Dear Stefan Ručman,

At this time, in our group research, We work on  Giant Magnetoresistance (GMR)  Sensor based on Thin Film Multilayer and Spin-Valve for Biosensor Applications. As far as I have read from some references, GMR is a  large change in electrical resistance in response to an external applied magnetic field.

If We back to the history of GMR, is purely born as an introduction of concept spin as an intrinsic property of electron  and combined with the presence of methods that can fabricate thin films in nanoscale  such as sputtering method.

The primary origin of GMR effect is related to Spin dependent scattering. Using Mott’s arguments, it is straightforward to explain GMR in magnetic systems. We assume that the scattering is strong for electrons with spin antiparallel to the magnetization direction and weak for electrons with spin parallel to the magnetization direction. This is supposed to reflect the asymmetry in the density of states at the Fermi level.

We can conclude that the way to measure the resistance of thin films and produce the magnetresistance (MR)  is related to the electron (include spin) is followed to our sample. In our group research, We conduct the MR effect by using Four Point Probe Method and Wheatstone Bridge Method.

In case using a scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level. The STM is based on the concept of quantum tunneling. When a conducting tip is brought very near to the surface to be examined, a bias (voltage difference) applied between the two can allow electrons to tunnel through the vacuum between them. The resulting tunneling current is a function of tip position, applied voltage, and the local density of states (LDOS) of the sample.Information is acquired by monitoring the current as the tip's position scans across the surface, and is usually displayed in image form.

In briefly speaking, We can say that STM doesn’t  work by the interaction of Spin and magnetization of the sample, but based on the concept of quantum tunneling, i.e. electrons behave as a wave.

Hopefully, it can help.

By the way, may I know the structure of your sample.

Cheers,

Indra Pardede.

I have different opinion. In principle, STM can do it after you have a spin-polarized tip, which is very sensitive to the surface spin at atomic scale. There has a lot of papers talking about spin-polarized STM. You google it. 

Hey Indra Pardede, thank you for answer, me too, I am developing concept of biosenzors (water pollutants detection), but STM/STS can be used for other measurments. not only imaging. What kind of nanoparticles layer you will use in your reserch?

Thank you Yang Wang, do you know price of that tip? and is it possible to do that on already existing STM? Do softer in that case need to be updated? or if you know a lab that have a such instrument?

Dear Stefan Ručman,

I am so sorry, I will try to learn and looking for the reference about GMR based on STM. At this time We are working on Biosensor using Magnetite Nanoparticles to detect some biological species such as bacteria, enzyme, alga etc.  For the thin films, We use Multilayer and spin-valve structure and data acquisition using FPPS and Wheatstone Bridge.  By the way, may I know the design of your experiment and kind of water pollutants that will be detected.

Cheers,

Indra Pardede.

Oh, very simular to me, except I use zerovalent iron and would use it for detection of heavy metals. Also I will use multilayers of doped polymers ( conductive polymers) and non-doped layers between them, something as diferent nanocomposites.

Making spin-polarised tip is tricky and I don't think there is such kind of commercial tip on market. Usually, people deposit Fe or Cr on W-tip, and the direction of spin at the end of the tip depends on the thickness of Fe or Cr film. You have to characterize the spin direction  on a well known system (like Cr(001) metal or Co/Au(111) surface) after the deposition.  R Wiesendanger's group have lots of excellent papers on this topic. You can follow them.

Over the last two decades a lot of experience has been collected on how to obtain STM tips capable of magnetic imaging. There is not one such recipe but many different ones, depending on the instrumental conditions you have available, and on the problem to be studied. In my paper Atomic-Scale Magnetism Studied by Spin-Polarized Scanning Tunneling Microscopy, published as a chapter in Fundamentals of Picoscience, ed. K. Sattler, CRC Press, I devoted a section on reviewing the various procedures of preparing magnetic STM tips (Note: some libraries provide access to the ebook version). By the way: you will have a hard time finding someone selling you such a tip. There is no market for it. Go ahead, find your own solution.

Are you refering to  this book? https://www.crcpress.com/Fundamentals-of-Picoscience/Sattler/9781466505094   I think my library have it. eighter way it looks like quite informative book (729pgs) ebook, is cheap, maybe I can buy it. Can STM be provide accurate data or it is advised to combine other techniques. ( VSM; NMR; SQUID; MRI; susceptibility metter..)

 Totally agree with Pietzsch.