Unhydrated Cr(V) Peroxychromates M3CrO8 (M = Na, K, Rb): Low-Dimensional Antiferromagnets Exhibiting Large Specific Heats at mK to 5 K Temperatures
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- 作者：Brant Cage and Nar S. Dalal
- 刊名：Chemistry of Materials
- 出版年：2001
- 出版时间：March 2001
- 年：2001
- 卷：13
- 期：3
- 页码：880 - 890
- 全文大小：280K
- 年卷期：v.13,no.3(March 2001)
- ISSN：1520-5002
文摘
The alkali-metal Cr(V) peroxychromates with the general formula M3CrO8 (M = Na, K,Rb, and combinations thereof) and the 3d1 ground state have been characterized by X-raydiffraction, variable frequency and variable temperature EPR, magnetic susceptibility, andthermodynamic techniques. K3CrO8 and Rb3CrO8 are isomorphous, with space groups asI
2m, whereas Na3CrO8 and K2NaCrO8 exhibit the orthorhombic space groups Cmc2 andPbcm, respectively. Lattice parameters are presented for all of these compounds and areshown to depend sensitively on the cation. EPR measurements reveal that while the electronicground state of Na3CrO8, K3CrO8, and Rb3CrO8 is 3dx2-y2, that of the mixed salts, such asK2NaCrO8 and Rb2NaCrO8, is 3dz2; the origin of this switch is not yet clear. Specific heatmeasurements showed that K3CrO8 undergoes an antiferromagnetic ordering transition atTN = 0.38 K and displays a broad peak around 0.8 K, which can be interpreted in terms ofa Bonner-Fisher model. Rb3CrO8 behaves similarly, with a broad peak at 0.52 K. Na3CrO8exhibits a 
-like antiferromagnetic transition at 2.35 K, with K2NaCrO8 behaving similarly,with TN lower than 1.8 K. The exchange constants and the transition temperatures dependsensitively on the cation. These compounds all are found to exhibit large specific heatsthroughout the mK to 5 K temperature range, and the possibility exists of tuning thethermodynamic properties via dilution with compatible diamagnetic lattices such as M3NbO8. Their specific heat data indicate that they could find applications as tunable heatsinks and magnetic refrigerants in the mK to 5 K range.
2m, whereas Na3CrO8 and K2NaCrO8 exhibit the orthorhombic space groups Cmc2 andPbcm, respectively. Lattice parameters are presented for all of these compounds and areshown to depend sensitively on the cation. EPR measurements reveal that while the electronicground state of Na3CrO8, K3CrO8, and Rb3CrO8 is 3dx2-y2, that of the mixed salts, such asK2NaCrO8 and Rb2NaCrO8, is 3dz2; the origin of this switch is not yet clear. Specific heatmeasurements showed that K3CrO8 undergoes an antiferromagnetic ordering transition atTN = 0.38 K and displays a broad peak around 0.8 K, which can be interpreted in terms ofa Bonner-Fisher model. Rb3CrO8 behaves similarly, with a broad peak at 0.52 K. Na3CrO8exhibits a -like antiferromagnetic transition at 2.35 K, with K2NaCrO8 behaving similarly,with TN lower than 1.8 K. The exchange constants and the transition temperatures dependsensitively on the cation. These compounds all are found to exhibit large specific heatsthroughout the mK to 5 K temperature range, and the possibility exists of tuning thethermodynamic properties via dilution with compatible diamagnetic lattices such as M3NbO8. Their specific heat data indicate that they could find applications as tunable heatsinks and magnetic refrigerants in the mK to 5 K range.