Antiferromagnetic ordering

The rare earths in their dodecaborides have the 3 + oxidation state except for Yb and Tm which have an intermediate valence state. A recoilless y-ray emission spectrum study of TmB,2 shows no magnetic ordering at 1.35 K the spectra of YbB,2 reveal no magnetic structure to 1.35 K. The compounds HoB,2, ErB,2 order antiferromagnetically, and ZrB,2 and LuB,2 become superconducting < 5.8 K and < 0.48 K, respectively. ... 

Prl3 (PuBr3-type of structure, for Lal3 d = 334pm (6x), 340 pm (2x) [21]). Pr2ls is a semiconductor which orders antiferromagnetically below Tn = 37(1) K [19,... 

As reported by Blanco et al. (1999), neutron diffraction patterns of powder and bulk polycrystalline samples of GdCu were obtained for both structures in the cubic CsCl type of structure, which orders antiferromagnetically at 7n 150 K, a propagation vector of ( j 0) has been found with the moments probably parallel to the c-axis (note that other noncollinear magnetic structures might give rise to the same neutron-diffraction pattern). In the orthorhombic low temperature phase (7n 45 K) the available diffraction patterns... 

Patil et al. (1998) reported on measurements of magnetic susceptibility, electrical resistivity and magnetoresistivity for the Ce3Rh3Sb4 in the temperature range 2 K to 300 K. The compound was found to order antiferromagnetically at 22 K. The magnetic resistivity shows a broad maximum at about 50 K. 

Figure 4. a) A hole at the initial site in a Neel-ordered antiferromagnet b) a hole... 

Mossbauer, magnetic, and electronic studies implicate interactions between Fe and Fe in neighboring sites. A phase change between 335 and 343 K is accompanied by thermally activated electron delocalization between 300 and 400 K. Below 120 K, ilvanite is ordered antiferromagnetically. Mossbauer studies (see Mineralogy) have helped elucidate this mixed valence behavior. 

LaMnOs is a prototype for a wide range of rare earth oxomanganates whose physical properties can be radically altered by partial substitution of alkaline earths for La or by similar replacement of Mn by a 3d or other small to medium sized cation. Lai j,Aj Mn03 (A = Ca, Sr, Ba) constitutes one of the more interesting systems for CMR applications. Pure stoichiometric LaMnOs is an insulator that orders antiferromagnetically at 135 K and it is only by introducing a critical amount of Mn+ into the stmcture that the CMR effect can be observed. Thus, some couuneut about the nature of the defect chemistry of LaMnOs is in order. 

A common feature of the compounds that we are discussing here is the large distance between the U atoms which ranges from 4.79 A for UNis to 5.29 A for UPts. The physical properties of UNis are similar to those of the compounds with the CU3AU structure that were mentioned above and in this sense not of interest here (10). UCU5, however, orders antiferromagnetically at Tfsj = 15 K and enters a heavy-elec-... 

The standard technique used for detection of sulfates is X-ray diffraction of the LTA. Nevertheless, we have observed that in some cases sulfates are present in the coal, but the X-ray does not show any line attributable to them (44). The most abundant divalent iron sulfate observed in the coals studied is FeS04 H20 (szomolnokite), a monoclinic crystal with a tetramolecular unit cell (45). This compound orders antiferromagnetically around 10 K with an effective internal field of 359 kOe (22, 23). Other sulfate minerals found less frequently are FeS04 -4H20 (rozenite) and FeS04 7H20 (melanterite) anhydrous ferrous sulfate was detected when the coal was stored under vacuum. The ferric sulfates commonly observed in several coals are coquimbite and jarosites (16). 

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