摘要:

Solid solutions of Fe2O3and Mn2O3with the bixbyite structure may be obtained to at least 50 mole % Fe2O3. Over the whole range, the lattice parameter is essentially constant. Mo¨ssbauer spectroscopy and susceptibility measurements indicate that these solid solutions become antiferromagnetic at much lower temperatures than does Mn2O3itself. In fact, 2 mole % Fe2O3causes a steep drop inTN, from ∼82° to ∼40°K. However, this value remains relatively unaffected by further increase in Fe2O3concentration. The susceptibility measurements also indicate a second transition, at about 15°K below the antiferromagnetic ones, to apparently weak ferromagnetism with extremely low residual moments (∼0.01&mgr;B/formula unit at 4.2°K). Mo¨ssbauer spectra of the 50 mole % powdered specimen at 55 kOe and at both 24° and 9°K exhibit a small polarization of the atomic spins, which in turn suggests either a small induced or small spontaneous moment.

ISSN:0021-8979    

DOI:10.1063/1.1709665

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A number of ordered perovskite‐type compounds A2BB′O6, in which B and B′ are, respectively, a 3dtransition metal cation and a diamagnetic cation, undergo antiferromagnetic transitions. The latter have been interpreted in terms of antiferromagnetic ordering of the second kind arising from appreciable superexchange interactions over quite long distances involving two anions and one diamagnetic cation. A neutron diffraction study has been made of polycrystalline samples of two such compounds, Ba2CoWO6and Ba2NiWO6. The crystal structures are cubic, and there is a slight displacement of the oxygen ions from the ideal perovskite positions towards the more highly charged W ions of about 0.1 Å. At 4.2°K the magnetic unit cell edge is double that of the crystallographic cell in both compounds and the observed magnetic peaks are consistent with ordering of the second kind. The spin direction in Ba2NiWO6is perpendicular to the [111] axis, but in Ba2CoWO6it appears to lie roughly 20° from the [111] axis.

ISSN:0021-8979    

DOI:10.1063/1.1709666

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Canted antiferromagnetism in CuCl2·2D2O has been confirmed in a neutron diffraction experiment. The neutron data agree well with the theoretical predictions of Moriya for a minor magnetization component of about 0.1&mgr;Bparallel to thecaxis. The angular dependence of the neutron data indicates that the spatial distribution of minor magnetization is quite different from that of the main component.

ISSN:0021-8979    

DOI:10.1063/1.1709667

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The heat capacities of the isostructural dihydrated formates of Mn2+, Fe2+, and Ni2+have been measured between 1.4° and 20°K. Sharp peaks associated with long‐range spin ordering are found at 3.72°K for Mn(HCOO)2·2H2O, 3.74°K for Fe(HCOO)2·2H2O, and 14.5°K for Ni(HCOO)2·2H2O. An additional sharp anomaly inCpis found at 1.72°K for the Mn+2salt, whileCpof the Ni+2salt exhibits a Schottky‐like maximum at 3°K. Each of these anomalies can be correlated with some feature of the observed magnetic susceptibilities.A unit cell in these salts contains two each of two inequivalent metal ion sites, types A and B. Formate groups constitute AA and AB bridges and appear to mediate the dominant superexchange couplings. A simplified molecular field treatment of Mn(HCOO)2·2H2O in whichJAA= 0.65k,JAB= −0.10k, andJBB= 0 provides interpretations of several striking effects. In particular, it shows that below a common transition temperature, B spins order much more slowly than A spins and are nearly ``free'' at 1°K as seen in both magnetic and thermal data. Analysis of the data for the Ni+2and Fe2+salts suggests that the effective spins of A and B ions may differ in a given substance.

ISSN:0021-8979    

DOI:10.1063/1.1709668

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A lack of symmetry in the susceptibility tensor &khgr;yxwas found experimentally by Naiman and Lawrence over the spin‐flopping region in CuCl2·2H2O when the external magnetic field was less than 10−3rad away from the easy axis. This fact cannot be explained by considering the effective field acting on the two‐sublattice system to be composed of exchange, anisotropy, and external magnetic fields. Additionally, the Dzialoshinski‐Moriya interaction for CuCl2·2H2O appears analytically only as a shift in the critical field while the wander of the easy axis influences the shape but not the symmetry of &khgr;yx. The demagnetizing field has been included exactly using a 2×2 tensor, and it was found that for an ellipsoidal spin‐flopping specimen the major effect on &khgr;yxis to shift the value of the critical field. According to Joseph and Schlo¨mann, the demagnetizing tensor components for bodies with ``corners'' need not be constant, and this could possibly explain the observed asymmetry in &khgr;yx. To test this theory, single crystals were shaped into spheres and &khgr;yxwas remeasured. The essential agreement between the results before and after shaping lead us to conclude that demagnetizing effects which depend on the crystal shape are not important. Possible crystalline inclusions and/or domain formation may play a significant role.

ISSN:0021-8979    

DOI:10.1063/1.1709669

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A magnetic‐susceptibility study of the Magne´li phases of the titanium‐oxygen system shows an anomalous dependence on the stoichiometry. The magnetic susceptibility has been fitted (where applicable) to a Curie‐Weiss law of the form &khgr; =C/(T+&thgr;) +A, using a least‐squares analysis. The Curie constantCincreases with increasing stoichiometry despite the apparent increasing magnetic dilution (addition of Ti4+ions) of the Ti3+ions. Some of these phases exhibit an antiferromagnetism; others show an apparent paramagnetic behavior; and several show semiconductor‐to‐metal transitions.

ISSN:0021-8979    

DOI:10.1063/1.1709670

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Heat capacities of PrCl3and NdCl3have been measured between 0.3° and 4°K. The dominant feature of the heat capacity curves is a broad anomaly indicating a region of extensive short‐range magnetic ordering. The anomaly in NdCl3has a maximum at 0.47°K and fits closely that of a linear Ising chain model. In addition, two small peaks appear at the same temperatures as the sharp spikes found in the magnetic susceptibility. PrCl3has a sharp peak in the heat capacity at 0.4°K which is presumably associated with long‐range ordering. The broad anomaly in PrCl3has a maximum at 0.8°K. The magnetic entropy change for the temperature region of the measurements is approximately 80% ofRloge2 for both salts.

ISSN:0021-8979    

DOI:10.1063/1.1709671

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The magnetic properties of FexO with long‐range order of defects was studied. The crystal structure appears to consist of periodically spaced complexes of vacant octahedral and occupied tetrahedral sites, with most of the octahedral ions in an ideal NaCl‐type environment. The Ne´el temperature, determined from measurements of susceptibility and modulus, increases very slightly asxis decreased. Octahedral‐tetrahedral ion exchange interactions are proposed to account for the increase inTN. The molar susceptibility obeys a Curie‐Weiss law, &khgr; = 3.56/(T+136). With &thgr; = 136°K andTNabout 200°K, &thgr;/TNis less than one. According to a treatment by Van Vleck one expects &thgr;/TNgreater than one for negative first‐near‐neighbor and second‐near‐neighbor interactions. A positive first‐near‐neighbor interaction may possibly arise through double exchange between Fe2+and Fe3+.

ISSN:0021-8979    

DOI:10.1063/1.1709672

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements have been made of the magnetic susceptibility of VF2at temperatures between 1° and 300°K. This compound was previously found [J. Appl. Phys.37,966 (1966)] to have the rutile structure and to have a gradual maximum in magnetic heat capacity at 27°K and a sharp heat‐capacity peak at 7.0°K associated with the development of long‐range order. The data were interpreted as indicating that the major exchange interactions between vanadium ions couple together one‐dimensional chains of atoms parallel to thecaxis. We have measured the magnetic susceptibility of powdered samples and of an oriented crystal sample made by stacking together small needle‐like single crystals. The high‐temperature susceptibility data show that the net exchange interactions are antiferromagnetic. There is a gradual maximum in magnetic susceptibility near 40°K, consistent with the development of a large amount of one‐dimensional short‐range order. At 77°K and lower temperature the susceptibility parallel to thecaxis is greater than that perpendicular to this direction.

ISSN:0021-8979    

DOI:10.1063/1.1709673

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The field dependence of the magnetic susceptibility of MnO powder has been studied in continuous fields up to 50 kOe, between 4.2° and 200°K. Each isotherm is measured from a virgin magnetic state to avoid hysteresis and viscosity complications. Above the antiferromagnetic Ne´el point, the susceptibility is field independent with a maximum value of (83±1)×10−6emu/g at 122°K. At 4.2°K, the susceptibility saturates with field at a value of 79×10−6emu/g. This is identified as the transverse susceptibility. It drops slightly with temperature to a broad minimum at 55°K. An attempt to analyze the field dependence using the model of Keffer and O'Sullivan suggests that the weak in‐plane anisotropy,K2, has orthorhombic symmetry. This model is rejected because it ignores domain wall displacement. A rough estimate ofK2at 4.2°K is 9×103erg/cc, assuming trigonal symmetry.

ISSN:0021-8979    

DOI:10.1063/1.1709674

出版商:AIP    

年代:1967

数据来源: AIP