Using spin-polarized low energy electron microscopy, we discovered a new type of domain wall structure in perpendicularly magnetized Fe/Ni bilayers grown epitaxially on Cu(100). Specifically, we observed unexpected Néel-type walls with fixed chirality in the magnetic stripe phase. Furthermore, we find that the chirality of the domain walls is determined by the film growth order with the chirality being right handed in Fe/Ni bilayers and left handed in Ni/Fe bilayers, suggesting that the underlying mechanism is the Dzyaloshinskii-Moriya interaction at the film interfaces. Our observations may open a new route to control chiral spin structures using interfacial engineering in transition metal heterostructures.

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We report detailed dc and ac magnetic susceptibilities, specific heat, and thermal conductivity measurements on the frustrated magnet ZnCr_{2}Se_{4}. At low temperatures, with an increasing magnetic field, this spinel material goes through a series of spin state transitions from the helix spin state to the spiral spin state and then to the fully polarized state. Our results indicate a direct quantum phase transition from the spiral spin state to the fully polarized state. As the system approaches the quantum criticality, we find strong quantum fluctuations of the spins with behaviors such as an unconventional T^{2}-dependent specific heat and temperature-independent mean free path for the thermal transport. We complete the full phase diagram of ZnCr_{2}Se_{4} under the external magnetic field and propose the possibility of frustrated quantum criticality with extended densities of critical modes to account for the unusual low-energy excitations in the vicinity of the criticality. Our results reveal that ZnCr_{2}Se_{4} is a rare example of a 3D magnet exhibiting a field-driven quantum criticality with unconventional properties.

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A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO4, a triangular lattice antiferromagnet with effective spin-1/2 Yb3+ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO4 is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual κ0/T term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO4. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO4.

An increasing number of unruptured intracranial aneurysms (UIAs) has been discovered in elderly patients in recent years, but the optimal treatment strategy for these patients remains controversial. We report our six-year experience treating UIAs in elderly patients (≥ 70 years old). A retrospective review was conducted of elderly patients who harbored UIAs treated by conservative observation, microsurgical clipping, or endovascular coiling between January 2009 and December 2014. The patients’ clinical and imaging information was recorded. Treating methods, procedure-related complications, imaging results, and clinical outcomes were analyzed. A total of 141 consecutive elderly patients with 166 UIAs were enrolled in our study. In all, 64 patients with 79 aneurysms were treated with coiling, and 14 patients with 14 aneurysms were treated with clipping. The remaining 63 patients with 73 aneurysms were placed under conservative observation. The average modified Rankin scale was 0.99 (range 0–6) in the full cohort after a mean follow-up of 50.4 months (range 0–70 months). There was no significant difference of modified Rankin scale in patients with UIAs treated by different methods. Multivariate analysis showed that age ( p=0.030) and aneurysm size ( p=0.011) were independent risk factors for unfavorable outcome of UIAs in the elderly. Patient age ( p=0.010) and aneurysm size ( p=0.020) were also significantly associated with unfavorable outcome of UIAs managed with observation initially. Our results indicated that endovascular coil embolization and clipping were both safe and effective treatment methods for UIAs in the elderly. Aggressive treatment for UIAs in elderly patients with risk factors of aneurysm rupture should be considered positively.