Terahertz Faraday rotation induced by an anomalous Hall effect in the itinerant ferromagnet SrRuO ₃

Abstract

The magnetoresistance across interfaces in the itinerant ferromagnetic oxide SrRuO 3 have been studied. To define appropriately the interfaces, epitaxial thin films have been grown on bicrystalline and laser-patterned SrTiO 3 substrates. Comparison is made with results obtained on similar experiments using the double-exchange ferromagnetic oxide La 2/3 Sr 1/3 MnO 3. It is found that in SrRuO 3 , interfaces induce a substantial negative magnetoresistance, although no traces of the low-field spin tunneling magnetoresistance are found. We discuss these results on the basis of the distinct degree of spin polarization in ruthenates and manganites and the different nature of the surface magnetic layer formed at interfaces. S0163-18299905134-6 Half-metallic ferromagnetic oxides such as chromium dioxide or the celebrated manganese perovskites are predicted to be almost fully spin-polarized systems. This is a requisite of ideal electrodes for the newcoming generation of magne-toelectronic devices. These materials also share the notable characteristic of being double-exchange DE ferromagnets, i.e., systems with localized atomic moments coexisting with itinerant ones and where the ferromagnetic coupling is transmitted via the mobile charge carriers. Owing to their 100% polarization, spin-polarized tunnel experiments in sandwiched FM/I/FM heterostructures FM is a ferromagnet and I an insulating tunnel barrier have indeed revealed a very large resistivity change upon reversing the relative magnetization of the FM electrodes. Resistivity changes of about 85% at 5 K have been reported for La 2/3 Sr 1/3 MnO 3 /SrTiO 3 /La 2/3 Sr 1/3 MnO 3 junctions. 1 Large magnetoresistance ratios have also been reported for artificial grain boundaries either in bicrystals 2 or even in granular materials. 3-6 However, a serious drawback has appeared: there is a sharp decay of the magnetoresistance MR of the junction when rising the temperature, and it becomes vanishingly small well below the Curie temperature T C when the magnetization M b of the sample is still almost saturated. This appears to be a common trend, observed in all DE materials either manganites 2-4 or CrO 2. 5 In contrast, the tunnel magnetoresistance observed in ceramic superexchange ferromagnets, such as Tl 2 Mn 2 O 7 , displays a weaker temperature dependence and the MR follows basically the magnetization. 7 It thus appears that the mechanism of magnetic interaction has profound effects on the temperature dependence of the magnetoresistance. It has been suggested that DE materials are prone to display carrier depolarization at interfaces, which reduces the observed magnetoresistance at low fields below its ideal 100% value and promotes the sharp decay with temperature. Experiments and theoretical models indicate that this may arise from the existence of a nonferromagnetic surface layer at interfaces. 4,8-10 In superexchange ferromagnets the strength of the magnetic interaction is independent of any charge transfer, and thus ferromagnetism at interfaces is expected to be more...

Gauge fields in real and momentum spaces in magnets: monopoles and skyrmions

“…Figure 4 shows an example of the low frequency data for s xy (u) in the ferromagnetic phase of SrRuO 3 . It is seen clearly that non-trivial structure exists at around 4 meV, which is well fitted by a model assuming the band (anti)crossing near the Fermi energy [19]. …”

“…s xy (u) in ferromagnetic materials, should provide important clues. Owing to the rapid progress of terahertz spectroscopy [18,19], the low-energy structures of s xy (u) are being revealed. Figure 4 shows an example of the low frequency data for s xy (u) in the ferromagnetic phase of SrRuO 3 .…”

Terahertz magneto-optics in the ferromagnetic semiconductor HgCdCr2Se4

“…To date, THz magneto-optical phenomena have been mostly studied either in conducting materials without magnetic order or in magnetically ordered non-conducting materials. [8][9][10][11][12][13][14][15][16][17][18][19] Moreover, the majority of these works studied the Faraday rotation, while other magneto-optical effects, like magnetization dependent linear birefringence and dichroism, may be equally important for establishing a link between electronic transport properties and THz magneto-optics. Measurements on magnetically ordered and conducting samples were reported in Refs.…”

Robustness of electric field vector sensing of electromagnetic waves by analyzing crystal angle dependence of the electro-optic effect

“…Various techniques are reported [11][12][13][14][15][16] to precisely detect a slight change in the polarization angles of terahertz electromagnetic waves after they pass through or are reflected from the sample; these changes are useful for sensitive detection of the polarization rotation caused by birefringence [17], magneto-optic effect [18][19][20], and optical activity [21]. Direct determination of the absolute angles of the terahertz electric field (E-field) vector is a quite powerful technique for investigating the spatial vector distribution of the vector beams [22] and precisely detecting the surface profile [10].…”