Nanomagnatism- A Big "Draw"

The study of magnetism on the nanoscale is a hot topic for technologists hoping to create new materials for use in super-miniaturized electronic devices. But according to BIU alumna Dr. Beena Kalisky – a new faculty member in the Institute of Nanotechnology and Advanced Materials (BINA) who recently returned to Israel after completing postdoctoral research at Stanford University – another cool thing about nanomagnets is their potential for use in medicine. And that’s something that this brainy recruit – who usually focuses on the nanoscience underlying the properties of advanced materials – enjoys putting her mind to.

“My colleagues at Stanford achieved significant improvement in the medical imaging of brain tumors by injecting the tumor tissue with magnetic bacteria – organisms that take in iron from the environment, which they use to grow a chain of magnetic particles that helps their bodies align with the earth’s magnetic field,” she says. “I’m currently characterizing individual magnetic bacteria, to understand exactly how their presence makes MRI imaging more effective.”

Kalisky’s research is based around an extraordinarily sensitive microscopy system known as SQUID (Superconducting QUantum Interference Device), which can characterize magnetic field strength of less than a hundred electrons.  Kalisky plans to use SQUID technology to characterize the properties of individual nanomagnets. “Whatever the nature of the material, there is a technical problem in measuring nano-sized samples: to accumulate a detectible signal using conventional techniques, we need to average the magnetic properties of millions of particles together. But the magnetic properties of nanomagnets are inherently sensitive to small variations in volume, shape and structure, which makes bulk characterization insufficient.  I believe that scanning SQUID will make it possible to examine the behavior of an ensemble of particles, while at the same time, detecting each individual in it. This will eventually give scientists more control over applications of nanomagnets for bio-medical applications.”

Improved control of magnetism is at the heart of two of Kalisky’s most recent publications. “My colleagues and I examined a structure made of two different materials grown one atop the other,” she says, referring to research that appeared in the prestigious journal Nature Communications.  “Although the materials were non-magnetic insulators, magnetism suddenly appeared in tiny ‘islands’ at the interface layer between them. We also found that physical contact with the tip of a SQUID probe makes it possible to dramatically change the magnetic properties of these small ferromagnetic islands – a study that was published in Nano Letters. This is particularly interesting because it demonstrates the possibility of manipulating magnetism – at particular points within a material – at will.” 

Another recent study, published in Nature Physics, relates to this structure’s ability to superconduct. Superconductors – materials that conduct electricity with near-zero resistance – have fascinated Kalisky since her days as a BIU PhD student, when she worked under the supervision of Director of BIU’s National Laboratory for Magnetic Measurements and former University Rector, Prof. Yosef Yeshurun. She continued her research of superconductors at the Weizmann Institute before leaving for her postdoc at Stanford.

“Materials that exhibit both superconductivity and magnetism are unique and interesting because these are properties that are generally considered to be mutually exclusive,” Kalisky says. “Materials that act as superconductors normally expel magnetic fields, while strong magnetic fields acting on a material can disrupt its superconductivity.” Using scanning SQUID, Kalisky and her co-authors showed how the interface between the two “sandwiched” non-magnetic insulators exhibits both magnetic and superconducting properties. “This may have important implications for understanding superconductivity, and may have applications in quantum computation and future nanoelectronics devices.”

As she settles into her new laboratory in the Leslie and Susan Gonda (Goldschmied) Nanotechnology Triplex, Kalisky is looking forward to using various techniques for sensitive magnetic measurements to examine a wide range of materials, including complex oxides, superconductors, nanotube coils, as well as magnetic bacteria and protein-templated nanocrystals for medical applications. Whatever she studies however, she believes that her greatest contribution is in asking the right questions.

“The laws governing nature can be very complicated,” she says.  “As a scientist, my job is to identify the experiments that will reveal them and simplify the picture.”