The synthesis, crystal structure determination, magnetic properties and bonding interaction analysis of a novel 3 d transition-metal complex, [CrBr 2 (NCCH 3 ) 4 ](Br 3 ), are reported. Single-crystal X-ray diffraction results show that [CrBr 2 (NCCH 3 ) 4 ](Br 3 ) crystallizes in space group C 2/ m (No. 12) with a symmetric tribromide anion and the powder X-ray diffraction results show the high purity of the material specimen. X-ray photoelectron studies with a combination of magnetic measurements demonstrate that Cr adopts the 3+ oxidation state. Based on the Curie–Weiss analysis of magnetic susceptibility data, the Néel temperature is found to be around 2.2 K and the effective moment (μ eff ) of Cr 3+ in [CrBr 2 (NCCH 3 ) 4 ](Br 3 ) is ∼3.8 µ B , which agrees with the theoretical value for Cr 3+ . The direct current magnetic susceptibility of the molecule shows a broad maximum at ∼2.3 K, which is consistent with the theoretical Néel temperature. The maximum temperature, however, shows no clear frequency dependence. Combined with the observed upturn in heat capacity below 2.3 K and the corresponding field dependence, it is speculated that the low-temperature magnetic feature of a broad transition inmore »
Magnetic Field Perturbations to a Soft X-ray-Activated Fe (II) Molecular Spin State Transition
The X-ray-induced spin crossover transition of an Fe (II) molecular thin film in the presence and absence of a magnetic field has been investigated. The thermal activation energy barrier in the soft X-ray activation of the spin crossover transition for [Fe{H2B(pz)2}2(bipy)] molecular thin films is reduced in the presence of an applied magnetic field, as measured through X-ray absorption spectroscopy at various temperatures. The influence of a 1.8 T magnetic field is sufficient to cause deviations from the expected exponential spin state transition behavior which is measured in the field free case. We find that orbital moment diminishes with increasing temperature, relative to the spin moment in the vicinity of room temperature.
- Publication Date:
- NSF-PAR ID:
- 10313700
- Journal Name:
- Magnetochemistry
- Volume:
- 7
- Issue:
- 10
- ISSN:
- 2312-7481
- Sponsoring Org:
- National Science Foundation
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For the spin crossover coordination polymer [Fe(L1)(bipy)] n (where L1 is a N 2 O 2 2− coordinating Schiff base-like ligand bearing a phenazine fluorophore and bipy = 4,4′-bipyridine), there is compelling additional evidence of a spin state transition. Both Fe 2p X-ray absorption and X-ray core level photoemission spectroscopies confirm that a spin crossover takes place, as observed by magnetometry. Yet the details of the temperature dependent changes of the spin state inferred from both X-ray absorption and X-ray core level photoemission, differ from magnetometry, particularly with regard to the apparent critical transition temperatures and the cooperative nature of the curve progression in general. Comparing the experimental spin crossover data to Ising model simulations, a transition activation energy in the region of 160 to 175 meV is indicated, along with a nonzero exchange J . Overall, the implication is that there may be perturbations to the bistability of spin states, that are measurement dependent or that the surface differs from the bulk with regard to the cooperative effects observed upon spin transition.
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We present structural, magnetic, and optical properties of hexagonal HoFeO3/Al2O3 thin films deposited by Magnetron Sputtering. The x-ray diffraction patterns of HoFeO3 thin films show the c-planes of a hexagonal structure. The magnetization data display an antiferromagnetic transition temperature, TN∼120 ± 5 K and the magnetization-field hysteresis loops were measured below 100 K, confirming a weak ferromagnetism arising from a spin canting of the Fe3+ moments. The magnetization data also show an anomaly around ∼40 K due to a spin-reorientation transition caused by the Ho3+- Fe3+ interactions. We observed comparable magnetization along the ab plane and c axis although the spin canting of Fe3+ sites has a preferential component along the c axis, suggesting that the Ho3+- Fe3+ interactions dominate in the low temperature magnetic structures of hexagonal-HoFeO3. The observed electronic excitations at ∼2.29, 2.87, 3.82, 4.79, and 6.53 eV have been assigned to the Fe3+ d to d on-site as well as O 2p to Fe 3d, Ho 6s, and 5d charge-transfer excitations, respectively. The room temperature energy band gap of the hexagonal-HoFeO3 thin film was measured to be ∼1.99 ± 0.04 eV.
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Fe(II) coordination complexes with ligands of an intermediate field strength often show witching between the high-spin (HS) and low-spin (LS) electronic configurations, known as spin crossover (SCO). This spin-state conversion is achieved by changes in temperature, pressure, or photoexcitation, which make SCO complexes promising materials for various applications that rely on bistable systems. Multifunctional materials that exhibit both spin-state switching and conductivity can be created by combining Fe(II) SCO complexes with organic TCNQ-type electron acceptors. In such complexes, TCNQ●d– radical anions are typically arranged in layers of one-dimensional stacks that provide conducting pathways (Fig. 1). The stacking distance can be affected by structural changes induced by the alteration in the electronic configuration and, thus, bond lengths at the Fe(II) center, resulting in synergy between SCO and conductivity. The synthesis of such materials can be approached in two ways: (1) by coordinating TCNQ●d– ligands directly to the Fe(II) center, which is partially protected by blocking ligands that limit the growth of extended structures or (2) by co-crystallizing completely blocked Fe(II) centers with free TCNQ●d– radicals. We will discuss several examples of the second approach, in which homoleptic Fe(II) cationic SCO complexes with tridentate 2,6-bispyrazolyl-pyridine (bpp) type ligands have been co-crystallized withmore »
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- Publisher's Version of Record
- https://doi.org/10.3390/magnetochemistry7100135
