The Impact of Local Strain Fields in Noncollinear Antiferromagnetic Films.

Antiferromagnets hosting structural or magnetic order that breaks time reversal symmetry are of increasing interest for "beyond von Neumann" computing applications because the topology of their band structure allows for intrinsic physical properties, exploitable in integrated memory and logic function. One such group are the noncollinear antiferromagnets. Essential for domain manipulation is the existence of small net moments found routinely when the material is synthesized in thin film form and attributed to symmetry breaking caused by spin canting, either from the Dzyaloshinskii-Moriya interaction or from strain. Although the spin arrangement of these materials makes them highly sensitive to strain, there is little understanding about the influence of local strain fields caused by lattice defects on global properties, such as magnetization and anomalous Hall effect. This premise is investigated by examining noncollinear antiferromagnetic films that are either highly lattice mismatched or closely matched to their substrate. In either case, edge dislocation networks are generated and for the former case, these extend throughout the entire film thickness, creating large local strain fields. These strain fields allow for finite intrinsic magnetization in seemingly structurally relaxed films and influence the antiferromagnetic domain state and the intrinsic anomalous Hall effect.

Intra- and interobserver variability of novel magnetic resonance imaging parameters for hip screening and treatment outcomes at age 5 years.

BACKGROUND: The outcome measure of neonatal hip screening is usually the radiographic acetabular index. OBJECTIVE: To assess the feasibility of magnetic resonance imaging (MRI) without sedation and compare the utility of outcome parameters measured from MRI images. MATERIALS AND METHODS: The invitation for MRI scanning at 5 years of age was incorporated into follow-up for babies who had more than one ultrasound examination during treatment or surveillance. RESULTS: Diagnostic images were obtained in 132 of 134 children. The mean osseous acetabular index (standard deviation [SD]) was 16.6 (3.3) degrees for the right hip and 17.8 (3.2) for the left; the values for the cartilaginous acetabular index were 3.1 (3) and 3.4 (3.2). The mean downslope of a tangent to the lateral bony acetabular roof was 10.4 (4.5) and 9.0 (4.3) with respect to Hilgenreiner's line and that of a line drawn through the apex to the margin of the acetabulum was 3.7 (4.6) and 3.9 (4.7). Intra- and interobserver variation was greater for measures specific to the lateral acetabular roof than for ossific and cartilaginous indices. There was significant negative correlation between the downslope of the tangent to the lateral roof index and the age at onset of treatment on both sides, but no significant correlation for ossific or cartilaginous acetabular indices or apex-marginal index. CONCLUSION: MRI without sedation at 5 years of age is feasible as an outcome measure for hip screening programmes. Parameters specific to the lateral acetabulum may better reflect acetabular sufficiency, despite having greater observer variation than cartilaginous and ossific acetabular indices.