JiunnYuan Lin Institute of Physics National Chiao Tung

Jiunn-Yuan Lin 林俊源 Institute of Physics 交大物理所 National Chiao Tung University

Contents Introduction to magnetism Introduction to superconductivity The best way of measuring the magnetic moment-SQUID! Specification of MPMS

Fundamentals of magnetism Diamagnetism Paramagnetism Ferromagnetism Antiferromagnetism

Diamagnetism Due to Faraday’s law

Paramagnetism

Ferromagnetism

Antiferromagnetism

Hysteresis

Magnetic domains To minimized the magnetostatic energy

Magnetic Force Microscope (MFM)

Introduction to superconductivity

The Race to Beat Cuprates? Hg - cuprate TI - cuprate ？ YBCO Fe-based superconductors Cuprates LSCO Mg. B 2 Nb 3 Ge Metallic alloys e-doped Sm. OFe. As e-doped La. OFe. P 70 The crusade of Room Temperature superconductors?

Josephson effect (1962) The electronic superconductors applications of

Speed(sec/gate) Thermal limit Quantum limit SC device Power consumption Speed & power consumption of SFQ device

SQUID

The SQUID Within a year of Brian Josephson’s discovery, the first Superconducting Quantum Interference Device (SQUID) was built In 1968, Professor John Wheatley of UCSD and four other international physicists founded S. H. E. Corp. (Superconducting Helium Electronics) to commercialize this new technology.

SQUID Magnetometers The first SQUID magnetometer was developed by Mike Simmonds, Ph. D. and Ron Sager, Ph. D. while at S. H. E. Corporation in 1976. In 1982, Mike and Ron, along with two other SHE employees, founded Quantum Design. In 1984, QD began to market the next generation SQUID magnetometer – the Magnetic Property Measurement System (MPMS). In 1996, QD introduced the MPMS XL as the latest generation SQUID magnetometer During the past 22 years, six companies have unsuccessfully designed and marketed SQUID magnetometers to compete with the MPMS.

MPMS XL Ever. Cool™ System

MPMS XL Temperature Control Patented dual impedance design allows continuous operation below 4. 2 K Sample tube thermometry improves temperature accuracy and control Transition through 4. 2 K requires no He reservoir refilling and recycling (no pot fills) Temperature sweep mode allows measurements while sweeping temperature at user controlled rate Increases measurement speed Smooth temperature transitions through 4. 2 K both cooling and warming

MPMS XL Temperature Control

MPMS XL Temperature Control

MPMS XL Temperature Control Temperature Range: 1. 9 - 400 K (800 K with optional oven) Operation Below 4. 2 K: Continuous Temperature Stability: ± 0. 5% Sweep Rate Range: 0. 01 - 10 K/min with smooth transitions through 4. 2 K Temperature Calibration ± 0. 5% typical Accuracy: Number of Thermometers: 2 (one at bottom of sample tube; one at the location of sample measurements)

Magnetic Field Control Very high homogeneity magnets (1, 5 and 7 Tesla) 0. 01% uniformity over 4 cm Magnets can be operated in persistent or driven mode Hysteresis mode allows faster hysteresis loop measurements Magnets have two operating resolutions: standard and high resolution

Hysteresis Measurement

Reciprocating Sample Measurement System (RSO) Improved measurement sensitivity Increased measurement speed No waiting for the SQUID to stabilize Very fast hysteresis loops up to 8 x faster than conventional MPMS Servo motor powered sample transport allows precision oscillating sample motion High precision data acquisition electronics includes a digital signal processor (DSP) SQUID signal phase locked to sample motion Improved signal-to-noise ration Low thermal expansion sample rods with sample centering feature

Reciprocating Sample Measurement System (RSO)

RSO Data The DC scan took 56 hours to take 960 points The RSO scan took 1600 points in under 24 hours! The RSO scan avoids subjecting the sample to field inhomogeneities that effected the DC scan.

Hysteresis Mode Data This measurement takes ~ 3. 5 hours in persistent mode

Reciprocating Sample Measurement System (RSO) Frequency Range: Oscillation Amplitude: Relative Sensitivity: Dynamic range 0. 5 - 4 Hz 0. 5 - 50 mm < 1 x 10 -8 emu; H 2, 500 Oe, T = 100 K(for 7 -tesla magnet) 6 x 10 -7 emu; H @ 7 tesla, T = 100 K (for 7 -tesla magnet) 10 -8 to 5 emu (300 emu with Extended Dynamic Range option)

MPMS System Options Transverse Moment Detection for examining anisotropic effects Second SQUID detection system SQUID AC Susceptibility 2 x 10 -8 emu sensitivity 0. 1 Hz to 1 k. Hz Ultra-Low Field Reduce remanent magnet field to ± 0. 05 Oe Extended Dynamic Range Vertical and Horizontal External Device Control user instruments with the MPMS 10 k. Bar Pressure Cell Sample Space Oven Temperatures to 800 K Environmental Magnetic Shields Fiber Optic Sample Holder Allows sample excitation with light Manual Insertion Utility Probe Perform elector-transport measurements in MPMS Measure moments to ± 300 emu Sample Rotators Liquid Nitrogen Shielded Dewar Ever. Cool Cryocooled Dewar No-Loss liquid helium dewar No helium transfers

SQUID AC Susceptibility Dynamic measurement of sample Looks also at the resistance and conductance Can be more sensitive the DC measurement Measures Real ( ) and Imaginary ( ) components is the resistance of the sample is the conductive part Proportional to the energy dissipation in the sample Must resolve components of sample moment that is out of phase with the applied AC field SQUID is the best for this because it offers a signal response that is virtually flat from 0. 01 Hz to 1 k. Hz Available on all MPMS XL systems Requires system to be returned to factory for upgrade

SQUID AC Susceptibility Features Programmable Waveform Synthesizer and high-speed Analog-to -Digital converter AC susceptibility measured automatically and can be done in combination with the DC measurement Determination of both real and imaginary components of the sample’s susceptibility Frequency independent sensitivity Specifications Sensitivity (0. 1 Hz to 1 k. Hz): 2 x 10 -8 emu @ 0 Tesla 1 x 10 -7 emu @ 7 Tesla AC Frequency Range: AC Field Range: DC Applied Field: 0. 01 Hz to 1 k. Hz 0. 0001 to 3 Oe (system dependent) ± 0. 1 to 70 k. Oe (system dependent)

SQUID AC Susceptibility

Ultra-Low Field Capability Actively cancels remanent field in all MPMS superconducting magnets Sample space fields as low as ± 0. 1 Oe achievable Custom-designed fluxgate magnetometer supplied Includes Magnet Reset Requires the Environmental Magnet Shield

Hysteresis measurement

Extended Dynamic Range Extends the maximum measurable moment from ± 5 emu to ± 300 emu (10 orders of magnitude) Automatically selected when needed in measurement Effective on both longitudinal and transverse SQUID systems

Sample Space Oven Provides high temperature measurement capability Ambient to 800 K Easily installed and removed by the user when needed A minimal increase in helium usage Approximately 0. 1 liters liquid helium/hour 3. 5 mm diameter sample space

MPMS Horizontal Rotator Automatically rotates sample about a horizontal axis during magnetic measurement 360 degrees of rotation; 0. 1 degree steps Sample platform is 1. 6 X 5. 8 Diamagnetic background signal of 10 -3 emu at 5 tesla

Manual Insertion Utility Probe Perform electro-transport measurement in the MPMS sample space 10 -pin connector Use with External Device Control (EDC) for controlling external devices (e. g. , voltmeter and current source) Creates fully automated electro-transport measurement system

External Device Control Allows control and data read back from third party electronics Allows custom control of MPMS electronics Use with Manual Insertion Utility Probe for automated electro-transport measurements MPMS Multi. Vu version written in Borland’s Delphi (Visual Pascal) programming language

Fiber Optic Sample Holder Allows sample to be illuminated by an external light source while making magnetic measurements Optimized for near UV spectrum (180 to 700 nm) Includes 2 -meter fiber optic bundle Sample bucket 1. 6 mm diameter and 1. 6 mm deep SMA connector Slide seal Fiber optic bundle