Antiferromagnetic Grains Research Articles

Role of (Pr20Nd80)60Tb15Cu15Ga10 intergranular addition on the magnetic properties of Nd-Fe-B sintered magnet

Intergranular addition using heavy rare earth (HRE) Dy/Tb containing alloys has been an effective way to modulate the microstructure and chemical distribution towards fabricating high-coercivity Nd-Fe-B sintered magnets. In this work, (Pr20Nd80)60Tb15Cu15Ga10 (at%) intergranular alloy powders were designed and introduced with dual purposes of forming Tb-rich matrix shell and antiferromagnetic RE6Fe13Ga grain boundary phase (GBP). With 3 wt% (Pr20Nd80)60Tb15Cu15Ga10 addition, the coercivity Hcj is significantly increased from 11.1 kOe to 17.9 kOe, accompanied with a high utilization efficiency of Tb (11.8 kOe/%) and a superior temperature coefficient of coercivity β(−0.531%/K). Microstructural analysis suggests that the improved wettability of grain boundary by (Pr20Nd80)60Tb15Cu15Ga10 addition is beneficial to form the Tb-rich matrix shell and antiferromagnetic RE6Fe13Ga GBP throughout the bulk magnets. Micromagnetic simulation is implemented to study the effect of formed ferromagnetic/antiferromagnetic GBP and Tb-rich matrix shell on the magnetization reversal process. Results show that the synergy of Tb-rich shell surrounding Nd/Pr-rich core and antiferromagnetic Nd/Pr-rich RE6Fe13Ga GBP is an effective way to promote the coercivity with high utilization efficiency of HRE Tb.

Enhancement of Magnetic Stability in Antiferromagnetic CoO Films by Adsorption of Organic Molecules.

Antiferromagnets are a class of magnetic materials of great interest in spintronic devices because of their stability and ultrafast dynamics. When interfaced with an organic molecular layer, antiferromagnetic (AF) films are expected to form a spinterface that can allow fine control of specific AF properties. In this paper, we investigate spinterface effects on CoO, an AF oxide. To access the magnetic state of the antiferromagnet, we couple it to a ferromagnetic Co film via an exchange bias (EB) effect. In this way, the formation of a spinterface is detected through changes induced on the CoO/Co EB system. We demonstrate that C60 and Gaq3 adsorption on CoO shifts its blocking temperature; in turn, an increase in both the EB fields and the coercivities is observed on the EB-coupled Co layer. Ab initio calculations for the CoO/C60 interface indicate that the molecular adsorption is responsible for a charge redistribution on the CoO layer that alters the occupation of the d orbitals of Co atoms and, to a smaller extent, the p orbitals of oxygen. As a result, the AF coupling between Co atoms in the CoO is enhanced. Considering the granular nature of CoO, a larger AF stability upon molecular adsorption is then associated with a larger number of AF grains that are stable upon reversal of the Co layer.

Tuning of exchange bias by regulating the microstructural parameters in Ni81Fe19 (5, 8, 11, 14, 17, and 20 nm)/Ir7Mn93(10 nm) bilayers probed using magnetoresistance

The investigation and tunning of positive exchange bias (PEB) and negative exchange bias (NEB) are reported at room temperature (RT) and low temperature (20 K), respectively, in a series of top-pinned Ni81Fe19(tFM = 5, 8, 11, 14, 17, and 20 nm)/Ir7Mn93(10 nm) polycrystalline heterostructure thin films grown in the presence of a 1 kOe in situ magnetic field by systematically controlling the microstructural parameters such as thickness, roughness, and crystallite/grain size. On decreasing the thickness (roughness) of NiFe from 20 nm (0.49 nm) to 5 nm (0.28 nm), an enhancement in PEB and NEB is observed from +12 to +22 Oe and −300 to −556 Oe at RT and 20 K, respectively. It is observed that both exchange bias and coercivity substantially depend on the atomic scale roughness of the interface width (NiFe/IrMn). The representative plane-view of transmission electron microscopy (TEM) measurements revealed the enhanced antiferromagnet (AF) grain size on decreasing the thickness of ferromagnetic, whereas cross-sectional TEM studies exhibited the sharp interfaces in the bilayer samples after magnetic annealing. A unique correlation between the training mechanism and the degree of asymmetry is established. Further, the training measurement data are fitted with various theoretical models that support the fact that not only interfacial but also bulk AF spins play a vital role in the exchange bias. Thus, the present study reveals the microstructural insights by varying the thickness of NiFe to address the unresolved issues of the EB by directly correlating it with interface roughness and the crystallite/grain size of AF in it, probed using the magnetoresistance technique.

Leveraging of both positive and negative magnetocaloric effects in ZnFe2O4 layers

The novel magnetocaloric thin film material with a tunable magnetic transition is the cornerstone of magnetic refrigeration, which plays a crucial role in cooling on-chip devices. Zn-ferrite (ZnFe2O4) occupies a significant place due to its interesting grain size-controlled magnetism. In this study, we investigate the magnetocaloric properties of Zn-ferrite layers consisting of a mixture of superparamagnetic (SPM), ferrimagnetic (FiM), and bulk-type antiferromagnetic (AFM) grains. Due to the co-existence of different magnetic grains, a crossover from the conventional magnetocaloric effect (MCE) to the inverse magnetocaloric effect (IMCE) is observed. The magnetic entropy change (-ΔSM) exhibits high-temperature positive values around the Curie temperature (TC) and low-temperature negative values around either the Néel temperature (TN) or blocking temperature (TB). The maximum value of -ΔSM (0.10 J/kg K) is almost double in AFM-dominant samples compared to SPM-dominant samples, while maintaining a relative cooling power (RCP) of 11.57–14.82 J/Kg under applied fields of 0 – 2T. FiM-dominant samples, with a wide working temperature window around room temperature, are suitable for large RCP applications. Thus, the discovery of new IMCE materials like single layers of Zn-ferrite is equally important in the search for suitable conventional MCE materials for magnetic refrigeration devices, which can exhibit multiple -ΔSM and RCP peaks in low and high temperatures.

Investigation and tailoring the strengths of positive and negative exchange bias in the ion-beam sputtered Ni81Fe19/Ir7Mn93 bilayers by tuning the grain size of the antiferromagnetic Ir7Mn93 layer

We report the investigation of large and tunable exchange bias in a series of top-pinned Ni81Fe19/Ir7Mn93 polycrystalline bilayer samples fabricated at room temperature in the presence of in situ magnetic field of 1000 Oe followed by magnetic annealing at 250°C in the presence of 3500 Oe by tuning the grain size of the antiferromagnetic (AF) Ir7Mn93 (IrMn) layer. These bilayers exhibit robust positive exchange bias (PEB) at room temperature, with a reasonably large positive shift of the center of MH-loop (i.e., exchange bias field, HEB) by ∼30 Oe observed in bilayers having the largest median grain size of ∼7.2 nm. However, on field cooling to 15 K in the presence of 3000 Oe, the magnetization hysteresis loops exhibited the conventional negative exchange bias (NEB). The PEB and NEB are found to be tailored in a controlled manner by a factor of ∼2.5 and ∼2, respectively, by systematically varying the grain size of the AF. In the training measurements, a relatively slower decay is observed in the magnitude of HEB on field cycling for the samples which possessed the largest-sized AF grains. This decay could not be understood within the framework of the thermal relaxation model. However, the decay in HEB is satisfactorily fitted by the spin relaxation model which considers decay in the metastable magnetic disorder at the magnetically frustrated interface during magnetization reversals.

Magnetic properties of Nd6Fe13Cu single crystals

The understanding of a coercivity mechanism in high performance Nd–Fe–B permanent magnets relies on the analysis of magnetic properties of all phases present in magnets. By adding Cu in such compounds, a new Nd6Fe13Cu grain boundary phase is formed; however, the magnetic properties of this phase and its role in the magnetic decoupling of matrix Nd2Fe14B grains are still insufficiently studied. In this work, we have grown Nd6Fe13Cu single crystals by the reactive flux method and studied their magnetic properties in detail. It is observed that below the Néel temperature (TN = 410 K), Nd6Fe13Cu is antiferromagnetic in zero magnetic field; whereas when a magnetic field is applied along the a-axis, a spin-flop transition occurs at approximately 6 T, indicating a strong competition between antiferromagnetic and ferromagnetic interactions in two Nd layers below and above the Cu layers. Our atomistic spin dynamics simulation confirms that an increase in the temperature and/or magnetic field can significantly change the antiferromagnetic coupling between the two Nd layers below and above the Cu layers, which, in turn, is the reason for the observed spin-flop transition. These results suggest that the role of an antiferromagnetic Nd6Fe13Cu grain boundary phase in the coercivity enhancement of Nd–Fe–B–Cu magnets is more complex than previously thought, mainly due to the competition between its antiferro- and ferromagnetic exchange interactions.

Low Temperature Magnetic Transition of BiFeO3 Ceramics Sintered by Electric Field-Assisted Methods: Flash and Spark Plasma Sintering

Low temperature magnetic properties of BiFeO3 powders sintered by flash and spark plasma sintering were studied. An anomaly observed in the magnetic measurements at 250 K proves the clear existence of a phase transition. This transformation, which becomes less well-defined as the grain sizes are reduced to nanometer scale, was described with regard to a magneto-elastic coupling. Furthermore, the samples exhibited enhanced ferromagnetic properties as compared with those of a pellet prepared by the conventional solid-state technique, with both a higher coercivity field and remnant magnetization, reaching a maximum value of 1.17 kOe and 8.5 10-3 emu/g, respectively, for the specimen sintered by flash sintering, which possesses the smallest grains. The specimens also show more significant exchange bias, from 22 to 177 Oe for the specimen prepared by the solid-state method and flash sintering technique, respectively. The observed increase in this parameter is explained in terms of a stronger exchange interaction between ferromagnetic and antiferromagnetic grains in the case of the pellet sintered by flash sintering.

Polycrystalline exchange-biased bilayers: Magnetically effective versus structural antiferromagnetic grain volume distribution

The magnetic characteristics of polycrystalline exchange-biased antiferromagnet/ferromagnet bilayers are determined by a complex interplay of parameters, describing structural and magnetic properties of the material system, including, in particular, the grain volume distribution of the antiferromagnet. An ideal characterization of such systems would be a nondestructive determination of the relevant parameters for each individual grain. This is in most cases not feasible, since typical characterization methods average over larger areas. Here, we show that it is, however, possible to determine averaged microscopic parameters from averaged macroscopic magnetic quantities measured by vectorial Kerr magnetometry in comparison to an elaborate model. In particular, we estimate the magnetically effective antiferromagnetic grain size distribution, being essential for the interface exchange coupling to the ferromagnetic layer. We found that the distribution of magnetically active grain sizes differs from the structural one, indicating that the antiferromagnetic order, relevant for the exchange bias, extends only over a part of the grains' structural volumes.

Angular Deviation of the Exchange Bias in Bilayer CoFe/IrMn Under Rotating Magnetic Field

A model of exchange bias in a polycrystalline bilayer based on thermal fluctuations was extended to account for an arbitrary magnetization angle of the ferromagnetic (FM) layer. It allows for a more accurate description of the thermally activated reversal of the Néel vector in antiferromagnetic (AFM) grains since the extended model takes into account the variation of barrier height resulting from the magnetization angle of the FM layer. Field-annealing (setting of the exchange bias) and further relaxation of the FM/AFM bilayer was simulated using a sequence of iterations based on this model. An array of AFM grains is generated based on a lognormal distribution of their volume. Chosen parameters of distribution are based on the fit to the experimentally measured temperature dependence of exchange bias in sputter-deposited CoFe/IrMn films. The angular deviation of the exchange bias and the degradation of its amplitude in an applied field, with relative angle varied from 0° to 180°, are calculated. Hysteresis of the exchange bias with field exposure is observed. A temperature–time ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau$ </tex-math></inline-formula> ) diagram of the deviation angle, predicting the stability of the exchange bias under specific temperature and time, is presented.

Fabrication, structural and magnetic behavior of novel one-dimensional Fe2MnGa nanostructures

Well aligned Fe2MnGa nanowires (NWs) have been synthesized through low cost and versatile electrochemical deposition technique with constant stirring during the growth process in anodic aluminum oxide (AAO) templates. The average diameter is 50 nm and the lengths up to a few micrometers have been confirmed through morphological analysis. The NWs are found to be in body centered cubic structure with (220) preferred orientation. The magnetic behavior has been investigated at room temperature (RT) as well as at low temperatures. The dominant shape anisotropy compelled the preferable magnetization axis to be in axial direction of NWs. Angular dependence of coercivity shows coherent rotation of magnetic domain on reversal of external magnetic field due to the stronger interwire couplings. At lower temperatures, superparamagnetic contributions from very small nanoparticles in blocking state significantly improved saturation magnetization (Ms) from 0.101 to 0.205 emu and coercivity from 1354 to 1632 Oe. A mixed behavior of exchange bias has been manifested by the NWs at lower temperatures owing to the rearrangement of atoms between the interface of antiferromagnetic and ferromagnetic grains. This causes significant disturbance for pining effect resulting fluctuating exchange bias phenomenon.

Viscous magnetization decrease in first-order reversal curves induced by rotatable magnetic anisotropy in polycrystalline exchange-biased bilayers

A prototypical polycrystalline in-plane exchange bias system exhibited a viscous decrease of the ferromagnetic magnetization upon increasing external magnetic field when measuring first-order reversal curves. The phenomenon is investigated by means of angular-resolved vectorial magneto-optical Kerr magnetometry complemented by fits of model calculations and by Kerr microscopy. It is found that the viscous magnetization decrease is mediated by a rotatable magnetic anisotropy arising from thermally unstable antiferromagnetic grains coupled to the probed ferromagnet. This additionally manifests itself by a creeping domain wall motion in the ferromagnet due to thermally activated processes in the antiferromagnet. The investigations are in agreement with a generalized description of polycrystalline exchange bias systems and emphasize the relevance of understanding minor loop behavior addressing nonsaturated magnetic states for systems susceptible to dynamic changes on the hysteresis loop timescale.

Magnetization Asymmetry in Exchange Bias Systems

We report on an experimental study on an observed asymmetry in the magnetisation of a sputtered polycrystalline Co-Fe/Ir-Mn exchange bias system. Such asymmetries have been predicted by numerical modelling but never measured in detail. In particular we observe the magnetisation asymmetry to increase with decreasing temperature down to 5.5 K. Given that the bulk of the antiferromagnetic grains is known to be stable below 300 K, this indicates that the asymmetry derives from interface spin effects at the ferromagnetic/antiferromagnetic interface. As the temperature is reduced, a peak in magnetisation asymmetry is observed below 10 K. We also observed that when measured at low temperature there is an increase in the hysteresis loop coercivity and the well-known training effect on the loop shift in exchange bias systems. These effects both derive from the ferromagnetic/antiferromagnetic interface.

Exchange bias in multigranular noncollinear IrMn3/CoFe thin films

Antiferromagnetic spintronic devices have the potential to greatly outperform conventional ferromagnetic devices due to their ultrafast dynamics and high data density. A challenge in designing these devices is the control and detection of the orientation of the antiferromagnet. One of the most promising ways to achieve this is through the exchange bias effect. This is of particular importance in large-scale multigranular devices. Previously, due to the large system sizes, only micromagnetic simulations have been possible, with an assumed distribution of antiferromagnetic anisotropy directions and grain size. Here, we use an atomistic model where the distribution of antiferromagnetic anisotropy directions occurs naturally and where the exchange bias occurs due to the intrinsic disorder in the antiferromagnet. We perform large-scale simulations of exchange bias, generating realistic values of exchange bias. We find a strong temperature dependence of the exchange bias, in agreement with experimental observations, approaching zero at the blocking temperature of the antiferromagnet. We find that the experimentally observed increase in the coercivity at the blocking temperature occurs due to the superparamagnetic flipping of the antiferromagnet during the hysteresis loop cycle. We find a large discrepancy between the exchange bias predicted from a geometric model of the antiferromagnetic interface, indicating the importance of grain edge effects in multigranular exchange biased systems. The grain size dependence shows the expected peak due to a competition between the superparamagnetic nature of small grains and reduction in the statistical imbalance in the number of interfacial spins for larger grain sizes. Our simulations confirm the existence of single antiferromagnetic domains within each grain. The model gives insights into the physical origin of exchange bias and provides a route to developing optimized nanoscale antiferromagnetic spintronic devices.

Exchange bias effect in epitaxial La0.35Sr0.65MnO3/La0.7Sr0.3MnO3 bilayers: Impact of antiferromagnet growth conditions

Antiferromagnets have shown great potential for replacing ferromagnets in spintronics applications in recent years. In this work, antiferromagnetic La0.35Sr0.65MnO3 (AFM-LSMO) thin films were grown on ultrathin ferromagnetic La0.7Sr0.3MnO3 (FM-LSMO) layer over a wide temperature range. The different AFM-LSMO growth temperatures introduced variation of strain states in the AFM-LSMO layer, changing the AFM-LSMO magnetic properties. Considering the thermally activated switching model of antiferromagnetic grains, the behaviour of AFM-LSMO growth temperature-dependent exchange bias effect are explained. This work demonstrates the modulation of exchange bias effect through the control of AFM-LSMO growth conditions, suggesting possibility to control and probe oxide antiferromagnets via exchange bias coupling.

Parametric spin pumping into an antiferromagnetic insulator

We report the observation of spin transport through antiferromagnetic insulators using spin pumping driven by short-wavelength magnons. The short-wavelength magnons are excited by parametric pumping in a $\mathrm{Pt}/\mathrm{NiO}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ trilayer. The parametrically excited magnons in the ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ layer inject a spin current into the NiO layer, which is detected electrically using the inverse spin Hall effect in the Pt layer. We found that the spin-pumping efficiency of the parametrically excited magnons in the $\mathrm{Pt}/\mathrm{NiO}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ film is nearly an order of magnitude smaller than that in the $\mathrm{Pt}/{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ film. The suppression of the parametric spin-pumping efficiency induced by inserting the NiO layer is comparable to that of the FMR spin-pumping efficiency. We further found that the suppression of the spin-pumping efficiency due to the NiO insertion for the dipole-exchange magnons with the wave number of $k\ensuremath{\sim}{10}^{3}\ensuremath{-}{10}^{4}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ is more significant than that for the exchange magnons with $k\ensuremath{\sim}{10}^{5}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. This difference is attributed to two-magnon scattering and spin pinning due to antiferromagnetic grains in the NiO layer. These results provide insight into the understanding of the spin pumping into antiferromagnetic insulators.

Influence of the antiferromagnetic grain volume distribution on exchange-bias in polycrystalline thin films: An X-ray diffractometry study

In this paper we present a model to calculate exchange-bias and coercive fields in a prototype exchange-bias layer system using the in-plane and out-of-plane grain size distributions of the polycrystalline antiferromagnet measured non-destructively by X-ray diffraction and the magnetic history of the exchange-bias system. The model is checked by comparing the computed values with measured ones considering a constant average magnetic anisotropy energy density for all samples and the average exchange coupling energy area density as a parameter for the calculation.

Antiferromagnetic thickness and temperature dependence of the exchange bias properties of Co/IrMn nanodots and continuous films: A Monte Carlo study

Abstract Motivated by the challenge of understanding the complex influence of the antiferromagnetic (AF) thickness and the temperature on exchange bias (EB) properties, and by the necessity of miniaturization of devices, we investigate EB properties of Co/IrMn nanodots and of continuous films by using kinetic Monte Carlo simulations. To that purpose, we use a granular model, which takes into account disordered interfacial phases in the AF layer and, in the case of nanodots, disordered phases at the edges in the AF layer. Our results show that the AF thickness dependence of the exchange field HE (measured at room temperature) in both nanodots and continuous films exhibits a maximum in agreement with experimental results. We explain these results in terms of superparamagnetic and blocked grains in the AF layer at room temperature and also not polarized AF grains during the initial field-cooling. The simulated values of HE in nanodots are smaller than that in continuous films for small AF thicknesses and larger for larger ones due to the contribution of the disordered phases at the edges in the AF layer. Also, we investigate the temperature and AF thickness effects on HE and on the coercive field HC. We found that HE slightly decreases at low temperatures due to the disordered interfacial phases. Importantly, at the maximum blocking temperature of the AF grains, HE vanishes and HC exhibits a maximum. Our numerical results are successfully compared to experimental data on Co/IrMn bilayers for various IrMn thicknesses and all temperatures. In addition, our results indicate that HE is smaller in nanodots at low measurement temperature due to the presence of disordered phases at the edges. Concerning HC, our data show that it can be either larger or smaller in nanodots depending on the measurement temperature.

Thickness effect on the easy axis distribution in exchange biased Co/IrMn bilayers

It is commonly assumed that in uncompensated FM/AF interfaces, the easy axes of antiferromagnetic grains are aligned toward the magnetic field direction applied during the film growth. However, due to several intrinsic and extrinsic factors, these easy axes can be aligned away from the unidirectional axis. In this context, the aim of this work is to study the relationship between the easy axes distribution (EAD) and thickness of both the ferromagnetic (FM) and antiferromagnetic (AF) layers in Co/IrMn bilayer systems. A phenomenological model for the free energy of the system that takes into account a domain wall formation in the AF layer and a Gaussian-type distribution of their easy axes is used. Thus, we simulate and fit the magnetization curves and get several magnetic parameters like rotatable anisotropy field, exchange bias field, coercivity and magnetic anisotropy. Our results show that when the AF thickness is increased, the width of the easy-axis distribution also increases following a power-law relationship. However, no correlation is observed when the FM thickness is varied. Furthermore, considering an easy-axis distribution we observe a significant reduction in coercivity as well as a slight decrease of the exchange bias field.

Exchange Bias in Bulk Nanocomposites for Permanent Magnet Applications.

Here we report on the microstructural factors influencing the formation of the interfacial exchange bias effect in three-dimensional transition-metal-based nanocomposite systems, with relevance to permanent magnet applications. Bulk phase-separated nanocomposites consisting of the ferromagnetic -Fe and metastable antiferromagnetic phases exhibit a notable low-temperature exchange bias and substantial coercivity ( , ) as well as a near room-temperature blocking temperature. Structural investigation by synchrotron X-ray diffraction, neutron scattering, and transmission electron microscopy confirm that the ferromagnetic -Fe phase nucleates as small precipitates ( ) at the grain boundaries of the antiferromagnetic grains ( ) and grows anisotropically upon heat treatment, resulting in an elliptical geometry. These results indicate that optimization of the exchange bias effect in bulk nanocomposite systems may be achieved through maximizing the surface-to-volume ratio of ferromagnetic precipitates in an antiferromagnetic matrix, enhancing the magnetocrystalline anisotropy of the antiferromagnetic phase to facilitate interfacial pinning and ensuring a balanced distribution of the ferromagnetic and antiferromagnetic phases. This work further clarifies critical factors influencing the formation of an exchange bias in an inexpensive transition-metal-based bulk nanocomposite system with potential for scalable production.

Unraveling the origin of training in granular Co-CoO exchange bias systems with buried antiferromagnetic constituents

Abstract Training is a common effect in exchange bias systems and accounts for the decrease of the exchange bias loop shift and coercivity with consecutively measured hysteresis loops until steady values. This is an ageing-like phenomenon that is related to the metastable state of the ferromagnetic/antiferromagnetic interface after field cooling. However, its origin still remains intriguing and not univoquely established. Here, by micromagnetic simulations considering discrete non-interacting antiferromagnetic grains embedded in a ferromagnetic matrix, it is demonstrated that the origin of training in granular Co-CoO exchange bias systems prepared by O ion implantation into Co thin films is linked to the perpendicular anisotropy of rotatable interface uncompensated spins. The simulations are compared to experimental data as reported in Physical Review B 89 (2014) 144407. The out-of-plane nature of the rotatable anisotropy of the system is also responsible for the magnetic reversal asymmetry between the first and the second magnetic reversals, evidencing the interconnection between training and magnetization reversal, suggesting that training effect and magnetization reversal asymmetry are ultimately interconnected through perpendicular anisotropy.