Lower Dimensional Magnetism

Abstract

Much of what has gone heretofore could come under the classification of short-range order. Certainly the intracluster magnetic exchange in Chap. 5 falls within this heading, and a significant part of the discussion of Chap. 6 also dealt with this subject. By "shortrange order," we shall mean the accumulation of entropy in a magnetic system above the long-range ordering temperature. Though this occurs with all magnetic systems, the physical meaning implied by the chapter title is that magnetic ions are assumed here to interact only with their nearest neighbors in a particular spatial sense. For operational purposes, the term will be restricted to magnetic interactions in one and two (lattice) dimensions. In that regard, it is interesting to note that the discussion is thereby restricted to the paramagnetic region. Let it be clear right at the beginning that this magnetic behavior follows directly from the structure of the various compounds.The study of magnetic systems which display large amounts of order in but one or two dimensions has been one of the most active areas recently in solid state physics and chemistry [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The reason for this seems to be that, though Ising investigated the theory of ordering in a one-dimensional ferromagnet as long ago as 1925 [21], it was not until recently that it was realized that compounds existed that really displayed this short-ranged order. The first substance recognized as behaving as a linear chain or onedimensional magnet is apparently CU(NH3)4S0 4' H 20 (CTS). Broad maxima at low temperatures were discovered in measurements of both the susceptibilities and the specific heat [22]. Griffith [23] provided the first quantitative fit of the data, using the calculations for a linear chain of Bonner and Fisher [24]. Fortunately, the theoreticians had been busy already for some time [4] in investigating the properties of onedimensional systems, so that the field has grown explosively once it was recognized that experimental realizations could be found. One-Dimensional or Linear Chain SystemsThere are very good theories available which describe the thermodynamic properties of one-dimensional (lD) magnetic systems, at least for 9'=t; what may be more surprising is that there are extensive experimental data as well of metal ions linked into uniform chains.The first point ofinterest, discovered long ago by Ising [21], is that an infinitely long ID system undergoes long-range order only at the temperature of absolute zero.R. L. Carlin, Magnetochemistry

Synthesis, Nuclear, and Magnetic Structures and Magnetic Properties of [Mn3(OH)2(SO4)2(H2O)2]

“…However, for an antiferromagnetic sample one would expect a decrease in the susceptibility of a randomly oriented sample below the Nÿel transition to a minimum value of 2/3 that at the maximum. [18] This is not the case here since, after a maximum at the transition, c increases again below T N , as shown in Figures 2 and 3. The isothermal magnetization of the polycrystalline sample at 2 K (not shown) displays a featureless increase with increasing field without any hysteresis.…”

“…FULL PAPER mum at 26 K. This behavior is characteristic of a ferrimagnet. [18] However, the transition at 26 K is not associated with long-range ferrimagnetic ordering, due to the absence of spontaneous magnetization in a small applied field, but is assigned to the Nÿel temperature T N of the long-range antiferromagnetic ordering, as confirmed by the l-type anomaly in the specific heat. At lower temperature an unusual gradual increase in susceptibility is observed.…”

Bis(acetylacetonato)ruthenium Complexes of Noninnocent 1,2‐Dioxolene Ligands: Qualitatively Different Bonding in Relation to Monoimino and Diimino Analogues

“…The spin canting is a well-known phenomenon that occurs when the local spins in the ordered magnetic state are neither perfectly parallel, nor antiparallel, but are canted. [21] In contrast to the magnetic behavior of 1, the variation of magnetization versus magnetic field for complex Na (5) is linear at 300 K up to 5 T, and at 2 K is linear up to 2 T (Figures S10 and S11 in the Supporting Information). The variation of the magnetization versus temperature has been measured at 1 T, at which point the magnetization towards the magnetic field is linear.…”

Huge Dielectric Response and Molecular Motions in Paddle‐Wheel [CuII2(Adamantylcarboxylate)4(DMF)2]⋅(DMF)2

“…The magnitude of DH in the frozen and rotation states of [18]crown-6 have been reported at about 60 and 10 kHz, whereas the dynamic disorder without the rotation of [18]crown-6 yielded DH values of 20-30 kHz. [16] Since DH 1 (ca.…”

“…[13] The molecular rotation of the spherical adamantylammonium (AD-NH 3 + ) moiety was easily realized, with a low activation energy compared to the p-planar anilinium derivatives. For example, the (AD-NH 3 [18]crown-6), and (AD-NH 3 + )(dicyclohexano [18]crown-6) supramolecular structures were introduced into the [NiA C H T U N G T R E N N U N G (dmit) 2 ] salts as molecular rotators, and their crystal structures, dielectric constants, 1 H NMR spectra, and magnetic susceptibilities were examined.…”