kalyana Laksmi Mam