Dusan A. Pejakovic

Cluster glass state and photoinduced effects on the freezing dynamics in KxCo[Fe(Cn)6]y⋅ZH2O (x∼0.16, y∼0.72, z∼4.4)

The magnetic properties and photoinduced magnetization of a Prussian blue analog, KxCo[Fe(Cn)6]y⋅ZH2O (x∼0.16, y∼0.72, z∼4.4) were systematically studied. The frequency dependence of the linear ac susceptibility, the irreversibility in the field-cooled/zero-field-cooled magnetization (MFC/MZFC), and the relaxation of MZFC suggest a cluster glass behavior. Illumination with red light leads to an increase in the magnetic irreversibility. While MFC is significantly increased after illumination, MZFC at low temperatures is decreased. The observed photoinduced magnetic effects are explained within a cluster glass model. The photoinduced increase in the concentration of spins leads to a shift of dynamics toward longer length and time scales, resulting in freezing of spin clusters at a higher temperature.

Photoinduced magnetism in a cluster glass: Co–Fe Prussian blue

Abstract Static and dynamic magnetic properties and photoinduced magnetism of a Co–Fe Prussian blue analog, K 1−2 x Co 1+ x [Fe(CN) 6 ]· y H 2 O ( x ≈0.2, y ≈4.9), are studied in detail. The magnetic behavior of the material is indicative of a cluster glass state. Our model of ‘spin doping’ of cluster glass is consistent with the observed photoinduced magnetic effects, including the previously unaccounted for increase in coercivity.

Manipulating magnets with light: Photoinduced magnetism of cobalt-iron Prussian blue analogs

Abstract An overview of the magnetic properties and photoinduced magnetism of cobalt–iron Prussian blue analogs is given. The presented results for K 1−2x Co 1+x [ Fe ( CN ) 6 ]·y H 2 O (0.2⩽x⩽0.4, y∼5) indicate that the materials are in a cluster glass state. Upon illumination with visible light, the materials exhibit substantial changes in magnetization, linear and nonlinear ac susceptibilities, characteristic temperatures and magnetic hysteresis. The results are consistent with our model of photoinduced spin-doping of a cluster glass.

Optical control of magnetic order in molecule-based magnet Mn(TCNE)x⋅y(CH2Cl2)

Studies of photoinduced magnetization and photoinduced absorption in molecule-based magnet Mn(TCNE)x⋅y(CH2Cl2) (x≈2, y∼0.8, TCNE=tetracyanoethylene) are reported. Optical excitation in the blue region of spectrum leads to increased magnetization, accompanied by changes in the electronic spectrum. These effects are preserved long after illumination, indicating formation of a highly metastable electronic state. Partial reversal of the photoinduced effects is obtained by excitation with lower energy visible light. The results suggest that the photoinduced effects are controlled by two distinct electronic transitions.

Photoinduced magnetization in molecule-based magnets KxCo[Fe(CN)6]y·zH2O (x≈0.31, y≈0.77, z≈3.54) and Mn(TCNE)x·y(CH2Cl2) (x≈2)

Abstract Studies of photoinduced magnetization (PIM) in two molecule-based magnets, Prussian blue analog K x Co[Fe(CN) 6 ] y · z H 2 O ( x ≈0.31, y ≈0.77, z ≈3.54) and Mn(tetracyanoethylene) x · y (CH 2 Cl 2 ) ( x ≈2), are presented. Detailed analysis of the dc magnetization and ac susceptibility of Co–Fe Prussian blue shows that the material is in a cluster glass state, with strong indications of cooperative freezing of the spin clusters. The PIM effects in the material are described within our model of photoinduced spin-doping of a cluster glass. High- T c magnet Mn(tetracyanoethylene) x · y (CH 2 Cl 2 ) ( T c =75 K) shows a substantial increase in magnetic susceptibility upon illumination with blue light. There are indications that physical mechanism responsible for this effect is different from the one in Prussian blue analogs. The effect is reversible and the material returns to the state before illumination after heating to ∼250 K.

Control of magnetic order by light in molecule-based magnets

An overview of recent progress in the optical control of magnetic properties of molecule-based magnets is given. In particular, we focus on the properties of cobalt iron Prussian blue magnets, in which we experimentally demonstrated coexistence of photoinduced magnetism and cluster glass-type magnetic order. These results will be contrasted with the recently discovered reversible photoinduced magnetic effects in the high-T C molecule-based magnet Mn(TCNE) x · y (CH 2 Cl 2 ).