Low dimensional quantum magnets are interesting because of the emerging collective behavior arising from strong quantum fluctuations. The one-dimensional (1D) S = 1/2 Heisenberg antiferromagnet is a paradigmatic example, whose low-energy excitations, known as spinons, carry fractional spin S = 1/2. These fractional modes can be reconfined by the application of a staggered magnetic field. Even though considerable progress has been made in the theoretical understanding of such magnets, experimental realizations of this low-dimensional physics are relatively rare. This is particularly true for rare-earth-based magnets because of the large effective spin anisotropy induced by the combination of strong spin–orbit coupling and crystal field splitting. Here, we demonstrate that the rare-earth perovskite YbAlO3 provides a realization of a quantum spin S = 1/2 chain material exhibiting both quantum critical Tomonaga–Luttinger liquid behavior and spinon confinement–deconfinement transitions in different regions of magnetic field–temperature phase diagram.

We report the low temperature magnetic properties of the DyScO3 perovskite, which were characterized by means of single crystal and powder neutron scattering, and by magnetization measurements. Below TN = 3.15 K, Dy 3+ moments form an antiferromagnetic structure with an easy axis of magnetization lying in the ab-plane. The magnetic moments are inclined at an angle of ∼ ±28 • to the b-axis. We show that the ground state Kramers doublet of Dy 3+ is made up of primarily |±15/2 eigenvectors and well separated by crystal field from the first excited state at E1 = 24.9 meV. This leads to an extreme Ising single-ion anisotropy, M ⊥ /M ∼ 0.05. The transverse magnetic fluctuations, which are proportional to M 2 ⊥ /M 2 , are suppressed and only moment fluctuations along the local Ising direction are allowed. We also found that the Dy-Dy dipolar interactions along the crystallographic c-axis are 2-4 times larger than in-plane interactions.

In this paper we report low-temperature magnetic properties of the rare-earth perovskite material YbAlO 3 . Results of elastic and inelastic neutron scattering experiment, magnetization measurements along with the crystalline electrical field (CEF) calculations suggest that the ground state of Yb moments is a strongly anisotropic Kramers doublet, and the moments are confined in the ab-plane, pointing at an angle of ϕ = ±23.5 • to the a-axis. With temperature decreasing below T N = 0.88 K, Yb moments order into the coplanar, but non-collinear antiferromagnetic (AFM) structure Ax G y, where the moments are pointed along their easy-axes. In addition, we highlight the importance of the dipole-dipole interaction, which selects the type of magnetic ordering and may be crucial for understanding magnetic properties of other rare-earth orthorhombic perovskites. Further analysis of the broad diffuse neutron scattering shows that one-dimensional interaction along the c-axis is dominant, and suggests YbAlO 3 as a new member of one dimensional quantum magnets.

In this paper we present a comprehensive study of magnetic dynamics in the rare-earth orthoferrite YbFeO 3 at temperatures below and above the spin-reorientation (SR) transition T SR = 7.6 K, in magnetic fields applied along the a, b and c axes. Using single-crystal inelastic neutron scattering, we observed that the spectrum of magnetic excitations consists of two collective modes well separated in energy: 3D gapped magnons with a bandwidth of ∼60 meV, associated with the antiferromagnetically (AFM) ordered Fe subsystem, and quasi-1D AFM fluctuations of ∼1 meV within the Yb subsystem, with no hybridization of those modes. The spin dynamics of the Fe subsystem changes very little through the SR transition and could be well described in the frame of semiclassical linear spin-wave theory. On the other hand, the rotation of the net moment of the Fe subsystem at T SR drastically changes the excitation spectrum of the Yb subsystem, inducing the transition between two regimes with magnon and spinon-like fluctuations. At T < T SR , the Yb spin chains have a well defined field-induced ferromagnetic (FM) ground state, and the spectrum consists of a sharp single-magnon mode, a two-magnon bound state, and a two-magnon continuum, whereas at T > T SR only a gapped broad spinon-like continuum dominates the spectrum. In this work we show that a weak quasi-1D coupling within the Yb subsystem J Yb-Yb , mainly neglected in previous studies, creates unusual quantum spin dynamics on the low energy scales. The results of our work may stimulate further experimental search for similar compounds with several magnetic subsystems and energy scales, where low-energy fluctuations and underlying physics could be "hidden" by a dominating interaction. entropy evolution [9], laser-pulse induced ultrafast spinreorientation [10-12] etc. Magnetic property investigations of the rare-earth orthoferrites RFeO 3 have shown that the Fe 3+ moments (S = 5 2 ) are ordered in a canted AFM structure Γ 4 at high temperature with T N ≈ 600 K (details of the notations are given in [13]), and the spin canting gives a weak net ferromagnetic moment along the c axis [ Fig. 1(c)] [13][14][15]. Furthermore, symmetry analysis and careful neutron diffraction measurements have found a second "hidden" canting along the b-axis, which is symmetric relative to the ac-plane and does not create a net moment [16,17]. With decreasing temperature, a spontaneous spin-reorientation (SR) transition from Γ 4 to the Γ 2 magnetic configuration occurs in many orthoferrites with magnetic R-ions [13,14] in a wide temperature range from T SR ≈ 450 K for SmFeO 3 down to T SR ≈ 7.6 K for YbFeO 3 , and the net magnetic moment rotates from the a to the c axis [see Fig. 1(c-e)]. Most of previous work that was devoted to the investigation of the SR transition in RFeO 3 , associated this phenomenon with the R-Fe exchange interaction, because orthoferrites with nonmagnetic R =La, Y or Lu preserve the Γ 4 magnetic structure down to the lowest temperatures.Taking into account three characteristic t...

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We investigate the magnetic dynamics of the orthorhombic perovskite TmFeO 3 at low temperatures, below the spin reorientation transition at T SR ≈ 80 K, by means of time-of-flight neutron spectroscopy. We find that the magnetic excitation spectrum combines two emergent collective modes associated with different magnetic sublattices. The Fe subsystem orders below T N ∼ 632 K into a canted antiferromagnetic structure and exhibits sharp, high-energy magnon excitations. We describe them using linear spin-wave theory, and reveal a pronounced anisotropy between in-and out-of-plane exchange interactions, which was mainly neglected in previous reports on the spin dynamics in orthoferrites. At lower energies, we find two crystalline electrical field (CEF) excitations of Tm 3+ ions at energies of ∼2 and 5 meV. In contrast to the sister compound YbFeO 3 , where the Yb 3+ ions form quasi-one-dimensional chains along the c axis, the Tm excitations show dispersion along both directions in the (0KL) scattering plane. Analysis of the neutron scattering polarization factor reveals a longitudinal polarization of the 2 meV excitation. To evaluate the effect of the CEF on the Tm 3+ ions, we perform point-charge model calculations, and their results quantitatively capture the main features of Tm single-ion physics, such as energies, intensities, and polarization of the CEF transitions, and the type of magnetic anisotropy.

We employed small-angle neutron scattering to demonstrate that the magnetic skyrmion lattice can be realized in bulk chiral magnets as a thermodynamically stable state at temperatures much lower than the ordering temperature of the material. This is in the regime where temperature fluctuations become completely irrelevant to the formation of the topologically non-trivial magnetic texture. In this attempt we focused on the model helimagnet MnSi, in which the skyrmion lattice was previously well characterized and shown to exist only in a very narrow phase pocket close to the Curie temperature of 29.5 K. We revealed that large uniaxial distortions caused by the crystal-lattice strain in MnSi result in stabilization of the skyrmion lattice in magnetic fields applied perpendicular to the uniaxial strain at temperatures as low as 5 K. To study the bulk chiral magnet subjected to a large uniaxial stress, we have utilized µm-sized single-crystalline inclusions of MnSi naturally found inside single crystals of the nonmagnetic material Mn11Si19. The reciprocal-space imaging allowed us to unambiguously identify the stabilization of the skyrmion state over the competing conical spin spiral.

The Heisenberg antiferromagnetic spin-1/2 chain, originally introduced almost a century ago, is one of the best studied models in quantum mechanics due to its exact solution, but nevertheless it continues to present new discoveries. Its low-energy physics is described by the Tomonaga-Luttinger liquid of spinless fermions, similar to the conduction electrons in one-dimensional metals. In this work we investigate the Heisenberg spin-chain compound YbAlO3 and show that the weak interchain coupling causes Umklapp scattering between the left- and right-moving fermions and stabilizes an incommensurate spin-density wave order at q = 2kF under finite magnetic fields. These Umklapp processes open a route to multiple coherent scattering of fermions, which results in the formation of satellites at integer multiples of the incommensurate fundamental wavevector Q = nq. Our work provides surprising and profound insight into bandstructure control for emergent fermions in quantum materials, and shows how neutron diffraction can be applied to investigate the phenomenon of coherent multiple scattering in metals through the proxy of quantum magnetic systems.