In this work we present the magnetic structures and spin reorientation (SR) transitions of the mixed orthochromite-orthoferrite perovskites RFe0.5Cr0.5O3 (R=Tb, Dy, Ho, Er). Magnetization as a ...function of temperature and external magnetic field as well as neutron powder diffraction measurements were used to characterize the magnetic transitions, including the SR transitions in the transition metal sublattice and the ordering of the rare earth sublattice. The studied compounds order antiferromagnetically below 270 K in a Gx configuration compatible with the Γ4 representation. As temperature decreases, all the compounds show a SR transition from Gx (Γ4) to Gz (Γ2). This transition occurs in a wide temperature range, where both magnetic configurations coexist. Below this SR, the behavior in each case depends on the rare earth. HoFe0.5Cr0.5O3 shows Ho3+ sublattice ordering at a relatively high temperature (45 K). DyFe0.5Cr0.5O3 and ErFe0.5Cr0.5O3 show a second SR transition of the transition metal sublattice, from Gz (Γ2) to Gy (Γ1) at low temperatures (15 and 8 K, respectively). Below these temperatures a metamagnetic (MM) transition is observed for these two compounds at an external magnetic field of H ≈ 7 kOe. The fact that this is only observed for compounds showing Gz (Γ2) to Gy (Γ1) transition suggests that there is a correlation between the Gy (Γ1) order and the MM transition. Finally, TbFe0.5Cr0.5O3 is a peculiar case, since it is the only compound in this family that shows a re-entrant SR to Gx (Γ4) at very low temperatures. By combining these results with previous reports on RFeO3, RCrO3, and RFe0.5Cr0.5O3, we develop a method to qualitatively estimate the SR temperature and the type of transition. We also propose a complete magnetic phase diagram containing the SR transitions and R3+ ordering temperatures for all the RFe0.5Cr0.5O3 (R=Tb, Dy, Ho, Er, Tm, Yb, and Lu) compounds.
Ni4Nb2O9 and Co4Nb2O9 have two different structures derived from corundum which show different magnetic and electrical properties. The ferrimagnetism (FIM) associated with magnetization reversal (MR) ...of the former and the antiferromagnetism (AFM) combined with the magnetic field control of the polarization of the latter are of interest for applications in spintronics. The exploration of the Ni4−xCoxNb2O9 series was thus appealing because it presents all ingredients to generate exotic magnetic ground states as a result of competing magnetic exchanges due to the framework of the O6 octahedra, around the magnetic transition metals, that share faces, edges and apices, leading to a structure described as the stacking of layers of honeycomb type and/or zigzag chains. This paper reports the domain of stability of each structure (Pbcn up to x = 2 and P3c1 for x ≥ 2.5) with the evolution of the structural and physical properties over the entire series. This overview allows a (T, x) phase diagram to be established on the base of room-temperature X-ray powder diffraction data and macroscopic magnetization characterizations in addition to dielectrical and electrical measurements. Four domains are identified increasing x, (i) Pbcn, FIM with MR, (ii) Pbcn, FIM without MR, (iii) coexistence of Pbcn and P3c1, and (iv) P3c1, AFM with linear magnetoelectric properties. Despite the change of structure, some characteristic parameters show a continuous evolution, such as the unit cell volume, which increases with x unlike the magnetic transition temperature, which decreases with x, from 77 K to 27 K.
In this work we present the architectural and performance studies concerning a prototype of a distributed Tier2 infrastructure for HEP, instantiated between the two Italian sites of INFN-Romal and ...INFN-Napoli. The network infrastructure is based on a Layer-2 geographical link, provided by the Italian NREN (GARR), directly connecting the two remote LANs of the named sites. By exploiting the possibilities offered by the new distributed file systems, a shared storage area with synchronous copy has been set up. The computing infrastructure, based on an OpenStack facility, is using a set of distributed Hypervisors installed in both sites. The main parameter to be taken into account when managing two remote sites with a single framework is the effect of the latency, due to the distance and the end-to-end service overhead. In order to understand the capabilities and limits of our setup, the impact of latency has been investigated by means of a set of stress tests, including data I/O throughput, metadata access performance evaluation and network occupancy, during the life cycle of a Virtual Machine. A set of resilience tests has also been performed, in order to verify the stability of the system on the event of hardware or software faults. The results of this work show that the reliability and robustness of the chosen architecture are effective enough to build a production system and to provide common services. This prototype can also be extended to multiple sites with small changes of the network topology, thus creating a National Network of Cloud-based distributed services, in HA over WAN.
Ternary chalcogenides (AB2X4) based on the spinel structure are gaining a great deal of attention because of the possibility of tuning their magnetic and optoelectronic properties not only by ...changing chemical composition but also by altering their degree of inversion. Here we report a rapid high‐pressure synthetic method for the synthesis of MIn2S4 powders starting from commercially available solid sulfides. We prove the versatility of our method by reporting the synthesis of six members of the MIn2S4 family (M = Mn, Fe, Co, Ni, Zn, and Cd) under high‐pressure conditions (3.5 GPa); these compounds show complete to moderate degrees of inversion. Furthermore, this family covers a spectral region that includes visible band gaps. Interestingly, the structural refinement carried out by X‐ray and neutron diffraction allows one to establish positive correlations between the gap and different parameters, including the degree of inversion. Finally, as a proof‐of‐concept, these ternary chalcogenides show moderate photocatalytic hydrogen production from aqueous solutions.
We describe a high‐pressure synthetic method for MIn2S4 powders starting from commercially available solid sulfides (M = Mn, Fe, Co, Ni, Zn, and Cd) that show variable inversion degrees. This family covers a spectral region that includes visible band gaps. As a proof‐of‐concept, these ternary chalcogenides show moderate photocatalytic hydrogen production from aqueous solutions.
Ni
Nb
O
is an insulating compensated ferrimagnet with
= 77 K and
= 33 K. We report here the study of the magnetic anisotropy using millimeter-size crystals grown in an image furnace. The ...magnetization measurements, vs temperature, performed with
aligned along the three main crystallographic axes, show similar Curie-Weiss temperatures (
≈ 190 K) and rather similar effective paramagnetic moments (from 3.5
to 3.6
). This suggests that the strongest magnetic interaction is the antiferromagnetic one, coupling the ferromagnetic distorted honeycomb layers and zigzag ribbons via face sharing NiO
octahedra. This strong antiferromagnetic coupling is supported by DFT calculations that do not evidence any inter site ferromagnetic interaction, leading to total compensation between magnetic moments of both Ni
sites. Measurements vs magnetic field below
reveal an anisotropic behaviour, with square magnetization loops for
in the
plane, whereas linear
(
) curves without hysteresis are observed for
. This anisotropy between
plane and
axis occurs also in the magnetization reversal (MR), which is observed in the
plane only. Starting from
(
) virgin curves collected just below
= 33 K with
or
, the memory-like effect was tested through magnetization switching induced by
or
alternating changes. Below
, smaller
is needed to switch
symmetrically for
along
than along
, and, for
switching (2 K interval, constant
), a larger
change is obtained along
than along
. The comparison with ferrimagnetic oxides which exhibit MR, like spinels or rare earth orthoferrites, shows that Ni
Nb
O
is unique since only one magnetic cation over two sites in octahedral coordination is at play, thus providing a unique platform to study
switching but also a challenge for theoretical interpretation.
Abstract
The magnetization reversal (MR) of the layered Ni
4
−
x
Zn
x
Nb
2
O
9
ferrimagnetic compounds, with
x
=
0
,
0.25
,
0.50
and 0.75, is studied in this work using Monte Carlo (MC) simulations ...and mean field (MF) calculations. First, we analyze the parent compound to set the parameters of our simulations; testing together MC simulations, MF calculations, and MR experiments reported by Bolletta
et al
(2022
J. Appl. Phys.
132
153901). Then using two different approaches we fit the MR curves of the series of compounds finding a quite good agreement between MC simulations and the experiments. According to these results, Zn substitutions change the relative contribution to the magnetization of the different layers. Here we present two possible hypotheses to explain this effect; one involving a heterogeneous distribution of Zn
2+
among the layers, and the other related to distortions of the NiO
6
octahedra.
Ni4Nb2O9is an insulating compensated ferrimagnet withTN= 77 K andTcomp= 33 K. We report here the study of the magnetic anisotropy using millimeter-size crystals grown in an image furnace. The ...magnetization measurements, vs temperature, performed withHaligned along the three main crystallographic axes, show similar Curie-Weiss temperatures (Θp≈ 190 K) and rather similar effective paramagnetic moments (from 3.5μBto 3.6μB). This suggests that the strongest magnetic interaction is the antiferromagnetic one, coupling the ferromagnetic distorted honeycomb layers and zigzag ribbons via face sharing NiO6octahedra. This strong antiferromagnetic coupling is supported by DFT calculations that do not evidence any inter site ferromagnetic interaction, leading to total compensation between magnetic moments of both Ni2+sites. Measurements vs magnetic field belowTNreveal an anisotropic behaviour, with square magnetization loops forHin theabplane, whereas linearM(H) curves without hysteresis are observed forH‖c. This anisotropy betweenabplane andcaxis occurs also in the magnetization reversal (MR), which is observed in theabplane only. Starting fromM(H) virgin curves collected just belowTcomp= 33 K withH‖aorH‖b, the memory-like effect was tested through magnetization switching induced byHorTalternating changes. BelowTcomp, smallerHis needed to switchMsymmetrically forHalongbthan alonga, and, forTswitching (2 K interval, constantH), a largerMchange is obtained alongathan alongb. The comparison with ferrimagnetic oxides which exhibit MR, like spinels or rare earth orthoferrites, shows that Ni4Nb2O9is unique since only one magnetic cation over two sites in octahedral coordination is at play, thus providing a unique platform to studyMswitching but also a challenge for theoretical interpretation.
Ni 4 Nb 2 O 9 and Co 4 Nb 2 O 9 have two different structures derived from corundum which show different magnetic and electrical properties. The ferrimagnetism (FIM) associated with magnetization ...reversal (MR) of the former and the antiferromagnetism (AFM) combined with the magnetic field control of the polarization of the latter are of interest for applications in spintronics. The exploration of the Ni 4− x Co x Nb 2 O 9 series was thus appealing because it presents all ingredients to generate exotic magnetic ground states as a result of competing magnetic exchanges due to the framework of the O 6 octahedra, around the magnetic transition metals, that share faces, edges and apices, leading to a structure described as the stacking of layers of honeycomb type and/or zigzag chains. This paper reports the domain of stability of each structure ( Pbcn up to x = 2 and P 3̄ c 1 for x ≥ 2.5) with the evolution of the structural and physical properties over the entire series. This overview allows a ( T , x ) phase diagram to be established on the base of room-temperature X-ray powder diffraction data and macroscopic magnetization characterizations in addition to dielectrical and electrical measurements. Four domains are identified increasing x , (i) Pbcn , FIM with MR, (ii) Pbcn , FIM without MR, (iii) coexistence of Pbcn and P 3̄ c 1, and (iv) P 3̄ c 1, AFM with linear magnetoelectric properties. Despite the change of structure, some characteristic parameters show a continuous evolution, such as the unit cell volume, which increases with x unlike the magnetic transition temperature, which decreases with x , from 77 K to 27 K.
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