Spin Slip Research Articles

Comparison of the minimum plastic spin and rate sensitive slip theories for loading of symmetrical crystal orientations

The plastic loading of face-centred cubic crystals along directions of symmetry leads to ambiguities in slip system selection. A solution to this problem has been proposed (Fuh & Havner, Proc. R. Soc. Lond . A 427, 193-239 (1989)) by postulating that the operating slip combination is the one which corresponds to the minimum plastic spin (MPS). A comparison is made between the MPS and rate-dependent slip theories. The predictions obtained are identical for the following cases: (i) (110) loading in channel die compression (with one exception) and (ii) all the multiple slip orientations in uniaxial tension. In the case of [100] pure plane strain compression, there is agreement for the four slip-system orientations, but not when six systems are required in the MPS analysis. It is shown that the symmetry of the slip distributions called for by the MPS and rate sensitive approaches is responsible for the broad equivalence between the predictions of the two theories. In each of the examples discussed, the number of operating slip systems is determined by symmetry considerations, leading to the operation of two, four, six or eight slip-systems, rather than by the number of prescribed constraints.

Observation of transitions to spin-slip structures in single-crystal holmium.

We present the results of magnetization measurements on single-crystal holmium using a SQUID magnetometer in the temperature range from 4.2 to 140 K in magnetic fields from 0.01 to 3 T applied along the {ital b} axis. Our magnetization data shows the Neel temperature to be {ital T}{sub {ital N}}=132 K. In addition, we observe anomalies in the temperature dependence of the magnetization at 21, 42, and 98 K. These anomalies can be accounted for within the spin-slip model; Bohr {ital et} {ital al}. (Physica (Amsterdam) 140{ital A}, 349 (1986)) have pointed out the existences of ferrimagnetic structures spin slip and Cowley and Bates (J. Phys. C 21, 4113 (1988)) additional structures that breaks the hexagonal symmetry.

Neutron diffraction study of HCP erbium-lanthanum alloys

The magnetic phase diagram of hcp Er-La alloys has been established by neutron diffraction on single crystals. The alloys with more than 97at.% Er successively transform from a longitudinal sinusoidal order to a cycloidal one. After that a conical structure appears upon decreasing temperature. In alloys with less than 97 at.% Er, the cycloidal order disappears and a simple ferromagnetic alignment newly appears at intermediate temperatures. The behavior of the magnetic ordering temperatures and turn angles with the deGennes factor is different from that of Er-Y alloys. The phase diagram and lock-in turn angles are discussed qualitatively on the basis of a competing interaction model and a spin slip model, respectively. The RKKY exchange interaction range contracts with increasing La concentration.

Magnetic phase diagram of hcp phases in binary systems between Ho and light rare-earths: La, Ce, Pr

Neutron diffraction studies have been made on single crystals of hcp Ho-La, Ho-Ce, and Ho-Pr alloys to establish the magnetic phase diagrams. Alloys with more than 85 at.% Ho show helical magnetic ordering below T N and a conical structure below T C . On the other hand, alloys with less than 80 at.% Ho have no ferromagnetic component but only the helical component in the basal plane down to low temperatures. T N decreases rapidly, while T C decreases gradually with increasing light rare earth concentration. T N , T C , initial and final turn angles follow the universal function of the average deGennes factor and show different behavior from the function for Ho-Y alloys. It is concluded that the range of an RKKY exchange interaction is shortened more with decreasing Ho concentration, because of the reduction of the mean free path of the conduction electrons, than in the Ho-Y alloys. The observed lock-in turn angles are discussed on the basis of a spin slip model.

The magnetic structure of holmium. I

The magnetic structure of the incommensurate spiral phase of holmium has been studied using elastic neutron scattering for temperatures between 30 and 18K, the temperature region just above the transition to a ferromagnetic cone phase with a wavevector of 1/6 c*. The results show that the structure consists of commensurate regions separated by spin discommensurations or spin slips. In the commensurate regions, pairs of spins (one on each sublattice) deviate by about 10 degrees from each of the easy directions within the plane, and there is evidence for a c axis antiferromagnetic component which changes domain type from one commensurate region to another. The spin slips, which occur on alternate sublattices, have one plane of spins aligned with the planar easy directions, and are found to disturb the commensurate regions for about three planes on either side of each spin slip.

Spin slips and lattice modulations in holmium: A magnetic x-ray scattering study

The analysis of data obtained in magnetic X-ray scattering experiments on rare earth metals, particularly holmium, has led to a phenomenological model for one-dimensional spatially propagating magnetic structures. Based on the concept of spin slips or discommensurations, this model explains the observed lock-in transitions in the magnetic spirals of the rare earths in terms of simple commensurate structures. Further, the anomalous intensities of previously observed higher harmonic magnetic satellites, as well as the qualitative behavior of the magnetic wave vector in the presence of a magnetic field, are understood directly within the spin slip description. We discuss how the presence of spin slips in the magnetic structure can lead to modulations of the crystal lattice as demonstrated by a recent magnetic X-ray study of holmium.

The Influence of Fluid Rheology on the Performance of Traction Drives

The performance of traction drives depends to a large extent on the rheological properties of the fluid in the EHL contact. Through the use of the recently proposed J + T constitutive equation, the influence of elastic effects in the fluids is examined. The results were compared with those obtained from conventional analysis. It is shown that essentially three regions of influence exist. For small values of spin and side slip the elastic effects in the fluid dominate and no consideration of the spin and side slip is required. At higher values of spin and side slip the elastic effect still exists but slip is influenced by the spin and slide slip. At still higher values of side slip and spin, the elastic effects in the fluid may be neglected. The various boundaries of the regions of influence depend on the aspect ratio of the contact.

Slip Forces for Bodies in Contact With Large Spin and Small Slip Velocities

Two elastic bodies are treated, which are in contact over an elliptical surface, are subjected to a large spin about an axis normal to the contact surface, and have small slip velocities tangential to that contact surface. It is shown that these slip velocities are proportional to the tangential components of force acting at the contact surface, and that the coefficients of proportionality can be written as simple expressions in terms of complete elliptic integrals of the first and second kind.