Magnetic ordering of the antiferromagnet Cu2MnSnS4 from magnetization and neutron-scattering measurements

Magnetization and neutron-diffraction measurements were performed on a single crystal of Cu2MnSnS4. This quartenary magnetic semiconductor has the stannite structure (derived from the zinc-blende structure which is common to many II-VI dilute magnetic semiconductors), and it orders antiferromagnetically at low temperature. The neutron data for the nuclear structure confirm that the space group is I42̄m. Both the neutron and magnetization data give TN=8.8 K for the Néel temperature. The neutron data show a collinear antiferromagnetic (AF) structure with a propagation vector k=[1/2,0,1/2], in agreement with earlier neutron data on a powder. However, the deduced angle θ between the spin axis and the crystallographic c direction is between 6° and 16°, in contrast to the earlier value of 40°. The magnetization curve at T≪TN shows the presence of a spin rotation (analogous to a spin flop), which indicates that the spin axis is indeed close to the c direction. The deduced magnetic anisotropy gives an anisotropy field HA≅2 kOe. At high magnetic fields the magnetization curve at T≪TN shows the transition between the canted (spin-flop) phase and the paramagnetic phase. The transition field, H=245.5 kOe, yields an intersublattice exchange field HE= 124 kOe. The exchange constants deduced from HE and the Curie-Weiss temperature Θ=-25 K show that the antiferromagnetic interactions are an order of magnitude smaller than in II-VI dilute magnetic semiconductors (DMS's). The much weaker antiferromagnetic interactions are expected from the difference in the crystal structures (stannite versus zincblende). A more surprising result is that the exchange constant which controls the AF order below TN is not between Mn ions with the smallest separation. This result contrasts with a prediction made for the related II-VI DMS, according to which the exchange constants decrease rapidly with distance.The work at Tufts University was partially supported by NSF Grant No. DMR-9219727. The research in Zaragoza was supported by CICYT Grant No. MAT94-0043. The work at Brown University was supported by NSF Grant No. DMR-9221141. The Francis Bitter National Magnet Laboratory was supported by NSF.Peer Reviewe

Metamagnetic Behavior of Linear Chain Pyridine Compounds: Co(Pyridine)\u3csub\u3e2\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e, Fe(Pyridine)\u3csub\u3e2\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e, Fe(Pyridine)\u3csub\u3e2\u3c/sub\u3e(NCS)\u3csub\u3e2\u3c/sub\u3e and Ni(Pyridine)\u3csub\u3e2\u3c/sub\u3eCl\u3csub\u3e2\u3c/sub\u3e

Magnetic phase transitions in the pyridine (pyr) compounds Co(pyr)2Cl2, Fe(pyr)2Cl2, Fe(pyr)2(NCS)2 and Ni(pyr)2Cl2 have been observed at applied magnetic fields of not, vert, similar0.7, 0.7, 1.1 and 2.7 kG respectively. These low field phase transitions are observed in the Fe and Ni compounds at T = 4.2 K, and in the Co compound at T \u3c 3K, and are consistent with metamagnetic behavior. Magnetic saturation is not achieved in any of these compounds for fields of 60 kG, reflecting high anisotropy

High-Field Studies of Band Ferromagnetism in Fe and Ni by Mössbauer and Magnetic Moment Measurements

High-field susceptibility χHF in Fe and Ni (at 4.2, 77, and 300°K) and high-field Mössbauer studies in Fe at 4.2°K are reported and related to the band structure of Fe and Ni and to band models of ferromagnetism. The Mössbauer effect was employed to measure the change in the hyperfine field Hn at the 57Fe nucleus with application of an external field. Assuming Hn to be proportional to the bulk magnetization, a microscopic equivalent to χHF is obtained. We also show how the high-field data may be used alternatively to determine the nuclear g factor. The macroscopic differential magnetic moment measurements are presented along with an extensive discussion of the experiments to 150 kG. We find χHF=4.3×10-5 emu/cc for Fe and 1.7×10-5 emu/cc for Ni at 4.2°K, where χHF is averaged from 50-150 kG. The interpretation of these low-temperature data (when reasonable estimates of Van Vleck susceptibility are made) indicates holes in both spin bands of Fe and a full band of one spin in N, in agreement with the accepted band theory picture for these metals and with recent spin-polarized and pseudopotential band calculations for magnetic Fe and Ni. The differential magnetic moment measurements at higher temperatures are in reasonable agreement with predictions of spin-wave theory. In the Appendices we include: (a) a tabulation of the fielddependent terms which enter into the spin-wave description of the magnetization and their derivatives with respect to field and temperature, (b) a discussion of depolarization effects and their influence on the approach to saturation, and (c) a discussion of the dependence of the magnetic moment measurements on sample positioning errors