Low Temperature Magnetic State Research Articles

Magnetic order in holmium and erbium formate: Parent frameworks for a potential random spin chain paramagnet

This work uses a combination of neutron diffraction and bulk property measurements to establish the low temperature magnetic states in the dense metal-organic frameworks Ho(HCO2)3 and Er(HCO2)3; whose structures feature chains of face-sharing LnO9 polyhedra packed into a triangular lattice. Below 0.7 K Ho(HCO2)3 is found to adopt a state in which the magnetic moment on its ferromagnetic chains vary from neighbouring chains but the sum around each triangle is constant. Er(HCO2)3 is found to be the first lanthanide formate to adopt an ordered magnetic state with antiferromagnetic coupling within its chains near 50 mK. The potential to combine the ferromagnetic and antiferromagnetic coupling within chains associated with Ho and Er cations, respectively, in the same compound has also been explored via the series Ho1-xErx(HCO2)3. Ho0.5Er0.5(HCO2)3 remains paramagnetic to 0.4 K, suggesting it may be a starting point to search for a random spin chain paramagnet.

High-Pressure Synthesis and Magnetic Property of a Novel Ferrimagnetic Quadruple Perovskite YMn<sub>3</sub>Co<sub>4</sub>O<sub>12</sub>

A novel quadruple perovskite oxide YMn3Co4O12 has been synthesized in high-pressure and high-temperature conditions of 16 GPa and 1473 K, respectively. Rietveld refinement of synchrotron X-ray powder diffraction data reveals that this oxide crystallizes in a cubic quadruple perovskite structure in a space group of Im3 (No. 204) with a 1:3-type atomic ordering of Y and Mn at A-sites, and the bond valence analysis suggests the valence state of YMn3+3Co3+4O12. A ferromagnetic-like transition is observed at ~125 K and the magnetization value reaches up to ~3 µB per formula unit at 5 K. The low-temperature magnetic state can be interpreted as ferrimagnetism with antiparallel alignment of A'-site Mn3+ (S = 2) and B-site Co3+ (high-spin, S = 2), which is in contrast to the antiferromagnetism in other A'-Mn-containing quadruple perovskite oxides. This finding proposes that the coexistence of A’-Mn3+ and B-Co3+ leading to ferrimagnetic state is realized in the specific structure with distinct crystallographic sites.

Role of Lanthanides and Bilayer Fe2As2 in the Electronic Properties of RbLn2Fe4As4O2 (Ln = Gd, Tb, and Dy) Superconductors.

The superconducting transition temperatures (Tc) of RbGd2Fe4As4O2, RbTb2Fe4As4O2, and RbDy2Fe4As4O2 are 35 K, 34.7 K, and 34.3 K without doping, respectively. For the first time, we have studied the high-temperature nonmagnetic state and the low-temperature magnetic ground state of 12442 materials, RbTb2Fe4As4O2 and RbDy2Fe4As4O2, using first principles calculations and comparing them with RbGd2Fe4As4O2. We also performed a detailed study of the effects of lanthanides and bilayer Fe2As2. We predict that the ground state of RbLn2Fe4As4O2 (Ln = Gd, Tb, and Dy) is spin-density-wave-type, in-plane, striped antiferromagnets, and the magnetic moment around each Fe atom is about 2 μB. We also found that the structural differences caused by the simple ionic radius have little effect on the properties of these three materials. Different lanthanide elements themselves play a major role in the electronic properties of the materials. It can be confirmed that the effect of Gd on RbLn2Fe4As4O2 is indeed different from that of Tb and Dy, and the presence of Gd is more conducive to interlayer electron transfer. This means that Gd can transfer more electrons from the GdO layer to the FeAs layer compared to Tb and Dy. Therefore, RbGd2Fe4As4O2 has a stronger internal coupling strength of the bilayer Fe2As2 layer. This can explain why the Tc of RbGd2Fe4As4O2 is slightly higher than that of RbTb2Fe4As4O2 and RbDy2Fe4As4O2.

Electrodynamics of MnBi2Te4 intrinsic magnetic topological insulators

We report on the electrodynamics of MnBi2Te4 thin films, an intrinsic magnetic topological material. We study its optical conductivity from terahertz (THz) to ultraviolet (UV) frequencies as a function of the film thickness, highlighting the presence of surface topological states superimposed on the bulk electrodynamics response. For the thinnest film, where the charge transport is dominated by Dirac surface states, we investigate the effect of the phase transition from the high-temperature topological protected state to the low-temperature magnetic (time-reversal broken) state by measuring the optical conductivity across the Néel temperature. At low temperatures, the breaking of the time reversal symmetry affects the optical conductivity, indicating that a magnetic-induced gap opens below TN.

Emergence of low-temperature glassy dynamics in Ru substituted non-magnetic insulator CaHfO3

Non-magnetic insulators/semiconductors with induced magnetism introduced via transition metal substitution are one of the promising materials in the field of spintronics, magnetoelectronics and magneto-optical devices. In this context, here, we focus on magnetism induced in a non-magnetic insulator CaHfO3, by the substitution of 4d element Ru, at Hf-site. Structural investigations indicate that substitution of Ru4+ (up to 50%) does not affect the original crystal structure of the parent compound. Magnetic studies divulge a crossover from a diamagnetic to paramagnetic state with 20% Ru substitution. Further replacement of Hf results in a glassy magnetic state in CaHf1−x Ru x O3 (0.3 ⩽ x ⩽ 0.5). The nature of the low temperature glassiness (below 20 K) in these compositions is confirmed through Vogel–Fulcher and Power law, along with, magnetic memory effect and relaxation dynamics. The observed glassiness is explained through the phenomenological ‘hierarchical model’. Our studies indicate that the presence of competing short range interactions among randomly arranged Ru cations in non-magnetic insulator CaHfO3 are responsible for the observed low temperature magnetic state in this series with compositions >0.25.

Coupled frustrated ferromagnetic and antiferromagnetic quantum spin chains in the quasi-one-dimensional mineral antlerite Cu3SO4 (OH) 4

Magnetic frustration, the competition among exchange interactions, often leads to novel magnetic ground states with unique physical properties which can hinge on details of interactions that are otherwise difficult to observe. Such states are particularly interesting when it is possible to tune the balance among the interactions to access multiple types of magnetic order. We present antlerite, Cu$_3$SO$_4$(OH)$_4$, as a potential platform for tuning frustration. Contrary to previous reports, the low-temperature magnetic state of its three-leg zigzag ladders is a quasi-one-dimensional analog of the magnetic state recently proposed to exhibit spinon-magnon mixing in botallackite. Density functional theory calculations indicate that antlerite's magnetic ground state is exquisitely sensitive to fine details of the atomic positions, with each chain independently on the cusp of a phase transition, indicating an excellent potential for tunability.

Enhancement of giant magnetoelectric effect in Ni-doped CaBaCo4O7

The polar ferrimagnet CaBaCo${}_{4}$O${}_{7}$ exhibits the largest magnetic field driven electric polarization change \ensuremath{\Delta}$P$ reported so far in a narrow temperature range. Here, the authors demonstrate that only 2.5% of Ni substitution for Co increases the magnitude of \ensuremath{\Delta}$P$ by about 30%, as well as expanding the temperature range in which the giant \ensuremath{\Delta}$P$ appears down to a low temperature. This is attributable to the switching of the low-temperature zero magnetic field state from a ferrimagnetic to an antiferromagnetic state.

Frustration, strain and phase co-existence in the mixed valent hexagonal iridate Ba3NaIr2O9

Using detailed synchrotron diffraction, magnetization, thermodynamic and transport measurements, we investigate the relationship between the mixed valence of Ir, lattice strain and the resultant structural and magnetic ground states in the geometrically frustrated triple perovskite iridate Ba3NaIr2O9. We observe a complex interplay between lattice strain and structural phase co-existence, which is typically not observed in this family of compounds. The low temperature magnetic ground state is characterized by the absence of long-range magnetic order, and points towards the condensation of a cluster glass state from an extended regime of short range magnetic correlations.

Evolution\ufeff of spin freezing transition and structural, magnetic phase diagram of Dy_{2-textit{x}}La_textit{x}Zr_{2}O_{7} (0 letextit{x}le 2.0)

Dy_{2}Zr_{2}O_{7} a disordered pyrochlore system, exhibits the spin freezing behavior under the application of the magnetic field. We have performed detailed magnetic studies of Dy_{2-textit{x}}La_textit{x}Zr_{2}O_{7} to understand the evolution of the magnetic spin freezing in the system. Our studies suggest the stabilization of the pyrochlore phase with the substitution of non-magnetic La along with the biphasic mixture of fluorite and pyrochlore phases for the intermediate compositions. We observed that the spin freezing (T_{f}sim 17 K) at higher La compositions (1.5 letextit{x}le 1.99) is similar to the field-induced spin freezing for low La compositions (0 letextit{x}le 0.5) and the well-known spin ice systems Dy_{2}Ti_{2}O_{7} and Ho_{2}Ti_{2}O_{7}. The low-temperature magnetic state for higher La compositions (1.5 letextit{x}le 1.99) culminates into a spin-glass like state below 6 K. Cole–Cole plot and Casimir-du Pracute{e} fit shows the narrow distribution of spin relaxation time in these compounds.

Low-temperature magnetic state of Ho7Rh3 studied by neutron diffraction and AC magnetic susceptibility

Low-temperature magnetic state of Ho₇Rh₃ studied by neutron diffraction and AC magnetic susceptibility

New nickel(II) and copper(II) complexes with 1-tert-butyl-1H- and 1,5-diaminotetrazoles

Novel nickel(II) and copper(II) coordination compounds with 1-tert-butyl-1H-tetrazole (L1) and 1,5-diaminotetrazole (L2) having compositions of Ni(L1)Cl2·H2O, Ni(L1)2Br2·2H2O, Cu(L1)Cl2, Cu(L1)Br2, Ni(L2)2(C2N3)2, Cu(L2)2(C2N3)2 were synthesized. The compounds were studied using the methods of infrared and diffuse reflectance spectroscopy, single-crystal and powder X-ray diffraction, static magnetic susceptibility. Crystal structures have been determined for Cu(L1)Br2 and Cu(L2)2(C2N3)2 complexes. Magnetic susceptibility measurements of Cu(II) and Ni(II) based complexes have revealed a wide spectrum of low-temperature magnetic states ranging from paramagnets composed of virtually isolated single magnetic ions or ferromagnetic chains to a weak ferromagnet with a remarkably strong magnetocrystalline anisotropy.

Tetramethyltetrathiafulvalene [(NbOF4)-]∞: One-Dimensional Charge Transfer Salt with an Infinite Anion Chain.

An unusual valence one-dimensional (1D) molecular charge transfer salt (TMTTF)(NbOF4) [TMTTF = tetramethyltetrathiafulvalene] with infinite anion chains was prepared. To understand the crystal structure and electronic states of the (TMTTF)(NbOF4) salt, we performed synchrotron X-ray diffraction, electron spin resonance, and static magnetization measurements. There is only one independent TMTTF molecule in the unit cell of (TMTTF)(NbOF4). The TMTTF1+ cation radicals stack to form 1D columns. The effective charge of the TMTTF molecule in the crystal was estimated to be +1. The electric charge of TMTTF donors is compensated by the infinite anion chains [(NbOF4)-]∞. The magnetic susceptibility of (TMTTF)(NbOF4) is 4 × 10-4 emu/mol at room temperature and shows weak temperature dependence above 60 K. However, some deviation appears below 60 K. The temperature dependence of the spin susceptibility shows a noticeable enhancement below 60 K. Below 5 K, the magnetization curve as a function of the magnetic field deviates from the straight line and shows a saturation tendency. The experimental results can be reproduced well with the S = 2 spin system at 2 K. The detailed analysis of the crystal structure and anomalous low-temperature magnetic state magnetic properties of (TMTTF)(NbOF4) are discussed.

Magnetism and electrical transport in Y-doped layered iridate Sr2IrO4

Here, we report an investigation of structural, magnetic and electronic properties in Y-doped layered iridate (Sr1-xYx)2IrO4 (x⩽0.1). The parent Sr2IrO4 is a well-studied spin-orbit coupling (SOC) induced insulator with an antiferromagnetic ground state. The Y-doping here equivalently acts for electron doping without altering the vital parameters such as, SOC and electron correlation. Experimental results show a minute change in structural parameters and an equivalent charge conversion from Ir4+ to Ir3+. Unlike similarly other electron-doped system, the low temperature magnetic and electronic state in present series is minimally influenced. The charge conduction mechanism follows 2-dimensional hopping model in whole series. Magnetoresistance (MR) data show an interesting sign change with both temperature and magnetic field. The positive MR both at low temperature follows weak antilocalization behavior where the sign change in MR is believed to be caused by an interplay between SOC and magnetic moment.

Structural and magnetic properties of the layered perovskite system Sr2−xPrxCoO4 (x = 0.7, 0.9, 1.1)

We report the detailed structural and temperature dependent magnetic properties of well characterized, polycrystalline samples of Sr2−xPrxCoO4 (x = 0.7, 0.9, 1.1), in the temperature range 5 K–300 K. In Sr2−xPrxCoO4 (0.7 ≤x≤ 1.1), short range or long range ferromagnetic (FM) order appears below TC~ 150 K. In general the low temperature magnetic state is a mixture of FM, paramagnetic (PM) and antiferromagnetic (AFM) matrices. The spin glass phase (SG) is observed in Sr1.1Pr0.9CoO4 below Tf = 15 K due to comparable strengths of FM and AFM interactions. With increasing x, the Jahn-Teller distortion weakens the FM interaction and AFM interaction starts dominating. Isothermal remanent magnetization (IRM) as a function of time (t) shows that the relaxation mechanism is associated with the interfaces between different types of magnetic matrices.

Non-equilibrium magnetic response of canonical spin glass and magnetic glass

Time and history dependent magnetization has been observed in a wide variety of materials, which are collectively termed as the glassy magnetic systems. However, such systems showing similar non-equilibrium magnetic response can be microscopically very different and they can be distinguished by carefully looking into the details of the observed metastable magnetic behavior. Canonical spin glass (SG) is the most well studied member of this class and has been extensively investigated both experimentally and theoretically over the last five decades. In canonical SGs, the low temperature magnetic state obtained by cooling across the SG transition temperature in presence of an applied magnetic field is known as the field cooled (FC) state. This FC state in canonical SG is widely believed as an equilibrium state arising out of a thermodynamic second order phase transition. Here, we show that the FC state in canonical SG is not really an equilibrium state of the system. We report careful dc magnetization and ac susceptibility measurements on two canonical SG systems, AuMn (1.8%) and AgMn (1.1%). The dc magnetization in the FC state shows clear temperature dependence. In addition, the magnetization shows a distinct thermal hysteresis in the temperature regime below the SG transition temperature. On the other hand, the temperature dependence of ac susceptibility has clear frequency dispersion below SG transition in the FC state prepared by cooling the sample in the presence of a dc-bias field. We further distinguish the metastable response of the FC state of canonical SG from the metastable response of the FC state in an entirely different class of glassy magnetic system namely magnetic glass, where the non-equilibrium behavior is associated with the kinetic-arrest of a first order magnetic phase transition.

Structure, magnetism and electrical transport in La1-x-yPryCaxMnO3 (y = 0.30, 0.35, 0.40; x = 0.40): Consequences of the interplay between intrinsic ionic radius and extrinsic particle size

The structural, microstructural, magnetic and electrical transport properties have been correlatively studied to decipher the complex consequences of variation of intrinsic parameter ,the average La-site cationic radii and extrinsic particle size on the magneto-electrical phase coexistence in La1-x-yPryCaxMnO3 (y = 0.30, 0.35, 0.40; x = 0.40). Polycrystalline powders prepared by sol-gel route were sintered at 600 °C, 900 °C, 1100 °C, and 1300 °C to facilitate particle size variation. Rietveld refinement of the powder X-ray diffraction data confirms that all samples have an orthorhombic structure with Pnma space group. The lattice constants decrease with decreasing ionic radii, while at a fixed ionic radius, the enhanced particle size increases them. The average apical Mn−O−Mn bond angles and the average Mn−O bond lengths decrease with rising ionic radii but increase with particle size at a fixed composition. Magnetization measurements show sequential paramagnetic (PM)-antiferromagnetic (AFM)-ferromagnetic (FM) transitions on lowering the temperature is lowered. The AFM-FM transition exhibits (i) pronounced hysteresis between field-cooled cooling (FCC) and field-cooled warming (FCW) (ii) strong divergence between zero-field cooling (ZFC) and FCW curves. The low-temperature magnetic state transforms from spin glass-like to a cluster glass-like as the ionic radii or the particle size decreases. These behaviors are caused by the mesoscale modifications in the magnetic phase profile where the AFM and FM phases due to the interplay between the average La-site cationic radii and the particle size. In general, the FM component increases with an increase in the particle size, but it decreases at lower ionic radii. The presence of a large thermal hysteresis in the insulator-metal transition (IMT) coupled with the one in FCC-FCW magnetization at particle sizes ~200 nm–160 nm, and ~460-400 nm demonstrates that this particle size regime is the most conducive to the phase separation. IMT disappears at smaller ionic radii and larger particle sizes due to the enhancement of AFM and charge-ordering. The PM and AFM regimes in all samples reveal variable range hopping conduction with particle size and ionic radii dependent activation. The observed phenomena have been explained in terms of the interplay between the ionic radii and particle size induced changes in the average apical Mn−O−Mn bond angles and the average Mn−O bond length.

Origins of superparamagnetism in self-accommodated and trained Ni50Mn37.5Sn12.5 single crystal

The low temperature magnetic state of martensite in the shape memory Ni50Mn37.5Sn12.5 single crystal was confirmed from DC and AC magnetization measurements. At temperatures below the martensite finish and above the Curie temperature of martensite the martensite phase shows superparamagnetic behavior. On cooling growing superparamagnetic clusters manifest a strong interaction and develop, below the freezing temperature (~200 K), into a nonconventional spin glass state. The amount of retained austenite evaluated by high-energy synchrotron radiation was estimated at the level of 1.5 – 2%. Subsequent training procedure cleansed martensite from any retained austenite fraction. The evaluated cluster magnetic moment decreased following training (~9.5%). It is demonstrated that the retained austenite effectively subsidizes but not warrants the superparamagnetic exchange in martensite, which descends from alterations in interatomic spacing inflicted by martensitic transformation.

Structural, magnetic and electronic properties of Ti-doped BaFeO3-δ exhibiting colossal dielectric permittivity

We report a systematical investigation of the structural, magnetic, electronic, and dielectric properties of BaFe1-xTixO3-δ (x = 0.05, 0.10, 0.15 and 0.20) samples synthesized via the solid-state reaction method. Rietveld refinement using a combination of room-temperature X-ray (XRD) and neutron powder diffraction (NPD) data confirms single phases with a 6H-type structure for all the samples. X-ray absorption spectroscopy (XAS) study reveals a coexistence of Fe3+ and Fe4+, whose ratio remains almost unchanged with increasing Ti concentration. Magnetization measurements reveal a low-temperature inhomogeneous magnetic state with coexisting ferromagnetic (FM), AFM clusters and a paramagnetic phase. Moreover, magnetization of x = 0.10 shows a pinched hysteresis loop behavior, suggesting the coexistence of hard and soft FM phases in samples with high Ti concentrations. Low-temperature NPD measurements also confirm the absence of any long-range magnetic order in the samples. A colossal dielectric permittivity and two relaxation processes are observed for most of the studied samples. There is a change in electric conduction mechanism from the small polaron hopping to the Mott's variable-range hopping with increasing Ti concentration.

Electron doping induced magnetic glassy state in phase separated YBaCo2O5.5-δ

The structural, magnetic and transport properties of the layered RBaCo$_2$O$_{5.5}$ cobaltites are sensitive to the oxygen stoichiometry. In this present study, we report the presence of a low-temperature magnetic glassy state in electron-doped polycrystalline YBaCo$_2$O$_{5.5}$ cobaltite. The ac magnetization studies show the absence of conventional spin glass features, while the various dc magnetization studies demonstrate the presence of non-equilibrium magnetic glassy state at low temperature. The magnetic glassy state of this sample results from the kinetic arrest of the first order ferro (or ferri) to antiferromagnetic transition. The role of electron doping in the occurrence of magnetic glassy phenomena is discussed in terms of magnetic phase separation involving the Co3+/Co2+ clusters of the ferrimagnetic phase in the Co3+/Co3+ antiferromagnetic matrix.

Multiple Competing Magnetic Interactions in Na4Ni7(PO4)6

The low-temperature magnetic behavior and ground state of the candidate sodium-ion battery cathode compound Na4Ni7(PO4)6 have been investigated by physical property measurements and neutron powder ...