1. Photodecrease Photoincrease
Magnetism of Mixed Prussian Blue Analogs and Low Dimensional Frustated Systems Mark W. Meisel (Physics, University of Florida) DMR
The ability to purposefully tune magnetic properties of synthetic materials has motivated progress in the area of molecule-based magnets.
Our studies show bulk powders of a Prussian blue analog, NaαNi1-xCox[Fe(CN)6]β·nH2O, possess photoinduced magnetism that can be either positive or negative (as shown at right), depending upon the cobalt fraction x, the applied magnetic field, and the temperature. The underlying mechanism of this phenomena is readily modeled [see (a) and (b)] and, thus, allows the photo-controlled magnetic properties to be designed by a choice of the transition metal ions and their concentrations.
These developments are now being extended to thin films and nanoparticles, and the magnetic transition temperatures are being shifted to technologically interesting temperatures near 77 K.
D.M. Pajerowski, J.E. Gardner, D.R. Talham, M.W. Meisel, J. Am. Chem. Soc., web publication: August 24, 2009, doi: /ja Ni Co Fe
Spair= 0
Spair=-1
Photodecrease
Spair=+1
Photoincrease
(a)
Title of paper cited in slide: Tuning the Sign of Photoinduced Changes in Magnetization: Spin Transitions in the Ternary Metal Prussian Blue Analogue NaαNi1−xCox[Fe(CN)6]β·nH2O
Abstract: Tuning the composition of the ternary transition-metal Prussian blue analogue NaαNi1−xCox[Fe(CN)6]β·nH2O allows the sign of the photoinduced change in magnetization to be controlled. The parent cobalt hexacyanoferrate material is well-known to display photoinduced and thermal charge-transfer-induced spin transitions (CTISTs). Upon partial replacement of Co ion sites with NiII, irradiation with halogen light can cause either an increase or a decrease in magnetization, depending upon the extent of NiII substitution, the applied field, and the temperature. For all compositions with x > 0, photoexcitation generates new moments according to the same mechanism observed for the parent x = 1 compound. However, the presence of NiII introduces a superexchange of opposite sign, providing a mechanism for controlling the sign of the change in magnetization with applied light. Additionally, dilution of the spin-crossover material reduces the magnitude and hysteresis of the thermal CTIST effect. These effects can be qualitatively explained by simple mean-field models.
Upper Left Figure: Structural model for NaαNi1−xCox[Fe(CN)6]β·nH2O.
Upper Right Figure: Magnetic increase of decrease for two different x values while at low temperature (5 K) and low magnetic field (10 G).
Figure (a): Decrease in the magnetization upon photoexcitation of a Ni-dominated material when there is atomic mixing and the spins are in an ordered state dictated by the exchange interactions JNiFe > 0 (ferromagnetic) and JCoFe < 0 (antiferromagnetic).
Figure (b): The usual increase in the magnetization with photoexcitation of a sufficiently Co-dominated material.
(b)

2. Magnetism of Mixed Prussian Blue Analogs and Low Dimensional Frustated Systems Mark W. Meisel (Physics, University of Florida) DMR
This interdisciplinary research builds upon our long-standing intramural (UF Physics-Chemistry and NHMFL High-B/T Lab) and international (Centre of Low Temperature Physics, Košice, Slovakia) and extends these links (e.g. High Magnetic Field Lab (HLD), Dresden, Germany).
The training of graduate and undergraduate students involves hands-on laboratory experiences and visits to national (e.g. SNS-ORNL and NHMFL) and international facilities and meetings.
The PI embraces Outreach Activities and his recent work focuses on K-8 teacher/student experiences involving “matter”. Elements of his work were used by the Florida PROMiSE Progam, and the PI is a developer and faculty participant.
Temperature (T) versus Magentic Field (B):
phase diagram of a novel two-dimensional magnet Cu(tn)Cl2, see A. Orendáčová et al.,
arXiv: and to be published.
Model of Chemical Reactions:
Cookie Sheet & Poker Chips!
Meisel leads discussion during
Duval (Jacksonville) PROMiSE
K-8 Teachers Outreach Program.
Other NSF grants providing collaborative support:
Daniel R. Talham, UF Chem (DMR ),
UF Physics Summer REU Program (DMR ),
NHMFL (DMR ).
With respect to the phase diagram of Cu(tn)Cl2: the apparent presence of a BKT (Berezinski-Kosterlitz-Thouless) phase transition at low temperature and in high magnetic fields is striking. This phase diagram was constructed from the data acquired in Kosice, Slovakia; Dresden, Germany; and Gainesville, FL. The work at UF involved the NSF supported NHMFL. This work is posted online ( and will appear in Phys. Rev. B.
Due to privacy issues (which are presently being resolved) related to the posting of images of participants, the PROMiSE photo shows the hand of Meisel, PI, while he describes some details of the 2HCl + Zn -> ZnCl2 + H2 closed reaction modeled by the cookie sheet and the poker chips. Photo taken during the K-8 Science Institute on “Matter” for Duval (Jacksonville) County Schools. Meisel was the “expert” during the two week, six hours per day program, and the website is
PROMiSE: Partnership to Rejuvenate and Optimize Mathematics and Science Education in Florida
Department of Physics
Department of Chemistry
Meisel Group “Leatherheads” Summer 2009: (left to right) Carrie Schindler, REU, Univ. Evansville; Elisabeth Knowles, UF grad student; Mark Meisel, PI; Daniel Pajerowski, UF grad student, Nick Lavini, REU, Manhattan College.