Dr. Anna Semisalova | Institute of Ion Beam Physics and Materials Research | www.hzdr.de 17-22 Sept. 2017, Bad Honnef, Germany Magnetoresistance effects Anna S. Semisalova Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Germany Lomonosov Moscow State University, Faculty of Physics, Russia Bad Honnef Physics School on Magnetism: From Fundamentals to Spin based Nanotechnology
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Magnetoresistance effects · Magnetoresistance effects Anna S. Semisalova Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Germany Lomonosov
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Dr. Anna Semisalova | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
17-22 Sept. 2017, Bad Honnef, Germany
Magnetoresistance effects
Anna S. Semisalova
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Germany
Lomonosov Moscow State University, Faculty of Physics, Russia
Bad Honnef Physics School on
Magnetism: From Fundamentals to Spin based Nanotechnology
Member of the Helmholtz AssociationPage 2
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Institute of Ion Beam Physics and Materials Research, HZDR
Member of the Helmholtz AssociationPage 3
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Spintronics
(also known as spin-electronics, magneto-electronics)
Electron = charge + spin
Idea: to use the spin in the
electronic devices
• Novel functionalities
• Higher speed
• Faster performance
• Lower power consumption
• …
Control,
Manipulation, and
Detection of spin state
Member of the Helmholtz AssociationPage 4
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Spintronics/nanomagnetism
Spintronicsapplications
Sensors
Magnetic recording
MRAM
Memristor applications
STT microwave devices
(oscillators)
Member of the Helmholtz AssociationPage 5
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
What is Magnetoresistance?
Change of electrical resistivity of the material under the application of
magnetic field
∆𝑅
𝑅% =
𝑅 𝐻 − 𝑅(0)
𝑅(0)∙ 100
MR ratio:
Magneroresistance converts magnetic signal
into electrical signal
MR ratio at RT & at low H (~1 mT) is important for device applications
From: S. Yuasa, IEEE Distinguished Lecturer
Member of the Helmholtz AssociationPage 6
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Outline
0. Positive and negative magnetoresistance in metals
1. Anisotropic magnetoresistance – AMR
2. Giant magnetoresistance – GMR
Spin valve
GMR for hard disk drivers
3. Tunneling magnetoresistance - TMR
4. Magnetic Random Access Memory – MRAM
Amorphous vs. Epitaxial tunnel barrier
5. New twist - Magnetoresistance in antiferromagnets
Member of the Helmholtz AssociationPage 7
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Positive magnetoresistance effect – old good one
The force on an electron:
Ԧ𝐹 = 𝑚𝑑 Ԧ𝑣
𝑑𝑡= 𝑒𝐸 + 𝑒 Ԧ𝑣 × 𝐵
Kohler’s rule
∆𝜌
𝜌= 𝜔𝑐𝜏
2 =𝑒𝐵
𝑚𝜏
2
=𝑛𝑒2𝜏
𝑚
1
𝑛𝑒𝐵
2
∆𝝆
𝝆=
𝑹𝑯
𝝆
𝟐
𝑩𝟐 ∝𝑩
𝝆
𝟐
Change of carrier trajectory due to
Lorentz force
increase of carrier path (curling of
path)
increase of scattering events and
resistance
Member of the Helmholtz AssociationPage 8
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Negative magnetoresistance effect - introduction
Resistivity normalized to their values at TC of Ni, 631 K (from Gerritsen (1956))
Resistivity of ferromagnet:
𝜌𝑝𝑎𝑟𝑎 - const at T>TC
𝜌𝑓𝑒𝑟𝑟𝑜 ≈ 𝜌𝑝𝑎𝑟𝑎 1 −𝑀𝑠(𝑇)
𝑀𝑠(0)
2
Member of the Helmholtz AssociationPage 9
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Negative magnetoresistance effect - introduction
Resistivity of ferromagnet:
𝜌𝑝𝑎𝑟𝑎 - const at T>TC
𝜌𝑓𝑒𝑟𝑟𝑜 ≈ 𝜌𝑝𝑎𝑟𝑎 1 −𝑀𝑠(𝑇)
𝑀𝑠(0)
2
~1-m2(T)
Member of the Helmholtz AssociationPage 10
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Spin disorder resistivity
Resistance decreases, if magnetic field is applied,
due to splitting of d-band for majority - and minority
spin
Less scattering of s-electrons into d-band → higher
mobility
Above TC: Scattering ofboth spin orientations ofs-electrons into empty d-states possible
Below TC: No scatteringof s-electrons into emptyd-states for majority spins larger mean free path smaller resistance resistance increaseswhen approaching TC
(spin-disorder increases)
Member of the Helmholtz AssociationPage 11
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Negative magnetoresistance
External magnetic field suppresses spin-disorder and produces relative
shift of spin-subbands, similar to (but much weaker than) exchange field
negative contribution
Member of the Helmholtz AssociationPage 12
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Outline
0. Positive and negative magnetoresistance in metals
1. Anisotropic magnetoresistance – AMR
2. Giant magnetoresistance – GMR
Spin valve
GMR for hard disk drivers
3. Tunneling magnetoresistance - TMR
4. Magnetic Random Access Memory – MRAM
Amorphous vs. Epitaxial tunnel barrier
5. New twist - Magnetoresistance in antiferromagnets
Member of the Helmholtz AssociationPage 13
Dr. Anna Semisalova | HZDR | Institute of Ion Beam Physics and Materials Research | www.hzdr.de
Magnetoresistance for data storage technologies
Yuasa & Djayaprawira J. Phys. D: Appl. Phys (2007)