From Tohoku University

Long gone are the days where all our data could fit on a 2MB floppy disk. In today’s information-based society, the increasing volume of information being handled demands that we switch to memory options with the lowest power consumption and highest capacity possible.

Magnetoresistive Random Access Memory (MRAM) is part of the next-gen of storage devices expected to meet these needs. Researchers at the Advanced Institute for Materials Research (WPI-AIMR) have investigated a cobalt-manganese-iron alloy thin film that demonstrates a high perpendicular magnetic anisotropy (PMA) – key aspects for fabricating MRAM devices using spintronics.

MRAM consists of semiconductor transistor (FET) and magnetic tunnel junctions with perpendicular magnetic anisotropy (Left panel). For non-volatile data retention over ten years in magnetic tunnel junction, thermal stability factor, Δ, needs to exceed 60; thus large perpendicular magnetic anisotropy K is required for nano-scale MTJs with magnetic layer with thickness t and radius D smaller than several tens nm. (right panel)
(© S. Mizukami)

“This is the first time a cobalt-manganese-iron alloy has strongly shown large PMA,” says Professor Shigemi Mizukami, Tohoku University, “We previously discovered this alloy showed a high tunnel magnetoresistance (TMR) effect, but it is rare that an alloy potentially shows both together.”

For example, Iron-cobalt-boron alloys, which are conventionally used for MRAM, possess both traits, but their PMA is not strong enough.

MRAM devices use magnetic storage elements instead of an electric charge to store data, which gives it several advantages such as reduced power consumption. Ideally, alloys for MRAM devices have both a high TMR and PMA, which allow them to integrate a large number of bits with high capacity and high thermal stability.

We demonstrated high TMR effect, which is prerequisite for MRAM, using novel metastable body-centered cubic (bcc) Co-Mn-Fe in a previous report [T. Ichinose et al. Journal of Alloys and Compounds 960, 170750 (2023). In this work, we demonstrated large perpendicular magnetic anisotropy (PMA) which can originate from the lattice strain.
(© D. Kumar et al. (Part of the data is used from D. Kumar et al. Science and Technology of Advanced Materials, 25 (1), 2421746 (2024).)

Click to enlarge

In order to find new, alternative materials to solve the issues seen with currently used alloys, researchers at Tohoku University have investigated the PMA of cobalt-manganese-iron alloy thin films, which were shown to have high TMR in their previous research. Remarkably, the alloy they produced was found to exhibit high PMA. They also demonstrated that the PMA in their multilayer films was large enough to be capable of its intended end purpose: large memory capacity for MRAM devices using a simulation.

The results of this research will offer a new candidate for memory materials, and contribute to the continuous development of novel spintronics memory devices, with the aim of creating a more sustainable society for everyone. These findings were published in Science and Technology of Advanced Materials on November 13, 2024.

This research was supported in part by Core Research for Evolutional Science and Technology (CREST) “Revolutional Material Development by Fusion of Strong Experiments with Theory/Data Science” [No.JPMJCR17J5] (JST) and X-NICS [No. JPJ011438] (MEXT).

Numerical simulation suggested that the Co-Mn-Fe multilayer films with PMA show the large thermal stability
factors delta exceeding 60 even in nano scale, which can be used for 10 nm scale MRAM.
(© D. Kumar et al. (The data is used from D. Kumar et al. Science and Technology of Advanced Materials, 25 (1), 2421746 (2024).)

Article: Metastable body-centered cubic CoMnFe alloy films with perpendicular magnetic anisotropy for spintronics memory

Science and Technology of Advanced Materials has published an article written by Deepak Kumar, Mio Ishibashi, WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan, Tufan Roy, Center for Science and Innovation in Spintronics, Tohoku University, Sendai, Japan, Masahito Tsujikawa, Research Institute for Electrical Communication, Tohoku University, Sendai, Japan, Masafumi Shirai, Research Institute for Electrical Communication, Tohoku University, Sendai, Japan;b Center for Science and Innovation in Spintronics, Tohoku University, Sendai, Japan, and Shigemi Mizukami, WPI Advanced Institute for Materials Research, Tohoku University, Sendai, Japan;b Center for Science and Innovation in Spintronics, Tohoku University, Sendai, Japan

Abstract: “A body-centered cubic (bcc) FeCo(B) is a current standard magnetic material for perpendicular magnetic tunnel junctions (p-MTJs) showing both large tunnel magnetoresistance (TMR) and high interfacial perpendicular magnetic anisotropy (PMA) when MgO is utilized as a barrier material of p-MTJs. Since the p-MTJ is a key device of current spintronics memory, i.e. spin-transfer-torque magnetoresistive random access memory (STT-MRAM), it attracts attention for further advance to explore new magnetic materials showing both large PMA and TMR. However, there have been no such materials other than FeCo(B)/MgO. Here, we report, for the first time, PMA in metastable bcc Co-based alloy, i.e. bcc CoMnFe thin films which are known to exhibit large TMR effect when used for electrodes of MTJs with the MgO barrier. The largest intrinsic PMAs were about 0.6 and 0.8 MJ/m³ in a few nanometer-thick CoMnFe alloy film and multilayer film, respectively. Our ab-initio calculation suggested that PMA originates from tetragonal strain and the value exceeds 1 MJ/m³ with optimizing strain and alloys composition. The simulation of the thermal stability factor indicates that the magnetic properties obtained satisfy the requirement of the data retention performance of X-1X nm STT-MRAM. The large PMA and high TMR effect in bcc CoMnFe/MgO, which were rarely observed in materials other than FeCo(B)/MgO, indicate that bcc CoMnFe/MgO is one of the potential candidates of the materials for X-1X nm STT-MRAM.“