Magnetic hyperfine field orbitals

Figure 11. The best fit has been found for 5 = 0.7 0.01 nuns, Aitg =—3.25 0.01 nuns, " =(2.11, 2.19, 2.00), "T/ nMn = (-45, 10, 19) T, tj = 0.74 0.1, D = 7.2 0.5 cm, and EID = 0.16 0.02. The zero-field splitting parameter D = 7.2 0.5 cm is comparable to that found for rabredoxin from Clostridium pasteurianum (D = 7.6cm Surprisingly, the rhombicity parameter E/D = 0.16 0.02 differs somewhat from that of rubre-doxin from C. pasteurianum (E/D = 0.28). The hyperfine coupling tensor has been determined to be A = (-14.5, -9.2, -27.5) T. The anisotropy of the hyperfine conpling tensor is cansed by spin-orbit confribntions to the internal magnetic hyperfine field.

Low-spin iron(III) ions have an electron hole in the t2g orbitals. Therefore, these centers have S = 1/2 and spin-orbit interaction contribntes considerably to the magnetic hyperfine field. Low-spin iron(III) componnds in solution always show a rather complicated magnetic Mossbauer pattern at temperatures around 4.2 K and low external fields, which means that the relaxation rate of these centers is lower than the nnclear precession rate of 10 s. Sometimes a magnetic sphtting is observed even at 77 K. Therefore, in order to pin down 8 and A g, it is advisory to measure between 100 and... 

E/Z) = 0.16 0.02 differs somewhat from that of rubredoxin from C. pasteurianum ElD = 0.28). The hyperfine coupling tensor has been determined to be A = (—14.5, —9.2, —27.5)T. The anisotropy of the hyperfine coupling tensor is caused by spin-orbit contributions to the internal magnetic hyperfine field. 

The magnetic hyperfine field is composed of three contributions the Fermi contact, the dipolar, and the orbital contributions. The Fermi contact term, which in most iron-containing materials is dominant, results from the interaction between the nuclear magnetic moment and the unpaired electron spin density at the nucleus. The dipolar and orbital terms represent the dipolar interaction between the nuclear magnetic moment and the electronic spin and orbital moments of their... 

Interaction between the nucleus and the orbital magnetic moment of the 3d electrons. For example, the magnetic hyperfine fields for Fe in Fe-, Co- and Ni-host at OK is —342, - -312 and +283 kOe respectively, while it is 622, 340 and 185 kOe in FeF3, FeF2 and FeS04 host materials. Contribution from the dipole interaction with the moment of the electron spin. 

For Fe " ions the spherical charge distribution results in zero contributions to the magnetic hyperfine field from the orbital component Borb and the dipolar component B ip. The hyperfine field is thus solely due to the contact term where... 

Within a nonrelativistic calculation of the hyperfine fields in cubic solids, one gets only contributions from s electrons via the Fermi contact interaction. Accounting for the spin-orbit coupling, however, leads to contributions from non-s elections as well. On the basis of the results for the orbital magnetic moments we may expect that these are primarily due to the orbital hyperfine interaction. Nevertheless, there might be a contribution via the spin-dipolar interaction as well. A most detailed investigation of this issue is achieved by using the proper relativistic expressions for the Fermi-contact (F), spin-dipolar (dip) and orbital (oib) hyperfine interaction operators (Battocletti... 

The magnetic hyperfine splitting (MHS) depends on the nuclear spin quantum numbers and /g of the excited and ground state of the Mossbauer nucleus and on the effective magnetic field at the Mossbauer nucleus, which includes contributions from the local electronic spin, from the orbital momentum, from dipole terms, and from external fields. 

The NpT2X2 compounds are usually treated as materials with localized 5f states, and crystalline electric-field effects are held responsible for the depression of the magnetic moments (2.4/tB is expected for the free-ion moment of Np). However, the heavy-fermion behaviour (found in NpCu2Si2) is able to introduce an instability of the localized 5f states. In this sense the reduction in hyperfine field at the Np nucleus could be understood as being due to a partial loss of the orbital moments resulting from 5f-electron delocalization. 

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