Uniform wustite Fe0.6 Mn0.4 O nanoflowers have been successfully developed as an innovative theranostic agent with T1 -T2 dual-mode magnetic resonance imaging (MRI), for diagnostic applications and therapeutic interventions via magnetic hyperthermia. Unlike their antiferromagnetic bulk counterpart, the obtained Fe0.6 Mn0.4 O nanoflowers show unique room-temperature ferromagnetic behavior, probably due to the presence of an exchange coupling effect. Combined with the flower-like morphology, ferromagnetic Fe0.6 Mn0.4 O nanoflowers are demonstrated to possess dual-modal MRI sensitivity, with longitudinal relaxivity r1 and transverse relaxivity r2 as high as 4.9 and 61.2 mm(-1) s(-1) [Fe]+[Mn], respectively. Further in vivo MRI carried out on the mouse orthotopic glioma model revealed gliomas are clearly delineated in both T1 - and T2 -weighted MR images, after administration of the Fe0.6 Mn0.4 O nanoflowers. In addition, the Fe0.6 Mn0.4 O nanoflowers also exhibit excellent magnetic induction heating effects. Both in vitro and in vivo magnetic hyperthermia experimentation has demonstrated that magnetic hyperthermia by using the innovative Fe0.6 Mn0.4 O nanoflowers can induce MCF-7 breast cancer cell apoptosis and a complete tumor regression without appreciable side effects. The results have demonstrated that the innovative Fe0.6 Mn0.4 O nanoflowers can be a new magnetic theranostic platform for in vivo T1 -T2 dual-mode MRI and magnetic thermotherapy, thereby achieving a one-stop diagnosis cum effective therapeutic modality in cancer management.

Synthesis of Ferromagnetic Fe0.6 Mn0.4 O Nanoflowers as a New Class of Magnetic Theranostic Platform for In Vivo T1 -T2 Dual-Mode Magnetic Resonance Imaging and Magnetic Hyperthermia Therapy.

The 10% Gd and Ti co-doped BiFeO3: A promising multiferroic material

Microstructural, optical and magnetic characterizations of BiFeO 3 multiferroic nanoparticles synthesized via a sol-gel process

We have investigated the effects of temperature on the magnetic properties of the Bi0.9Gd0.1Fe1−x Ti x O3 (x = 0.00–0.20) multiferroic system. Unexpectedly, the coercive fields (H c ) of this multiferroic system increased with increasing temperature. The coercive fields and remanent magnetization were higher over a wide range of temperatures in sample x = 0.10, i.e. in a sample with a composition Bi0.9Gd0.1Fe0.9Ti0.1O3 than those of x = 0.00 and 0.20 compositions. Therefore, we carried out temperature-dependent magnetization experiments extensively for sample x = 0.10. The magnetic hysteresis loops at different temperatures exhibit an asymmetric shift towards the magnetic field axes, which indicates the presence of an exchange bias effect in this material system. The hysteresis loops were also carried out at temperatures of 150 K and 250 K by cooling down the sample from 300 K in various cooling magnetic fields (). The exchange bias field () values increased with and decreased with temperature. The values were tunable by field cooling at temperatures of up to 250 K.

https://iopscience.iop.org/article/10.1088/0022-3727/49/9/095001/pdf

Anomalous coercivity enhancement with temperature and tunable exchange bias in Gd and Ti co-doped BiFeO 3 multiferroics

In this investigation, undoped BiFeO$_3$, Gd doped Bi$_{0.9}$Gd$_{0.1}$FeO$_3$, and Gd-Ti co-doped Bi$_{0.9}$Gd$_{0.1}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.10, 0.20) materials were synthesized to report their multiferroic properties. The structural analysis and phase identification of these multiferroic ceramics were performed using Rietveld refinement. The Rietveld analysis has confirmed the high phase purity of the 10% Gd-Ti co-doped Bi$_{0.9}$Gd$_{0.1}$Fe$_{0.9}$Ti$_{0.1}$O$_3$ sample compared to that of other compositions under investigation. The major phase of this particular composition is of rhombohedral \textit{R3c} type structure (wt% $>99\%$) with negligible amount of impurity phases. In terms of characterization, we address magnetic properties of this co-doped ceramic system by applying substantially higher magnetic fields than that applied in previously reported investigations. The dependence of temperature and maximum applied magnetic fields on their magnetization behavior have also been investigated. Additionally, the leakage current density has been measured to explore its effect on the ferroelectric properties of this multiferroic system. The outcome of this investigation suggests that the substitution of 10% Gd and Ti in place of Bi and Fe, respectively, in BiFeO$_3$ significantly enhances its multiferroic properties. The improved properties of this specific composition is associated with homogeneous reduced grain size, significant suppression of impurity phases and reduction in leakage current density which is further asserted by polarization vs. electric field hysteresis loop measurements.

The 10% Gd and Ti co-doped BiFeO$_3$: A promising multiferroic material

Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal magnetoresistance perovskite below the Curie temperature $T_{C}$ = 70 K and attributed to an antiferromagnetic (AFM) - ferromagnetic (FM) spontaneous phase segregated state of this compound. Field cooled magnetic hysteresis loops exhibit shifts toward negative direction of the magnetic field axis. The values of exchange field $H_{EB}$ and coercivity $H_{C}$ are found to be strongly dependent of temperature and strength of the cooling magnetic field $H_{cool}$. These effects are attributed to evolution of the FM phase content and a size of FM clusters. A contribution to the total magnetization of the system due to the FM phase has been evaluated. The exchange bias effect decreases with increasing temperature up to $T_{C}$ and vanishes above this temperature with disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of the compound manifests itself through a training effect also observed while studying EB in Nd2/3Ca1/3MnO3.

Exchange bias in phase-segregated Nd2/3Ca1/3MnO3 as a function of temperature and cooling magnetic fields

Effect of Y-doping on the magnetic and charge orderings in Nd2/3Ca1/3MnO3

The exchange bias (EB) phenomenon has been found in Nd2/3Ca1/3MnO3 perovskite. The phenomenon manifests itself as a negative horizontal shift of magnetization hysteresis loops. The EB phenomenon is evident of an interface exchange coupling between coexisting antiferromagnetic (AFM) and ferromagnetic (FM) phases and confirms the phase separated state of the compound at low temperatures. The EB effect is found to be strongly dependent on the cooling magnetic field and the temperature, which is associated with the evolution of spontaneous AFM - FM phase separated state of the compound. Analysis of magnetic hysteresis loops has shown that ferromagnetic moment $M_{FM}$ originating from the FM clusters saturates in a relatively low magnetic field about H ~ 0.4T. The obtained saturation value $M_{FM}$(1T) ~ 0.45$\mu_{B}$ is in a good agreement with our previous neutron diffraction data.

Exchange bias associated with phase separation in the Nd2/3Ca1/3MnO3 manganite

Specific heat of layered Na x CoO 2 single crystals (x=0.76-0.87) down to 100 mK and the dc-susceptibility down to 2 K in magnetic field applied parallel to the layers has been measured. The specific heat data of single crystals of exceptional high quality with 0.71 ≤ x ≤ 0.747 reported in L. Balicas et al. [Phys. Rev. Lett., 100, 126405 (2008)] with the kind permission of the authors have been also analyzed. Non-Fermi liquid (NFL) features observed in Na concentration dependent temperature region have been analyzed and discussed in terms of disorder induced NFL behavior with quantum Griffiths phases in the background. The phase diagram is proposed, the results indicate possible quantum critical point below x = 0.7 and closeness to metal-insulator transition at doping above x = 0.87.

M. Kajnakova

Papers

Exchange bias in phase-segregated Nd2/3Ca1/3MnO3 as a function of temperature and cooling magnetic fields

Effect of Y-doping on the magnetic and charge orderings in Nd2/3Ca1/3MnO3

Exchange bias associated with phase separation in the Nd2/3Ca1/3MnO3 manganite

Phase diagram of the sodium-rich NaxCoO2 cobaltates

Magnetic properties of anion-radical salt [FeII(dipy)3](TCNQ)4·(CH3)2CO