H. Forstat

Antiferromagnetism in Rb2MnCl4·2H2O☆

Abstract Specific heat measurements in the temperature range 1.38° – 4.03°K indicated a λ-type anomaly at 2.24°K which has been identified as a paramagnetic-antiferromagnetic transition. Short range ordering accounts for approximately 25% of the total entropy change. The calculated sublattice magnetization is compared to several statistical models.

A calorimetric study of CoxNi1−xCl2⋅6H2O

Using a standard He4 adiabatic calorimeter, we have measured the specific heats of a series of mixed crystals with chemical formula CoxNi1−xCl2⋅6H2O. All the samples studied show fairly sharp λ‐type transitions in the liquid He4 region. The Neel temperatures vary from 2.43 °K to 4.47 °K for x ranging from 0.89 to 0.13. We find that the critical behaviors of the mixed crystals can be explained by assuming that the Ni and Co spins behave like Ising spins randomly distributed on a square lattice. The TN vs concentration diagram can be reasonably well accounted for by (a) the annealed Ising model, (b) the annealed Bethe‐Peierls‐Weiss (BPW) model and to a lesser extent, (c) the quenched BPW model. The experimental specific heats have also been compared with theoretical predictions. In all cases, the annealed Ising model fits the data the best near and above the critical temperatures. For high Ni concentrations, the quenched BPW model fits the data better than the annealed BPW model but predicts critical temper...

Spin Flopping in LiCuCl3·2H2O

Single crystal magnetic measurements of LiCuCl3·2H2O in the liquid‐helium temperature region revealed the presence of a spin‐flop state above 9 kG. By means of the magneto‐caloric effect it has been possible to trace out the antiferromagnetic‐spin‐flop boundary. A least squares fit of the data indicated that this boundary could be represented by Hc=9.36+0.078T+0.173T2 with Hc in kG. The spin‐flop‐paramagnetic and antiferromagnetic‐paramagnetic boundaries were obtained by specific‐heat measurements. Calculations gave the anisotropy field (HA) as 3.0 kG, and the exchange field (HE) as 11.0 kG. All of the above measurements were made with the external field parallel to the easy axis of magnetization.

Specific heat of antiferromagnetic K Mn Cl3·2H2O☆

Specific heat measurements of single crystal K Mn Cl3·2H2O from 1.0° - 6.8°K indicated a magnetic transition to an antiferromagnetic state at 2.70 ± 0.01°K. A smaller anomaly, due to a magnetic impurity, has also been observed at 1.6°K. The calculated sublattice magnetization is compared to the molecular field theory as well as a semi-classical statistical model.

Antiferromagnetism in Mn0.27Co0.73Cl2·6H2O

Abstract The specific heat of Mn 0.27 Co 0.73 Cl 2 ·6H 2 O has been measured in the temperature range 1.4 K to 4.4 K. A λ-type anomaly was observed at 2.10 K, corresponding to an antiferromagnetic-paramagnetic transition. Approximately 50% of the entropy is recovered above the Neel temperature. Using the specific heat data, a calculated sublattice magnetization was obtained and compared to several statistical models.

Zero and non-zero magnetic field measurements on CsMnCl3 · 2D2O

Abstract The specific heat and the magnetic phase diagram of single crystal CsMnCl 3 · 2D 2 O have been measured in the temperature range 2.0–20.0°K. The zero-field Neel temperature is 5.06 ± 0.01°K which is approximately 4% higher than the hydrated form of this compound. The magnetic phase diagram also indicates a displacement to higher values.

Magnetic transition in Rb2CoCl4·2H2O

Abstract Specific heat measurements in the temperature region 0.95 – 8.0 K revealed a λ-type anomaly at 1.26 K, suggesting a magnetic transition from a paramagnetic to an antiferromagnetic state. A considerable amount of short range order exists since approximately 70% of the total entropy is recovered above the transition temperature. The calculated sublattice magnetization is compared to several statistical models.

Spin-flopping in azurite☆

Abstract Magnetothermal measurements on single crystal azurite [Cu 3 (CO 3 ) 2 (OH) 2 ] indicated that spin flopping occurred above 19.0 kG. The spin-flop-antiferromagnetic boundary could be represented by an equation H c = 16.5 + 1.20 T 2 with H c in kG. The triple point ( T 3 ) was determined as T = 1.60°K and H c = 19.5 kG. The antiferromagnetic-paramagnetic boundary was compared to the molecular field theory for both the parallel and perpendicular orientations.

The magnetic phase diagram of deuterated manganese chloride

Abstract The magnetic phase diagram of MnCl 2 ·4D 2 O. from 1°K to the Neel temperature, has been traced out, using an adiabatic calorimetric technique. The triple point was located at T = 1.19° K and H c = 7550 Oe .

Spin - flopping in CoBr2 · 6H2O☆

Abstract By using calorimetric techniques, it has been possible to trace out the magnetic phase diagram for single crystal CoBr 2 ·6H 2 O up to external fields of 10 kOe. The triple point obtained in this way was at T = 2.91 ± 0.01°K, H c = 9320 ± 40 Oe.