Angle-dependent magnetoresistance in epitaxially strain-engineered thin films

This thesis reports on magnetoresistance studies in strained thin films of La0.67Sr0.33MnO3 (LSMO) on LaAlO3 and SrTiO3. Strain-engineering thin films is a method to alter material properties such as the magnetization and electronic transport to alter them to a more desirable state. In this thesis, the magnetic anisotropy of the films by varying temperature, applied magnetic field and the angle between current and field in etched LSMO Hall bars is studied. Based on these studies three different magnetic phases when rotating the magnetic field in-plane. At temperatures between 10 to 125 K, a fourfold symmetry is observed, indicating a biaxial anisotropy parallel to the (110) and (1-10) directions . A second magnetic phase between 125 K to 250 K is observed and characterized by a twofold in-plane angle-dependent magnetoresistance signal. Increasing the temperature, leads to a paramagnetic insulating phase. The results show that the temperature variation of the angular dependence of the magnetoresistance is a reliable and alternative approach to study the different kinds of anisotropy induced in such strained oxide films and can complement torque-based magnetometry studies. In the second angle-dependent study (chapter 5) the aim was to find the strain at which the magnetic easy-axis would rotate out-of-plane. The strong (1.9%) compressive strain indeed caused the magnetic easy axis to point in the out-of-plane direction and remain present up to 80 K. The observed trend indicates a gradual change from in-plane to out-of-plane anisotropy with increasing compressive strain

Temperature-dependent periodicity halving of the in-plane angular magnetoresistance in La0.67Sr0.33MnO3 thin films on LaAlO3

Strain-engineering is used as a tool to alter electronic and magnetic properties like anisotropy energy. This study reports the different angle-dependent magnetoresistance properties of the strain-engineered La0.67Sr0.33MnO3 (LSMO) thin films, grown on LaAlO3, compared to their bulk analogs. Upon increasing temperature, a symmetry change from fourfold [cos(4θ)] to twofold [cos(2θ)] is observed in the angle-dependent resistance measurements. This systematic study with increasing temperature allows us to define three distinct temperature-dependent phases. The fourfold symmetric signal originates from magnetocrystalline anisotropy, whereas the twofold symmetric signal is believed to be the conventional anisotropic magnetoresistance. Our observations show that strain-engineering creates the possibility to manipulate the anisotropy, which, for example, can ultimately lead to observations of noncollinear quasi-particles like skyrmions in single layer thin films of LSMO. This work was realized using NanoLab NL facilities and is a part of the research program Skyrmionics: Towards New magnetic Skyrmions and Topological Memory (Project No. 16SKYR04). A.A.B. acknowledges financial support from the Netherlands Organisation for Scientific Research (NWO). We thank G. R. Blake, M. V. Mostovoy, A. Das, D. Ottomano, J. J. L. van Rijn, E. P. Vallabhaneni, P. Zhang, A. S. Goossens, and S. Chen for useful scientific discussions and J. G. Holstein and H. H. de Vries for technical assistance

Cut-rose production in response to planting density in two contrasting cultivars

Growing in lower planting density, rose plants produce more assimilates, which can be used to produce more and/or heavier flowering shoots. The effect of planting density was investigated during a period including the first five flowering flushes of a young crop. In a heated greenhouse two cut-rose cultivars were grown under bent canopy management. ‘Akito’ on own-roots and ‘Ilios’ on ‘Natal Briar’ rootstock were planted with densities of 8 and 4 plants per m2. Starting at the end of June 2007, flowering shoots were harvested over a time span of eight months. Based on ‘flowering flushes’, times of high harvest rate, the harvesting time span could be divided into five consecutive periods, each including one flush. The cultivars showed contrasting responses to planting density. In the first three periods the response in ‘Ilios’ was extraordinary, because at low density plants did not produce more flowering shoots, as would be expected. However, the response in shoot fresh weight was larger for ‘Ilios’ than for ‘Akito’, 35% compared to 21% over the entire study period. The results imply that there was a genetic difference in the effect of assimilate availability and/or local light environment. During the first three periods, these factors can not have influenced shoot number in ‘Ilios’, while they did in ‘Akito’. It is suggested that decreases of assimilate availability in winter caused the shoot number response to emerge for ‘Ilios’ later on

Temperature-dependent out-of-plane anisotropy in compressively strained La_0.67Sr_0.33MnO₃ thin films

We studied the temperature and strain dependence of the perpendicular magnetic anisotropy in La0.67Sr0.33MnO3 thin films by performing temperature- and angle-dependent magnetotransport measurements. Three films of similar thickness (14 u.c., 14 u.c. and 15 u.c.) but with different out-of-plane crystallographic strain (1.9%, 0.9% and -0.7%) are studied. The films are grown on LaAlO3 and SrTiO3 substrates by pulsed laser deposition. We observe a clear increase in the out-of-plane magnetic anisotropy with increasing out-of-plane strain in the angle-dependent magnetotransport measurements which is present up to 80 K for the highest (1.9%) strained sample. The deformation of the unit cell, as discussed in earlier reports, point to the magnetocrystalline anisotropy as the main driver altering the magnetic easy axis direction. Our results highlight the utility of the effective magnetocrystalline anisotropy as a tool to control the desired anisotropy in crystalline thin films of La0.67Sr0.33MnO3

Body fatness, relative weight and frame size in young adults

1. Body-weight, body height, knee width, wrist width and skinfold measurements were made on males (n 139) and females (n 167) in three age-groups (20–22, 25–27 and 30–32 years). Percentage of body fal was calculated from skinfold thicknesses using regression equations according to Durnin & Womersley (1974), Three indices of relative weight were calculated: W/H2, W/Hp and W/Ŵ, where W is body-weight, H is body height, p is the exponent that made the index of relative weight independent of height and W is the weight, estimated from body height and frame size. 2. The standard error of the estimate of body-weight was only reduced by 5% in males and by 13% in females when, in addition to body height, knee width was taken into account.The addition of wrist width did not improve the accuracy of estimation of body-weight in either sex. Therefore in further analyses W was estimated from body height and knee width. In the present population the exponent p was 1·7 in males and 1·6 in females. 3. The correlations between the percentage of body fat and the indices, W/H2, W/HP, and W/Ŵ, were all very similar, being approximately 0·8 in both sexes. 4. A positive relationship was observed between percentage of body fat and knee width in females, which may be explained by an artifact of measurement. 5. In conclusion it can be stated that the accuracy of estimation of percentage of body fat was not improved when the index of relative weight was adjusted for knee width or wrist width in the present population. The W/H2was the most preferable of the three indices which were calculated