The Ising triangular-lattice antiferromagnet neodymium heptatantalate as a quantum spin liquid candidate.

Disordered magnetic states known as spin liquids are of paramount importance in both fundamental and applied science. A classical state of this kind was predicted for the Ising antiferromagnetic triangular model, while additional non-commuting exchange terms were proposed to induce its quantum version-a quantum spin liquid. However, these predictions have not yet been confirmed experimentally. Here, we report evidence for such a state in the triangular-lattice antiferromagnet NdTa7O19. We determine its magnetic ground state, which is characterized by effective spin-1/2 degrees of freedom with Ising-like nearest-neighbour correlations and gives rise to spin excitations persisting down to the lowest accessible temperature of 40 mK. Our study demonstrates the key role of strong spin-orbit coupling in stabilizing spin liquids that result from magnetic anisotropy and highlights the large family of rare-earth (RE) heptatantalates RETa7O19 as a framework for realization of these states, which represent a promising platform for quantum applications.

Origin of Magnetic Ordering in a Structurally Perfect Quantum Kagome Antiferromagnet.

The ground state of the simple Heisenberg nearest-neighbor quantum kagome antiferromagnetic model is a magnetically disordered spin liquid, yet various perturbations may lead to fundamentally different states. Here we disclose the origin of magnetic ordering in the structurally perfect kagome material YCu_{3}(OH)_{6}Cl_{3}, which is free of the widespread impurity problem. Ab initio calculations and modeling of its magnetic susceptibility reveal that, similar to the archetypal case of herbertsmithite, the nearest-neighbor exchange is by far the dominant isotropic interaction. Dzyaloshinskii-Moriya (DM) anisotropy deduced from electron spin resonance, susceptibility, and specific-heat data is, however, significantly larger than in herbertsmithite. By enhancing spin correlations within kagome planes, this anisotropy is essential for magnetic ordering. Our study isolates the effect of DM anisotropy from other perturbations and unambiguously confirms the predicted phase diagram.

Field-Induced Instability of a Gapless Spin Liquid with a Spinon Fermi Surface.

The ground state of the quantum kagome antiferromagnet Zn-brochantite, ZnCu_{3}(OH)_{6}SO_{4}, which is one of only a few known spin-liquid (SL) realizations in two or three dimensions, has been described as a gapless SL with a spinon Fermi surface. Employing nuclear magnetic resonance in a broad magnetic-field range down to millikelvin temperatures, we show that in applied magnetic fields this enigmatic state is intrinsically unstable against a SL with a full or a partial gap. A similar instability of the gapless Fermi-surface SL was previously encountered in an organic triangular-lattice antiferromagnet, suggesting a common destabilization mechanism that most likely arises from spinon pairing. A salient property of this instability is that an infinitesimal field suffices to induce it, as predicted theoretically for some other types of gapless SLs.

Spin-stripe phase in a frustrated zigzag spin-1/2 chain.

Motifs of periodic modulations are encountered in a variety of natural systems, where at least two rival states are present. In strongly correlated electron systems, such behaviour has typically been associated with competition between short- and long-range interactions, for example, between exchange and dipole-dipole interactions in the case of ferromagnetic thin films. Here we show that spin-stripe textures may develop also in antiferromagnets, where long-range dipole-dipole magnetic interactions are absent. A comprehensive analysis of magnetic susceptibility, high-field magnetization, specific heat and neutron diffraction measurements unveils ß-TeVO4 as a nearly perfect realization of a frustrated (zigzag) ferromagnetic spin-1/2 chain. Notably, a narrow spin-stripe phase develops at elevated magnetic fields due to weak frustrated short-range interchain exchange interactions, possibly assisted by the symmetry-allowed electric polarization. This concept provides an alternative route for the stripe formation in strongly correlated electron systems and may help understanding of other widespread, yet still elusive, stripe-related phenomena.

Strain-induced extrinsic high-temperature ferromagnetism in the Fe-doped hexagonal barium titanate.

Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases.

Persistent spin dynamics intrinsic to amplitude-modulated long-range magnetic order.

An incommensurate elliptical helical magnetic structure in the frustrated coupled-spin-chain system FeTe(2)O(5)Br is surprisingly found to persist down to 53(3) mK (T/T(N)~1/200), according to neutron scattering and muon spin relaxation. In this state, finite spin fluctuations at T→0 are evidenced by muon depolarization, which is in agreement with specific-heat data indicating the presence of both gapless and gapped excitations. We thus show that the amplitude-modulated magnetic order intrinsically accommodates contradictory persistent spin dynamics and long-range order and can serve as a model structure to investigate their coexistence.

Role of antisymmetric exchange in selecting magnetic chirality in Ba3NbFe3Si2O14.

We present an electron spin resonance (ESR) investigation of the acentric Ba(3)NbFe(3)Si(2)O(14), featuring a unique single-domain double-chiral magnetic ground state. Combining simulations of the ESR linewidth anisotropy and the antiferromagnetic-resonance modes allows us to single out the Dzyaloshinsky-Moriya (DM) interaction as the leading magnetic anisotropy term. We demonstrate that the rather minute out-of-plane DM component d(c)=45 mK is responsible for selecting a unique ground state, which endures thermal fluctuations up to astonishingly high temperatures.

Spin amplitude modulation driven magnetoelectric coupling in the new multiferroic FeTe2O5Br.

The magnetic and ferroelectric properties of the layered geometrically frustrated cluster compound FeTe2O5Br were investigated with single-crystal neutron diffraction and dielectric measurements. An incommensurate transverse amplitude modulated magnetic order with the wave vector q=(1/2,0.463,0) develops below T(N)=10.6(2) K. Simultaneously, a ferroelectric order due to exchange striction involving polarizable Te4+ lone-pair electrons develops perpendicular to q and to Fe3+ magnetic moments. The observed magnetoelectric coupling is proposed to originate from the temperature dependent phase difference between neighboring amplitude modulation waves.

Prognostic factors in invasive bladder carcinoma treated by combined modality protocol (organ-sparing approach).

PURPOSE: The results of bladder sparing approach for the treatment of muscle-invasive bladder cancer, using a combination of transurethral resection (TUR), chemotherapy, and radiotherapy, are encouraging. The survival of patients treated by this method is similar to the survival of patients treated by radical cystectomy. The aim of our study was to find out which pretreatment characteristics influence the survival of patients treated by organ sparing approach that would enable us to identify the patients most suitable for this type of treatment. METHODS AND MATERIALS: The prognostic value of different factors, such as age, gender, performance status, hemoglobin level, clinical stage, histologic grade, presence of obstructive uropathy, and completeness of TUR, has been studied in 105 patients with invasive bladder cancer, who received a bladder sparing treatment in the period from 1988 to 1995. They were treated with a combination of TUR, followed by 2-4 cycles of methotrexate, cisplatinum, and vinblastine polychemotherapy. In complete responders the treatment was completed by radiotherapy (50 Gy to the bladder and 40 Gy to the regional lymph nodes), whereas nonresponders underwent cystectomy whenever feasible. RESULTS: Our study has confirmed an independent prognostic value of performance status, histologic grade, and obstructive uropathy, for the disease-specific survival (DSS) of bladder cancer patients treated by a conservative approach. We believe that performance status best reflects the extent of disease and exerts significant influence on the extent and course of treatment, while obstructive uropathy is a good indicator of local spread of the disease, better than clinical T-stage. Our finding that histologic grade is one of the strongest prognostic factors shows that tumor biology also is a very important prognostic factor in patients treated by conservative approach. CONCLUSION: Patients with muscle-invasive bladder cancer who are most likely to benefit from conservative treatment approach include those with good performance status, absence of hydronephrosis, and histologic low grade transitional cell carcinoma.

Invasive bladder cancer: our experience with bladder sparing approach.

PURPOSE: Muscle-invasive bladder cancer (MIBC) is a disease associated with several unresolved therapeutic questions. Radical cystectomy still represents the most frequent treatment approach. The aim of our study was to evaluate the effect and feasibility of bladder-sparing treatment by transurethral resection (TUR) and sequential chemoradiotherapy in patients with biopsy-proven invasive bladder cancer. METHODS AND MATERIALS: After maximal TUR, 105 patients were treated with two to four cycles of methotrexate, cisplatinum, and vinblastine polychemotherapy. In complete responders, the treatment was continued by radiotherapy (50 Gy to the bladder and 40 Gy to the regional lymph nodes), whereas in nonresponders, cystectomy was performed when feasible. RESULTS: Complete response after TUR and chemotherapy was achieved in 52% of patients. After a median follow-up of 42 months, 52 of 75 patients (69%) selected for bladder preservation were without evidence of disease in the bladder. Freedom from local failure in complete responders to chemotherapy was 80% [95% confidence interval (CI), 69-91%) at 4 years. The actuarial survival of the entire group was 58% (95% CI, 47-69%), whereas the survival rate with the bladder intact was 45% (95% CI, 34-56%) at 4 years. Survival was significantly better in patients who responded to chemotherapy (79%) than in nonresponders (35%, p < 0.0001). There was no significant difference in survival between nonresponders who underwent cystectomy and nonresponders who completed treatment with radiotherapy (approximately 30% at 3 years). CONCLUSION: The present study confirms that MIBC is a heterogeneous disease, and that in more than half of patients who are affected, a bladder-sparing approach is safe. Our study has also demonstrated that in nonresponders, radical cystectomy as the treatment of choice is questionable.