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The interplay of spin-transfer torque (STT) and spin-orbit torque (SOT) highlights the potential of current-induced magnetization reversal for the ultrahigh-speed and ultralow-power memory applications. However, the ultrafast field-free switching and its dynamic mechanism have not been clarified yet. Here, we experimentally demonstrate the sub-nanosecond field-free switching by the interplay of STT and SOT in perpendicular magnetic tunnel junctions (MTJs). The dynamic investigations of the STT and SOT switching reveal that the applied SOT current can highly decrease the incubation time and current density of STT, which leads to the achievement of ultra-fast switching. Besides, the timing scheme investigations of SOT and STT pulses are performed. The firstly applied SOT current further decreases the transition time of the magnetization switching, which could result from the different nucleation and motions of domains. The interplay and the timing operations of STT and SOT provide more flexible solutions for high-speed, large-scalability and energy efficient memory applications.

Negative thermal expansion (NTE) behavior with giant thermal hysteresis exceeding 450 K has been observed in Fe3NiBx. This behavior is desirable in the field of pipe joint or encapsulation. The temperature dependent X-ray diffraction and magnetization indicate that NTE behavior with giant thermal hysteresis is related to crystal structure transition between face-centered cubic (fcc) and body-centered cubic (bcc), but not to the magnetic transition. The introduction of boron can reduce the NTE temperature range and stabilize the high temperature fcc phase. Therefore, we can obtain the NTE behavior below room temperature during cooling process, which is important for the practical application.

Spin orbit torque (SOT) has drawn widespread attention in the emerging field of magnetic memory devices, such as magnetic random access memory (MRAM). To promote the performance of SOT-MRAM, most efforts have been devoted to enhance the SOT switching efficiency by improving the damping-like torque. Recently, some studies noted that the field-like torque also plays a crucial role in the nanosecond-timescale SOT dynamics. However, there is not yet an effective way to tune its relative amplitude. Here, we experimentally modulate the field-like SOT in W/CoFeB/MgO trilayers through tuning the interfacial spin accumulation. By performing spin Hall magnetoresistance measurement, we find that the CoFeB with enhanced spin dephasing, either generated from larger layer thickness or from proper annealing, can distinctly boost the spin absorption and enhance the interfacial spin mixing conductance Gr. While the damping-like torque efficiency increases with Gr, the field-like torque efficiency is found to decrease with it. The results suggest that the interfacial spin accumulation, which largely contributes to the field-like torque, is reduced by higher interfacial spin transparency. Our work shows a new path to further improve the performance of SOT-based ultrafast magnetic devices.

The influences of Fe substitutions on magnetic properties, phase transformations and magnetocaloric effects of Mn3Cu1-xFexN have been investigated. The magnetic phase transition temperature (Tc) increases but the first-order phase transition temperature decreases with increasing the Fe content. Fe doping separates the first-order phase transition into first-order and second-order phase transitions in Mn3Cu1-xFexN. The second-order (paramagnetic-ferromagnetic) transition coexists with first-order (ferromagnetic-ferrimagnetic) transition in Mn3Cu0.95Fe0.05N. Introduction of the second-order magnetic transition broadens the phase transition span, which greatly enhances the relative cooling power of Mn3CuN. The results indicate that resolving complex magnetic phase transition may improve the cooling capacity of antiperovskite compounds.

Effects of Ni substitution on magnetic and thermal expansion properties in Mn 3 Ga 1−x Ni x N (0 ≤ x ≤ 1.0) were investigated. The magnetic structure for Mn 3 GaN is a typical noncollinear antiferromagnetic Γ 5 g . After Ni was introduced to the Ga site, the spin alignment was changed from antiferromagnetic to ferromagnetic. In addition, the magnetic transition temperature first decreased and then increased with increasing Ni content, which could be ascribed to the competition between the electron-type doping effect and the lattice effect. Near the magnetic transition, Mn 3 Ga 1−x Ni x N showed an abrupt lattice contraction with increasing temperature and the magnitude of the lattice contraction gradually decreased from 0.38% (for x = 0) to 0.09% (for x = 1.0) with increasing Ni substitution. In particular, zero thermal expansion behavior below 150 K was observed in Mn 3 Ga .6 Ni .4 N, and thermal expansion coefficient α was estimated to be 0.311 × 10 −6 K −1 . The obtained zero thermal expansion is very useful for practical applications in precision devices. The zero thermal expansion behavior was assumed to be associated with the ferromagnetic characteristic induced by the Ni substitution, which stabilized the Γ 5 g antiferromagnetic structure.

The antiperovskite Mn 3 Zn 0.77 Mn 0.19 N 0.94 was investigated by in situ neutron powder diffraction (NPD) in the temperature region 5–300 K. Here, a noncollinear-antiferromagnetic/collinear-ferrimagnetic phase separation (PS) showing different lattice parameters was firstly revealed in antiperovskites. The NPD results prove that the noncollinear antiferromagnetic phase, even coexisting with the collinear ferrimagnetic phase, could be responsible for the zero thermal expansion behavior of Mn 3 Zn 0.77 Mn 0.19 N 0.94 below 110 K. These findings suggest that Mn 3 ZnN based materials could open a new avenue for further exploring the noncollinear magnetic PS and correlated physical properties of antiperovskites.

Owing to improved thermal stability and scalability, materials with perpendicular magnetic anisotropy (PMA) are extremely attractive. The all perpendicular magnetic tunnel junction ([Formula: see text]-MTJ) devices are primarily devoted to spin transfer torque (STT)-induced switching and few works report their microwave emission. Here, we demonstrate the basic results of RF function in nanoscale [Formula: see text]-MTJ which has two different thickness free layers separated by atom-thick tungsten insertion. The ultrathin W spacer layer not only enables the two CoFeB free layers precess as a single layer but also greatly enhances the PMA which further induces high-emission frequency. The all perpendicular spin transfer torque nano-oscillator (STNO) exhibited high frequency (7.6[Formula: see text]GHz) and large current modulation capability of [Formula: see text] at moderate external magnetic field. Along with our previous work on STT switching utilizing the similar stack, such a multifunctional structure could bring low cost solutions to Internet of Things (IoT) network applications.

The thermodynamic properties and negative thermal expansion (NTE) behavior of metal-organic framework MOF-5 are investigated within the quasi-harmonic approximation, by using density functional theory. For nanoporous MOF-5, the temperature dependence of bulk modulus increases with increasing temperature, indicating that the resistance to compression is enhanced gradually. The large NTE behavior is obtained, which agrees reasonably with the experimental data. From the Gruneisen parameter as a function of temperature, it can be found that low-frequency phonons are closely associated with the NTE of MOF-5. The corresponding vibrational modes can be viewed as the results of local deformations (translation, rotation, twisting) of BDC (1,4-benzenedicarboxylate) linker and zinc clusters. The lowest-frequency phonon mode (the transverse motion of carboxylate groups and benzene ring, zinc clusters being as rigid units) is confirmed to be most responsible for thermal contraction.

Antiperovskite intermetallic Mn3−xCrxZnN (0≤x≤0.5) compounds have been prepared to study the Cr doping effect on the electronic transport properties. The temperature dependent resistivity ρ(T) for x≤0.3 shows notable and broader slope change. Meanwhile, with increasing Cr doping, the slope change shifts to lower temperatures and is gradually suppressed for x>0.3. For x=0.0 and 0.5, the measurements of magnetization from 10 K to 350 K reveal that Mn3−xCrxZnN compounds go through a transition from the dominant AFM interactions to one where the FM and AFM interactions coexist. For low-temperature region (15–80 K), the electron–electron scattering is dominant, and the number of phonons abruptly increases with increasing temperature. Small polaron hopping model (SPH) is used to understand the temperature dependence of electrical resistivity in the high-temperature range of 200–300 K and a clear decrease of the polaron activation energy was observed for x≤0.2. The residual resistivity ratio (RRR) decreases while the residual resistivity increases (ρ0) with increasing Cr-doping level. The maximum total entropy change (ΔSmax) decreases by increasing the Cr doping from x=0.0 to 0.2.

The Cr doping effect on the lattice and magnetic properties in Mn3−xCrxZnN was reported in the antiferromagnetic intermetallic host material Mn3ZnN. The lattice parameter decreases with the increase of the Cr concentration. Measurements of magnetization from 10 K to 350 K reveal that sharp antiferromagnetic (AFM)-to-paramagnetic (PM) transitions of the host material exist at 185 K (ZFC) and 177 K (FC). The peak is broadened clearly as the Cr doping was increased and when the Cr concentration exceeded 0.3, a significant ferromagnetic (FM) character was found to coexist with an AFM phase. At x=0.4 and 0.5, the M–H curves exhibit small magnetic hysteresis loop, indicating the dominant FM interactions in these samples. Also, a positive value of Weiss Temperature (ΘW) at x=0.5 in H/M–T plot suggests that the FM interaction is dominant when the Cr doping increases.

The antiperovskite compounds Mn 3 Ag x Mn y N with Ag vacancies and Mn doping at Ag site were synthesized and investigated. The introduction of Ag vacancies has a very small influence on magnetic transitions. However, the magnetic transitions at T N (Neel temperature) and T t (transition at lower temperature) gradually overlap with Mn doping accompanied by broadening of negative thermal expansion behavior. We also observed the nearly zero temperature coefficient of resistivity (NZ-TCR) behavior above magnetic order–disorder transition. The tunable TCR values from positive to negative could be achieved in Mn 3 Ag x Mn y N by reducing the contribution of (electron–phonon) e–p scattering in resistivity. Our results reveal the significance of e–p scattering for the evolution of TCR values, which could enrich the understanding of NZ-TCR behavior in antiperovskite manganese nitrides.

One of the specific subjects in frustrated magnetic systems is the phenomenon coupled with noncollinear magnetism, such as zero or negative thermal expansion (ZTE or NTE) in antiperovskite compounds. The first-principles calculations and neutron powder diffraction (NPD) are used to reveal the control of the noncollinear Γ5g antiferromagnetic (AFM) structure and corresponding thermal expansion properties in Mn3Zn0.875X0.125N (X = Mn, Ge, and Sn). Based on the optimal exchange-correlation functional, our results demonstrate that X (X = Mn, Ge, and Sn) doping at Zn site could stabilize the noncollinear Γ5g AFM structure and produce magnetovolume effect (MVE). The predictions of Γ5g AFM ground state and MVE is further verified by the NPD results of Mn3Zn0.83Mn0.15N0.99. Intriguingly, this special magnetic structure with strong spin–lattice coupling can be tunable to achieve ZTE behavior. On the basis of these results we suggest that frustrated magnetic systems with noncollinear Γ5g AFM structure of Mn atoms i...

The antiperovskite Mn3+xNi1–xN compounds have been synthesized and characterized by a variety of experimental techniques. After Mn doping at the Ni site, both ferromagnetic characteristics and an Invar-like effect were observed in the antiferromagnetic host material. The observed Invar-like behavior was assumed to be related to the characteristic magnetic structure induced by the doping. Neutron diffraction results prove that the Mn doping stabilizes the special Γ5g antiferromagnetic phase with strong spin–lattice coupling that can be tuned to achieve Invar-like behavior. The magnetovolume effect (MVE) and significant correlation between spin and lattice were confirmed for the Γ5g magnetic phase by the first-principles calculations. Moreover, Mn 3d electrons were revealed to be the key factor for the MVE from the calculations. Our study presents a new mechanism for precisely controlling the zero thermal expansion of a single compound by achieving the special Γ5g magnetic phase of Mn atoms.

An Mn3Cu0.5Ge0.5N/Cu composite was synthesized with 50 wt.% Cu and 50 wt.% Mn3Cu0.5Ge0.5N. The composite has a nearly zero thermal expansion behavior around room temperature and consists of Cu, Mn3Cu0.5Ge0.5N with a small number of MnO particles. There are no chemical reactions between these phases and the thermal expansion property of the composite is stable. Based on the distribution of Cu and Mn3Cu0.5Ge0.5N phases in the composite, we built a structure model to clarify the stability of Mn3Cu0.5Ge0.5N/Cu composite.

We report a large magnetic entropy change observed in the antiperovskite Mn 3 Cu 0.89 N 0.96 . Based on the heat flow peak measured by differential scanning calorimetry, the total entropy change according to the structural transition (tetragonal to cubic) was calculated to be ∼60 J kg –1 K –1 while the magnetic entropy change accounts for ∼22.5% of the total entropy under a 50 kOe magnetic field at 145 K. To clarify the origin of the magnetic entropy change, we managed to control the structure transition using a magnetic field. It was found that the magnetic entropy change originates from the transformation from antiferromagnetic (AFM) to ferromagnetic (FM) as well as from the phase transition from cubic to tetragonal under the magnetic field. In the tetragonal phase, a magnetic field can drive the AFM component to transform gradually to the FM component. The magnetic field can also change the phase fraction in the tetragonal and cubic two-phase coexistence region, a similar behavior to that induced by temperature. In the current system, only 5.4% of the cubic phase transforms to the tetragonal phase at 5 Tesla (T), indicating there is still much latent entropy in Mn 3 Cu 0.89 N 0.96 .

We report a robust perpendicularly magnetized β-W/CoFeB/MgO multilayer structure. For the first time, we demonstrate efficient spin–orbit torque (SOT) switching and a highly thermally stable annealing process with this structure using X-ray diffraction tests, the harmonic technique, and SOT-driven magnetization switching measurements. These results may enable applications of SOT-based magnetic random access memory, which is required for integration in the CMOS back-end-of-line process.

A baromagnetic effect in a novel tetragonal magnetic structure is introduced by vacancies in Mn3 Ga0.95 N0.94 , due to the change of the Mn-Mn distance and their spin re-orientation induced by a pressure field. This effect is proven for the first time in antiperovskite compounds by neutron powder diffraction analysis. This feature will enable wide applications in magnetoelectric devices and intelligent instruments.

The near-zero temperature coefficient of resistivity (NZ-TCR) behavior is reported in the antiperovskite compounds Mn3+xNi1−xN (0 ≤ x ≤ 0.333). Our results indicate that the broad temperature range (above 275 K extending to above 220 K) of NZ-TCR is obtained by Mn doping at the Ni site. The short-range magnetic ordering is revealed by both neutron powder diffraction and inverse magnetic susceptibility. Further, we find a strong correlation between the anomalous resistivity change of Mn3+xNi1−xN from the metal-like to the NZ-TCR behavior and the lack of the long-range magnetic ordering. The possible mechanism of NZ-TCR behavior is discussed using the spin-disorder scattering model.

The effects of N substitution on the magnetic properties of Mn3InC1−xNx (0.0 ≤ x ≤ 0.7) are investigated systematically. Partial substitution of N for C leads to the monotonic reduction in both the Curie temperature TC and saturated magnetization MS. The final results obtained from thermo-magnetic curves demonstrate that Mn3InC1−xNx samples show a magnetic phase transition from a paramagnetic (PM) state to a ferrimagnetic (FIM) state consisting of ferromagnetic (FM) and antiferromagnetic (AFM) components. In addition, there is a competition between the AFM component and the FM component in the FIM state with the change of the N-doped content. Magnetic measurements of Mn3InC at 100 Oe and 5000 Oe indicate the metastability and the coexistence of different magnetic phases at lower temperature. The spans of FIM phase broaden gradually with further N doping. The mechanism for the induction of the complicated magnetic state is still in controversy. However, the results clearly show that the doping at the X site in antiperovskite Mn3AX materials is as useful as that of the A and Mn sites.