THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center Quantum Design PPMS T: 350mK K H: T Transport facilities magnetoresistance hall effect impedance spectroscopy tunneling spectroscopy: inelastic tunneling spectroscopy (IETS) spin polarization (Meservey-Tedrow) Radiant ferroelectric tester custom electronics I(V,T) dI/dV(V,T) d 2 I/dV 2 (V,T) Z(ω,θ,H,T)

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center Examples... Magnetoresistance I(V) dI/dV (V)

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center thin film SC in a field (~2-3T) Zeeman split quasiparticle DOS dI/dV ~ N sc N fm asymmetry = spin polarization robust, microscopic theory “directly” gives spin imbalance of tunneling current Meservey-Tedrow tunneling

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center Co / Al 2 O 3 / Al spin polarization of Co films onset of ferromagnetism: Ni on Bi Examples...

The University of Alabama Inelastic Tunneling Spectroscopy (IETS) tunneling electrons excite vibrational modes –see Raman & IR modes –no strong selection rules tells us –the molecule is still there –it participates in transport when eV ≥ hv –stepped increase in dI/dV –new set of final states available example: studying model catalysts –CO on Rh/Al 2 O 3 -- CO vibrations “tunneling energy loss spectroscopy” detail: tiny signals … challenging d 2 I/dV 2 dI/dV V hv V Lambe & Jaklevic, Phys. Rev. 165, 821 (1968)

The University of Alabama IETS: we really have transport through the molecule, it is intact Al/Al 2 O 3 /X-benzoic acid/Co, T = 2K

The University of Alabama ν: stretch β: in-plane bend γ: out-of-plane bend indexing - compare with ATR-FTIR aromatic is intact chemisorbed benzoate ion absence of C=O, presence of COO -

The University of Alabama Al/Al 2 O 3 /4-iodobenzoic/Co IETS ATR-FTIR But … what is the state of the I substituent? aromatic-halogen modes insensitive probe with XPS

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center Impedance spectroscopy of thin films

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center How? apply ac voltage, measure current & phase gives Z(ω) model system with an equivalent circuit each component physically meaningful probing dielectric/spectral function ac lock-in techniques or ‘impedance analyzer’ complementary: dI/dV vs V at fixed freq

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center physical realizations lossy capacitor tunnel junction imperfect dielectric cell walls, to an extent electrochemistry...

impedance spectroscopy magneto-dielectric measurements

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center Example: MgO-MTJ high-frequency operation for MRAM, reader MTJ is like a capacitor too... what is C doing? significant magnetocapacitance.../CoFeB/MgO/CoFeB... via Anelva

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center Bi 2 NiMnO 6 –La 2 NiMnO 6 superlattices magnetodielectric materials strongly T-dependent capacitance ‘lossy’ near FM Curie temp coupling of FM and dielectric order!

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center near transition temperature, strong variation of dielectric constant with magnetic field fluctuations in electric & magnetic dipole ordering interface-induced stress changes in dielectric constant correlate with magnetization

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center VO 2 metal-insulator transition still poorly-explained metal-insulator transition percolation of metallic regions? impedance spectra should help...

THE UNIVERSITY OF ALABAMA CENTER FOR MATERIALS FOR INFORMATION TECHNOLOGY An NSF Science and Engineering Center capacitance vanishes at M-I transition resistance drops ‘leaky’ capacitor model percolation of metallic regions? ‘dielectric’ changes little below transition

The University of Alabama Center for Materials for Information Technology P. LeClair Toshali Sands, Puri, 8 Jan 2009 How to measure a derivative? drive system with V dc +  V ac sin  t measure response at  or  frequency / phase sensitive technique … lock-in amplifiers … a lot of electronics

The University of Alabama Center for Materials for Information Technology P. LeClair Toshali Sands, Puri, 8 Jan 2009 How to measure a derivative?