Magnetization switching without charge or spin currents J. Stöhr Sara Gamble and H. C. Siegmann, SLAC, Stanford A. Kashuba Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine

Switching with charge or spin currents Conventional H field pulses created by current flow through wires Time and amplitude limited by inductance laws and Joule heat in wires Switching with spin polarized currents has same problem

switching time limited by field strength H and spin-lattice relaxation time ~100 ps Today’s Switching Process 190 years of “Oersted switching”….

end of field pulse M Fastest H (B) Field Switching = Ballistic Switching Patent issued December 21, 2000: R. Allenspach, Ch. Back and H. C. Siegmann Relaxation into easy axis is governed by spin-lattice relaxation - but process is deterministic ! Precise timing for  =180 o reduces time

Beyond direct switching by magnetic fields ---- how about electric fields ? Stöhr et al., Appl. Phys. Lett. 94, (2009)

Magnetic field has same symmetry properties as magnetization - can switch magnetization - Electric Field is a time-even “polar vector” Magnetic Field is a time-odd “axial vector” Electric field cannot directly switch magnetization

E-fields can produce magnetic anisotropy axis magnetocrystalline anisotropy caused by anisotropic atomic positions “bonding fields” distort valence charge, create axis Ambiguity remains with respect to direction of M

The concept of the magnetic anisotropy field creates “direction” H E = 2KE2KE M cos   but…rotation of M limited to < 90 o after some time ……~ 100 ps M realigns along H E

Cannot rotate past 90 o – cannot “switch” Cannot switch through rotation of M into H E

Use Concept of Ballistic Switching – pulsed fields ballistic switching with H field pulse of length   100 ps This concept works with E fields, too !

Comparison of H and E field ballistic switching Imagine that E field can create H E fast

So what does it take to switch with E-field ? Strong enough E field to induce dominant anisotropy axis and field H E E field should be at angle  ~ 45 o to original easy axis Field pulse has to be fast (  < 100 ps) before M aligns with H E Process is completely determined by “write pulse” length  not by precession and damping time which may be slower

Two potential methods 1.Create new transient anisostropy axis in suitable multiferroic by E field pulse – optimum angle 45 o 2.Use strong E field pulse to distort atomic valence charge in any material E second order Stark effect ~ E 2 Field strength needs to be > 1 Volt / nm comparable to valence potential

thin Co film on Si wafer premagnetized Magnetic writing with SLAC Linac beam 100 fs - 5 ps 1nC or electrons J. Stöhr and H. C. Siegmann Magnetism: From Fundamentals to Nanoscale Dynamics Springer Series in Solid State Sciences 152

Experiment with ultrastrong fields electric field strength is up to 20 GV / m (2 V / Angstrom)

Magnetic pattern is severely distorted --- does not follow circular B-field symmetry Calculation of pattern with Landau-Lifshitz-Gilbert theory known magnetic properties of film, known length, strength, radial dependence of fields B-field only B-field and E-field

B-field torqueE-field torque Magneto-electronic anisotropy is strong ~ E or about 1000 times stronger than with previous 5 ps pulses

B field cancels, E 2 field does not cancel Use photon pulse instead of e-beam pulse E field only switching should be possible with THz photons

The End