United States

Spin-orbitronics and single pulse alloptical switching (AOS) of magnetization are two major successes of the fast advancing field of nanomagnetism in recent years, with high potential for enabling novel fast and energy-efficient memory and logic platforms. Fast current induced domain wall motion and single shot AOS have been individually demonstrated in different ferrimagnetic alloys. However, the stringent requirement for their composition control makes them challenging material for wafer scale production. Here, we demonstrate simultaneously fast current-induced domain wall motion and energy efficient AOS in a synthetic ferrimagnetic system based on [Co/Gd]2 multilayers. We firstly show AOS is present in its full composition range. We find current driven domain wall velocities over 2 km/s at room temperature conditions is achieved by compensating the total angular momentum through layer thickness tuning. Furthermore, analytical modelling of the current-induced domain wall motion reveals that Joule heating needs to be treated transiently to properly describe the current-induced domain wall motion for our sub-ns current pulses. Our studies establish Co/Gd based synthetic ferrimagnets to be a unique material platform for domain wall devices with access to ultrafast single pulse AOS [1].&lt;br&gt;&lt;br&gt;
**References** [1] Pingzhi Li, Thomas J Kools, Bert Koopmans and Reinoud Lavrijsen. Ultrafast racetrack based on compensated Co/Gd-based synthetic ferrimagnet with all-optical switching. arXiv preprint arXiv:2204.11595, 2022.

MMM 2022

Ultrafast racetrack based on compensated Co/Gd based synthetic ferrimagnet with all

Spin-orbitronics and single pulse alloptical switching (AOS) of magnetization are two major successes of the fast advancing field of nanomagnetism in recent years, with high potential for enabling novel fast and energy-efficient memory and logic platforms. Fast current induced domain wall motion and single shot AOS have been individually demonstrated in different ferrimagnetic alloys. However, the stringent requirement for their composition control makes them challenging material for wafer scale production. Here, we demonstrate simultaneously fast current-induced domain wall motion and energy efficient AOS in a synthetic ferrimagnetic system based on [Co/Gd]2 multilayers. We firstly show AOS is present in its full composition range. We find current driven domain wall velocities over 2 km/s at room temperature conditions is achieved by compensating the total angular momentum through layer thickness tuning. Furthermore, analytical modelling of the current-induced domain wall motion reveals that Joule heating needs to be treated transiently to properly describe the current-induced domain wall motion for our sub-ns current pulses. Our studies establish Co/Gd based synthetic ferrimagnets to be a unique material platform for domain wall devices with access to ultrafast single pulse AOS [1]. 
**References** [1] Pingzhi Li, Thomas J Kools, Bert Koopmans and Reinoud Lavrijsen. Ultrafast racetrack based on compensated Co/Gd-based synthetic ferrimagnet with all-optical switching. arXiv preprint arXiv:2204.11595, 2022.

technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

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Multiferroic materials having good magnetoelectric coupling are of great interest due to their enormous applications in the field of spintronic devices (1). Magnetoelectric (ME) gallium ferrite is an interesting material due to its room temperature (RT) piezoelectricity and near RT ferrimagnetism along with significant ME coupling (10−11 s/m at 4.2 K) (2). The motive of this work is to increase the magnetic transition temperature (TC) of the material above RT so that the material can have strong ME coupling at room temperature and can be implemented for practical applications. Several earlier reports have shown the magnetic transition temperature of Ga2−xFexO3 increases with higher Fe contents (3). Hence, we chose to study the properties of Ga2−xFexO3 (GFO) only for x = 1.2. Y3Fe5O12 (YIG) is another material which is RT ferromagnet with very high resistivity (resistivity ~ 1012 Ω.cm) (4). 
In this work, by forming GFO-YIG composite with only 10% concentration of YIG, phase transition temperature is increased beyond room temperature from ~ 289 K for GFO to ~ 309 K for 0.9 GFO – 0.1 YIG as shown in Fig. 1. The remnant magnetisation is also enhanced from 0.211 emu/g to 2.82 emu/g [inset of Fig. 2] reporting a magnetisation of ~ 8.2 emu/g at 30 kOe [Fig. 2].
References [1] J. F. Scott, Nature Materials, vol. 6, no. 4, pp. 256–257, Mar. 2007.
[2] J. P. Remeika, Journal of Applied Physics, no. 5, 1960.
[3] T. Arima et al., Physical Review B - Condensed Matter and Materials Physics, vol. 70, no. 6, 2004.
[4] W. Swee Yin, J. Hassan, W. Mohd, and D. W. Yusoff, Solid State Science and Technology, vol. 19, pp. 259–267, 2011. 


 Fig. 1 dM/dT versus Temperature plot indicating the phase transition temperature (TC) 




Fig. 2 Magnetic hysteresis loop obtained at room temperature. Inset of (b) shows the zoomed-out magnetic hysteresis loop of 0.9 Ga0.8Fe1.2O3 – 0.1 Y3Fe5O12 composite at a magnetic field range of 4 kOe.

Enhancement of phase transition temperature beyond room temperature by formation of Ga0.8Fe1.2O3 – Y3Fe5O12 composite

Topological materials have great potential for ultralow power spin-orbit torque (SOT) spintronic devices thanks to their giant spin Hall effect originated from their topological surface states (TSSs). However, the giant spin Hall angle (θSH > 1) is limited to a few chalcogenide-based topological insulators (TIs) with toxic elements and low melting points, making them challenging for device integration during the silicon Back-End-of-Line (BEOL) process. Here, we focus on a half-Heusler alloy topological semimetal, YPtBi, to overcome this difficulty. We synthesized YPtBi thin films by using co-sputtering method with YPt and Bi targets while changing the growth temperature. Figure 1 (a) shows the X-ray diffraction (XRD) spectra for YPtBi films grown at various temperature. YPtBi(111) peaks were clearly observed up to 600oC. Figure 1 (b) shows the Bi composition measured by X-ray fluorescence (XRF). Bi composition is stable up to 600oC. These results indicate that YPtBi crystal is stable up to 600oC which is high enough for BEOL process. To evaluate the spin Hall effect for YPtBi, we conducted the second harmonic Hall effect measurements in CoPt/YPtBi heterostructures [1]. By controlling the electric conductivity of YPtBi and spin transparency at the CoPt/YPtBi interface, we successfully realized a giant θSH up to 4.1. Figure 2 shows SOT magnetization switching by pulse currents with pulse width of 50 μs to 10 ms under an external magnetic field of 0.5 kOe applied parallel to the current. Thanks to the giant spin Hall effect originated from TSS, small threshold current of about 1×106 A/cm2 was observed, which is one order magnitude smaller than that in heavy metals [2]. Our work opens the door to the next generation spin Hall materials with both giant θSH and high thermal stability [3]. Acknowledgment: this work was supported by Kioxia corporation. The authors thank Tsuyoshi Kondo of Kioxia corporation for fruitful discussion. 
**References** [1] M. Hayashi, J. Kim, M. Yamanouchi, and H. Ohno, Phys. Rev. B, Vol. 89, p.144425 (2014).
[2] B. Jinnai, C. Zhang, A. Kurenkov, M. Bersweiler, H. Sato, S. Fukami, and H. Ohno, Appl. Phys. Lett. Vol. 111, p.102402 (2017).
[3] T. Shirokura, T. Fan, N. H. D. Khang, T. Kondo, and P. N. Hai, Sci. Rep. Vol. 12, p.2426 (2022).
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e55a173b772a01bc435c06c1e664cbaa.png)

Giant spin Hall effect in a half Heusler alloy topological semimetal with high thermal stability

NiFe2O4 (NFO) [1], is an insulating ferrimagnet with an inverse spinel structure and already has gained a considerable attention of scientific community due to its potential applications in spintronic devices. For NFO thin films, a coherent strain can be introduced by growing them on different substrates: ZnGa2O4 (ZGO) and MgAl2O4 (MAO) with lattice mismatch of 0.06% and 3.1% respectively. This strain greatly affects physical properties such as magnetic damping, where damping for the NFO film grown on ZGO is considerably smaller than the damping of the NFO film grown on MAO film [2]. Magnetic damping should also affect ultrafast processes such as the demagnetization and remagnetization time of the system. Koopmans et al. [3] showed that the demagnetization time is inversely proportional to the effective Gilbert damping.

In this work we explore the underlying mechanisms ultrafast demagnetization processes of strained NFO films by using table-top high harmonic generation (HHG) in the extreme ultraviolet (XUV) regime [4], which enables element-specific tracking of spin dynamics. To understand the HHG asymmetry spectra, we compare the discrete HHG spectra to the reflectivity spectra acquired using a continuous synchrotron-based source. The comparison shows good agreement, thereby facilitating assignment of HHG asymmetry features. Time-resolved HHG scans indicate that the demagnetization amplitude is larger for NFO on the MAO substrate while NFO films on both substrates exhibit the similar demagnetization and remagnetization times. In contrast to damping of spin motion at longer timescales, which is highly sensitive to issues such as defect density, the similarity in the magnetization dynamics in the first few ps following a demagnetization pulse reveals the local nature of the ultrafast dynamics. The results display the utility of M-edge spectroscopy for studying spin dynamics in insulating oxide films, which is highly relevant for spintronics based on ferrimagnetic insulators. 
**References** [1] R. Knut et al., J. Phys.: Condens. Matter 33, 225801(2021)
[2] A. V. Singh et al., Advanced Materials 29, 1701222 (2017).
[3] B. Koopmans et al., Physical Review Letters 85, 844 (2000).
[4] S. Jana et al., Phys. Rev. Research 2, 013180 (2020).
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/fb28c8ff3af1ad7c1e8abb55b96774c9.png)

Element specific ultrafast magnetization dynamics of strained NFO films using ultra short XUV pulses

Fluctuations are ubiquitous in nanometer-scale systems, spanning orders of magnitude in space and time. Real-space access to fluctuating states is impeded by a dilemma
between spatial and temporal resolution. Averaging over an extended period of time (or repetitions) is key for the majority of high-resolution imaging experiments, especially in weak
contrast systems. If, by lack of better knowledge, averaging is indiscriminate, it leads to a loss of temporal resolution and to motion-blurred images. We present coherent correlation imaging (CCI) – a high-resolution, full-field imaging technique that realizes multi-shot, time-resolved imaging of stochastic processes. The key of CCI is
the classification of camera frames that correspond to the same physical state (Fig. 1) even at low photon count, where imaging is not possible. CCI combines a correlation-based similarity
metric with powerful classification algorithm developed for genome research [1] realizing informed, non-sequential signal averaging while maintaining single frame temporal resolution. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state. Our material is a Co-based chiral ferromagnetic multilayer with
magnetic pinning low enough to exhibit stochastically recurring dynamics that resemble thermally-induced Barkhausen jumps near room temperature. CCI reconstructs sharp, high-contrast
images of all domain states by phase retrieval [2] and, unlike previous approaches, also tracks the time when these states occur. The spatiotemporal imaging reveals an intrinsic transition
network between the states and unprecedented details of the magnetic pinning landscape (Fig. 2). 
**References** 
[1] G. Sherlock, et. al., Current Opinion in Immunology 12, 201-205 (2000)
[2] Flewett, S. et al., Optics Express 20, 29210–29216, 2012 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/575255bbb0f7b8891a22722531593fa6.png) 
Principle of time-resolved coherent correlation imaging. Top: Sequence of camera frames showing Fourier-space coherent scattering patterns. Coherent correlation imaging classifies
scattering frames by their underlying domain state, as indicated by the colors. Bottom: Real-space images reconstructed from an informed average of same-state frames. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/c06609f11a71267f63b9f1a35eff95c7.png) 
Map of attractive (blue dots) and repulsive (red areas) pinning sites. The background shows the position of the domain walls and their relative occurrence observed in the experiment.

Coherent Correlation Imaging: Resolving fluctuating states of matter

We discuss thermally activated switching between micromagnetic states in nanodisks with perpendicular anisotropy and a large strength of the interfacial Dzyaloshinskii-Moriya interaction, D. For large D, the magnetization on infinite planes acquires a cycloidal configuration in the ground state. However, Isolated singularities that are analogous to disclinations of cholerestic phases [1] are topologically protected and prevent the system from reaching the cycloidal phase (for examples see Fig. 1). In confined geometries, a rich variety of possible configurations with complex magnetization textures that are also energy minima of the energy landscape [2] has been observed. We argue that characterizing these different states as arrangements of disclinations is an effective way for understanding them. We support this statement on results of String Method [3] calculations done using OOMMF to examine the energy landscape of nanodisks (Fig. 2). We found that the transition states correspond to motion of individual merons across the device's edge (first maximum in Fig. 2), and to merging of disclinations inside the structure (2nd, 3rd and 4th maxima in Fig. 2). An additional advantage of emphasizing the importance of these magnetic singularities is the possibility of adopting them for collective coordinate descriptions which can be treated using low-dimensional stochastic methods to study their dynamics in the presence of thermal noise. 

**References** 
[1] Phys. Rev. B 99, 214408 (2019)
[2] The Philosophical Magazine. 22:178, 739-749
[3] J. Chem. Phys. 126, 164103 (2007)
This research was supported in part by the National Science Centre Poland under OPUS funding Grant No. 2019/33/B/ST5/02013 (GDC, PK) and U.S. National Science Foundation Grant
DMR 1610416 (DLS). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/bc16da61cb6378eeaa848cb0834b87f6.png) 

Examples of disclinations on the cycloidal phase of a ferromagnet with large DMI. (a) cycloidal phase without singularities. Disclinations occur when the helical axis rotates by a multiple
of π. (b,c,e,f) Examples of disclinations, respectively their values are: (π,2π,-π,-2π). (d) a skyrmion shown as a 2π disclination embedded in a cycloidal background, (g) a meron shown as a
π disclination embedded in a cycloidad background. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/55824035ff74275789c3c3d8097028e3.png) 
Results of String Method calculations on nanodisks with high DMi for thermally activated switching between two different micromagnetic configurations. The highest maxima occurs
when a meron reaches the in-plane edge. The other maxima are the result of -π disclinations merging briefly into a +2π disclination resulting on re-acommodation of adjacent skyrmionic
domains.

The Role of Disclinations in the Thermal Stability of Magnetization Textures in Confined Helimagnetic Nanostructures

Rare-earth transition metal thin films hold great potential for implementation in devices at the micro and nanoscale [1-3]. While Nd2Fe14B and Pr2Fe14B share almost the same intrinsic magnetic properties (Ms, Ku…), Nd2Fe14B has a limited use for low temperature applications (i.e. aerospace) due to the spin reorientation that occurs at 135 K [4]. This limitation can be overcome using Pr2Fe14B, whose magnetization direction remains along the c-axis until 4.2 K [4]. The understanding and optimization of these systems is of great importance when attempting their integration in novel miniaturized devices [5].
In this study, high coercivity PrFeB thin films of 100 nm have been fabricated by magnetron sputtering. The effect on the substrate temperature (Ts) in the structure and morphology and its resulting impact on the magnetic properties has been evaluated. 
Our research stablishes the optimum Ts to be 600oC where a highly textured growth of Pr2Fe14B is achieved according to the X-Ray Diffraction (XRD) analysis (Fig. 1a). Pr2Fe14B crystalline phase is accompanied by a Pr-rich phase that can be identified in all the XRD patterns. The role that these Pr-rich areas play in the magnetism of these systems has also been thoroughly studied by Energy Dispersive X-Ray Spectroscopy (EDX) (Fig. 1c). Regardless of Ts, all films present strong perpendicular magnetic anisotropy (Fig.2c,d) which is in good accordance with the c-axis oriented preferential growth. Out of plane coercivities up to 14 kOe have been obtained at RT. Atomic and Magnetic Force Microscopy (AFM and MFM, respectively) have also been used to determine influence of Ts on the roughness and magnetic domains (Fig 2a,b). 
**References:** 
[1] X. Liu, T. Okumoto, M. Matsumoto, A. Morisako. J. Appl. Phys. 97, 10K301 (2005). 
[2] T.-S. Chin, J. Magn. Magn. Matter. 209, 75-79 (2000). 
[3] A. Bollero, V. Neu, V. Baltz et al., Nanoscale, 12, 1155-1163 (2020). 
[4] TT. B. Lan, G.C. Hermosa and A.C. Sun, J. Phys. Chem. Solid. 144, 109506 (2020). 
[5] H2020 FET-OPEN project “UWIPOM2”: https://cordis.europa.eu/project/id/857654. 

**Acknowledgements:** 
Authors acknowledge financial support from EU through the H2020 FET Open UWIPOM2 project (Ref. 857654). J. S-M. acknowledges financial support from Comunidad de Madrid (PEJD-2019-PRE/IND-17045). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/955034a15cdb0a0f619d8946ed3387f8.png) 
Fig. 1. a) XRD pattern of PrFeB thin films grown at different Ts, b) Scanning electron microscopy (SEM) image of a PrFeB film grown at 600oC, c) EDX mapping of a PrFeB film with a Ts = 600oC showing the distribution of Pr and Fe (c.1) Prdistribution (c.2) Fe distribution (c.3). The scale bar is 800 nm in all cases. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/10cb6499fc26bfe27947f0693ed28999.png) 
Fig. 2. a) AFM and b) MFM image of a PrFeB film grown at 600oC, c) Out of plane and d) In Plane room temperature hysteresis loops with a maximum applied field of 20 kOe for PrFeB thin films grown at different Ts.

High coercive PrFeB Films with Strong Perpendicular Magnetic Anisotropy

Hybrid magnetic layer systems consisting of a heavy metal, an ultrathin ferromagnet (F), and an antiferromagnet (AF) are interesting material systems that potentially exhibit both the interface-driven exchange bias (EB) effect and the asymmetric exchange interaction, known as Dzyaloshinskii-Moriya interaction (DMI) [1]. The DMI is essential for stabilizing chiral spin-structures like skyrmions, which are promising candidates for magnetic memory technologies [2]. Due to the DMI and the resulting Néel domain walls with chirality set by DMI, tilted magnetic moments are present at the domain edges [3]. Experimentally, this effect has been observed as asymmetric domain propagation while applying in-plane and perpendicular magnetic fields simultaneously [4]. While the DMI and EB can be modified independently from each other [5], only few studies so far have focused on the interplay between chiral DMI and the unidirectional EB anisotropy, affecting the magnetic domain texture and the resulting magnetization reversal. 
We report on a systematic study of the magnetization reversal in perpendicularly exchange biased Ti/Au/Co/NiO/Au micro stripes by high-resolution Kerr microscopy. Thereby, the magnetization reversal process is observed to be asymmetric with respect to the two branches of the hysteresis loop. We are able to quantify this as an asymmetry of the nucleation density formed in the two field branches as a function of the structure width. Additionally, a local asymmetry in the domain nucleation and domain wall movement within each stripe is observed. This phenomenon is investigated by field-cooling and the application of additional in-plane magnetic fields during the magnetization reversal. Additionally, XMCD/XMLD-PEEM experiments were performed to reveal the corresponding domain patterns in the F and AF. The results pave the way in the understanding of the interplay between chiral DMI and the unidirectional EB anisotropy in micro- and nanostructures. 
**References:** 
[1] F. Hellman et al., “Interface-induced phenomena in magnetism,” Rev. Mod. Phys., vol. 89, no. 2, pp. 1–79, 2017, doi: 10.1103/RevModPhys.89.025006. 

[2] A. Manchon et al., “Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems,” Rev. Mod. Phys., vol. 91, no. 3, 2019, doi: 10.1103/RevModPhys.91.035004. 

[3] S. Rohart and A. Thiaville, “Skyrmion confinement in ultrathin film nanostructures in the presence of Dzyaloshinskii-Moriya interaction,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 88, no. 18, pp. 1–8, 2013, doi: 10.1103/PhysRevB.88.184422. 

[4] P. Kuswik et al., “Asymmetric domain wall propagation caused by interfacial Dzyaloshinskii-Moriya interaction in exchange biased Au/Co/NiO layered system,” Phys. Rev. B, vol. 97, no. 2, pp. 1–7, 2018, doi: 10.1103/PhysRevB.97.024404. 

[5] P. Kuswik, M. Matczak, M. Kowacz, F. Lisiecki, and F. Stobiecki, “Determination of the Dzyaloshinskii-Moriya interaction in exchange biased Au/Co/NiO systems,” J. Magn. Magn. Mater., vol. 472, no. April 2018, pp. 29–33, 2019, doi: 10.1016/j.jmmm.2018.10.002. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/fdc9f6be29f2cd8a09625f05a98c3f93.png) 
Fig. 1: Asymmetric nucleation in 10 μm wide Ti/Au/Co/NiO/Au stripes. The Kerr images show that for the decreasing field branch a)-c) the domains are formed preferentially at one edge, smaller ones are formed equally at both edges for the increasing field branch d)-f).

Chirality induced asymmetric magnetization reversal in perpendicularly exchange biased micro stripes

We present a magneto-impedance (MI) sensor having a low power consumption of 2.44 μW per pulse and driven by Wiegand pulses at 10 Hz. The oscillator circuit
conventionally used for a MI sensor is replaced by a Wiegand sensor to generate a pulse voltage. The MI sensor exhibited a good output linearity of 0.04 mV/μ0T for detecting magnetic
field in the range of ±150 μT when Wiegand pulses of amplitude 1 V were supplied. This method reduces the power consumption of MI sensor down to μT level, enabling its use as
battery-less sensors and Internet of Things (IoT) devices in Intelligent Transport Systems (ITS) and bio-sensing fields [1, 2].
The Wiegand sensor consisted of a twisted FeCoV wire (Wiegand wire) and a 3000-turn pick-up coil. The length and diameter of the wire were 11 mm and 0.25 mm, respectively. A 10 Hz
AC magnetic field of 5 mT/μ0 was applied to the Wiegand sensor. A fast magnetization reversal of the wire induced a pulse voltage [3]. Alternating Wiegand pulses of 12 V (±2 V) and 20
μs width were induced in the pick-up coil.
The impedance of an amorphous wire changes sensitively with the external magnetic field with an applied AC current. This is called the MI effect [4]. The pulse parameters affecting the
MI effect have been explored. For pulse frequency below 500 kHz, the rise time and the excitation current control the MI effect.
The MI effect driven by pulses with rise times in microseconds is too small to be observed and is greatly affected by fluctuations in the voltage. A fast rise time pulse shaping circuit was
designed to shape the Wiegand pulse with a fixed amplitude and a rise time less than 100 ns, as shown in Fig. 1. The shaping IC input voltage VCC can be adjusted and supplied by a coin
cell. The low power consumption was achieved under the conditions of the 100 ns rise time and 0.3 mA excitation current. The characteristic of the output voltage of the MI sensor Ew with
respect to the applied magnetic field Hex is shown in Fig. 2. A DC power supply using the Wiegand pulses was designed [5], which could make the MI sensor completely battery-less. 

**References** 

1) T. Uchiyama, J. Ma, Journal of Magnetism and Magnetic Materials, Vol.514, 2020, 167148 
2) Y. Takemura, N. Fujinaga, A. Takebuchi, etc., IEEE Trans. Magn., 53, 4002706, 2017. 
3) J. R. Wiegand and M. Velinsky, U.S. Patent 3,820,090, (25 June 1974). 
4) K. Mohri, T. Uchiyama, L.P Shen, etc., Journal of Magnetism and Magnetic Materials, Vol.249, p.351-356, 
5) Sun, X.; Iijima, H.; Saggini, etc. Energies 2021, 14, 5373. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/f44f244dd24dad8b739a58e88cb59519.png)

Low Power High Precision MI Sensor Driven by Low Frequency Wiegand Pulse

In our previous work, we developed the highly sensitive thin film sensor and indicated the successful measurement of Magnetocardiogram signals without the magnetic
shielding [1]. But the sensitivity was poor around the ferromagnetic resonance frequency (in GHz bands) since the sensor had the severe reflection loss because of the impedance
mismatching [2]. In this research, we have improved the impedance matching of the sensor by employing the slits in the magnetic thin-film and evaluated the appropriate slit width. As
shown in Fig. 1, the proposed sensor composes of CoNbZr, SrTiO, and Cu/Cr films. The CoNbZr film was annealed in rotating and static magnetic fields to induce transverse magnetic
anisotropy. Several sensors having 6, 10, 26, 36, and 50 mm slit widths were fabricated and evaluated from the phase and the amplitude of the transmission coefficient (S21) measured by
the network analyzer (Advantest Corp., R3767CG). In the measurement, the DC magnetic field of 0-20 Oe was applied to the longitudinal direction of the coplanar by a Helmholtz coil.
The amplitude of S21 was improved about five times larger by employing the narrow slits. Although the changes of the amplitude and the phase by the magnetic field were small as the
narrow slit, the maximum amplitude of S21 became large. Fig. 2 shows the sensor sensitivity versus the slit width. The sensitivity of the sensor was evaluated by assuming it to be
proportional to the product of the phase and the amplitude gradients as the magnetic field and the carrier signal strength [3]. The appropriate slit width was around 10 mm for the coplanar
line type thin film magnetic field sensor and the sensitivity will enhance more than 10 times higher than the sensor without slits [1]. However, it is expected that the sensor can get higher
sensitivity by using amplitude modulation. 

**References:** 

[1] S. Yabukami et al, J. Magn. Soc. Jpn., Vol. 38, pp. 25-28 (2014) [2] T. Ishihara et al, Journal of Magnetic of Japan, vol. 6 (2022) [3] N. Horikoshi et al, Journal of
Magnetic of Japan, vol. 29, pp. 472 (2005) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/100387c7642046f3efe5cb725ebc980a.png)

Evaluation of Coplanar Line Type Thin Film Magnetic Field Sensor with Narrow Slits.

To improve magnetic memories, significant efforts are made to reduce the size and spacing of magnetic bits. This implies that failures and defects can only be discovered with a non-invasive technique that can resolve small magnetic fields with high spatial resolution. Scanning NV magnetometry (SNVM) is the emerging quantum sensing technique that offers the required sensitivity. We will demonstrate magnetic images of a few hot candidate materials for future magnetic memory devices. We will look at memory bits in antiferromagnetic chromia, antiferromagnetic cycloids in BiFeO3 [1], cobalt nanomagnets and ultra-scaled CoFeB nanowires [2]. We will reveal magnetic textures that are undetectable with standard characterization techniques. In this context, we will more broadly discuss the potential of SNVM as a powerful magnetic characterization tool.

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