摘要:

Magnetically uniaxial epitaxial films of Eu2Er1Ga0.7Fe4.3O12and Er2Eu1Ga0.7Fe4.3O125–20‐&mgr; thick have been grown free of cracks from PbO·B2O3solutions on (110) and (111) Gd3Ga5O12substrates, respectively. Bubble propagating T‐Bar and Y‐Bar circuits of nickel‐cobalt‐phosphorus were electrolessly deposited on these films. Operation in excess of one hundred steps has been achieved in T‐Bar and Y‐Bar bubble domain shift registers. Details of the growth procedure, magnetic properties, and circuit preparation are presented.

ISSN:0021-8979    

DOI:10.1063/1.1660212

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A general argument is presented that a change in the nature of the short‐range order will occur above a precisely located temperatureTD, the disorder point, for a class of magnetic models. The possibility of detecting a disorder point by neutron scattering is investigated by calculating the relative scattering intensity for a one‐dimensional model.

ISSN:0021-8979    

DOI:10.1063/1.1660213

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Models with competing nearest‐neighbor and very long‐range interactions are solved exactly for several one‐dimensional cases, including the usual Ising chain (ICCI), theXYmodel (XYCI), the transverse Ising model (TICCI), and the spherical model (SCCI). For certain ratios of the competing interaction strengths,ICCIandXYCIdisplay triple points and two critical points in a field. In addition TICCI has an apparently enclosed phase in anH‐Tphase diagram; however, this phase is really paramagnetic as can be seen when an extended phase diagram is used. The extended phase diagrams forICCI, XYCI, andTICCIdisplay tricritical points and the tricritical exponents have different values from the usual classical values. In contrast to the rich phase behavior of the preceding models,SCCIshows very simple phase behavior, which is directly related to the ground state. Finally, the introduction of a staggered field toICCIand a simple transformation allows reinterpretation as a metamagnetic model. UsingICCIas a guide the observability of the tricritical exponents is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1660214

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

It is shown that depending on how one analyzes measurements of the temperature dependence of magnetization near the Curie temperature it is possible to conclude that the critical exponent changes nearTc. An apparent change in &bgr; can be obtained from analyzing data generated from an equation of state in which &bgr; does not change. The mathematical and experimental difficulties in the use of the kink‐point locus method are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1660215

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The thermodynamic properties of theN×Ntwo‐dimensional Ising square lattice have been studied using a Monte Carlo technique. The critical temperature and types of long‐range order have been investigated over a wide range of ratios of nearest‐neighbor to next‐nearest‐neighbor interaction strengths.

ISSN:0021-8979    

DOI:10.1063/1.1660216

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The temperature dependence of the EPR linewidth in single crystal MnS and MnO have been measured at 35 GHz. The EPR in MnS abruptly stops at 152°±0.5°K as the temperature is decreased. The linewidth in MnS is proportional to (T‐TN)−3/8for 1° ≤ (T‐TN) ≤ 6°K. In both MnS and MnO the linewidth is proportional toT/(T‐TN) forT‐TN> 10°K. In this high‐temperature region the constants of proportionality are 80 and 280 Oe, respectively. An applied field of 12 500 Oe does not shift the Ne´el temperature in MnS.

ISSN:0021-8979    

DOI:10.1063/1.1660217

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Data for the surface of magnetization, temperature, and field for single crystal nickel are compared with the parametric equation of state of Schofield, Litster, and Ho [Phys. Rev. Lett.23, 1098 (1969)]. An excellent fit to the magnetic isotherms is obtained by choosing a reduced temperature for each isotherm, and the variation of the reduced temperature with measured temperature is linear above and below the critical temperature. But whereas the five parameter equation would demand that the slope be the same above and belowTc, the experiments show a 15% change in slope. It is argued that a six parameter equation is needed for the experimental fit and a suitable equation is given.

ISSN:0021-8979    

DOI:10.1063/1.1660218

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

EPR linewidth measurements at 24.43 GHz have been made near the critical pointTNof MnF2. Comparison with similar measurements at 9 and 35 GHz shows that the EPR linewidth nearTNdepends on the Larmor frequency, its magnitude at a given temperature being smaller at higher frequencies. This is the first observation of this effect recently predicted by Kawasaki. It is suggested that the observed frequency dependence nearTNis due to breakdown of the usual exchange narrowing condition.

ISSN:0021-8979    

DOI:10.1063/1.1660219

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The specific heat of a single crystal of CoCl2·6H2O has been measured with high resolution nearTN= 2.291 K using the continuous heating method. Our data have been fitted to the usual asymptotic form:C/R=A&egr;−&agr;+B, where &agr;,A, andBmay assume different values below and aboveTN. By plotting log (∂C/∂T) vs log (&egr;) for different values ofTNwe obtained values for &agr;′, &agr; from the slopes of linear fits. Limits on the ``unrounded critical region'' were defined by deviations from linearity on these plots. A least‐square fit of the unrounded critical regions was also made. Both techniques yield the same results: the specific heat is rounded over a region about 8 mK wide,TN‐Tmax= 4 mK, &agr;′ = −0.18±0.03 belowTN, and &agr; = +0.32±0.07 aboveTN. We have compared our results with the earlier measurements of Skalyo and Friedberg1on a polycrystalline sample. Our specific heat peak is sharper nearTNand rises to a maximum about 7% higher, but for &egr;>4×10−2the two sets of data agree quite well. Analysis of the rounding of the two peaks was made assuming the existence of subsystems having Gaussian distributions of ordering temperatures. Using this technique, we were able to fit our data in the rounded region quite well, and using the same form for the unrounded specific heat, but with a distribution half‐width twice as large, we obtained good agreement with the data of Skalyo and Friedberg.

ISSN:0021-8979    

DOI:10.1063/1.1660220

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Magnetic characteristics of 12 REPd3(RE = a rare earth) compounds have been studied between 4° and 300°K. Electrical resistivity measurements have been made on the Ce, Gd, and Ho compounds. All compounds are paramagnetic at room temperature; all except CdPd3, SmPd3, and EuPd3exhibit Curie‐Weiss behavior with paramagnetic moments in close agreement with that expected for the free tripositive ion. The susceptibility behavior of CePd3is ascribed to the Kondo phenomenon (spin compensation) while that of SmPd3and EuPd3to the narrowness of the multiplet spacings. This interpretation for CePd3is supported by its resistivity‐temperature behavior. Evidence for magnetic ordering is found only for GdPd3, which seems to order ferromagnetically below 7°K.

ISSN:0021-8979    

DOI:10.1063/1.1660221

出版商:AIP    

年代:1971

数据来源: AIP